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Porosity and moisture of grapevine buds. (A) At the top, a sectioned bud is shown to depict the three evaluated parts of the bud: the green tissue, the trichomes, and the outer scales. The porosity and the moisture are represented as percentages and were determined by tissue density and weight, respectively. Asterisks indicate statistically significant differences between the different types of tissue using a Tukey comparison (n=5, P<0.0001). (B) Section of a µCT scan representing the four types of tissues evaluated to calculate the porosity by pixel analysis. (C) Comparison of porosity determined by pixel analysis at 0 h and 168 h. Different letters indicate statistically significant differences between the different types of tissue using a Tukey comparison (n=3, P<0.0001). No statistically significant differences were observed between 0 h and 168 h for any type of tissue. Downloaded from https://academic.oup.com/jxb/article-abstract/71/2/719/5481731 by guest on 05 April 2020
Source publication
The physiological constraints on bud burst in woody perennials, including vascular development and oxygenation remain unresolved. Both light and tissue oxygen status have emerged as important cues for vascular development in other systems, however, grapevine buds have only a facultative light requirement, and data on the tissue oxygen status has be...
Contexts in source publication
Context 1
... molecular volume, determined by the electron density of the optimized structures, was greater for eosin Y than for the other molecules ( Fig. 2A). Indeed, the molecular volume ( Supplementary Fig. S5) positively correlated with the molecular weight of the molecules, being the lowest for rhodamine green ( Supplementary Fig. S5). The charges and the electrostatic potential of these molecules were also evaluated to understand if their different mobilities are due to different physical-chemical properties. ...
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... molecular volume, determined by the electron density of the optimized structures, was greater for eosin Y than for the other molecules ( Fig. 2A). Indeed, the molecular volume ( Supplementary Fig. S5) positively correlated with the molecular weight of the molecules, being the lowest for rhodamine green ( Supplementary Fig. S5). The charges and the electrostatic potential of these molecules were also evaluated to understand if their different mobilities are due to different physical-chemical properties. ...
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... pO 2 of the meristematic core of the bud (between 2000 µm and 2400 µm depth) was elevated following the initiation of bud burst. Exploring the structural context further, we then determined the tissue porosity and moisture content, two variables known to affect O 2 diffusion, of the scales, the trichomes, and the green tissue of grapevine buds (Fig. 5A). These variables were first determined by weight and volume data. The greatest porosity (% gas spaces per unit tissue volume) was found in the trichomes, 77%, followed by 30% for the outer scales and 12% for the green tissue. Humidity (% water per unit tissue weight) was the lowest for the trichomes (14%), 18% for the scales, and 41% ...
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... 12% for the green tissue. Humidity (% water per unit tissue weight) was the lowest for the trichomes (14%), 18% for the scales, and 41% for the green tissue. We further investigated the porosity analysing the structural data obtained by µCT, being able also to evaluate the porosity of the base of the bud, the trichome, bracts, and outer scales (Fig. 5B). The values were 85-88% for the trichomes, 37-38% for the outer scale, 5-6% for the bracts, and 8-10% for the base, at 0 h and 168 h (Fig. 5C). Overall, the results of porosity from the structural images correlated well with the other results. However, the differences between the tissues were enhanced. No statistically significant ...
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... the green tissue. We further investigated the porosity analysing the structural data obtained by µCT, being able also to evaluate the porosity of the base of the bud, the trichome, bracts, and outer scales (Fig. 5B). The values were 85-88% for the trichomes, 37-38% for the outer scale, 5-6% for the bracts, and 8-10% for the base, at 0 h and 168 h (Fig. 5C). Overall, the results of porosity from the structural images correlated well with the other results. However, the differences between the tissues were enhanced. No statistically significant differences were observed between 0 h and 168 h in terms of porosity of the ...
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... on the tissue, the limiting diameter of these pores can vary. In grapevine buds, considering that rhodamine green was shown to be transported ( Jones et al., 2000), the information of acid fuchsin and eosin Y was used to determine the pore size of the apoplast in grapevine prior to bud burst ( Supplementary Fig. S5). Our value of 2.1 nm diameter pore size in buds is much lower than those observed in other tissues. ...
Citations
... Much of the supply of grapevine fruits is reliant on the successful timing of budburst [11]. Phytohormones, xylem pressure, tissue oxygen status, callose deposition, photoperiod, and soil temperature are already reported to be involved in this phase transition [12][13][14]. ...
In grapevine, the transition from a dormant bud to budburst is a critical developmental process related to vegetative and reproductive growth. We generated a time series analysis (five sampling time points) and used transcriptome, small RNA, and whole-genome bisulfite sequencing to characterize this transition. Ecodormant buds took an average of 17 days to budburst. Transcriptome analysis identified a total of 7002 differentially expressed genes across all sampling times and revealed that the brassinosteroid metabolism and the linoleic acid metabolism pathways are upregulated and downregulated respectively across all time points. Gene expression cluster analysis identified the activation of the photosynthesis pathway and photosynthesis related genes during this transition. miRNA expression analysis identified a steady increase in expression of two miRNAs, miR159a and miR159b during the transition from dormancy to budburst. Our analysis suggests that these two miRNAs promote budburst by repressing the expression of auxin responsive genes. Finally, a continued increase in CG methylation levels was observed during the dormancy to budburst transition. Differential methylation analysis, considering dormant buds as the control stage, yielded 6354 differentially methylated regions across the genome. Two glucosidase genes exhibited increases in promoter methylation and a corresponding decrease in gene expression in our analysis. This study provides a multi-omics view of grapevine bud transition from dormancy to bud burst and unveils the interacting genetic and epigenetic networks regulating this process.
... The method has been used to extensively characterize species and genotypic variation for winter cold tolerance in several studies (Londo and Kowaleski, 2017;Mills et al., 2006;North and Kovaleski, 2022), suggesting DTA as a reliable tool to evaluate cold survival, although methods for monitoring quantitatively ecodormancy release dynamics are still lacking. Usually, growth resume in grapevine buds manifests after the occurrence of specific physiological and metabolic events such as an increase in xylem pressure followed by high concentration of phytohormones and sugars in the xylem sap (Meitha et al., 2018) as well as a rise in tissue oxygen status (Signorelli et al., 2020). Meitha et al. (2018) showed a strong regulation of genes linked to photosystems in quiescent buds suggesting the presence of a priming strategy to develop autotrophic metabolism even in the absence of light. ...
Early budburst is becoming an increasingly challenging topic in viticulture. Anticipating vegetative resume results in an overall phenological advance, in potential higher risks of late frost and subsequent negative effects on berry quality and overall vine productivity. Phenotypic variation for date of budburst onset (BBCH07) is known in Vitis vinifera and potential exploitation of data regarding thermal requests to reach BBCH07 are critical in defining new avenues for viticulture. Nevertheless, reproducible methods are lacking in defining phenological progression in grapevine and further efforts are needed to standardize quantitative dataset associated with early growth stages appearance. In this work, a panel of twenty-one Vitis vinifera varieties grown in an experimental vineyard were assessed for early phenological onset (pre-to-post budburst) via visual observation, quantum yield of photosystem II in the dark adapted (F v /F m) bud section and growing degree days accumulation over three years. Further experiments were carried out under controlled environmental conditions to evaluate the effect of different simulated late frost on bud viability. Our data proposes F v /F m from bud section as a quantitative and reliable tool, although destructive following our pipeline, to monitor early phenological events in grapevine with significant non-linear associations of the F v /F m with growing degree days on base 6 • C (GDD 6) and phenology. We observed significant (p < 0.001) inter-varietal variation for thermal requests to reach budburst ranking from 140 to 260 GDD 6 although some varieties showed inconsistent data between years (i.e. a plastic response). Late frost damage was associated with phenological progression suggesting a linear and positive correlation between cold injury and de-acclimation from cold hardiness up until first leaf appearance. However, monitoring F v /F m in selected varieties provided evidence of varietal-specific response to late frost with e.g., Chardonnay and Gewürztraminer showing maintenance of photosystem II activity even at advanced phenological stages. This suggests the presence of preferable acclimation mechanisms to late frost in Vitis vinifera that will deserve further investigation. Our data provides a comprehensive analysis of early phenological events in grapevine, providing novel methods of assessment (F v /F m), varieties possessing escape strategies (i.e. large thermal accumulation to reach BBCH07) and varieties with putative late frost tolerance even after budburst. Overall, further work is ongoing to define the mechanisms underlying late frost tolerance per se and to identify novel varieties with preferable combination of traits.
... After chill requirements are satisfied, buds enter the ecodormancy stage, followed by growth resumption under favourable conditions, which is associated with a reopening of some transport pathways (Savage and Chuine, 2021). In more details, xylem continuity between twig and buds during dormancy could indeed be disrupted in order to prevent ice formation as a protection against frost (Ashworth, 1984;Sperry, 1993;Ameglio et al., 2002), potentially due to the presence of immature xylem cells or modifications to cell walls or tannin like substance (Goodwin, 1967), as shown in grape (Signorelli et al., 2020) and in pine trees (Lapa et al., 2017). However, recent studies have suggested that the symplasmic pathway may have the primary role in the dynamics of transport capacity throughout dormancy in trees (Rinne et al., 2011;Tylewicz et al., 2018). ...
... Genes coding for these proteins are inhibited during endodormancy in rice and could reduce the water transport (Afzal et al., 2016). Moreover, the apoplastic pathway is also regulated by changes in the cell wall structure allowing a restricted conductance of large macromolecule such as sugars until the transition to bud burst (Maurel et al., 2004;Signorelli et al., 2020). ...
... Calcein tracer could be a reliable marker for transport capacity during dormancy Previous studies have attempted to visualize transport capacity to the bud with a main focus on the transition from endodormancy to ecodormancy (Ashworth and Rowse, 1982;Rinne et al., 2001;Xie et al., 2018;Signorelli et al., 2020). Their results led to the hypothesis that transport capacity resumption was associated with endodormancy release and the initiation of bud burst. ...
Introduction
To avoid the negative impacts of winter unfavorable conditions for plant development, temperate trees enter a rest period called dormancy. Winter dormancy is a complex process that involves multiple signaling pathways and previous studies have suggested that transport capacity between cells and between the buds and the twig may regulate the progression throughout dormancy stages. However, the dynamics and molecular actors involved in this regulation are still poorly described in fruit trees.
Methods
Here, in order to validate the hypothesis that transport capacity regulates dormancy progression in fruit trees, we combined physiological, imaging and transcriptomic approaches to characterize molecular pathways and transport capacity during dormancy in sweet cherry (Prunus avium L.) flower buds.
Results
Our results show that transport capacity is reduced during dormancy and could be regulated by environmental signals. Moreover, we demonstrate that dormancy release is not synchronized with the transport capacity resumption but occurs when the bud is capable of growth under the influence of warmer temperatures. We highlight key genes involved in transport capacity during dormancy.
Discussion
Based on long-term observations conducted during six winter seasons, we propose hypotheses on the environmental and molecular regulation of transport capacity, in relation to dormancy and growth resumption in sweet cherry.
... cwINV activity is generally associated with organ sink strength [41,53,93,94]. Previous studies have also linked cwINV activity to sink strength generation in the context of bud development and to a commitment to bud break: firstly, increasing cwINV activities were observed in the context of bud break in the buds of different plant species [89,95]. Secondly, it has been proposed that cwINV activity potentially contributes to sink strength generation in buds by mediating sugar transport in the apoplast [89,95]. ...
... Previous studies have also linked cwINV activity to sink strength generation in the context of bud development and to a commitment to bud break: firstly, increasing cwINV activities were observed in the context of bud break in the buds of different plant species [89,95]. Secondly, it has been proposed that cwINV activity potentially contributes to sink strength generation in buds by mediating sugar transport in the apoplast [89,95]. Thirdly, an increase in the levels of cwINV-encoding transcripts was observed in grapevine leaf buds as the temperatures grew warmer and the buds resumed growth [3]. ...
Bud dormancy enables deciduous fruit trees to endure unfavorable conditions during winter, and considerably impacts growth and reproduction in spring. We investigated acid invertase activities during dormancy release until bud break under natural (orchard) conditions in two consecutive years. Our aim was to relate the activity patterns to the developmental progression and to air temperature, which is a major factor influencing the developmental processes at that stage. The enzyme assays were performed on extracts from leaf buds of the cultivar Idared, sampled from early March to April in the years 2020 and 2021. The air temperature was continually monitored during the observation periods. cwINV activity showed a trend of slight increase at the earlier developmental stages and sharply increased during bud break in both years. cwINV is known to contribute to organ sink strength. Its up-regulation may, therefore, be related to the increasing developmental demand for carbohydrates in apple leaf buds during dormancy release until bud break. vacINV activity was relatively constant at the earlier stages and also showed a pronounced increase in activity during bud break in both years. However, in both years, we observed drops in vacINV activity following cold spells. vacINV activity has been associated with growth via cell elongation through the regulation of cell turgor and may, thus, be involved in bud break. Therefore, we suggest that the down-regulation of vacINV activity as a consequence of cold spells might contribute to a delay in bud break to protect young leaf tissues from exposure to cold stress conditions.
... 10°C were observed during 364 the bud break period (late April -May; Fig. 1). The timing of budbreak, by creating a flow of 365 water towards the expanding organs through the enlargement of apoplastic pores from the stem 366 to the bud (Rinne et al., 2001;Signorelli et al., 2020) and the influx of solutes into the buds 367 (Bonhomme et al., 2009), is likely to influence the relationship between soil temperature and 368 water content. Indeed, differential budbreak in the canopy would induce greater variability 369 between stems, explaining why these points deviate from the regression (Fig. 1). ...
Water content is a key variable in plant physiology, even during the winter period. To simulate stem water content (WC) during the dormant season, a series of experiments were carried out on walnut trees under controlled conditions. In the field, WC was significantly correlated with soil temperature at 50 cm depth (R2 = 0.526). In the greenhouse, WC remained low as long as soil temperature was kept cold (<+5 °C) and increased after soil temperature was warmed to +15 °C, regardless of the date. Stem dehydration rate was significantly influenced by WC and evaporative demand. A parsimonious model with functions describing the main experimental results was calibrated and validated with field data from 13 independent winter dynamics in Juglans regia orchards. Three functions of water uptake were tested and gave equivalent accuracies (RMSE = 0.127-8; RMSEP = 0.116). However, only a sigmoid function describing the relationship between root water uptake and soil temperature gave values in agreement with the experimental results. Finally, the simulated WC provided similar accuracy in predicting frost hardiness compared to the measured WC (RMSE ca. 3 °C) and was excellent in spring (RMSE ca. 2 °C). This model may be a relevant tool for predicting the risk of spring frost in walnut trees. Its genericity should be tested in other fruit and forest tree species.
... Thus, viral spreading at early developing bud tissues is made through plasmodesmata. Plasmodesmata have a narrow diameter and, specifically in grapevine, their molecular exclusion size is around 2 nm at bud burst (Signorelli et al., 2020). This pore size is not sufficient for the transport of viral agents such as GFLV and GFkV, whose diameter is around 30 nm, or of GLRaV-1 and GLRaV-3, which are 12 nm in diameter. ...
Viral diseases in grapevine cause large economic losses due to decreased irregular yield and unbalanced ripening, and can even lead to plant mortality. There is a large number of grapevine viral agents, and a few of them have a prominent impact due to their worldwide distribution, virulence, and incidence. Although previous research has evaluated variations in viral load between organs and time since infection, there is still a lack of knowledge on how the viruses are transported toward developing tissues. In this work, we present the results of two experiments that contribute to understanding the spread dynamics of four major grapevine viruses (GFLV, GFkV, GLRaV-1, and GLRaV-3). Bud and leaf tissues were sampled from shoots obtained from cv. 'Garnacha' cuttings known to be infected with one of these viruses. Bud samples taken at early development stages were used to understand short-distance transport, while leaves taken from young shoots represented long-distance transport, driven mainly through the phloem. Our results show that all viruses were able to invade tissues from the beginning of development. The dissemination ability of GFLV was considerable, as the viral load detected in young organs was as high as in the dormant shoot. Furthermore, for GFLV and GFkV, it was shown that the viral load in young shoots does not follow the general assumption of older tissues accumulating a higher viral load but, conversely, a higher viral load closer to the shoot tip might be driven by the sink strength.
... Data represented as scatterplots of raw data (n = 3) fitted with a LOESS regression curve and 95% confidence intervals shown as 'grey shading'. (noise in data is caused by probe moving through different regions within the complex bud; Signorelli et al., 2018). Dotted line indicates pO 2 = 10 kPa. ...
Abstract Grapevine (Vitis vinifera L.) is the most widely cultivated fruit crop worldwide, contributing substantially to rural economies. The production cycle and productivity depend on seasonal cues and can range from a strongly deciduous habit in cool‐temperate climates to evergreen in subtropical and tropical climates. The influence of the different seasonal conditions on the dynamics of the perennating bud, including the degree of growth and metabolic quiescence, cell cycle status and internal tissue oxygen status between different climatic zones is largely unknown. This knowledge is important for adapting to changing climate conditions and for crop expansion to wider regions. This study investigated the growth and metabolic physiology of the perennating bud of commercially grown cv. Flame Seedless table grapes from Mediterranean and subtropical climate in Western Australia, from summer until late winter. Climate data were obtained, showing differences in minimum (night) temperature between the two climates, reflected by differences in calculated chilling units. Bud dormancy increased during autumn of both climates;however, the onset and depth of dormancy of buds from the subtropical region were attenuated relative to the Mediterranean condition. Stark contrasts were also observed in metabolism. The respiration of subtropical‐grown buds increased over fivefold during late autumn and winter, while that of Mediterranean‐grown buds increased less than twofold. This was also reflected in less desiccation of the subtropical‐grown buds, and an apparently greater degree of hypoxia within the bud during late winter, prior to bud burst. Collectively, these data show pronounced differences in growth and metabolic physiology of commercially grown table grapes, which provide a foundation for investigating the influence of differing climate and seasonality on the growth and productivity of table grapes and how these may be managed through breeding and agronomy.
... However, the use of oxygen microsensors is being extended to determine oxygen production in air phase, placing the device and the sample in a grease sealed microchamber under slow agitation. This setup was used to measure respiration in grapevine buds (Signorelli et al., 2020). When different volumes of the sample are expected, their volumes need to be determined to avoid over or under-estimation of the oxygen consumption/production rates. ...
Photosynthesis is an essential metabolic pathway for plants, contributing to growth and biomass production. Environmental adverse conditions have a negative impact on photosynthetic activity, reducing crop yield and productivity, a situation that has been worsen due to the actual global climate change scenario. Plants have different mechanisms to cope with this changing environment, ranging from photo-protective mechanisms to adaptive processes aiming acclimation. To understand these processes, and in the search for resistant varieties of crops, plant scientists have been assessing photosynthetic activity under different conditions and in different plant species. There are multiple methodologies to study photosynthesis; however, not all of them are suitable for every working condition or plant species. In this review, we offer an overview of the available methodologies to assess photosynthesis, from the most conventional to other less well known. We highlight the strength and weakness of each technique, and discuss how photosynthetic measurements can be linked and integrated to other methodologies (e.g. omics). Moreover, we address how photosynthesis is affected by intra-plant and inter-plants factors, as well as environmental variables. The analysis of the photosynthetic process from a wider and systemic perspective will lead to a closer understanding of plant physiology, ultimately improving crop yield and land use efficiency.
... As a result, the structure of vessels, including secondary wall thickening, perforation pits of vessel elements, and arrangement of fruit xylem cells in the fruit, is still a mystery. Currently, new methods using confocal laser scanning microscopy (CLSM), micro computed tomography (micro-CT) and nuclear magnetic resonance (NMR) have been applied in structural and functional research in plant sciences (Signorelli et al., 2020;Xiao et al., 2021aXiao et al., , 2021bAbera et al., 2014). These techniques have provided new information about the characteristics of vessel elements in grapevine stems, but in fruit tissue these advanced technologies have failed to be effective due to limits of current methods of sample preparation. ...
The visualization and evaluation of fruit vascular bundles in grape are indispensable for understanding the development and growth of the fruit. The vascular bundles in grape are as thin as human hair, and strongly adhere to flesh cells, making it difficult to isolate individual intact vessel elements. Currently there is little information about methods to characterize grape vascular tissue. In this study, we describe an easy and effective technique to visualize the xylem cell structure of the ‘Red Globe’ grape (Vitis L.). The intact vascular bundles of the grape were isolated through enzymatic degradation of flesh cells by hydrolases which were effective in removing flesh cells from vascular bundles. This enabled the illustration of the fine surface structure of vessel elements and their arrangement in the vascular bundles of the grape. This modified method to separate the vascular bundles into individual vessel elements was more effective than former methods of manually shaking to isolate individual vessels. Clear images of xylem vessel arrangement and structural characteristics of individual vessel element were acquired by light microscopy (BX51, Olympus, Tokyo, Japan), transmission electron microscopy (Tecnai 12, Philips, Netherlands) and scanning electron microscopy (GeminiSEM 300, Carl Zeiss, Germany). In addition, the 3D structure of vessel elements was observed using confocal laser scanning microscopy (Zeiss: model: LSM-880, Oberkochen, Germany). The imaging techniques for visualizing and analyzing the structure of xylem vessels in grape described in this study are an improvement of past methods. An effective method to isolate grape vascular bundles from flesh cells was also developed, which enables the imaging of the fine surface structure of vessel elements and their arrangement in grape vascular bundles. By adjusting the process of maceration of vascular bundles, an easy and effective method was developed to gently disrupt the plant tissue and isolate individual vessel elements. These improved techniques are suitable to observe the intact morphology of vascular bundles in the grape, improve experimental efficiency and accelerate new discoveries on the anatomical structure of the grape.
... This is not surprising since cell wall invertases can undergo post-transcriptional regulation and can be inactivated by binding to inhibitor proteins [59]. In any case, cell wall invertases have a recognized role in regulating developmental transitions [62], and their expression was induced shortly before bud break in buds of peach [63], suggesting the catabolic activity can increase the sink strength, which, in turn, triggers a commitment to bud burst [64]. This hypothesis appears consistent with our findings, being VvINV significantly upregulated in February and March when hexoses also showed a slight increase. ...
Perennial fruit crops enter dormancy to ensure bud tissue survival during winter. However, a faster phenological advancement caused by global warming exposes bud tissue to a higher risk of spring frost damage. Tissue dehydration and soluble sugars accumulation are connected to freezing tolerance, but non-structural carbohydrates also act as metabolic substrates and signaling molecules. A deepened understanding of sugar metabolism in the context of winter freezing resistance is required to gain insight into adaptive possibilities to cope with climate changes. In this study, the soluble sugar content was measured in a cold-tolerant grapevine hybrid throughout the winter season. Moreover, the expression of drought-responsive hexose transporters VvHT1 and VvHT5, raffinose synthase VvRS and grapevine ABA-, Stress- and Ripening protein VvMSA was analyzed. The general increase in sugars in December and January suggests that they can participate in protecting bud tissues against low temperatures. The modulation of VvHT5, VvINV and VvRS appeared consistent with the availability of the different sugar species; challenging results were obtained for VvHT1 and VvMSA, suggesting interesting hypotheses about their role in the sugar–hormone crosstalk. The multifaceted role of sugars on the intricate phenomenon, which is the response of dormant buds to changing temperature, is discussed.
