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Leaf vs. inflorescence: differences in photosynthetic activity of grapevine
Abstract
Using measures of gas exchanges and photosynthetic chain activity, we found some differences between grapevine inflorescence and leaf in terms of photosynthetic activity and photosynthesis regulations. Generally, the leaf showed the higher net photosynthesis (P
N) and lower dark respiration than that of the inflorescence until the beginning of the flowering process. The lower (and negative) PN indicated prevailing respiration over photosynthesis and could result from a higher metabolic activity rather than from a lower activity of the photosynthetic apparatus. Considerable differences were observed between both organs in the functioning and regulation of PSI and PSII. Indeed, in our conditions, the quantum yield efficiency and electron transport rate of PSI and PSII were higher in the inflorescence compared to that of the leaf; nevertheless, protective regulatory mechanisms of the photosynthetic chain were clearly more efficient in the leaf. This was in accordance with the major function of this organ in grapevine but it highlighted also that inflorescence seems to be included in the whole carbon balance of a plant. During inflorescence development, the global PSII activity decreased and PSI regulation tended to be similar to the leaf, where photosynthetic activity and regulations remained more stable. Finally, during flowering, cyclic electron flow (CEF) around PSI was activated in parallel to the decline in the thylakoid linear electron flow. Inflorescence CEF was double compared to the leaf; it might contribute to photoprotection, could promote ATP synthesis and the recovery of PSII.
... Changes in transcription and translation of plastids may be linked to the transition from chloroplast to chromoplasts [42]. The decrease in photosystem II activity during flower development also is known in other species such as grapevines, but a substantial decrease in photosystem I activity has not been previously observed [43]. Additionally, it is noteworthy that, among genes associated with enriched GO terms, there were 36 up-regulated and 13 down-regulated genes whose homologues in Arabidopsis have been previously reported as involved in any flowering-related pathway, according to the Flowering Interactive Database (FLOR-ID) [18]. ...
... chloroplast to chromoplasts [42]. The decrease in photosystem II activity during flower development also is known in other species such as grapevines, but a substantial decrease in photosystem I activity has not been previously observed [43]. Additionally, it is noteworthy that, among genes associated with enriched GO terms, there were 36 up-regulated and 13 down-regulated genes whose homologues in Arabidopsis have been previously reported as involved in any flowering-related pathway, according to the Flowering Interactive Database (FLOR-ID) [18]. ...
The tropical common bean (Phaseolus vulgaris L.) is an obligatory short-day plant that requires relaxation of the photoperiod to induce flowering. Similar to other crops, photoperiod-induced floral initiation depends on the differentiation and maintenance of meristems. In this study, the global changes in transcript expression profiles were analyzed in two meristematic tissues corresponding to the vegetative and inflorescence meristems of two genotypes with different sensitivities to photoperiods. A total of 3396 differentially expressed genes (DEGs) were identified, and 1271 and 1533 were found to be up-regulated and down-regulated, respectively, whereas 592 genes showed discordant expression patterns between both genotypes. Arabidopsis homologues of DEGs were identified, and most of them were not previously involved in Arabidopsis floral transition, suggesting an evolutionary divergence of the transcriptional regulatory networks of the flowering process of both species. However, some genes belonging to the photoperiod and flower development pathways with evolutionarily conserved transcriptional profiles have been found. In addition, the flower meristem identity genes APETALA1 and LEAFY, as well as CONSTANS-LIKE 5, were identified as markers to distinguish between the vegetative and reproductive stages. Our data also indicated that the down-regulation of the photoperiodic genes seems to be directly associated with promoting floral transition under inductive short-day lengths. These findings provide valuable insight into the molecular factors that underlie meristematic development and contribute to understanding the photoperiod adaptation in the common bean.
... PSI activity is also dependent on the donor side limitation Y(ND) 58 . For all experimental conditions, Y(ND) tended to increase at 2 dpi with significantly different values by comparison two by two with the other timespoints (Student's test; p value < 0.05) (Fig. 3b). ...
... Therefore, Y(NPQ) could be stimulated by the xanthophylls cycle if excitation energy is in excess. Without this energy dissipation, singlet O2 and other reactive oxygen species could be formed and therefore, allowed an increase of Y(NO) parameter 58 . In this way, the alterations caused by the pathogen probably reflect the inability of the barley to regulate it mechanisms of photoprotection, resulting in photooxidative damage to the infected host tissue. ...
Recognized as the causal agent of net blotch, Drechslera teres is responsible for major losses of barley crop yield. The consequences of this leaf disease are due to the impact of the infection on the photosynthetic performance of barley leaves. To limit the symptoms of this ascomycete, the use of beneficial bacteria known as "Plant Growth Promoting Rhizobacteria" constitutes an innovative and environmentally friendly strategy. A bacterium named as strain B25 belonging to the genus Burkholderia showed a strong antifungal activity against D. teres. The bacterium was able to limit the development of the fungus by 95% in detached leaves of bacterized plants compared to the non-bacterized control. In this study, in-depth analyses of the photosynthetic performance of young barley leaves infected with D. teres and/or in the presence of the strain B25 were carried out both in and close to the necrotic area. In addition, gas exchange measurements were performed only near the necrotic area. Our results showed that the presence of the beneficial bacterium reduced the negative impact of the fungus on the photosynthetic performance and modified only the net carbon assimilation rate close to the necrotic area. Indeed, the presence of the strain B25 decreased the quantum yield of regulated non-photochemical energy loss in PSII noted as Y(NPQ) and allowed to maintain the values stable of maximum quantum yield of PSII photochemistry known as F v /F m and close to those of the control in the presence of D. teres. To the best of our knowledge, these data constitute the first study focusing on the impact of net blotch fungus and a beneficial bacterium on photosynthesis and respiratory parameters in barley leaves.
... Most often, the control of carbohydrate variations is reliable with feedback regulation of photosynthesis by carbon metabolites [19,20], affecting the related enzyme activities [21][22][23]. In the developing inflorescence of grapevine, it was shown that carbohydrates are supplied by reserve mobilization from perennial organs [17] and by photosynthesis in both leaves [24] and inflorescences [25][26][27]. ...
... Consequently, sugar contents fluctuate differently according to the metabolism of the cultivar and inflorescences become a sink for carbohydrates from BBCH57 stage. It was already reported that the leaf photosynthetic rates are lower in GW than in PN [41] and that inflorescences have shown fluctuations in the photosynthetic activity during the flower development [6,26,27]. ...
p>In order to further understand the relationships between flower development and sugar metabolism in grapevine, the fluctuations of both starch and sucrose contents were compared with the activity of their related enzymes, in the inflorescences, from the appearance of flower buds until the fruit set. The measurements were carried out on GW and PN cvs., differing in their sensitivity to the flower abscission. The meiosis stage, which is a crucial step for the achievement of sexual reproduction, was particularly screened. Results indicate that the main differences in carbohydrate metabolism occur during meiosis. In the inflorescences of both cvs., variations of enzyme activities can be correlated with their differences in sugar contents. Starch fluctuations were mediated by the activity of amylases (alpha- and beta-) rather than by starch synthase. Changes of sucrose were correlated with the activity of Starch Synthase degradation, both cytoplasmic and wall-bounded invertases but not with the Sucrose Phosphate Synthase activity. Finally, the significant increase of sucrose degrading enzyme activities, such as Starch Synthase degradation, cytoplasmic invertase, and wall-bound invertase, observed after the flower separating stage was interpreted as the first sign of the strong physiological modifications occurred in the ovaries between fertilization and the fruit formation.</p
... Meanwhile, qP reflects the relationship between photochemical electron transfer and the light energy absorbed by the PSII antenna pigment (Cao et al., 2013). The qP value also represents the openness of the PSII reaction center to some extent (Sawicki et al., 2017). In In our study, we found that the F o value value reached to aa maximum under R and decreased with the addition of blue LED light light, while while the F m increased with the addition of blue light and reached its maximum under R:B = 7:3. ...
... When exposed to elevated CO 2 concentrations, the strobilus carbon budget became positive, thus indicating a strong photosynthetic sugar-producing role in the later stage of the hop strobilus. Similar to prior studies on other reproductive structures, we found that the carbon cost in terms of a strobilus carbon balance may be fully compensated for by increasing photosynthetic rates of the reproductive structure [2,22,23]. Though leaves cannot be ruled out as a carbon source for strobilus development at the onset of the reproductive stage, leaves showed clear signs of senescence during the strobilus generative phase, whereas strobilus photosynthetic capacity did not decline during the hop flowering phase [24]. This indicates that under optimal environmental conditions, strobili can function autonomously with respect to carbon assimilation in the latter phase of the hop growing cycle. ...
The economic value of Humulus lupulus L. (hop) is recognized, but the primary metabolism of the hop strobilus has not been quantified in response to elevated CO2. The photosynthetic contribution of hop strobili to reproductive effort may be important for growth and crop yield. This component could be useful in hop breeding for enhanced performance in response to environmental signals. The objective of this study was to assess strobilus gas exchange, specifically the response to CO2 and light. Hop strobili were measured under controlled environment conditions to assess the organ’s contribution to carbon assimilation and lupulin gland filling during the maturation phase. Leaf defoliation and bract photosynthetic inhibition were deployed to investigate the glandular trichome lupulin carbon source. Strobilus-level physiological response parameters were extrapolated to estimate strobilus-specific carbon budgets under current and future atmospheric CO2 conditions. Under ambient atmospheric CO2, the strobilus carbon balance was 92% autonomous. Estimated strobilus carbon uptake increased by 21% from 415 to 600 µmol mol−1 CO2, 14% from 600 to 900 µmol mol−1, and another 8%, 4%, and 3% from 900 to 1200, 1500, and 1800 µmol mol−1, respectively. We show that photosynthetically active bracts are a major source of carbon assimilation and that leaf defoliation had no effect on lupulin production or strobilus photosynthesis, whereas individual bract photosynthesis was linked to lupulin production. In conclusion, hop strobili can self-generate enough carbon assimilation under elevated CO2 conditions to function autonomously, and strobilus bracts are the primary carbon source for lupulin biosynthesis.
... Modifying sugar signalling can improve photosynthetic performance through regulating the source-sink balance [70], while photosynthesis can supply the carbon required for flower development and is performed not only in leaves but also in the flowers themselves, such as in the bracts, sepals, anthers, corolla, or flower stalks [71]. A previous report on grapevines showed that the global photosynthetic activity in inflorescences decreased during inflorescence development; this may be dissimulated by intense respiratory activity [72], as the mechanisms underlying photosynthesis in flowers remain to be fully elucidated. We hypothesised that due to the formation of flower colour, the contents of photosynthesis-related pigments, such as chlorophyll and carotenoid, might be reduced, which might influence photosynthesis. ...
Published genome sequences can facilitate multiple genome sequencing studies of flower development, which can serve as the basis for later analysis of variation in flower phenotypes. To identify potential regulators related to flower morphology, we captured dynamic expression patterns under five different developmental stages of petunia flowers, a popular bedding plant, using transcriptome and miRNA sequencing. The significant transcription factor (TF) families, including MYB, MADS, and bHLH, were elucidated. MADS-box genes exhibited co-expression patterns with BBR-BPC, GATA, and Dof genes in different modules according to a weighted gene co-expression network analysis. Through miRNA sequencing, a total of 45 conserved and 26 novel miRNAs were identified. According to GO and KEGG enrichment analysis, the carbohydrate metabolic process, photosynthesis, and phenylalanine metabolism were significant at the transcriptomic level, while the response to hormone pathways was significantly enriched by DEmiR-targeted genes. Finally, an miRNA–RNA network was constructed, which suggested the possibility of novel miRNA-mediated regulation pathways being activated during flower development. Overall, the expression data in the present study provide novel insights into the developmental gene regulatory network facilitated by TFs, miRNA, and their target genes.
... Although leaves are the principal source of photosynthates, the reproductive structures of many plant species are also reported to be photosynthetically active, assimilating significant amounts of carbon [30] to partly compensate for reproduction costs. In the grapevine, we demonstrated that the inflorescence shows photosynthetic activity [31] and is able to assimilate and export the majority of the assimilated carbon, thus playing a crucial role in carbon balance by sustaining the early development of leaves [32]. ...
Low temperature is a critical environmental factor limiting plant productivity, especially in northern vineyards. To clarify the impact of this stress on grapevine flower, we used the Vitis array based on Roche-NimbleGen technology to investigate the gene expression of flowers submitted to a cold night. Our objectives were to identify modifications in the transcript levels after stress and during recovery. Consequently, our results confirmed some mechanisms known in grapes or other plants in response to cold stress, notably, (1) the pivotal role of calcium/calmodulin-mediated signaling; (2) the over-expression of sugar transporters and some genes involved in plant defense (especially in carbon metabolism), and (3) the down-regulation of genes encoding galactinol synthase (GOLS), pectate lyases, or polygalacturonases. We also identified some mechanisms not yet known to be involved in the response to cold stress, i.e., (1) the up-regulation of genes encoding G-type lectin S-receptor-like serine threonine-protein kinase, pathogen recognition receptor (PRR5), or heat-shock factors among others; (2) the down-regulation of Myeloblastosis (MYB)-related transcription factors and the Constans-like zinc finger family; and (3) the down-regulation of some genes encoding Pathogen-Related (PR)-proteins. Taken together, our results revealed interesting features and potentially valuable traits associated with stress responses in the grapevine flower. From a long-term perspective, our study provides useful starting points for future investigation.
... This indicates that inflorescence and stem photosynthesis compensates for leaf photosynthesis to a large degree, although storage of photoassimilate in other organs prior to defoliation was not considered. Nevertheless, results from these studies are in keeping with high photosynthetic rates observed in the inflorescences of Arabidopsis and grapevine (Leonardos et al., 2014;Sawicki et al., 2017). ...
During seed development, carbon is reallocated from maternal tissues to support germination and subsequent growth. As this pool of resources is depleted post-germination, the plant begins autotrophic growth through leaf photosynthesis. Photoassimilates derived from the leaf are used to sustain the plant and form new organs, including other vegetative leaves, stems, bracts, flowers, fruits, and seeds. In contrast to the view that reproductive tissues act only as resource sinks, many studies demonstrate that flowers, fruits, and seeds are photosynthetically active. The photosynthetic contribution to development is variable between these reproductive organs and between species. In addition, our understanding of the developmental control of photosynthetic activity in reproductive organs is vastly incomplete. A further complication is that reproductive organ photosynthesis (ROP) appears to be particularly important under suboptimal growth conditions. Therefore, the topic of ROP presents the community with a challenge to integrate the fields of photosynthesis, development, and stress responses. Here, we attempt to summarize our understanding of the contribution of ROP to development and the molecular mechanisms underlying its control.
... Moreover, in eight tomato cultivars that grow under heat stress conditions, the photosynthetic rate was higher in the vegetative stage of the heattolerant genotypes compared to the heat-sensitive genotypes; the peak was observed in the flowering stage and the photosynthetic rate decreased in the fruit stage (Abdelmageed and Gruda, 2009), confirming our data. The main cause of reduced Pn could be changed in g w and Ci (Sawicki et al., 2017). Furthermore, Sicher (2013) revealed that the net rate of photosynthesis of soybean leaves increased by 20% at 36 • C compared to 28 • C. In heat-tolerant tomato genotypes exposed to high temperatures, photosynthesis, and transpiration were significantly higher than in non-tolerant genotypes in seedlings, flowering, and early stages of the fruit (Nkansah and Ito, 1994). ...
Abnormal temperatures induce physiological and biochemical changes resulting in the loss of yield. The present study investigates the impact of the PsJN strain of Paraburkholderia phytofirmans on tomato (Lycopersicon esculentum Mill.) in response to heat stress (32°C). The results of this work showed that bacterial inoculation with P. phytofirmans strain PsJN increased tomato growth parameters such as chlorophyll content and gas exchange at both normal and high temperatures (25 and 32°C). At normal temperature (25°C), the rate of photosynthesis and the photosystem II activity increased with significant accumulations of sugars, total amino acids, proline, and malate in the bacterized tomato plants, demonstrating that the PsJN strain had a positive effect on plant growth. However, the amount of sucrose, total amino acids, proline, and malate were significantly affected in tomato leaves at 32°C compared to that at 25°C. Changes in photosynthesis and chlorophyll fluorescence showed that the bacterized tomato plants were well acclimated at 32°C. These results reinforce the current knowledge about the PsJN strain of P. phytofirmans and highlight in particular its ability to alleviate the harmful effects of high temperatures by stimulating the growth and tolerance of tomato plants.
Spathiphyllum floribundum is an important indoor flower species. Thus, optimizing its growth by regulating the light quality under indoor low-light conditions may be critical for generating high-quality flowers. In this study, the effects of the following six light-quality treatments on peroxidase and superoxide dismutase activities in two S. floribundum cultivars (‘Sweet Chico’ and ‘Queen’) were analyzed: monochromatic light comprising 100% red (R, 657 nm) or 100% blue (B, 450 nm) light, a combination of R and B lights [80% R + 20% B (8:2), 70% R + 30% B (7:3), and 60% R + 40% B (6:4)], and white light. The light treatments were performed using light-emitting diodes. The light intensity and photoperiod were set to 45±2 µmol·m-2·s-1 and 14 h·d-1, respectively. The results of this study revealed that an appropriate R:B light ratio may lead to increased pigment contents, thereby increasing the synthesis and accumulation of photosynthetic products, which will result in increased stress resistance and enhanced growth. These findings provide the basis for future investigations on the growth and production of S. floribundum and other indoor ornamental plants.
This paper demonstrates the potential of using hyperspectral imaging for detecting age and defects of grapevine leaves. For age detection studies a number of grapevine healthy leaves and for defect detection analysis 9 different defective leaves have been selected. Hyperspectral images of these leaves covered spectral wavelengths from 380 nm to 1000 nm. A number of features from the brightness in ultra violet (UV), visible (VIS) and near infrared (NIR) regions were derived to obtain the correlation of age and defect. From the experimental studies it has been observed that the mean brightness in terms of original reflection in visible range has correlation with different ages of grapevine leaves. Moreover, the position of mean 1st derivative brightness peak in VIS region, variation index of brightness and rate of change of brightness i.e., mean 1st derivative brightness at NIR provide a good indication about the age of the leaves. For defect detection whole area and selective areas containing the defects on the leaves have been experimentally analysed to determine which option provides better defect detection. Variation index of brightness was also employed as a guide to obtain information to distinguish healthy and unhealthy leaves using hyperspectral imaging. The experimental results demonstrated that hyperspectral imaging has excellent potential as a non-destructive as well as a non-contact method to detect age and defects of grapevine leaves.
The non-rectangular hyperbola (NRH) equation is the most popular method that plots the photosynthetic light-response (PLR) curve and helps to identify plant photosynthetic capability. However, the PLR curve can’t be plotted well by the NRH equation at different plant growth phases due to the variations of plant development. Recently, plant physiological parameters have been considered into the NRH equation to establish the modified NRH equation, but plant height (H), an important parameter in plant growth phases, is not taken into account. In this study, H was incorporated into the NRH equation to establish the modified NRH equation, which could be used to estimate photosynthetic capability of herbage at different growth phases. To explore photosynthetic capability of herbage, we selected the dominant herbage species Potentilla anserina L. and Elymus nutans Griseb. in the Heihe River as the research materials. Totally, twenty-four PLR curves and H at different growth phases were measured during the growing season in 2016. Results showed that the maximum net photosynthetic rate and the initial slope of PLR curve linearly increased with H. The modified NRH equation, which is established by introducing H and an H-based adjustment factor into the NRH equation, described better the PLR curves of P. anserina and E. nutans than the original ones. The results may provide an effective method to estimate the net primary productivity of grasslands in the study area.
Why evergreen fruit tree species accumulate starch in the ovary during flower bud differentiation in spring, as deciduous species do during flower bud dormancy, is not fully understood. This is because in evergreen species carbon supply is assured by leaves during flower development. We suggest the existence of an autonomous mechanism in the flowers which counteracts the competition for photoassimilates with new leaves, until they become source organs. Our hypothesis is that starch accumulated during Citrus ovary ontogeny originates from 1) its own photosynthetic capacity and 2) the mobilization of reserves.
Through defoliation experiments, we found that ovaries accumulate starch during flower ontogeny using a dual mechanism: 1) the autotrophic route of source organs activating Rubisco (RbcS) genes expression, and 2) the heterotrophic route of sink organs that hydrolyze sucrose in the cytosol. Defoliation 40 days before anthesis did not significantly reduce ovary growth, flower abscission or starch concentration up to 20 days after anthesis (i.e. 60 days later). Control flowers activated the energy depletion signaling system (i.e. SnRK1) and RbcS gene expression around athesis. Defoliation accelerated and boosted both activities, increasing SPS gene expression (sucrose synthesis), and SUS1, SUS3 and cwINV (sucrose hydrolysis) to maintain a glucose threshold which satisfied its need to avoid abscission.
Photosynthetic characteristics of ear and flag leaves of wheat species, tetraploid Triticum dicoccoides Kom and hexaploid Bima1, were studied in plants grown under well-watered (WW) and water-stressed (WS) conditions. Compared to ears, flag leaves exhibited higher photosynthetic rate (PN) at the filling stage, but more severe decrease under WS. PN in the tetraploid wheat ear remained higher than that in the hexaploid wheat during the grain-filling stage. Water stress decreased PN in both the organs; this decline was caused by a reduction in Rubisco activity, not by drought-induced stomatal limitation. Tetraploid wheat ears exhibited higher relative water content and water-use efficiency than that of hexaploid wheat, under WS. The change in phosphoenolpyruvate carboxylase activity and carbon isotope composition indicated the absence of C4 metabolism in the ears of both species under both conditions. The improved performance of the tetraploid wheat ears under WS was associated with better water relations.
Sugars play an important role in grapevine flowering. This complex process from inflorescence initiation to fruit maturity takes two growing seasons. Currently, most of the available data concern the involvement of sugars as energy sources during the formation of reproductive structures from initiation of inflorescen-ces during the summer of the first year, until flower opening during the following spring. Sugars devoted to the development of reproductive structures are supplied either by wood reserves or by photosynthe-sis in leaves or inflorescences, depending on the stage of development. Female meiosis appears to be a key point in the success of flower formation because (i) flowers are vulnerable at this stage and (ii) it corresponds in the whole plant to the transition between reserve mobilization from perennial organs (roots, trunk, and canes) towards efficient leaf photo-synthesis. The perturbation of reserve replenishment during the previous year provokes perturbation in the development of inflorescences, whereas altering the photosynthetic sources affects the formation of flowers during the same year. In particular, a lack of sugar availability in flowers at female meiosis caused by various environmental or physiological fluctuations may lead to drastic flower abortion. Apart from energy, sugars also play roles as regulators of gene expression and as signal molecules that may be involved in stress responses. In the future, these two topics should be further investigated in the grapevine considering the sensitivity of flowers to environmental stresses at meiosis.
In plants, flowering is a crucial process for reproductive success and continuity of the species through time. Fruit production requires the perfect development of reproductive structures. Abscission, a natural process, can occur to facilitate shedding of no longer needed, infected, or damaged organs. If stress occurs during flower development, abscission can intervene at flower level, leading to reduced yield. Flower abscission is a highly regulated developmental process simultaneously influenced and activated in response to exogenous (changing environmental conditions, interactions with microorganisms) and endogenous (physiological modifications) stimuli. During climate change, plant communities will be more susceptible to environmental stresses, leading to increased flower and fruit abscission, and consequently a decrease in fruit yield. Understanding the impacts of stress on the reproductive phase is therefore critical for managing future agricultural productivity. Here, current knowledge on flower/fruit abscission is summarized by focusing specifically on effects of environmental stresses leading to this process in woody plants. Many of these stresses impair hormonal balance and/or carbohydrate metabolism, but the exact mechanisms are far from completely known. Hormones are the abscission effectors and the auxin/ethylene balance is of particular importance. The carbohydrate pathway is the result of complex regulatory processes involving the balance between photosynthesis and mobilization of reserves. Hormones and carbohydrates together participate in complex signal transduction systems, especially in response to stress. The available data are discussed in relation to reproductive organ development and the process of abscission.
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Grapevine flower development and fruit set are influenced by cold nights in the vineyard. To investigate the impact of cold stress on carbon metabolism in the inflorescence, we exposed the inflorescences of fruiting cuttings to chilling and freezing temperatures overnight and measured fluctuations in photosynthesis and sugar content. Whatever the temperature, after the stress treatment photosynthesis was modified in the inflorescence, but the nature of the alteration depended on the intensity of the cold stress. At 4°C, photosynthesis in the inflorescence was impaired through non-stomatal limitations, whereas at 0°C it was affected through stomatal limitations. A freezing night (-3°C) severely deregulated photosynthesis in the inflorescence, acting primarily on photosystem II. Cold nights also induced accumulation of sugars. Soluble carbohydrates increased in inflorescences exposed to -3°C, 0°C and 4°C, but starch accumulated only in inflorescences of plants treated at 0 and -3°C. These results suggest that inflorescences are able to cope with cold temperatures by adapting their carbohydrate metabolism using mechanisms that are differentially induced according to stress intensity.
An improved method is introduced for the determination of the quantum yield of photosystem I. The new method employs saturating light pulses with steep rise characteristics to distinguish, in a given physiological state, centers with an open acceptor side from centers with a reduced acceptor side. The latter do not contribute to PSI quantum yield (I). Oxidation of P700 is measured by a rapid modulation technique using the absorbance change around 830 nm. The quantum yield I is calculated from the amplitude of the rapid phase of absorbance change (A; 830 nm) upon application of a saturation pulse in a given state, divided by the maximal A (830 nm) which is induced by a saturation pulse with far-red background illumination. Using this technique, I can be determined even under conditions of acceptor-side limitation, as for example in the course of a dark-light induction period or after elimination of CO2 from the gas stream. Thus determined I values display a close-to-linear relationship with those for the quantum yield of PSII (II) calculated from chlorophyll fluorescence parameters. It is concluded that the proposed method may provide new information on the activity of the PSI acceptor side and thus help to separate the effects of acceptorside limitation from those of cyclic PSI, whenever a non-linear relationship between II and the P700-reduction level is observed.
Photoinhibition of photosynthesis was investigated in Vitis berlandieri and Vitis rupestris leaves under field conditions at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) and photosynthetic electron transport measurements. When the photochemical efficiency of PS2, Fv/Fm, markedly declined, F0 increased significantly in leaves of V. berlandieri, while F0 did not increase in V. rupestris leaves. Isolated thylakoids of leaves of V. berlandieri showed significant inhibition of whole chain and PS2 activities at midday. A smaller inhibition was observed for V. rupestris. Later, the leaves reached maximum PS2 efficiencies similar to those observed early in the morning during sampling at evening. The artificial exogenous electron donor Mn2+ failed to restore PS2 activity in both species, while DPC and NH2OH significantly restored PS2 activity in V. rupestris midday leaf samples. Quantification of the PS2 reaction centre protein D1 and 33 kDa protein of water splitting complex following midday exposure of leaves showed pronounced differences between V. berlandieri and V. rupestris leaves. The marked loss of PS2 activity noticed in midday samples was mainly due to the marked loss of D1 protein in V. berlandieri while in V. rupestris it was the 33 kDa protein.
Photoinhibition of photosynthesis was investigated in control (C) and chilling night (CN) leaves of grapevine under natural
photoperiod at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable
to maximum chlorophyll fluorescence (Fv/Fm) and photosynthetic electron transport measurements. When the potential efficiency of photosystem (PS) 2, Fv/Fm was measured at midday, it markedly declined with significant increase of F0 in CN leaves. In isolated thylakoids, the rate of whole chain and PS2 activity were markedly decreased in CN leaves than
control leaves at midday. A smaller inhibition of PS1 activity was also observed in both leaf types. Later, the leaves reached
maximum PS2 efficiencies similar to those observed in the morning during sampling at evening. The artificial exogenous electron
donors diphenyl carbazide, NH2OH, and Mn2+ failed to restore the PS2 activity in both leaf types at midday. Thus CN enhanced inactivation on the acceptor side of PS2
in grapevine leaves. Quantification of the PS2 reaction centre protein D1 following midday exposure of leaves showed pronounced
differences between C and CN leaves. The marked loss of PS2 activity in CN leaves noticed in midday samples was mainly due
to the marked loss of D1 protein of the PS2 reaction centre.
Linear and cyclic electron fluxes through Photosystem I in 1% CO(2) were quantified in spinach leaf tissue under severe water stress. Using actinic light with a peak at 697 nm for preferential light absorption by Photosystem I while also stimulating Photosystem II to improve redox poising, the cyclic electron flux after 60 s of illumination was a substantial proportion (33-44%) of the total electron flux through PSI at irradiances up to ~1,070 micromol photons m(-2) s(-1). At the maximum irradiance, the cyclic electron flux changed little with the progressive water loss from leaf tissue up to ~60%; by contrast, the linear electron flux was approximately halved. A reason for this differential effect of water stress on the capacity for cyclic and linear electron flow could be the increased crowding of soluble proteins in the stroma due to chloroplast shrinkage. Indeed the confinement of soluble proteins to a smaller chloroplast volume was indicated by cryo-scanning electron microscopy. It is known that the diffusion coefficient of large proteins is decreased when the background concentration of small proteins is raised; by contrast, the diffusion coefficient of small proteins is not affected by increasing the concentration of a large protein (Muramatsu and Minton in Proc Natl Acad Sci USA 85:2984-2988, 1988). Therefore, we suggest that linear electron flow, being coupled to the Calvin-Benson cycle, is limited by the diffusion of large macromolecules, especially the ribulose 1, 5-bisphosphate carboxylase/oxygenase complex. By contrast, cyclic electron flow, involving relatively small macromolecules such as ferredoxin, is less susceptible to inhibition by crowding in the stroma.
The distribution of carbon (C) into whole grapevine fruiting cuttings was investigated during flower development to determine
the relative contribution of inflorescence and leaf photoassimilates in the total C balance and to investigate their partitioning
towards other plant organs. A 13C labelling procedure was used to label C photoassimilates by leaves and inflorescences in grapevine. Investigations were
carried out at various stages of flower/berry development, from separated cluster to fruit set, using grapevine fruiting cuttings
with four leaves (Vitis vinifera L. cv. Chardonnay). This is the first study reporting that, during its development, (i) the carbon needs of the inflorescence
were met by both leaf and inflorescence photosynthesis, and (ii) the inflorescence amazingly participated significantly to
the total C balance of grapevine cuttings by redistributing an important part of its own assimilates to other plant organs.
With regard to flowering, 29% of C assimilated by the inflorescence remained in the inflorescence, while partitioning towards
the stem reached 42% and, as a lower proportion, 15% in leaves, and 14% in roots.
Our previous study indicated that PSII is more sensitive to chilling and light stress than PSI in tropical trees, and Erythrophleum guineense is more sensitive to chilling stress than Dalbergia odorifera and Khaya ivorensis, but the underlying physiological mechanisms are unclear. Although recent studies have reported that cyclic electron flow (CEF) plays an important role in photoprotection, the role of CEF in protecting PSI and PSII of tropical tree species remains unclear. We investigated the effect of temporal chilling temperature on energy distribution in PSII, the redox state of P700 and CEF in the above-mentioned tropical evergreen tree species grown in an open field. Our results indicated that the overclosure of PSII reaction centers at chilling temperature led to excess excitation pressure in PSII. At the temporal chilling temperature under low light, PSI acceptor side limitation [Y(NA)] was lower than those at 25°C for all species. Although the effective quantum yield of CEF [Y(CEF)] was not significantly stimulated in E. guineense and K. ivorensis under temporal chilling at low light levels, the ratio of Y(CEF) to the effective quantum yield of PSII [Y(II)] significantly increased. Under chilling conditions Y(CEF)/Y(II) was stimulated much more in K. ivorensis and D. odorifera compared with that in the chilling-sensitive E. guineense. These results suggested that stimulation of Y(CEF)/Y(II) plays an important role in protecting PSI and PSII from photoinhibition caused by chilling stress.
Although cyclic electron flow (CEF) is essential for repair of PSII, it is unclear whether the CEF is stimulated and what the role of stability of PSI is during the recovery. In order to explore these two questions, mature leaves of Dalbergia odorifera were treated with the chilling temperature of 4°C under a photosynthetic flux density (PFD) of 650 μmol m(-2) s(-1) for 2 h and then were transferred to 25°C under a PFD of 100 μmol m(-2) s(-1) for recovery. The maximum quantum yield of PSII (F(v)/F(m)), the maximum photo-oxidizable P700 (P(m)), the energy distribution in PSII and the redox state of P700 at 25°C under a PFD of 100 μmol m(-2) s(-1) were determined before and after chilling treatment and during subsequent recovery. We found that the CEF was significantly stimulated during the recovery after photodamage. There is a significant positive correlation between stimulation of CEF and photodamage of PSII during recovery. Our results indicated that CEF was significantly stimulated in order to enhance the synthesis of ATP for the fast repair of PSII. The stability of PSI activity favored the fast repair of PSII activity through stimulation of CEF.
Fast cyclic electron transport (CET) around photosystem I (PS I) was observed in sunflower (Helianthus annuus L.) leaves under intense far-red light (FRL) of up to 200 μmol quanta m−2 s−1. The electron transport rate (ETR) through PS I was found from the FRL-dark transmittance change at 810 and 950 nm, which was deconvoluted into redox states and pool sizes of P700, plastocyanin (PC) and cytochrome f (Cyt f). PC and P700 were in redox equilibrium with K
e = 35 (ΔE
m = 90 mV). PS II ETR was based on O2 evolution. CET [(PS I ETR) − (PS II ETR)] increased to 50–70 μmol e− m−2 s−1 when linear electron transport (LET) under FRL was limited to 5 μmol e− m−2 s−1 in a gas phase containing 20–40 μmol CO2 mol−1 and 20 μmol O2 mol−1. Under these conditions, pulse-saturated fluorescence yield F
m was non-photochemically quenched; however, F
m was similarly quenched when LET was driven by low green or white light, which energetically precluded the possibility for active CET. We suggest that under FRL, CET is rather not coupled to transmembrane proton translocation than the CET-coupled protons are short-circuited via proton channels regulated to open at high ΔpH. A kinetic analysis of CET electron donors and acceptors suggests the CET pathway is that of the reversed Q-cycle: Fd → (FNR) → Cyt cn → Cyt bh → Cyt bl → Rieske FeS → Cyt f → PC → P700 →→ Fd. CET is activated when PQH2 oxidation is opposed by high ΔpH, and ferredoxin (Fd) is reduced due to low availability of e− acceptors. The physiological significance of CET may be photoprotective, as CET may be regarded as a mechanism of energy dissipation under stress conditions.
The site of photoinhibition at low temperatures in leaves of a chilling-sensitive plant, cucumber, is photosystem I [Terashima et al. (1994) Planta 193: 300]. As described herein, selective photoinhibition of PSI can also be induced in isolated thylakoid membranes in vitro. Inhibition was observed both at chilling temperatures and at 25°C, and not only in the thylakoid membranes isolated from cucumber, but also in those isolated from a chilling-tolerant plant, spinach. Comparison of these observations in vitro to the earlier results in vivo indicates that (1) photoinhibition of PSI is a universal phenomenon; (2) a mechanism exists to protect PSI in vivo; and (3) the protective mechanism is chilling-sensitive in cucumber. The chilling-sensitive component seems to be lost during the isolation of thylakoid membranes. Very weak light (10-20μmol m-2 s-1) was sufficient to cause the inhibition of PSI. About 80% of the oxygen-evolving activity by PSII was maintained even after the activity of PSI had decreased by more than 70%. This is the first report of the selective photoinhibition of PSI in vitro.
Gas-exchange activity and seasonal evolution of some anatomical and biological characteristics linked to CO2 assimilation processes were analyzed in different green structures on field-grown Cabernet Sauvignon grapevine. Before anthesis, each flower showed 22+/-3 (mean +/- SE) regular stomata in the calyx and 9+/-3 in the apical part of the caliptrae. Irrespective of position, stomata size was 58+/-11 microm2. Just after anthesis, the stomata density was approximately 7+/-2 stomata per berry. Young tendrils had 27+/-4 active and functional stomata per mm2, whereas no stomata were found on rachises. Ultrastructural views of the chloroplasts on the flower calyx and young tendrils showed little or no differentiation in distinct grana and stroma lamellae and large and small starch granules, respectively. From two weeks before to eight weeks after anthesis, the flower, grape berry, and tendril did not reach the compensation point and therefore did not fix atmospheric CO2. In the light, the main photosynthetic role of these organs and structures was the reassimilation of respiratory CO2. During anthesis, progressive decreases in direct light resulted in a progressive increase in respiration activity. The CO2 refixation activity decreased during berry and tendril development; this decline paralleled the reduction of chlorophyll a and b, carotenoids, and nitrogen content and the increase of wax weight per unit surface. The transpiration rate in flower, berry, and tendril decreased throughout development and was increased by direct sunlight. These results indicate features that could have important physiological implications when modeling canopy carbon gain of grapevines.
Limitations in photosystem function and photosynthetic electron flow were investigated during leaf senescence in two field-grown plants, i.e., Euphorbia dendroides L. and Morus alba L., a summer- and winter-deciduous, shrub and tree, respectively. Analysis of fast chlorophyll (Chl) a fluorescence transients and post-illumination fluorescence yield increase were used to assess photosynthetic properties at various stages of senescence, the latter judged from the extent of Chl loss. In both plants, the yield of primary photochemistry of PSII and the content of PSI remained quite stable up to the last stages of senescence, when leaves were almost yellow. However, the potential for linear electron flow along PSII was limited much earlier, especially in E. dendroides, by an apparent inactivation of the oxygen-evolving complex and a lower efficiency of electron transfer to intermediate carriers. On the contrary, the corresponding efficiency of electron transfer from intermediate carriers to final acceptors of PSI was increased. In addition, cyclic electron flow around PSI was accelerated with the progress of senescence in E. dendroides, while a corresponding trend in M. alba was not statistically significant. However, there was no decrease in PSI activity even at the last stages of senescence. We argue that a switch to cyclic electron flow around PSI during leaf senescence may have the dual role of replenishing the ATP and maintaining a satisfactory nonphotochemical energy quenching, since both are limited by hindered linear electron transfer.
Carbohydrate metabolism is important in plant sexual reproduction since sugar contents are determining factors for both flower initiation and floral organ development. In woody plants, flowering represents the most energy-consuming step crucial to reproductive success. Nevertheless, in these species, the photosynthesis performed by flowers supplies the carbon required for reproduction. In grapevine (Vitis vinifera), the inflorescence has a specific status since this organ imports carbohydrates at the same time as it exports photoassimilates. In this study, fluctuations in carbohydrate metabolism were monitored by analyzing gas exchanges, photosynthetic electron transport capacity, carbohydrate contents and some activities of carbohydrate metabolism enzymes, in the inflorescences of Pinot noir and Gewurztraminer, two cultivars with a different sensitivity to coulure phenomenon. Our results showed that photosynthetic activity and carbohydrate metabolism are clearly different and differently regulated during the floral development in the two cultivars. Indeed, the regulation of the linear electron flow and the cyclic electrons flow are not similar. Moreover, the regulation of PSII activity, with a higher Y(NPQ)/Y(NO) ratio in Gewurztraminer, can be correlated with the higher protection of the photosynthetic chain and consequently with the higher yield under optimal conditions of this cultivar. At least, our results showed a higher photosynthetic activity and a better protection of PSI in Pinot noir during the floral development.
The role of calyx lobes in CO2 exchange in persimmon (Diospyros kaki Thunb.) fruit was investigated during fruit growth and development. Carbon dioxide exchange rates of attached and detached fruit were measured in light and dark conditions in the field after calyx lobes were removed. Calyx lobes were removed at fruit growth stages I and III, which were defined as the period when fruit diameter increases >0.3 mm · d-1 (Zheng et al., 1990). Removing calyx lobes at stage I significantly inhibited fruit growth, while removing them at stage III had no effect on growth. Two weeks after calyx lobes were removed at stage 1, CO2 exchange decreased 80% in light and dark conditions compared with the control fruit. The rapid decreases of CO2 exchange rate by calyx lobe removal at stage I were obvious if expressed per fruit or on a fresh weight basis. In contrast, treatment at stage III had no effect on CO2 exchange rate of fruit and no effect on fruit growth. However, when the calyx lobe scars were sealed with Vaseline soon after calyx lobe removal at stage III, an immediate decline in CO2 exchange rate in the dark occurred with simultaneous inhibition of the final swell in fruit growth. A possible relationship between fruit growth potential and gas-exchange capacity is discussed.
Cyclic electron transport around photosystem I generates ATP without the accumulation of NADPH in chloroplasts. In angiosperms, electron transport consists of a PGR5-PGRL1 protein-dependent pathway and a chloroplast NADH dehydrogenase-like complex-dependent pathway. Most likely, the PGR5-PGRL1 pathway corresponds to the cyclic phosphorylation discovered by Arnon and contributes mainly to ΔpH formation in photosynthesis. ATP synthesis utilizes this ΔpH formed by both linear and PSI cyclic electron transport. Furthermore, acidification of the thylakoid lumen downregulates light energy utilization in photosystem II and also electron transport through the cytochrome b6f complex. In the absence of PGR5, chloroplast NDH compensates for the reduced ΔpH formation to some extent. Additionally, proton conductivity is upregulated, probably through ATPase, in pgr5 mutants. The photosynthetic machinery likely forms a complex network to maintain high photosynthesis activity under fluctuating light conditions.
A series of experiments is presented investigating short term and long term changes of the nature of the response of rate of CO2 assimilation to intercellular p(CO2). The relationships between CO2 assimilation rate and biochemical components of leaf photosynthesis, such as ribulose-bisphosphate (RuP2) carboxylase-oxygenase activity and electron transport capacity are examined and related to current theory of CO2 assimilation in leaves of C3 species. It was found that the response of the rate of CO2 assimilation to irradiance, partial pressure of O2, p(O2), and temperature was different at low and high intercellular p(CO2), suggesting that CO2 assimilation rate is governed by different processes at low and high intercellular p(CO2). In longer term changes in CO2 assimilation rate, induced by different growth conditions, the initial slope of the response of CO2 assimilation rate to intercellular p(CO2) could be correlated to in vitro measurements of RuP2 carboxylase activity. Also, CO2 assimilation rate at high p(CO2) could be correlated to in vitro measurements of electron transport rate. These results are consistent with the hypothesis that CO2 assimilation rate is limited by the RuP2 saturated rate of the RuP2 carboxylase-oxygenase at low intercellular p(CO2) and by the rate allowed by RuP2 regeneration capacity at high intercellular p(CO2).
A comparative study of hydrogen peroxide accumulation under the effect of heat shock (42°C) during brief exposures is performed
in chloroplasts of various wheat varieties characterized by heat resistance. With consideration of the wheat variety and time
of action of temperature stress, a different stimulating effect of hydrogen peroxide concentration on cyclic photophosphorylation
activity is revealed.
In order to test the positive net CO2-fixation ability of tepals in the flower bud of Lilium hyb. enchantment, photoautotrophic characters were studied during pollen development in tepals and then compared with those in the leaf. Although mesophyll structure, plastid ultrastructure, stomata density and chlorophyll content were significantly different in both organs, tepals performed positive net CO2-fixation from the microspore mother cell stage up to pollen mitosis but not during pollen maturation. The measurements of CO2-fixation were performed in the Linear part of the saturation curve of the L-5 leaf at 100 mu mol photon m(-2) s(-1). In the tepals, CO2-fixation reached its maximal intensity at the tetrad stage with 1.83 +/- 0.12 mu mol CO2 m(-2) s(-1), against 3.17 +/- 0.27 mu mol CO2 m(-2) s(-1) in the L-5 leaf. Under these conditions, tepal CO2-fixation corresponded to 57.7% of the leaf assimilation, whereas the maximum chlorophyll concentration in the tepal represented 21.9% of the chlorophyll concentration in the leaf. The flower bud of Lilium may be considered not solely as a sink structure for the whole plant but also as a partly autonomous organ in terms of photosynthates.
We investigated CO2-fixation potential in the flower bud of Lilium hyb. enchantment by testing the ability of inner flower organs to perform photosynthesis during pollen development. We first showed that photosynthetically active radiation crosses the tepals and reaches the inner fertile organs. Despite the absence of leaflike photoautotrophic tissue, the anther exhibited most characteristics compatible with CO2-fixation from premeiosis to the vacuolated microspore stage: (1) chlorophyll fluorescence and anatomical structures associated with photosynthetically active tissues were localized in the connective tissue, the epidermis, the endothecium and the middle layers; (2) in these cell types, plastids contained well-developed thylakoids and grana; (3) the photoautotrophic cell layers in the anthers had a chlorophyll concentration reaching 17.6% of the L-5 leaf concentration and a Chi a/b ratio within a range of 1.5-1.9; (4) stomata density was more than twofold higher in the anther than in the L-5 leaf; and (5) in anthers, CO2-assimilation at 100 mu mol photon m(-2) s(-1) was 2.3 +/- 0.29 mu mol m(-2) s(-1) at the tetrad stage, which represented 72.6% of L-5 leaf CO2-fixation. In the filament, the ovary, and the style, the Chi a/b ratio was similar to that of the anther, bur plastid membranes were less developed and the low stomata density (less than 2 stomata mm(-2)) did not allow these organs to perform gas exchange rapidly.
Reproductive effort, or the proportion of an organism's resources allocated to reproduction, is a crucial aspect of an organism's life history; the optimal allocation of resources to reproduction in different environments has been the subject of much theorizing. Adequate tests of these theories have been hampered by the difficulties involved in assessing reproductive effort. In this paper, we address the problem of determining which structures and activities should be considered part of reproduction, using Agropyron repens as the experimental material. We approached the problem by first determining the structures and activities necessary for vegetative growth and then determining reproductive structures and activities by subtraction. Using carbon as the currency of allocation, we defined vegetative growth as those structures directly involved in the capture of carbon (i.e., leaves) plus all necessary support structures and activities. The necessary support structures and activities were determined by comp...
Photosynthesis is the incorporation of carbon, nitrogen, sulphur and other substances into plant tissue using light energy from the sun. Most of this energy is used for the reduction of carbon dioxide and, consequently, there is a large body of biochemical and biophysical information about photo synthetic carbon assimilation. In an ecophysiological context, we believe that most of today’s biochemical knowledge can be summarized in a few simple equations. These equations represent the rate of ribulose bisphosphate (RuP2)-saturated carboxylation, the ratio of photorespiration to carboxylation, and the rates of electron transport/photophosphorylation and of “dark” respiration in the light. There are many other processes that could potentially limit CO2 assimilation, but probably do so rarely in practice. Fundamentally this may be due to the expense, in terms of invested nitrogen, of the carboxylase and of thylakoid functioning. To reach our final simple equations we must first discuss the biochemical and biophysical structures — as they are understood at present — that finally reduce the vast number of potentially rate-limiting processes to the four or five listed above. A diagrammatic representation of these processes is given in Fig. 16.1.
In the past, ecophysiologically oriented photosynthesis research has been governed by gas-exchange measurements, mainly involving sophisticated (and costly) systems for simultaneous detection of CO2 uptake and H2O evaporation (see, e.g., Field et al. 1989). With the help of these methods, fundamental knowledge on in situ photosynthesis has been gained. Only recently, progress has been made in the development of alternative practical methods for nonintrusive assessment of in vivo photosynthesis which have the potential of not only evaluating overall quantum yield and capacity, but also allowing insights into the biochemical partial reactions and the partitioning of excitation energy (see, e.g., Snel and van Kooten 1990). As a consequence, photosynthesis research at the level of regulatory processes has been greatly stimulated, leading to important new concepts (see reviews by Foyer et al. 1990; Demmig-Adams 1990; Melis 1991; Allen 1992). In particular, chlorophyll fluorescence has evolved as a very useful and informative indicator for photosynthetic electron transport in intact leaves, algae, and isolated chloroplasts (reviews by Briantais et al. 1986; Renger and Schreiber 1986; Schreiber and Bilger 1987, 1992; Krause and Weis 1991; Karukstis 1991).
The carbon dioxide exchange rates of inflorescences, capsules, pseudobulbs and leaves were studied during the flowering and capsule development period in order to determine the carbon balance between photosynthetic organs and reproductive organs in a Laeliocattleya plant. The inflorescence consumed large amounts of carbon for respiration and tissue component, the leaf on the same shoot only supplied 6% of the consumed carbon. Consequently, the process of developing flowers and maintaining them until fading is mainly dependent on carbon sources from the pseudobulbs or carbon translocated from older leaves.In contrast, during the period of capsule development, the leaf on the same shoot could fix 42% of the carbon required for capsule development. Besides the leaf, carbon flows from fading flowers after pollination and the photosynthetic activity of developing capsules is supposed to contribute to the carbon balance in the pollinated plants.
As a part of a project aimed at elucidating the causal relationship between reserve mobilisation and the extent of shedding in Vitis vinifera L., we compared storage and fate of carbon (C) and nitrogen (N) reserves in two varieties differing in their susceptibility to fruitlet abscission. Merlot (susceptible) and Pinot Noir (P. Noir, not susceptible) vines were grown in trenches under semi-controlled conditions over a 3-y period after planting. Mobilisation of stored C and N, distribution of reserve materials within the vines and 15N uptake were followed particularly during the spring growth flush and floral development in the third year. At dormancy, starch levels in the perennial tissues (roots, trunk, canes) were higher in Merlot than in P. Noir. During the spring growth flush, starch level decreased markedly in the roots of both cultivars until early bloom. At that time, starch started to accumulate in P. Noir but not in Merlot. Similar variations were found with total N. Accordingly, 15N analysis showed that translocation of storage N to the annual tissues was nearly achieved at early bloom in P. Noir while it continued until pea berry size in Merlot. In parallel, N uptake increased during the spring growth flush, and it was higher in P. Noir than in Merlot. These results indicate that transition between heterotrophic (root) and autotrophic (leaf) mode of nutrient allocation towards the developing inflorescences occurs earlier in P. Noir. Possible consequences are discussed in relation to the susceptibility of each cultivar to shedding.
REPRODUCTION is often a lethal or semi-lethal activity, and for iteroparous plants it is often possible to show that reproduction has costs that are expressed in a reduced growth rate and/or an increased death rate1. Attempts have been made to compare life history patterns in flowering plants by measuring the fraction of a plant's annual dry matter production (or calorific value) that is allocated to reproduction (for example refs 2–4). The assumption is that the reproductive parts represent a cost in energy or materials. Clearly mineral nutrients and water must be gained by the reproductive structures from the remainder of the plant, but this is not necessarily true for the energetic and carbon economy of the reproductive structures. Many flowers and fruits are green and a fraction of the energy and carbon might be obtained by direct photosynthesis within these structures. This might be especially important during embryo growth if carpels and other organs that remain attached after flowering are green. In such cases the conventional estimation of reproductive effort (dividing seed weight by plant weight) would be incorrect and comparison of life history patterns and their evolutionary meaning would be invalid. There are reports of significant contributions of in situ photosynthesis in flower and seeds to their growth. Biscoe et al. have estimated that 47% of the carbon required for seed production in barley is provided by photosynthesis of reproductive and immediately adjacent plant structures5. Bazzaz and Carlson have shown that in the annual weed Ambrosia trifida L., net photosynthesis by reproductive structures amounts to 41 and 51%, respectively, of the carbon required for male and female inflorescences6. Here we report an analysis of the carbon budget of reproduction for 15 temperate deciduous trees. The budget was determined by measuring the weight, photosynthesis and dark respiration of flowers or inflorescences from bud break until seed maturity.
The photosynthetic contribution of a fruit to its carbon requirement throughout ontogeny and under different growing conditions was quantified in cucumber (Cucumis sativus L. cv. Corona). In addition, the effects of shading on fruit dry matter accumulation and the diurnal course of the elongation rate were studied. Fruit darkening had no photomorphogenic effect on fruit growth, while the cumulative photosynthetic contribution of a fruit to its own carbon requirement ranged from 1 to 5%. During the day there was always a net CO2 efflux. The photosynthetic rate per fruit, calculated as the difference between rates of CO2 exchange in light and dark, increased during fruit ontogeny, while the photosynthetic rate per unit fruit surface area declined. The latter was not dependent on fruit size. The photosynthetic activity per unit surface area of fruits was estimated to be about 20–30% as efficient as that of leaves. The rate of calculated photosynthesis was reduced by 60–65% when the photosynthetically active radiation incident on the fruit decreased from 200 to 50 μmol m−2 s−1. Temperature (20–30°C) had no pronounced effect on the rate of calculated fruit photosynthesis when fruits of the same developmental stage (temperature sum) were compared. However, the relative photosynthetic contribution of a fruit to its carbon requirement increased when temperature decreased. Moreover, this contribution increased when irradiance increased or fruit growth was reduced by competing fruits. During fruit ontogeny the daily photosynthetic contribution was highest (up to 15%) in young and old fruits, with a small growth rate.
Corollas of Petunia hybrida (cv. Hit Parade Rosa) flowers fixed 14CO2 under both light and dark conditions. Rates of light fixation were much higher in mature pink corollas than in young, green corollas [57 and 9 nmol (ngchl)1 min-1], paralleling the development of chloroplasts in these tissues. Stomatal conductance in corollas was only 12% of that in green leaves, mainly due to the presence of few, and non-functioning stomata in the corolla. The activity and concentration of ribulose bisphosphate carboxylase (EC 4.1.1.39) in corolla extracts were only about 30% (per unit Chi) of those in extracts from green leaves. These results, together with previous results, might indicate a coordinated reduction in activity of systems participating in photosynthesis in corollas. The fixation products following a 6 s pulse with 14CO2, were typical of C, plants in both corollas and green leaves, but a higher level of β-carboxylation products was found in the corollas. The activity of phosphoenol-pyruvate carboxylase (EC 4.1.1.31) (per unit protein) was similar in both tissues. Although the total carbon fixed by the corolla constituted only a small part of the metabolites required for flower development, certain photosynthetic metabolites might have a regulatory role in flower development.
In addition to photosynthesis as in the leaf, fruit possess a system which refixes CO2 from the mitochondrial respiration of predominantly imported carbon. This pathway produces malate by the action of phosphoenolpyruvate carboxylase, PEPC, (E.C. 4.1.1.31) and appears to be regulated primarily by the cytosolic concentration of HCO3/CO2 and malate. Malate is stored in the vacuole as malic acid, constituting a major carbon pool and a potential substrate for respiration. The PEPC in apple fruit proves to be an efficient form of the enzyme with low Michaelis constants, i.e. Km = 0.09 mol m-3 PEP and 0.2 mol m–3 HCO3, and large Ki= 110 mol m-3 HCO3. In fleshy fruit, chlorophyll and chloroplasts are unevenly distributed; they resemble the C3 sun-type and arc concentrated in the perivascular tissue, with smaller chloroplasts, fewer grana per chloroplast and a larger degree of vacuolation than commonly found in a leaf of the same species. Fruit photosynthesis often compensates for respiratory CO2 loss in the light. However, due to respiration in the dark, CO2 loss is in excess of photosynthetic gain in the light, such that a continual loss of CO2 was observed in the diurnal cycle and which is maintained throughout fruit development. The rate of CO2 exchange decreases on a fresh weight or surface basis, but increases with fruit ontogeny on a per fruit basis, causing accumulation of several percent CO2 in the internal cavity. Stomata are present in the outer epidermis of those fruits examined, but with a 10-to 100-fold lesser frequency than in the abaxial epidermis of leaf of the same species. The number of Stomata is set at anthesis and remained constant, while the stomatal frequency decreases as the fruit surface expands. Stomata are as sensitive as in leaves in the early stages of fruit development, but often are transformed into lenticels during fruit ontogeny, thereby decreasing the permeability of the outer epidermis. The discrepancy between the CO2-concentrating mechanism provided by PEPC analogous to C4/CAM Photosynthesis and the kinetics of fruit PEPC, characteristic of C3/non-autotrophic tissue, suggests the definition of a new type of ‘fruit photosynthesis’ rather than its categorization within an existing type.
Gas exchanges, chlorophyll (Chl) a fluorescence and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) were determined in tomato (Lycopersicon esculentum Mill.) fruits picked at different developmental stages (immature, red-turning, mature, and over-ripe). The fruits did not show signs of CO2 fixation. However, photochemical activity was detectable and an effective electron transport was observed, the values of Chl fluorescence parameters in green fruits being similar to those determined in the leaves. The RuBPCO activity, which was similar to those recorded in the leaves at the immature stage of the fruit, decreased as the fruit ripened. PEPC activity was always higher than RuBPCO activity.
The Gewurztraminer (GW) and the Pinot noir (PN) cultivars of grapevine differ in their sensitivity to environmental factors that can cause flower abscission, cv. GW being the most sensitive. In order to further define the mechanisms leading to abscission, and owing to the importance of sugars in the achievement of sexual organ ontogenesis, we attempted to correlate the chronology of flower ontogenesis with the variations of carbohydrates in the inflorescence. In the vineyard, under optimal climatic conditions, fruit set of cv. GW and cv. PN was 82% and 65%, respectively. The sugar distribution was different in their inflorescences during the entire duration of flower development. Between stages 15 and 17, flowers of GW and PN reached the crucial meiosis stage. At that time, the inflorescences of cv. GW exhibited higher concentrations of starch and sucrose, whereas those of PN presented higher levels of glucose and fructose. Despite higher starch concentrations in GW inflorescences, starch reserves were present in the ovules and anthers of PN but not in those of GW. These results suggest that the higher content of reserve and transport carbohydrates in the inflorescences of GW favour flower development and fruit set under optimal environmental conditions. Furthermore, since meiosis represents a key step of female development, the different sugar concentrations in the inflorescences of the two cultivars at stages 15 and 17 could be related to the sensitivity to flower abscission under climatic stress. In particular, the presence of starch granules in PN ovules and anthers might explain the higher resistance of this cultivar to flower abscission.
Photosynthetic rates by flowers of the shrubs Encelia farinosa and E. californica were studied during three phenological stages of flower development. Both gross photosynthesis and dark respiration rates in the flowers were of similar magnitude and decreased with floral development. Floral photosynthetic rates were saturated by an irradiance equivalent to one half full noon sunlight. Net photosynthesis of flowers was rarely positive and decreased substantially with increased flower temperature. Gas exchange by the flower was unaffected by the water vapor pressure gradient. These results are analyzed in terms of the microclimate experienced by the flowers and the relative contribution of floral photosynthesis to the economy of the flower.
Cyanobacteria and plastids harbor a putative NAD(P)H- or ferredoxin-plastoquinone oxidoreductase that is homologous to the NADH-ubiquinone oxidoreductase (complex I) of mitochondria and eubacteria. The enzyme is a multimeric protein complex that consists of at least 11 subunits (NDH-A-K) and is localized in the stroma lamellae of the thylakoid membrane system. We investigated the expression of the different subunits of the enzyme in mesophyll and bundle-sheath chloroplasts of Sorghum bicolor [L.] Moench, a C4 plant of the NADP-malic enzyme type. The relative amounts of the subunits NDH-H, -J and -K were strongly increased in bundle-sheath plastids as compared to mesophyll plastids. This increase was accompanied by enhanced transcript levels for all subunits except NDH-I. Because the main function of the protein complexes in the thylakoid membranes of bundle-sheath chloroplasts (photosystem I, cytochrome b
6/f-complex and ATPase) is the generation of ATP for CO2 fixation via cyclic electron transport, we conclude that the NAD(P)H/ferredoxin-plastoquinone oxidoreductase is an essential component of the cyclic electron-transport pathway in chloroplasts.
The gas exchange of flowerheads was determined in Arctium tomentosum and A. lappa during their development. The light, temperature and CO2 responses were used to estimate flowerhead photosynthesis and the in situ contribution of carbon assimilation to the carbon requirement of the plant for supporting a flowerhead. Changes in vapour pressure deficit had no effect on flowerhead photosynthesis rates and were not included in the model.
In both species assimilatory capacity correlated with total bract chlorophyll content. Light, temperature and CO2 response curves were very similar in form between species, differing only in absolute rates. During all stages of development, flowerheads always exhibited a net carbon loss, which was mainly determined by temperature. The respiration rate decreased in the light, the difference of CO2 exchange in the dark and in the light was interpreted as photosynthesis. This rate was larger in A. lappa than in A. tomentosum. 30% of the total C requirement of A. lappa flowerheads was photosynthesized by its bracts, the total contribution offlowerhead photosynthesis in A. tomentosum was only 15%. The potential competitive advantages of variation in flowerhead photosynthesis are discussed.
SummaryIn addition to the green leaves, commonly considered as the primary sources of photosynthate production, higher plants can potentially use almost all vegetative and reproductive structures to perform photosynthetic CO2 assimilation. Green leaves, stems and green sterile flower organs, optimized for light harvesting and photosynthetic performance, are characterized by net photosynthetic assimilation utilizing mainly the atmospheric carbon dioxide. In contrast, chlorophyll-containing bark and wood tissue, most fruit, root and fertile flower organs are principally sub-ordinated to non-photosynthetic functions, but typically perform an effective internal CO2 recycling using the respiratory released CO2. Non-foliar photosynthesis, either manifested as net photosynthesis or internal CO2 refixation is regarded as an important strategy of additional carbon-acquisition. While chlorophyllous stems or aerial roots even can serve as primary photosynthetic organs, reproductive structures could derive up to 60%; of their total carbon requirement from own CO2 fixation. In the review, the main strategies of additional carbon acquisition by non-foliar photosynthetic organs are illustrated, presenting an extensive compilation of published data completed with relevant own studies.
Measurements of the quantum yields of chlorophyll fluorescence and CO2 assimilation for a number of plant species exposed to changing light intensity and atmospheric CO2 concentrations and during induction of photosynthesis are used to examine the relationship between fluorescence quenching parameters and the quantum yield of non-cyclic electron transport. Over a wide range of physiological conditions the quantum yield of non-cyclic electron transport was found to be directly proportional to the product of the photochemical fluorescence quenching (qQ) and the efficiency of excitation capture by open Photosystem II (PS II) reaction centres (Fv/Fm). A simple fluorescence parameter, ΔφF/φFm, which is defined by the difference in fluorescence yield at maximal φFm, and steady-state φFs, divided by φFm, can be used routinely to estimate changes in the quantum yield of non-cyclic electron transport. It is demonstrated that both the concentration of open PS II reaction centres and the efficiency of excitation capture by these centres will determine the quantum yield of non-cyclic electron transport in vivo and that deactivation of excitation within PS II complexes by non-photochemical processes must influence the quantum yield of non-cyclic electron transport.
This study examined the cost of reproduction and photosynthetic characteristics of the reproductive structures of Spiranthes cernua, an agamospermic, terrestrial orchid. Reproduction was frequent: two-thirds of the plants flowered at least 2 yr in a row and one-fourth of the consecutive-year runs were ~3 yr. Neither a significant decrease in leaf area nor a reduced likelihood of flowering was observed following 1 or 2 yr of inflorescence production. While there was a tendency for plants producing >16 flowers to have decreased size the next year, plants with the greatest number of flowers (31+) were the most likely to reproduce. Leaf and reproductive gas exchange were measured in the field. Low but positive rates of net photosynthesis were documented at all stages of inflorescence development. The average rates of photosynthesis for each stage were: leaves, 9.2 mmol CO2/m2s; inflorescence in bud, 3.7 mmol CO2/m2s; inflorescence in flower, 2.5 mmol CO2/m2s and infructescence, 0.2 mmol CO2/m2s. Based on diurnal gas exchange, the contribution of leaves and reproductive structures to seasonal carbon assimilation was 91.6 and 8.4%, respectively. The role of the inflorescence as a source and sink for carbon assimilation may lower the cost of reproduction and support frequent inflorescence production.
Having long been debated, it is only in the last few years that a concensus has emerged that the cyclic flow of electrons around Photosystem I plays an important and general role in the photosynthesis of higher plants. Two major pathways of cyclic flow have been identified, involving either a complex termed NDH or mediated via a pathway involving a protein PGR5 and two functions have been described-to generate ATP and to provide a pH gradient inducing non-photochemical quenching. The best evidence for the occurrence of the two pathways comes from measurements under stress conditions-high light, drought and extreme temperatures. In this review, the possible relative functions and importance of the two pathways is discussed as well as evidence as to how the flow through these pathways is regulated. Our growing knowledge of the proteins involved in cyclic electron flow will, in the future, enable us to understand better the occurrence and diversity of cyclic electron transport pathways. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts.
Cyclic electron flow around photosystem I (CEF1) is thought to augment chloroplast ATP production to meet metabolic needs. Very little is known about the induction and regulation of CEF1. We investigated the effects on CEF1 of antisense suppression of the Calvin-Benson enzymes glyceraldehyde-3-phosphate dehydrogenase (gapR), and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit (SSU), in tobacco (Nicotiana tabacum cv. Wisconsin 38). The gapR, but not ssuR, mutants showed substantial increases in CEF1, demonstrating that specific intermediates, rather than slowing of assimilation, induce CEF1. Both types of mutant showed increases in steady-state transthylakoid proton motive force (pmf) and subsequent activation of the photoprotective q(E) response. With gapR, the increased pmf was caused both by up-regulation of CEF1 and down-regulation of the ATP synthase. In ssuR, the increased pmf was attributed entirely to a decrease in ATP synthase activity, as previously seen in wild-type plants when CO₂ levels were decreased. Comparison of major stromal metabolites in gapR, ssuR and hcef1, a mutant with decreased fructose 1,6-bisphosphatase activity, showed that neither the ATP/ADP ratio, nor major Calvin-Benson cycle intermediates can directly account for the activation of CEF1, suggesting that chloroplast redox status or reactive oxygen species regulate CEF1.
We investigated the development of the locule tissues of Gasteria verrucosa (Mill.) H. Duval during microsporogenesis using electron microscopy and summarized it in detailed pen-drawings.In the early stages of development, the epidermis, endothecium and middle layer show no remarkable processes relating to tapetum and pollen development.The tapetum regulates the disappearance of the original cell walls and the callose walls from the microspores and itself. These wall materials partly turn into starch in both tissues.The spherical shape of the meiotic callose walls and the presence of the cytomictic channels enable the pollen mother cells to divide into equally shaped microspores, which is important for random dispersal.