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Periclinal Chimeras in Datura stramonium in Relation to Development of Leaf and Flower
... Moreover, the contribution of cell layers can vary between the same organ in different species: for instance Datura stramonium (Datura) petals are derived from all 3 layers, in contrast to Arabidopsis (Satina and Blakeslee, 1941). Finally, even in one organ from a single species, cell layer contribution is not always homogeneous in different parts of the organ: in Datura petals, the L3 only participates to the vasculature at the base of the organ, and the L1 invades the mesophyll at the petal edges (Satina and Blakeslee, 1941). ...
... Moreover, the contribution of cell layers can vary between the same organ in different species: for instance Datura stramonium (Datura) petals are derived from all 3 layers, in contrast to Arabidopsis (Satina and Blakeslee, 1941). Finally, even in one organ from a single species, cell layer contribution is not always homogeneous in different parts of the organ: in Datura petals, the L3 only participates to the vasculature at the base of the organ, and the L1 invades the mesophyll at the petal edges (Satina and Blakeslee, 1941). ...
... In petunia, no clonal analysis has been performed so far, hence one can only assume which cell layers participate to petal development based on clonal analyses performed in closely-related species. In Datura, member of the Solanaceae family like petunia, periclinal chimeras induced by colchicine treatment and refined histological observations have provided a detailed clonal analysis for cell layers in floral organs (Satina and Blakeslee, 1941). The first visible event of petal initiation is a periclinal cell division from the L2 layer, and further growth of the petal depends primarily on cell divisions from the L2, both anticlinal and periclinal. ...
Floral homeotic MADS-box transcription factors ensure the correct development of floral organs with all their mature features, i.e. organ shape, size, colour and cellular identity. Furthermore, all plant organs develop from clonally-independent cell layers, deriving from the meristematic epidermal (L1) and internal (L2 and L3) layers. How cells from these distinct layers acquire their floral identities and coordinate their growth to ensure reproducible organ development is unclear. Here we study the development of the Petunia x hybrida (petunia) corolla, which consists of five fused petals forming a tube and pigmented limbs. We present petunia flowers expressing the B-class MADS-box gene PhDEF in the epidermis or in the mesophyll of the petal only, that we called wico and star respectively. Strikingly, the wico flowers form a very small tube while their limbs are almost normal, and the star flowers form a normal tube but very reduced and unpigmented limbs. Therefore, the star and wico phenotypes indicate that in the petunia petal, the epidermis mainly drives limb growth and pigmentation while the mesophyll mainly drives tube growth. As a first step towards the identification of candidate genes involved in specification of petal layer identities and tube/limb development, we sequenced the star and wico whole petal transcriptome at three developmental stages. Among downregulated genes in star petals, we found the major regulator of anthocyanin biosynthesis ANTHOCYANIN 1 ( AN1 ), and we showed that, in vitro , PhDEF directly binds to its terminator sequence, suggesting that it might regulate its expression. Altogether this study shows that layer-specific expression of PhDEF drives petunia tube or limb development in a highly modular fashion, which adds an extra layer of complexity to the petal development process.
... Then, the investigation of variegation led Erwin Baur's on the path of non-Mendelian inheritance [6]. Later, colchicine treatment on Datura seeds revealed periclinal chimeras [7] which allowed the understanding of cell lineages and ontogenesis of plant organs [8][9][10]. Indeed, two main types exist: sectorial and periclinal chimeras. ...
... The consequences of a chimera depend on its position on the genome, in our study 33% are located in a gene body region and 15% are located in a coding region and could modify the protein which can be perceived on the phenotype (Table 7, 8,9,10,11). Although our data con rms this possibility, the phenomena appears to be a rare event. ...
Chimerism is the phenomenon when several genotypes coexist in a single individual. Used to understand plant ontogenesis they also have been valorised through new cultivar breeding. Viticulture has been taking economic advantage out of chimeras when the variant induced an important modification of wine type such as berry skin colour. Crucial agronomic characters may also be impacted by chimeras that aren’t identified yet. Periclinal chimera where the variant has entirely colonised a cell layer is the most stable and can be propagated through cuttings. In grapevine, leaves have two functional cell layers, L1 and L2. However, lateral roots are formed from the L2 cell layer only. Thus, comparing DNA sequences of roots and leaves allows chimera detection. In this study we used new generation Hifi long reads sequencing, recent bioinformatics tools and trio-binning with parental sequences to detect periclinal chimeras on ‘Merlot’ grapevine cultivar. Sequencing of cv. ‘Magdeleine Noire des Charentes’ and ‘Cabernet Franc’, the parents of cv. ‘Merlot’, allowed haplotype resolved assembly. Pseudomolecules were built with a total of 33 to 47 contigs and in few occasions a unique contig for one chromosome. This high resolution allowed haplotype comparison. Annotation was transferred from PN40024 VCost.v3 to all pseudomolecules. After strong selection of variants, 51 and 53 ‘Merlot’ specific periclinal chimeras were found on the Merlot-haplotype-CF and Merlot-haplotype-MG respectively, 9 and 7 been located in a coding region. These results open new perspectives on chimera detection as an important resource to improve cultivars through clonal selection or breeding.
... WT seedlings grown on HU-containing medium exhibited smaller cotyledons, shorter roots and shorter hypocotyls than those grown on control medium ( Figure 8A) compared to WT seedlings ( Figure 8B). A strong correlation between cell size and ploidy was substantiated by numerous studies (Satina and Blakeslee, 1941;Melaragno et al., 1993;Gendreau et al., 1998). To test whether the elongation of hypocotyl cells of Pro35S:DHFR-TS3 seedlings grown on 1 mM HU was accompanied by an increase in ploidy level, a ploidy distribution analysis was conducted. ...
... Up-regulation of dNTP synthesis was reported to be essential for survival upon DNA Since an increase in cell size is often accompanied by an increase in DNA ploidy level (Satina and Blakeslee, 1941;Melaragno et al., 1993;Gendreau et al., 1998), which is attained by switching from the mitotic cell cycle to the endocycle (Sugimoto-Shirasu et al., 2002;del Pro35S:DHFR-TS3 plants was first assumed to be accompanied by an increase in ploidy level. ...
... In the mid-20 th century, so-called 'histogenetic' studies tried to interpret organs as foliar or axial (cauline) based on whether they were initiated in the second or third cell layer of the apical meristem, and thus from the 'tunica' or 'corpus'. In studies on Datura stramonium L. (Solanaceae), Satina & Blakeslee (1941, 1943, working with periclinal chimaeras, found that sepals and petals are initiated by periclinal cell divisions in the second cell layer of the floral apex, but stamens and the placenta of the carpels by such divisions in the third layer. Because foliage leaves are usually initiated in the second layer and lateral shoots in the third layer, these authors concluded that in Datura L. sepals and petals are of 'foliar' nature, but stamens and the placenta of carpels are of 'axial' or 'cauline' nature. ...
... However, these two sentences are misleading. As already mentioned, Taylor (1991) referred to the old, misinterpreted studies by Satina & Blakeslee (1941, 1943, see above), and Doyle (1994) just mentioned Taylor (1991) but did not support the hypothesis of Satina & Blackeslee (loc. cit.). ...
Carpels and ovules have been differently interpreted over the past two centuries. In this review, some of these interpretations are highlighted, with particular emphasis on the current situation. Ovules are part of and are enclosed in carpels in all living angiosperms. Living angiosperms are monophyletic, and the evolutionary association between ovules and the leaf-like part, the carpel wall, had taken place at or before the time the clade of extant angiosperms was established. From what we know at present, there are no â € cauline' ovules in extant angiosperms. Developmentally, carpel walls and ovules are not always synchronous across all extant angiosperms. In early development ovules may be relatively precocious or relatively late compared with carpel walls. They are late in early-diverging angiosperms (ANITA grade, magnoliids, some early-diverging eudicots) but precocious in some more derived groups (e.g. some Caryophyllales and Primulaceae). Carpel primordia have a certain depth in the floral apex, and the entire activated area of a carpel primordium may be several cell layers thick. Thus, the carpel is â € embedded' or â € rooted' within the remaining floral apex. The parts of a carpel develop at different times in carpel ontogeny and probably evolved at different times on the line leading to the angiosperms, which needs to be considered in interpretations. Carpel development depends on a complex genetic network, which increased stepwise over evolutionary time and contains hundreds of genes revealed in molecular developmental biology. The evolutionary history of such networks in carpel walls and ovules is unlikely to be easily disentangled, as most of these genes are not transcription factors.
... cells in Pro35S:DHFR-TS3 did not increase upon HU supplementation compared with wild-type seedlings ( Figure 8B). A strong correlation between cell size and ploidy was substantiated by numerous studies (Satina and Blakeslee, 1941;Melaragno et al., 1993;Gendreau et al., 1998). To test whether the elongation of hypocotyl cells of Pro35S:DHFR-TS3 seedlings grown on 1 mM HU was accompanied by an increase in ploidy level, a ploidy distribution analysis was conducted. ...
... Since an increase in cell size is often accompanied by an increase in DNA ploidy level (Satina and Blakeslee, 1941;Melaragno et al., 1993;Gendreau et al., 1998), which is attained by switching from the mitotic cell cycle to the endocycle (Sugimoto-Shirasu et al., 2002;Castellano et al., 2004;Vlieghe et al., 2005), the elongation of the hypocotyl of HU-treated Pro35S:DHFR-TS3 plants was first assumed to be accompanied by an increase in ploidy level. However, this was not the case, thereby providing additional evidence for the notion that an increase in ploidy level is not always a prerequisite for cell growth, as was reported in several other studies (De Veylder et al., 2001Beemster et al., 2002;Schnittger et al., 2003). ...
Folates (B9 vitamins) are essential cofactors in one-carbon metabolism. Since C1 transfer reactions are involved in synthesis of nucleic acids, proteins, lipids, and other biomolecules, as well as in epigenetic control, folates are vital for all living organisms. This work presents a complete study of a plant DHFR-TS (dihydrofolate reductase-thymidylate synthase) gene family that implements the penultimate step in folate biosynthesis. We demonstrate that one of the DHFR-TS isoforms (DHFRTS3) operates as an inhibitor of its two homologs, thus regulating DHFR and TS activities and, as a consequence, folate abundance. In addition, a novel function of folate metabolism in plants is proposed, i.e., maintenance of the redox balance by contributing to NADPH production through the reaction catalyzed by methylenetetrahydrofolate dehydrogenase, thus allowing plants to cope with oxidative stress.
... The number of cells in Pro35S:THY3 did not increase upon HU supplementation as compared to WT seedlings ( Figure 8B). A strong correlation between cell size and ploidy was substantiated by numerous studies (Satina and Blakeslee, 1941;Melaragno et al., 1993;Gendreau et al., 1998). To test whether the elongation of hypocotyl cells of Pro35S:THY3 seedlings grown on 1 mM HU was accompanied by an increase in ploidy level, a ploidy distribution analysis was conducted. ...
... Since an increase in cell size is often accompanied by an increase in DNA ploidy level (Satina and Blakeslee, 1941;Melaragno et al., 1993;Gendreau et al., 1998), which is attained by switching from the mitotic cell cycle to the endocycle (Sugimoto-Shirasu et al., 2002;del Mar Castellano et al., 2004;Vlieghe et al., 2005), the elongation of the hypocotyl of HU-treated Pro35S:THY3 plants was first assumed to be accompanied by an increase in ploidy level. However, this was not the case, thereby providing additional evidence for the notion that an increase in ploidy level is not always a prerequisite for cell growth, as was reported in several other studies (De Veylder et al., 2001;Beemster et al., 2002;De Veylder et al., 2002;Schnittger et al., 2003). ...
Folates (B9 vitamins) are essential cofactors in one-carbon metabolism. Since C1 transfer reactions are involved in synthesis of nucleic acids, proteins, lipids and other biomolecules, as well as in epigenetic control, folates are vital for all living organisms. This work presents the first complete study of a plant DHFR-TS (dihydrofolate reductase-thymidylate synthase) gene family that implements the penultimate step in folate biosynthesis. We demonstrate that one of the DHFR-TS isoforms (THY3) operates as an inhibitor of its two homologs, thus regulating DHFR and TS activities and, as a consequence, folate abundance. In addition, a novel function of folate metabolism in plants is proposed, i.e., maintenance of the redox balance by contributing to NADPH production through the reaction catalysed by methylenetetrahydrofolate dehydrogenase (MTHFD), thus allowing plants to cope with oxidative stress.
... In an elegant paper published in 1981, Whitham and Slobodchikoff 3 proposed that mosaicism offers a unique adaptive advantage for plants by allowing introduction of genetic variants into the gene pool either through vegetative propagation or through sexual reproduction. They further propose that mutations arising somatically have a greater probability of being incorporated into the gene pool than mutations that arise in the gametes 3 precisely because germ line cells are derived from somatic tissues that arise late in the developmental history of the plant 4,5 . ...
... As posited by Whitham and Slobodchikoff 3 , somatic sector formation permits the introduction of genetic variants into the gene pool either through vegetative propagation or through sexual reproduction. As these authors point out, germ line cells are derived from somatic tissues that arise late in the developmental history of the plant and therefore somatic mutations are more likely to introduce genetic variation than mutations that arise in the gametes 3,4,46 . ...
Concern over the tremendous loss of genetic diversity among many of our most important crops has prompted major efforts to preserve seed stocks derived from cultivated species and their wild relatives. Arabidopsis thaliana propagates mainly by self-fertilizing, and therefore, like many crop plants, theoretically has a limited potential for producing genetically diverse offspring. Despite this, inbreeding has persisted in Arabidopsis for over a million years suggesting that some underlying adaptive mechanism buffers the deleterious consequences of this reproductive strategy. Using presence-absence molecular markers we demonstrate that single Arabidopsis plants can have multiple genotypes. Sequence analyses reveal single nucleotide changes, loss of sequences and, surprisingly, acquisition of unique genomic insertions. Estimates based on quantitative analyses suggest that these genetically discordant sectors are very small but can have a complex genetic makeup. In ruling out more trivial explanations for these data, our findings raise the possibility that intrinsic drivers of genetic variation are responsible for the targeted sequence changes we detect. Given the evolutionary advantage afforded to populations with greater genetic diversity, we hypothesize that organisms that primarily self-fertilize or propagate clonally counteract the genetic cost of such reproductive strategies by leveraging a cryptic reserve of extra-genomic information.
... The shoot apical meristem (SAM) is known to comprise three structurally distinct cell layers (L1 to L3) 20 . The L1 and L2 layers contribute to the formation of epidermal and subepidermal tissues, respectively 20 . ...
The CRISPR/Cas9 system has revolutionized the field of plant genetic engineering. Here we report a smart genome editing system of soybean by using iPB-RNP method without introducing foreign DNA and requiring traditional tissue culture processes such as embryogenesis and organogenesis. Shoot apical meristem (SAM) of embryonic axes was used the target tissue for genome editing, because the SAM in soybean mature seeds has stem cells and specific cell layer developing germ cells during reproductive growth stage. In the iPB-RNP method, the complex of ribonucleoprotein (RNP) and Cas9 protein was directly delivered into SAM stem cells via particle bombardment and genome-edited plants were generated from these SAMs. Soybean allergenic gene Gly m Bd 30K , which we previously generated genome-editing soybean by using Agrobacterium -mediated transformation and particle bombardment in our previous studies, was targeted in this study. Many E 0 (the first generation of genome-edited) plants in this experiment harbored mutant alleles at the targeted locus. Editing frequency of inducing mutations transmissible to the E 1 generation was approximately 0.4 to 4.6 % of all E 0 plants utilized in various soybean varieties. Furthermore, Gly m Bd 30K protein in mature seeds was not detected by western blot analysis due to flame-sift mutations. Our results offer a practical approach for both plant regeneration- and DNA-free genome editing achieved by delivering RNP into the SAM of dicotyledonous plants.
... Slow growth of stem cells likely minimizes mutations by reducing cell cycles per sexual or clonal generation 12 . In plants, the stem cells are organized in three clonally isolated histogenic layers called L1, L2 and L3 13,14 . In the meristem, L1 and L2 are single-cell layers in which cells divide only anticlinally. ...
The upper plant body is formed by the continued growth of shoot apical meristems. In angiosperms, meristems are organized in three cell layers that tend to remain clonally isolated. Somatic variants emerge when mutant cells overtake part or all of a meristem. During sexual reproduction, only one layer, the L2, contributes to the next generation by forming gametes. The L2 is known to frequently invade and replace the L3, while L1-L2 separation is persistent. The role of different meristem layers in mutation accumulation is unknown. We discovered a potato periclinal chimera in which the L2 and L3, but not the L1, are marked by a chromosomal translocation. This enabled the identification of plants regenerated from leaf protoplasts originating from either the L1 or L2+L3. Leveraging these layer-specific clones, we identified and compared mutations that accumulated in the layers in the clonal parent for several decades. Here we show that the L1 accumulates mutations at 1.9 times the rate of the L2, indicating that plants might protect the germline by mechanisms that reduce the rate of mutation accumulation in the L2. In contrast to these layer-specific mutations, we found no evidence of somatic mutation fixation in all three meristem layers. Our findings highlight how periclinal chimeras are formed by independent mutational processes in which a mutation-prone epidermal layer could increase clonal variation.
... Then, the investigation of variegation led Erwin Baur's on the path of non-Mendelian inheritance [6]. Later, colchicine treatment on Datura seeds revealed periclinal chimeras [7] which allowed the understanding of cell lineages and ontogenesis of plant organs [8][9][10]. Indeed, two main types exist: sectorial and periclinal chimeras. ...
Chimerism is the phenomenon when several genotypes coexist in a single individual. Used to understand plant ontogenesis they also have been valorised through new cultivar breeding. Viticulture has been taking economic advantage out of chimeras when the variant induced an important modification of wine type such as berry skin colour. Crucial agronomic characters may also be impacted by chimeras that aren’t identified yet. Periclinal chimera where the variant has entirely colonised a cell layer is the most stable and can be propagated through cuttings. In grapevine, leaves are derived from both meristem layers, L1 and L2. However, lateral roots are formed from the L2 cell layer only. Thus, comparing DNA sequences of roots and leaves allows chimera detection. In this study we used new generation Hifi long reads sequencing, recent bioinformatics tools and trio-binning with parental sequences to detect periclinal chimeras on ‘Merlot’ grapevine cultivar. Sequencing of cv. ‘Magdeleine Noire des Charentes’ and ‘Cabernet Franc’, the parents of cv. ‘Merlot’, allowed haplotype resolved assembly. Pseudomolecules were built with a total of 33 to 47 contigs and in few occasions a unique contig for one chromosome. This high resolution allowed haplotype comparison. Annotation was transferred from PN40024 VCost.v3 to all pseudomolecules. After strong selection of variants, 51 and 53 ‘Merlot’ specific periclinal chimeras were found on the Merlot-haplotype-CF and Merlot-haplotype-MG respectively, 9 and 7 been located in a coding region. A subset of positions was analysed using Molecular Inversion Probes (MIPseq) and 69% were unambiguously validated, 25% are doubtful because of technological noise or weak depth and 6% invalidated. These results open new perspectives on chimera detection as an important resource to improve cultivars through clonal selection or breeding.
... Lineage information obtained from periclinal chimeras of a number of dicotyledonous species indicates that leaves are derived from the three germ layers of the apical meristem (Satina et al. 1940;Satina and Blakeslee, 1941;Dulieu, 1968;Stewart and Burk, 1970;Stewart and Dermen, 1975). The LI layer of the meristem gives rise solely to the epidermis of the leaf, the L2 (subepidermal) layer gives rise to the upper palisade and the lower spongy mesophyll near the center of the leaf and all of the mesophyll at the leaf margin. ...
Leaf shape in cotton is regulated by the developmental age of the shoot and by several major genes that affect leaf lobing. The effect of these factors was investigated by allometric analysis, cell lineage analysis, and by studying the expression of the leaf shape mutation, Okra, in genetic mosaics. Allometric analysis of leaf growth suggests that leaf shape is determined during the initiation of the primordium rather than during the expansion phase of leaf growth. Clonal analysis demonstrates that both the rate and duration of cell division are fairly uniform throughout the leaf. Cells in the marginal region of the developing cotton leaf contribute more to the growth of the lamina than they do in tobacco. The Okra mutation acts early in the development of a leaf and appears to accentuate a developmental pattern that is also responsible for heteroblastic variation in leaf shape. The expression of this mutation in genetic mosaics demonstrates that its effect does not diffuse laterally within the leaf primordium.
... The difference in cell size between diploid and triploid appears small, but the tetraploid cell is more than double the volume of the diploid. Fig. 2D, E, and F illustrates shoot apices of certain chimeras produced from colchicine treatment, all of which are tetraploid in one or more histogenic layers (4,8). Fig. 2D shows a (4-2-2) chimera, i.e., tetraploid in L-I and diploid in L-II and L-III. ...
A study of shoot apex size and initiatory activity in August-harvested ‘Ace’ bulbs following 0, 6, and 18 weeks vernalization at 40°F showed negetative correlations between leaf and flower number and length of vernalization treatment, and between apex size and this cold treatment. Growth acceleration as reflected in earlier shoot emergence, internode elongation and rapid leaf unfolding was evident following 6 weeks’ 40°F storage, but prolonged (18 weeks) treatment drastically reduced subsequently initiatory activity and rate of leaf unfolding.
... The difference in cell size between diploid and triploid appears small, but the tetraploid cell is more than double the volume of the diploid. Fig. 2D, E, and F illustrates shoot apices of certain chimeras produced from colchicine treatment, all of which are tetraploid in one or more histogenic layers (4,8). Fig. 2D shows a (4-2-2) chimera, i.e., tetraploid in L-I and diploid in L-II and L-III. ...
A study of shoot apex size and initiatory activity in August-harvested ‘Ace’ bulbs following 0, 6, and 18 weeks vernalization at 40°F showed negetative correlations between leaf and flower number and length of vernalization treatment, and between apex size and this cold treatment. Growth acceleration as reflected in earlier shoot emergence, internode elongation and rapid leaf unfolding was evident following 6 weeks’ 40°F storage, but prolonged (18 weeks) treatment drastically reduced subsequently initiatory activity and rate of leaf unfolding.
... The floral meristems are organized similarly to the SAM (Bowman and Eshed, 2000;Jenik and Irish, 2000;D. Reinhardt et al., 2003;Satina et al., 1940;Satina and Blakeslee, 1941). ...
In plants, the development of aerial organs is indeterminate: it takes place throughout their lifespan. In contrast, the development of floral organs is determinate in Arabidopsis thaliana, each flower has the same number of floral organs. This difference in development is due to the maintenance or not of the pool of stem cells present in the stem cell niches, the meristems. During my thesis I showed that the transcriptional regulator VIP3 contributes to the regulation of the switch from indeterminate to determinate in flowers. This also revealed that the control of flower termination is not as robust as classically thought. Because VIP3 is also involved in the regulation of epigenetic marks and response to external mechanical stimuli, this work opens new questions on the role of mechanical signals in indeterminacy. On a more technical standpoint, the analysis of shoot development suffers from a lack of imaging methods with high temporal resolution and in-depth optical sectioning. During the last decade, light sheet microscopy has emerged as a competitive imaging modality in developmental biology. However, in plants, the technique has mainly been used in roots because of limits in the microscope design. During my thesis, I developed protocols allowing the imaging of aerial organs in A. thaliana using a novel light sheet set-up (Phaseview Alpha3) where shoot samples can be observed while in water. I set up an imaging pipeline from sample mounting to quantitative analysis, with a focus on local dynamics of microtubules in cotyledon epidermis in relation to cell shape. Altogether, this work provides both conceptual and technical prospects for future quantitative projects in plant development.
... Dermen (1940) described chimeras as plants in which, after colchicine treatment, only a portion becomes polyploid, whereas the others remain diploid. The frequent production of chimeras by colchicine indicates that not all cells in the histogenic layers of the meristems are treated uniformly (Satina and Blakeslee, 1941). Thus, confirmation of stability of tetraploid plants is a crucial part of the process. ...
St. Augustinegrass is well suited for lawns and commercial landscapes. While many genotypes are cross‐fertile, all cultivars are propagated vegetatively in sod production. To ensure varietal purity, development of sterile triploid hybrids by crossing tetraploid and diploid genotypes has been successfully used in other warm‐season turfgrasses. Applying this model in St. Augustinegrass would be beneficial to sod producers and turf managers who require purity for certification and uniformity for performance, respectively. This study was conducted to develop colchicine‐induced tetraploid lines of St. Augustinegrass. Seeds of cultivar ‘Raleigh’ were treated with four colchicine concentrations at four exposure times. A non‐treated control was included among the treatments. Seedlings that germinated were screened for genome size changes using flow cytometry. Line DSA 13005 and two progeny lines derived through selfing, DSA 16001 and DSA 16016, were corroborated as tetraploids (2n = 4x = 36) through chromosome counts. These lines will be used in future breeding efforts to attempt development of sterile triploid cultivars of St. Augustinegrass.
... Each lobe consists of central meiocytes [also referred to as pollen mother cells (PMCs) or microsporocytes] surrounded by non-meiotic cell layers comprising of outer epidermis, endothecium, middle layer and inner tapetum (Fig. 1). The floral meristem consists of three concentric histogenic layers, designated as L1, L2 and L3, which give rise to different anther tissues following stamen primordia initiation [7]. Except for the epidermis and the connective tissue, which arise from L1 and L3 layers of anther primordium, respectively, the remaining tissues originate from the L2 layer. ...
Background
Molecular analysis of meiosis has been hindered by difficulties in isolating high purity subpopulations of sporogenous cells representing the succeeding stages of meiosis. Isolation of purified male meiocytes from defined meiotic stages is crucial in discovering meiosis specific genes and associated regulatory networks.
Results
We describe an optimized method termed MeioCapture for simultaneous isolation of uncontaminated male meiocytes from wheat (Triticum spp.), specifically from the pre-meiotic G2 and the five sub-stages of meiotic prophase I. The MeioCapture protocol builds on the traditional anther squash technique and the capillary collection method, and involves extrusion of intact sporogenous archesporial columns (SACs) containing meiocytes. This improved method exploits the natural meiotic synchrony between anthers of the same floret, the correlation between the length of anthers and meiotic stage, and the occurrence of meiocytes in intact SACs largely free of somatic cells. The main advantage of MeioCapture, compared to previous methods, is that it allows simultaneous collection of meiocytes from different sub-stages of prophase I at a very high level of purity, through correlation of stages with anther sizes. A detailed description is provided for all steps, including the collection of tissue, isolation and size sorting of anthers, extrusion of intact SACs, and staging of meiocytes. Precautions for individual steps throughout the procedure are also provided to facilitate efficient isolation of pure meiocytes. The proof-of-concept was successfully established in wheat, and a light microscopic atlas of meiosis, encompassing all stages from pre-meiosis to telophase II, was developed.
Conclusion
The MeioCapture method provides an essential technique to study the molecular basis of chromosome pairing and exchange of genetic information in wheat, leading to strategies for manipulating meiotic recombination frequencies. The method also provides a foundation for similar studies in other crop species.
Electronic supplementary material
The online version of this article (10.1186/s12870-018-1514-z) contains supplementary material, which is available to authorized users.
... Periclinal chimerism for polyploidy, and later also for chlorophyll mu-tations (Dulieu 1967b) has been used extensively to prove the existence of stable layers and to deduce the origin of different organs or tissues (Avery et al. 1959, Dermen 1947, Satina 1945, Satina and Blakeslee 1941. The L 2 producing the pollen and embryo (Dermen 1947, Dermen and is important for mutation research in generatively reproducing plants while the layer(s) responsible for leaf shape, tuber colour, etc. may be important in vegetatively reproducing plants (Howard 1969, Klopfer 1965a. ...
p/>Chimerism is the concurrence of genotypically different tissues in one individual and usually results from a mutation early in the development of that individual. With the possibility to induce mutations came the problem of chimerism which gives heterogeneous plants and, allegedly, loss of mutations by diplontic selection, i.e. selection between genetically different tissues within an individual where the mutated tissue is assumed to be at a disadvantage.
Literature on anatomy, morphology and development, and on the. mutation process gives the explanation for various aspects of chimerism: The appearance of chimerism depends on the constitution of the material treated and on the action of the mutagen used. Periclinal and sectorial chimerism are related to the structure of the apex i.e. the existence of independent cell layers and of a few central (apical) initial cells. The development of chimerism after a mutagenic treatment is determined by the differentiation already present in the material treated (usually seed), in which the destiny of most of the cells is already fixed.
The presented experiments (on arabidopsis and sunflower) indicate that the mutagenic action of the mutagens used (EMS and colchicine applied separately or simultaneously) was mainly confined to the duration of the treatment. In addition the mutagens influenced development, stimulating it at first and later (especially colchicine) retarding it, which has consequences for sensitivity with combined treatments, and which may affect chimerism. Differences in average distribution of mutations (from seed versus seedling treatment, "first" versus "second" mutation) were ascribed to differential mutagen (EMS) sensitivity of cells destined to form the various parts of the plant (main inflorescence, side shoots). Chimerism in the sporogenic tissue (pollen and M <sub>2</sub> were scored) occurred as sectors (usually 2 in the inflorescence and up to 4 in the stem of arabidopsis) which often seemed twisted probably due to the (twisted) growth of the plants. Generally chimerism was lost, apparently at random with regard to the observed mutations (polypIoidy and M <sub>2</sub> chlorophyll, mutants).
Although diplontic selection is often mentioned in the literature, most of the cases reported can be explained equally well, and often better, as aspects of normal development or as the result of differential (mutagen) sensitivity. Environmental conditions influence the development of the plant and also the (observed) mutation rate, but this influence may be indirect i.e. through the effect on chimerism. Chimerism depends on the stability of the apical initial cells which will be related to the stability of the apex and therefore to plant development and thus indirectly to environmental conditions.
Plants from experiments with various growth conditions (greenhouse vs field, daylength) differed in development and vigour, and simultaneously, in degree and persistence of chimerism, vigorous plants showing more chimerism. Treatments which retard apical development at an early stage (etiolation, vernalization) decreased chimerism. In both cases effects on the stability of the apex were probably responsible.
This loss of chimerism, at random with regard to the genotype, may be called diplontic drift. It depends on conditions affecting plant growth and may offer an opportunity to manipulate chimerism. Chimerism decreases the chance to detect a mutation but increases the number of (different) mutations that can be obtained from one plant, so that the degree of chimerism desired, may vary.
... For example, L1 layer replacement with a different anthocyanin background can change the flower color, given that anthocyanin pigment is present only in the L1-derived epidermal cells of petals. In contrast, germ cells are normally derived from the L2 layer (Satina 1945;Satina and Blakeslee 1941), so that transgenes in the L1 layer are rarely transmitted to progeny. The risk of transgene flow from transgenic chrysanthemum to wild relatives would be reduced by L1-specific gene modification. ...
Periclinal chimeras play important roles in vegetatively propagated plants such as chrysanthemum (Chrysanthemum morifolium). For example, periclinal chimerism causes flower color variation in chrysanthemums. In this study, a method for periclinal chimera production in chrysanthemum was examined. A wild-type plant of chrysanthemum ‘Taihei’ and its transgenic plant carrying a yellowish-green fluorescent protein gene from the marine plankton Chiridius poppei (CpYGFP) were used as plant materials. The cut faces of the leaf explants of both materials were partially attached and then were detached for further culture. Mosaic calli consisted of transgenic and wild-type cells formed on the detached faces of the explants. We examined 996 regenerated shoots from 4,120 explants and found only a single chimeric shoot that appeared to show mericlinal chimerism. Repeated axillary bud elongation from the nodes of the mericlinal chimera produced one L1-fluorescent and one L3-fluorescent chimeric plant. The L1 chimera showed fluorescence in the epidermal cells and trichomes of leaf and stem. The L3 chimera showed fluorescence in the cells of the central parts of stem and leaf, as well as in the whole root tissues. In summary, we obtained chrysanthemum periclinal chimeras through regeneration from leaf explants using the fluorescent protein transgene as a selection marker.
Colchicine treatment of several azalea cultivars induced polyploidy. The effect of colchiploidy varied between cultivars but there was a general increase in size and firmness of flowers. Some of the induced polyploids were complete, but many were chimeral.
Colchicine treatment of several azalea cultivars induced polyploidy. The effect of colchiploidy varied between cultivars but there was a general increase in size and firmness of flowers. Some of the induced polyploids were complete, but many were chimeral.
Chimeras – organisms that are composed of cells of more than one genotype – captured the human imagination long before they were formally described and used in the laboratory. These organisms owe their namesake to a fire-breathing monster from Greek mythology that has the head of a lion, the body of a goat, and the tail of a serpent. The first description of a non-fictional chimera dates back to the middle of the seventeenth century when the Florentine gardener Pietro Nati discovered an adventitious shoot growing from the graft junction between sour orange ( Citrus aurantium ) and citron ( C. medica ). This perplexing chimera that grows with sectors phenotypically resembling each of the citrus progenitors inspired discussion and wonder from the scientific community and was fittingly named the ‘Bizzaria’. Initially, the ‘Bizzaria’ was believed to be an asexual hybrid that formed from a cellular fusion between the grafted parents; however, in-depth cellular analyses carried out centuries later demonstrated that the ‘Bizzaria’, along with other chimeras, owe their unique sectored appearance to a conglomeration of cells from the two donors. Since this pivotal discovery at the turn of the twentieth century, chimeras have served both as tools and as unique biological phenomena that have contributed to our understanding of plant development at the cellular, tissue, and organismal level. Rapid advancements in genome sequencing technologies have enabled the establishment of new model species with novel morphological and developmental features that enable the generation of chimeric organisms. In this review, we show that genetic mosaic and chimera studies provide a technologically simple way to delve into the organismal, genetic, and genomic inner workings underlying the development of diverse model organisms. Moreover, we discuss the unique opportunity that chimeras present to explore universal principles governing intercellular communication and the coordination of organismal biology in a heterogenomic landscape.
Full text available on request or in open access at https://ore.exeter.ac.uk/repository/handle/10871/35377#
Evolutionary novelty, the origin of new characters such as the turtle shell or the flower, is a fundamental problem for an evolutionary view of life. Accordingly, it is a central research topic in contemporary biology involving input from several biological disciplines and explanations at several levels of organization. I study the evolution of research on novelty from the 1950s to the present. The problem of novelty has recently been appropriated by evolutionary developmental biology or evo-devo, a synthesis of evolutionary and developmental biology that started emerging in the 1980s following technological advances and discoveries in developmental genetics. I focus instead on three neglected dimensions of the problem of novelty: the functional-historical approach to the problem, research on novelty in the late Modern Synthesis era (1950-1980) and novelty in plants. My argument runs against the view of some scientists and historians, often tied to evo-devo, who oppose structuralist and functionalist approaches in biology and who claim that the origin of novelty is a structuralist problem. I advocate an approach to novelty that ties together structural and functional dimensions and show how some research programs of the last eighty years implemented different versions of this approach.
Many commercial chrysanthemum cultivars display unusual somatic variability. The ‘Indianapolis’ family of chrysanthemum sports was analyzed for the genetic potential for color of each of the three layers in the apical meristem of their shoots. Populations of each cultivar were grown and sectors and off-color plants recorded. The location of the pigment within cells and between tissues was determined by microscopic examination of free-hand sections of fresh petals. Adventitious buds were forced from the stems of each cultivar by excising all normal lateral buds. These observations, showed 12 of the 16 ‘Indianapolis’ cultivars to be periclinal chimeras. Adventitious shoots often originated from two or more cells, derived from at least two different apical layers, and thus were themselves periclinal chimeras. While somatic mutation is the ultimate source of the variability in ‘Indianapolis’ chrysanthemums, the most frequent type of sporting resulted from the loss in mitosis of a chromosome carrying a supressor for the formation of yellow chromoplasts, giving a yellow sector or shoot. Sectors resulting from rearrangement of layers in the periclinal chimeras were less frequent than the sectors from chromosome loss.
Two mutant plastogenes in all possible chimeral combinations were followed in Pelargonium X hortorum Bailey (geranium) shoots. The part of stem, leaf, or other structure derived from each apical layer was clearly apparent on a cell to cell basis. Shoots typically were composed of derivatives of three apical layers but we found derivatives of as many as four apical layers in some leaves and of five layers in some stems. In chimeras with one of the mutants, Dpl W1, the amount of tissue derived from the various apical layers was the same, whether the layer was mutant or wild type. We suggest that there are independent apical layers and cell lineages derived from them in nonchimeral shoots, and that their contribution in normal ontogeny is like that of the layers in Dpl W1 chimeras. In chimeras carrying the second mutant, Dpl W2, there was much less tissue derived from mutant than from wild-type apical layers. The phenotypic expression of the plastogenes was unchanged by their transmission through male or female gametes. Comparisons of the ontogeny of geranium plants carrying the W1 or W2 mutant suggested that, while there was competition between the apical layers and between their derivatives, the genome imposed a definite harmonious interaction or accommodation which led to a final normal morphology of all plant parts and organs through quite different ontogenetic pathways.
Six different homoplastidic periclinal chimeras of tobacco carrying the plastogene DP1 were selected after somatic segregation in heteroplastidic seedlings. Direct observation of the plane of division in epidermal cells of young leaves, and the number and size of sub-epidermal green spots on leaves with the Green-White-White (G-W-W) pattern of variegation, indicated that the ratio of periclinal to anticlinal divisions in L-I during development of the lamina was 1:3100. The number of green and white seedlings obtained from the different chimeral branches indicated a similar frequency of periclinal divisions in development of the ovary. The arrangement of green and white tissue in mature leaves of the various chimeral types indicated the extent of participation by the three apical layers in the initiation of the buttress, development of the axis, and formation of the lamina. During development of the lamina there must be three independent initial-groups present. L-I and L-II initials remain marginal, but early in the growth of the lamina the leading edge of tissue derived from L-III becomes separated from the submarginal (L-II) initials by the products of frequent periclinal divisions of the L-II initials.
Cell lineages were followed throughout floral ontogeny in cytochimeral peaches [Prunus persica (L.) Batsch] by observations of chromosome number and nuclear size. The contribution of the three apical cell layers to the organs of the flowers was determined. In addition to the epidermal tissue, L-I produced several layers of cells at the suture of the ovary wall, seven or eight cell layers of the nucellus at the micropylar end of the ovule, and almost all of the integuments. L-II gave rise to extensive internal tissue in the calyx and corolla tubes and to all internal tissue of the petal, anther, and ovule except for a small region at the base of the latter two organs. L-III contributed significantly only to the central region of the calyx and corolla tubes and the ovary wall. A single apical layer gave rise to several different tissues, and at times a single tissue was made up of cells from 1–3 different apical layers. Within the limits imposed by their genotype the final form of differentiated cells was determined by their position in the mature organ and not by the apical layer from which they were derived. The corolla tube was shown to be a single structure, congenitally fused, and the ovary to be ontogenetically fused at the suture.
Chimeral seedlings from a “semigametic” strain of cotton were used as the basis for a clonal analysis of events in the progressive organization of the nascent shoot apex. At the time the proembryo becomes a globular stage embryo with a distinct dermatogen, the surface of the embryo contains an eight-celled compartment for each cotyledon, a two-celled compartment for the first leaf, a one-celled compartment for the second leaf, and a three-celled compartment for the apical initials and all subsequent leaves and aerial structures. The developmental history of the first two leaves differs in a fundamental way from that of all the other leaves.
Somatic sectors induced by ionizing radiation provide a great deal of information about cell lineage patterns in both plants and animals. Somatic sectors arise when the dominant allele of a mutation with a visible, cell-autonomous phenotype is lost as a result of a deletion or somatic recombination. In addition to marking the fate of cells in a primordium at different stages of development and in different tissues, this technique also provides information about the distribution, orientation, rate, and duration of cell division. The technology and underlying assumptions of this method, termed clonal analysis, are described in this paper.
Periclinal chloroplast chimeras are genetic mosaics which possess shoot apices composed of one or more chlorophyll-deficient histogens and can exist as a series of arrangements of normal and mutant layers (A-B-B, A-B-A, etc.). Three periclinal chimeral cultivars of Sansevieria trifasciata L., each of which possesses normal green cell layer(s) but a genetically different chlorophyll-deficient cell layer(s), were utilized to study the effect of genotype on the ability of the cell layers of leaf cuttings and of cultured leaf tissue to regenerate shoots. The epidermis and LI derivatives were apparently incapable of shoot regeneration via leaf cutting, yet in two cultivars produced some shoots in vitro. In two of the cultivars, the chlorophyll-deficient cells never produced shoots. In the third, the capability of chlorophyll-deficient cell layers to produce shoots was less in vitro than in vivo, indicating that when determining morphogenic potential, direct comparisons between in vitro and in vivo systems may not be valid. Results also demonstrate that because genetically different albino cell layers can differ in their morphogenic response, utilizing a series of periclinal chimeras is useful only if the series is composed of the same two genotypes.
A histogenetic investigation of the synandrous androecium and syncarpous gynoecium in the flower of Downingia bacigalupii Weiler (Campanulaceae; Lobelioideae) was undertaken for the purpose of comparing the modes of initiation, early growth and fusion in these floral whorls with that reported previously for the perianth in this species. Stamens are initiated as separate organs from the second tunica layer and underlying corpus regions of the concave floral meristem. Subsequent growth of stamens involves apical and intercalary growth in length and rudimentary marginal growth in breadth. Tissues of the four microsporangia originate from hypodermal sporangial initial cells and the filament is formed by intercalary growth at the base of the anther. Lateral fusion of stamens is ontogenetic and involves cuticular fusion of adjacent epidermal layers. The two emergent carpel primordia arise as crescentic organs by periclinal divisions in the second tunica layer and corpus zones. Carpel primordia also undergo apical and intercalary growth in length as well as extensive marginal growth in breadth. Radial growth in carpels is mediated by an adaxial meristem which shows its greatest concentration of activity at the carpel margins. Carpel fusion appears to be partially ontogenetic accompanied by zonal growth. Closure of the stylar canal is by the formation of a transmitting tissue derived from the protodermal layers of the adaxial carpel surfaces. A discoid nectary is initiated around the base of the style and formation of the inferior ovary is by intercalary growth of the base of the concave floral bud. The two parietal placentae originate as longitudinal outgrowths from the walls of the floral cup. Ovule initiation is simultaneous at first and then intercalary during subsequent elongation of the ovary. The ovules are anatropous, unitegmic and tenuinucellate. Stamen and carpel procambium shows a slight delay in differentiation when compared to that reported for the perianth and bract, but in all other respects carpels resemble other floral organs in their patterns of histogenesis and early growth. Stamens diverge from the other floral organs in their early pattern of growth, but a consideration of all features of their histogenesis suggests an appendicular rather than an axial interpretation of these organs.
In this study, we revealed how the petals of Saintpaulia fuse into a corolla by using pinwheel phenotype cultivars. Striped patterns in petal, called pinwheel in Saintpaulia, are attractive phenotypes and thought to be the result of periclinal chimerism. For the selection of a genuine periclinal chimeric cultivar from three pinwheel cultivars, adventitious shoots were induced from leaf lamina. Shoot regeneration was observed from the epidermis in all cultivars by microscopic observation. All regenerated shoots from ‘Kaname’ flowered as monochromatic pink flowers, corresponding to an L1 phenotype of the cultivar. From the other two cultivars, many shoots flowered not only as an epidermal phenotype but also as a phenotype of the inner layer. In addition, shoot regeneration was induced from epidermis-peeled petioles from these three cultivars. All shoots from ‘Kaname’ flowered as monochromatic blue flowers, corresponding to an L2 phenotype. On the other hand, many shoots from ‘Kilauea’ flowered not only as monochromatic flowers, corresponding to an L2 phenotype, but also as bi-colored flowers. ‘Innocent Pink’ did not produce shoots from epidermal-peeled petioles. These results suggested that ‘Kaname’ is a genuine periclinal chimera, while the other two cultivars have other mechanisms for pinwheel expression. Genomic PCR using primers that amplifies almost the full length of flavonoid 3′,5′-hydroxylase (F3ʹ5ʹH) revealed the gene to be non-functional in pink flowers from L1 of ‘Kaname’. From monochromatic pink plants and pink portions of the corolla of ‘Kaname’, full-length F3ʹ5ʹH was not amplified. Similar results were obtained by quantitative PCR. Finally, we observed the fused portion of the petals and revealed that the petal fusion did not occur by postgenital fusion but by “connection”. The process, in Saintpaulia, comprises periclinal cell division in L1 during petal development, active cell division at the edge of the petal, adhesion to the next petals, and fusion. These steps create a striped flower color in Saintpaulia.
Flower initiation marks the transition from vegetative to reproductive growth in seed plants. It is thus a crucial event in the life of these plants, particularly so because of the peculiar relation of vegetative and reproductive development in seed plants which is in turn an outcome of the morphological nature of the flower. Flowers are modified shoots which are produced by modified shoot meristems, the flower primordia. However, once a meristem has been determined as a flower primordium, it is usually unable — except perhaps at the very earliest stages — of reverting to vegetative growth. Vegetative growth and reproductive development in seed plants are thus in a certain sense mutually exclusive; as far as a particular meristem is concerned, flower initiation means the end of its life. The central problem of the physiology of flower initiation is to understand which factors cause a shoot meristem to become a flower primordium, and how they consummate their action.
Die Blütenentwicklung bei Saxifragaceen wurde am Beispiel von Tellima grandiflora untersucht. Die Blüten sind pentazyklisch und mit Ausnahme des zweikarpelligen Gynaeceums pentamer.
The occurrence of diploid sports in the haploid Thuja gigantea gracilis is primarily conditioned through spontaneous diploidization of cells of the shoot apex. The shoot apex possesses two temporarily independent layers; periclinal divisions in L1 frequently appear.
The recovery of periclinal chimeras in which tissue from different interspecific or intergeneric origins is combined in a single clonal plant, has wide-ranging but largely unexploited potential for crop improvement. Periclinal chimeras allow a discrete replacement of strategic tissues such as the plant epidermis for improved resistance and plant performance. Once synthesized, vegetative propagation allows immediate grower access to these value-added clonal cultivars, as well as almost indefinite maintenance of the economically valuable chimera arrangements that would otherwise be lost if propagated by seed. The increased use of vegetative propagation for traditionally seed-propagated crops such as tomato and melons for greenhouse production has recently expanded opportunities for cultivar development using chimeras. Essential components targeted for improvement include chimera induction, selection efficiency, histogen identification, characterization, and stabilization. This chapter reviews the interspecific chimeras with emphasis to species of the Brassicaceae, Euphorbiaceae, Rutaceae, and Solanaceae.
Echinacea purpurea L. is one of the important ornamental and medicinal plant species. Ploidy manipulation is a valuable tool for improving plant quality or production in E. purpurea as well as in many other plants. To study the segregation of pure ploidy plantlets from colchicine-induced ploidy chimeras in E. purpurea, we used a chimera plantlet that consisted of 1.93% diploid, 35.04% tetraploid, and 63.03% octoploid cells as the source material for experiments. The results showed that three factors significantly influenced the segregation, i.e., the component ratios of different ploidy cells in the chimera, the number of sequential passages, and the methods of segregation culture of the chimera plantlets. Other factors, such as explant types (i.e., leaf, petiole, or root) and 6-benzyladenine (BA) concentrations (i.e., 0.2, 0.4, 0.8, and 1.2 mg·L-1) occasionally influenced the segregation. Pure chromosome-doubled polyploids are not easily obtained in various plant species, so segregation culture of ploidy chimeras may potentially be more effective. The morphological characteristic and content of cichoric acid were compared among diploid, tetraploid, and octoploid plants. Results indicated that tetraploid and octoploid plants had more stunted growth, larger stomata, lower stomata frequency, more chloroplast number in guard cells, and higher cichoric acid content than original diploid lines. © 2016, American Society for Horticultural Science. All rights reserved.
Chimeras – organisms that are composed of cells of more than one genotype – captured the human imagination long before they were formally described and used in the laboratory. These organisms owe their namesake to a fire-breathing monster from Greek mythology that has the head of a lion, the body of a goat, and the tail of a serpent. The first description of a non-fictional chimera dates back to the middle of the seventeenth century when the Florentine gardener Pietro Nati discovered an adventitious shoot growing from the graft junction between sour orange (Citrus aurantium) and citron (C. medica). This perplexing chimera that grows with sectors phenotypically resembling each of the citrus progenitors inspired discussion and wonder from the scientific community and was fittingly named the'Bizzaria’. Initially, the'Bizzaria’ was believed to be an asexual hybrid that formed from a cellular fusion between the grafted parents; however, in-depth cellular analyses carried out centuries later demonstrated that the ‘Bizzaria’, along with other chimeras, owe their unique sectored appearance to a conglomeration of cells from the two donors. Since this pivotal discovery at the turn of the twentieth century, chimeras have served both as tools and as unique biological phenomena that have contributed to our understanding of plant development at the cellular, tissue, and organismal level. Rapid advancements in genome sequencing technologies have enabled the establishment of new model species with novel morphological and developmental features that enable the generation of chimeric organisms. In this review, we show that genetic mosaic and chimera studies provide a technologically simple way to delve into the organismal, genetic, and genomic inner workings underlying the development of diverse model organisms. Moreover, we discuss the unique opportunity that chimeras present to explore universal principles governing intercellular communication and the coordination of organismal biology in a heterogenomic landscape.
The formation of floral organs on the meristem follows on the heels of evocation and overlaps with evocation. The conventional angiosperm flower is made up of four whorls of modified leaves constituting the sterile and fertile parts. The sterile parts consist of an outer whorl of sepals that are usually green and enclose the rest of the flower before it opens, and an inner whorl of brightly colored petals that aid in attracting insects and other pollinators. Aggregates of sepals and petals in a flower are known, respectively, as the calyx and the corolla. The fertile organs of the flower directly concerned with sexual reproduction are the stamens, representing the male units, and the carpels (or the pistil, consisting of one or more carpels), representing the female units. Collectively, the stamens and carpels constitute, respectively, the androecium and the gynoecium. These four whorls are produced in acropetal sequence by the floral meristem in the correct numbers of units and are precisely determined according to a blueprint characteristic of each species.
Cells and groups of cells in developing organisms become progressively committed to form specific structures. This remarkable process is known as determination (1). In spite of its importance -- E. B. Wilson (2) called it “the fundamental problem...which includes all others” -- determination has received far less attention from molecular biologists than has cell differentiation. One reason may be that determination is not a visible property of cells. It is only discernible when the normal process of development is experimentally manipulated.
This chapter describes patterns of cell growth and differentiation in plants. There are well-defined developmental patterns in coenocytic organisms or tissues that lack cross-walls, as in the coenocytic algae and fungi, the megagametophyte of the heterosporous ferns and lycopods, the gymnosperms, and in the embryo sac and endosperm of the angiosperms. Frequently cross-walls appear after an initial coenocytic stage. Cellular patterns in plants can be interpreted in developmental terms with greater or lesser precision. Coupled with the relative rigidity of the cell walls is the usual lack of anything like the cell migrations and rearrangements that are so characteristic of vertebrate development. There are conspicuous changes in size and form of plant organs in their development. The nature of plant cells makes for some degree of maintenance of their relative spatial relationships during growth and development. A plant leaves a record of its development in the geometric pattern of its cells and tissues. In a number of plants, the origin of all of the tissues of the shoot or root can be traced back to a single apical cell.
Genetic mosaics are plants which are composed of tissues of two or more genotypes. They should not be confused with plant hybrids, which possess only one genotype; a genotype which is the product of recombination following fertilization. Mosaics can arise spontaneously or can be induced with chemical or physical mutagens. In mutagenized plants most of the mutant sectors arise outside the shoot apex (i.e., “extra-apical mosaicism”, described by Bergann 1967).
The genetic control of floral development has been a field which has seen remarkable progress in recent years, largely due to the efforts of Meyerowitz and Coen and their colleagues, working with Arabidopsis thaliana and Antirrhinum majus, respectively. The research has developed consistent testable genetic models of the control of the identity of the organs in the floral whorls. It has also led to the molecular cloning of several of these loci with subsequent identification of some of the gene products as transcription factors. This research has been inspiring, and has lead to a resurgence of mutational analysis of a number of aspects of floral development, beyond the genes that control organ identity within the floral whorls.
The cells of plant meristems and embryos are arranged in an organized, and sometimes extremely beautiful, layered pattern. This pattern is maintained by the controlled orientation of cell divisions within layers. However, despite this layered structure, cell behaviour during plant development is not lineage dependent, and does not occur in a mosaic fashion. Many studies, both classical and recent, have shown that plant cell identity can be re-specified according to position, allowing plants to show remarkable developmental plasticity. However, the layered structure of meristems and the implications of this during plant development, remain subjects of some speculation. Of particular interest is the question of how cell layers communicate, and how communication between cell layers could allow coordinated developmental processes to take place. Recent research has uncovered several examples both of the molecular mechanisms by which cell layers can communicate, and of how this communication can infringe on developmental processes. A range of examples is used to illustrate the diversity of mechanisms potentially implicated in cell-layer communication during plant development.
In the plant in the course of differentiation cells formed in particular tissues enlarge and become committed to particular developmental histories. In the course of these, two types of change maybe recognised: (a) Structural modifications of form which have frequently been examined, and (b) metabolic changes of state which have only recently been noticed. It is certain of the latter which form the subject of this chapter. It is not proposed to consider the whole range of metabolic differentiation, but only those aspects of it that are involved in the expansion and differentiation of cells in the apical meristems of roots and shoots. The metabolic differentiation of the cell may be regarded in two connections; the initial expansion which occurs in meristems and in which all cells are involved, and the secondary commitment to particular histological forms. Here it is proposed to review only the cytochemical information available with regard to the first, since cell differentiation in the meristem is the prior and the most general phase of differentiation and any information with respect to it is therefore basic to the elucidation of the second, derivative phase. Also, since considerably more is known about the first phase a consideration of it may provide the basis for the development of concepts regarding the nature of differentiation in general.
Utilization of induced periclinal chimeras in deter-mining the constitution of organs and their origin from the three germ layers in Datura
- A F Blakeslee
- S Satna
- And A G Avery
BLAKESLEE, A. F., S. SATNA, AND A. G. AVERY. 1940. Utilization of induced periclinal chimeras in deter-mining the constitution of organs and their origin from the three germ layers in Datura. Science 91: 423.
Sporophylles et organes floraux, tige et axe floral La morphogenese et l'autonomie mor-phologique de l'appareil floral
- Gre Goire
GRE'GOIRE, V. 1935. Sporophylles et organes floraux, tige et axe floral. Recueil Trav. Bot. Neerland. 32: 453-468. 6.. 1938. La morphogenese et l'autonomie mor-phologique de l'appareil floral. La Cellule 47: 287-452.
Die Scheitelzellgruppe im Vege-tationspunkt der Phanerogamen. Festschr. Nie-derrhein. Ges. Natur u. Heilk
- J Hansteiw
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1932-33. The old morphology and the new
- H Thomas
- Hamshaw
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On the place of on-togeny in floral enquiry
- J Thaompsow
- Mcleam
THaoMpsow, J. McLEAM. 1937. On the place of on-togeny in floral enquiry. Publ. Hartl. Bot. Labs. No. 17: 1-20.
Die morphologische Natur der Kar-pelle
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