Quantitative comparison of foliage development amongDryopteris monticola,D. tokyoensis and a putative hybrid,D. kominatoensis in Northern Japan

Developmental leaf architecture was quantitatively described in terms of measurements of various parameters on leaf blade from different size of sporophytes inDryopteris monticola, D. tokyoensis and a putative hybrid,D. kominatoensis in the natural site of Hokkaido, to compare the ontogenetic differentiation in foliage structure among allied ferns. The morphological stage of leaf and sporophyte was tentatively quantified by the number of midrib branches of the leaf (NV, number of veins), which exhibited a significant correlation to the leaf-shape complexity from a circle (DI=marginal length/2×(3.14×square)^1/2) of leaf blade. D. kominatoensis showed intermediate values between others in following characters; DI increase, maximum NV (also blade length), maximum number of costa branches of pinnae (NVMP), number of costa branches of the lowest pinna (NVLP), difference between NVMP and NVLP (NVMP-NVLP), during heteroblastic leaf development. A larger number of leaves per sporophyte was found inD. kominatoensis than in others. The fertility rate (%) and initiation of fertility (IF) in the relative developmental stage (RDS) ofD. kominatoensis shifted to that ofD. tokyoensis, while the order of pinnae with NVMP shifted to that ofD. monticola. Even in the intermediate characters inD. kominatoensis, slight shifts in characters to those of putative parents were found during heteroblastic leaf development. Contribution No. 3145 from the Institute of Low Temperature Science, Hokkaido University.     

Quantitative expression of fern leaf development and fertility inPolystichum tripteron (Aspidiaceae)

To elucidate the quantitative and qualitative expression of fern development, various features of leaf-size and morphology were examined on leaves ofPolystichum tripteron (Aspidiaceae) in Japan. Among ten parameters, the number of branches of the leaf midrib (NV) proved to be the most successful for discrimination between fertile and sterile leaf populations. In the phase-change from sterile to fertile leaves, the NV parameter also gave the strongest correlation, increasing with fertility (r = 0.983), and is therefore a useful tool for research into the life history characteristics of ferns.Contribution no. 2751 from the Institute of Low Temperature Science, Hokkaido University.     

The role of carbon dioxide and oxygen in determining chlorophyll fluorescence quenching during leaf development

Chlorophyll fluorescence emission at 680 nm (F680) and the rate of CO₂ fixation were measured simultaneously in sections along the length of wheat and maize leaves. These leaves possess a basal meristem and show a gradation in development towards the leaf tip. The redox state of the primary electron acceptor, Q, of photosystem II was estimated using a non-invasive method. Distal mature leaf sections displayed typical F680 induction curves which were generally anti-parallel with CO₂ fixation and during which Q became gradually oxidised. In leaf-base sections net assimilation of CO₂ was not detectable, F680 quenched slowly and monotonously without displaying any of the oscillations typical of mature tissue and Q remained relatively reduced. Sections cut from mid-regions of the leaf showed intermediate characteristics. There were no major differences between the wheat and maize leaf in the parameters measured. The results support the hypothesis that generation of the transthylakoid proton gradient and associated ATP production is not a major limitation to photosynthesis during leaf development in either C₃ or C₄ plants. Removal of CO₂ from the mature leaf sections caused little change in steady-state F680 and produced about 50% reduction of Q. When O₂ was then removed, F680 rose sharply and Q became almost totally reduced. In immature tissue unable to assimilate CO₂, removal of O₂ alone caused a similar large rise in F680 and reduction of Q whilst removal of CO₂ had negligible effects on F680 and the redox state of Q. It is concluded that in leaf tissue unable to assimilate CO₂, either because CO₂ is absent or the tissue is immature, O₂ acts as an electron acceptor and maintains Q in a partially oxidised state. The important implication that O₂ may have a role in the prevention of photoinhibition of the photochemical apparatus in the developing leaf is discussed.Abbreviations F680 chlorophyll fluorescence emission at 680 nm - PSI photosystem I - PSII photosystem II - Q PSII primary electron acceptor - pH transthylakoid proton gradient     

Stage-related expression of mRNAs during pollen development in lily and tobacco

Homogeneous populations of developing microspores and pollen from anthers of lily (Lilium longiflorum Thumb.) and tobacco (Nicotiana tabacum L.) show a continuous production of biomass, reaching a maximum in young pollen. The rate of RNA synthesis was 460 fg · h^–1 in young binucleate cells, 138 fg · h^–1 in late binucleate cells and 56 fg · h^–1 in microspores. The mRNA population in developing pollen can be separated into three groups. In the first group, certain types of mRNAs are present at a constant level during all stages of development. A second group is characteristic of young pollen and increases quantitatively until anthesis. A third group is seen transiently; to this belong mRNAs present only before mitosis or at a distinct cell stage after mitosis. Some of the translation products of this latter group of mRNAs showed similarities between lily and tobacco on two-dimensional gels in respect of molecular weight and isolectric point, indicating that those mRNAs and proteins play a role in the regulation of pollen development.Abbreviations cDNA copy DNA - pI isolectric pointTo whom correspondence should be addressed.     

Changes in the density of microtubular networks in mesophyll cells and mesophyll derived protoplasts of Nicotiana and Triticum during leaf development

Changes in the density of microtubular mesh-works were analysed in mesophyll cells and mesophyll derived protoplasts of Nicotiana tabacum L. and Triticum aestivum L. during leaf development. The main purpose of this study was to test whether the low density, if not lack, of microtubular networks recently described in protoplasts that had been isolated from fully differentiated mesophyll cells happened during protoplast isolation or whether the loss of microtubules actually occurred during differentiation of the leaf tissue. Immunofluorescence microscopy showed that the density of the microtubular cytoskeleton in the leaf tissue decreased steadily after cessation of cell growth in both species. Nevertheless, in Triticum microtubule disappearance was swifter and occurred along a gradient from the base to tip of the leaf, a phenomenon reflecting the differences in the ontogeny between the dicotyledonous Nicotiana and the mono-cotyledonous Triticum leaves. Protein extraction from leaf tissues and Western blot analysis indicated that in both species the disappearance of microtubules was the result of a degradation of tubulin and not only due to a depolymerisation into tubulin subunits. When the cell walls were removed from live cells and the protoplasts released, the original patterns of the microtubules became obscured and, particularly in differentiated cells, the integrity and density of the microtubule strands deteriorated. The potential application of the density of the microtubular cytoskeleton as a marker in studies on differentiation and dedifferentiation in mesophyll cells and protoplasts is discussed.We wish to thank Silke Heichel for excellent technical assistance. We also express our thanks to the group of A.M. Lambert at CNRS, Strasbourg, France, for advice during establishment of our Western blot system. The work was supported by a grant of the German Ministry of Science and Technology (BMFT).     

Cytokinins and leaf development in sweet pepper (Capsicum annuum L.)

Stimulation of leaf expansion by an exogenous cytokinin was studied in isolated leaf discs of sweet pepper with emphasis on the assimilate utilization of the tissue. Leaf discs were floated on solutions containing sucrose and plant growth regulators. Benzyladenine (BA) promoted the area expansion rate of the leaf discs. Sucrose at 100 mM resulted in increased area expansion rate compared with 10 mM sucrose. However, the increased sucrose concentration had no influence on the effect of BA. Over a period of 24 h, treatment with BA did not result in any change of sucrose uptake nor of the partitioning of assimilated carbon in the leaf discs. Neither did BA treatment affect the activity of acid invertase (EC 3.2.1.26) or pyrophosphate-dependent phosphofructokinase (EC 2.7.1.90) in the leaf discs. We conclude that the observed promotion of leaf area expansion by exogenous BA is not mediated through the uptake of sucrose or the carbohydrate metabolism of the leaf tissue.Abbreviations BA N⁶-benzyladenine - GA₃ gibberellic acid - PPi-PFK pyrophosphate-dependent phosphofructokinase (EC 2.7.1.90) This study was supported by grants from the Danish Research Counsil (SJVF 13-4148 and 13-4547 to P.U. SJVF 13-4146 and 13-4494 to T.H.N.) and from The Research Center for Plant Biotechnology to P.U.     

Changes in the activities of chloroplast and cytosolic isoenzymes of glutamine synthetase during normal leaf growth and plastid development in wheat

Soluble protein extracts and chloroplasts from a serial sequence of transverse sections of a 7-d-old wheat leaf (Triticum aestivum cv. Maris Huntsman) were used to study changes in the activity of glutamine synthetase (GS; EC 6.3.1.2) during cell and chloroplast development. Glutamine synthetase activity increased more than 50-fold per cell from the base to the tip of the wheat leaf. Two isoenzymes of GS were separated using fast protein liquid chromatography (FPLC). Glutamine synthetase localized in the cytoplasm (GS1) eluted at about 0.21 M NaCl, and the isoenzyme localized in the chloroplast (GS2) eluted at about 0.33 M NaCl. The increase in GS activity during leaf development was found to be caused primarily by an increase in the activity of the chloroplast GS2. The activity of the cytoplasmic GS1 remained constant as the cells were displaced from the base to the tip of the leaf, whereas GS2 activity increased within the chloroplast throughout development. At the base of the leaf, 26% of total GS activity was cytoplasmic; the remaining 74% was in the chloroplast. At 10 cm from the base, only 4% of the activity was cytoplasmic, and 96% was in the chloroplast. The results indicate that the chloroplast GS2 is probably responsible for most of the ammonia assimilation in the mature wheat leaf, whereas cytoplasmic GS1 may serve a role in immature developing leaf cells.Abbreviations FPLC fast protein liquid chromatography - GS glutamine synthetase - GS1 cytoplasmic glutamine synthetase - GS2 chloroplast glutamine synthetase     

The cellular parameters of leaf development in tobacco: a clonal analysis

The cellular parameters of leaf development in tobacco (Nicotiana tabacum L.) have been characterized using clonal analysis, an approach that provides unequivocal evidence of cell lineage. Our results indicate that the tobacco leaf arises from a group of around 100 cells in the shoot apical meristem. Each of these cells contributes to a unique longitudinal section of the axis and transverse section of the lamina. This pattern of cell lincage indicates that primordial cells contribute more or less equally to the growth of the axis, in contrast to the more traditional view of leaf development in which the leaf is pictured as arising from a group of apical initials. Clones induced prior to the initiation of the lamina demonstrate that the subepidermal layer of the lamina arises from at least six files of cells. Submarginal cells usually divide with their spindles parallel to the margin, and therefore contribute relatively little to the transverse expansion of the lamina. During the expansion of the lamina the orientation and frequency of cell division are highly regulated, as is the duration of meristematic growth. Initially, cell division is polarized so as to produce lineages that are at an oblique angle to the midrib; later cell division is in alternating perpendicular planes. The distribution of clones generated by irradiation at various stages of development indicates that cell division ceases at the tip of the leaf when the leaf is about one tenth its final size, and then ceases in progressively more basal regions of the lamina. Variation in the mutation frequency within the lamina reflects variation in the frequency of mitosis. Prior to the mergence of the leaf the frequency of mutation is maximal near the tip of the leaf and extremely low at its base; after emergence, the frequency of mutation increases at the base of the leaf. In any given region of the lamina the frequency of mutation is highest in interveinal regions, and is relatively low near the margin. Thus, both the orientation and frequency of cell division at the leaf margin indicate that this region plays a minor role in the growth of the lamina.Abbreviation MF mutation frequency     

Gibberellins in developing fruits of Pisum sativum cv. Alaska: Studies on their role in pod growth and seed development

Gibberellins A₁, A₈, A₂₀ and A₂₉ were identified by capillary gas chromatography-mass spectrometry in the pods and seeds from 5-d-old pollinated ovaries of pea (Pisum sativum cv. Alaska). These gibberellins were also identified in 4-d-old non-developing, parthenocarpic and pollinated ovaries. The level of gibberellin A₁ within these ovary types was correlated with pod size. Gibberellin A₁, applied to emasculated ovaries cultured in vitro, was three to five times more active than gibberellin A₂₀. Using pollinated ovary explants cultured in vitro, the effects of inhibitors of gibberellin biosynthesis on pod growth and seed development were examined. The inhibitors retarded pod growth during the first 7 d after anthesis, and this inhibition was reversed by simultaneous application of gibberellin A₃. In contrast, the inhibitors, when supplied to 4-d-old pollinated ovaries for 16 d, had little effect on seed fresh weight although they reduced the levels of endogenous gibberellins A₂₀ and A₂₉ in the enlarging seeds to almost zero. Paclobutrazol, which was one of the inhibitors used, is xylem-mobile and it efficiently reduced the level of seed gibberellins without being taken up into the seed. In intact fruits the pod may therefore be a source of precursors for gibberellin biosynthesis in the seed. Overall, the results indicate that gibberellin A₁, present in parthenocarpic and pollinated fruits early in development, regulates pod growth. In contrast the high levels of gibberellins A₂₀ and A₂₉, which accumulate during seed enlargement, appear to be unnecessary for normal seed development or for subsequent germination.Abbreviations GA_(a) gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - PFK perfluorokerosene - PVP polyvinylpyrrolidone     

The development of the activity of the chloroplastic and cytosolic isoenzymes of phosphoglycerate kinase during barley leaf ontogenesis

The catalytic activities of the chloroplastic and cytosolic isoenzymes of phosphoglycerate kinase (PGK; EC 2.7.2.3) have been followed during the development of the first leaf of barley (Hordeum vulgare L.) grown for 7 d in darkness followed by transfer to continuous illumination. The investigation has included both the study of a standard leaf section, measured from the leaf tip, over the whole life of the leaf and the study of serial sections of leaf, measured from the leaf base, at a standard sampling time. The results of both approaches were fully compatible. As the catalytic activity of each isoenzyme in the standard assay is directly proportional to the amount of isoenzyme protein present, the catalytic activities may be interpreted wholly in terms of enzyme synthesis and degradation. Both isoenzymes are synthesized in darkness and in etiolated barley are present at a ratio of about 2674 for the cytosolic to chloroplastic isoenzymes. Illumination results in a fivefold or greater increase in chloroplast PGK over a number of days with little change of the cytosolic isoenzyme, resulting in an eventual ratio of cytosolic to chloroplastic isoenzymes approaching the green-leaf value of about 991. Prior to any detectable onset of senescence a 15-fold increase in cytosolic isoenzyme commenced while the amount of chloroplast PGK remained constant. It is suggested that the increased cytosolic PGK may be involved in the export of carbohydrate reserves (starch) prior to leaf senescence. Both isoenzymes subsequently decline in parallel to total protein and chlorophyll in the course of senescence.Abbreviations DHAP reductase dihydroxyacetone-phosphate reductase - GS glutamine synthetase - LHCP light-harvesting chlorophyll-a/b-binding protein - PGK phosphoglycerate kinase - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase This work was supported by the Science and Engineering Research Council (grant no. GR/E54504).     

Effect of light and gibberellic acid on cell division in the first foliage leaf of durum wheat (Triticum durum Desf.)

The present paper is part of a research program which aims at a quantitative analysis of the effects of light and gibberellic acid (GA₃) on growth of the first foliage leaf in durum wheat (Triticum durum Desf.). Since leaf growth is the combined result of the increase in cell number (cell division) and cell enlargement, the influence of light and GA₃ treatment on cell division in the basal meristem of the first leaf in two cultivars, Cappelli and Creso, was investigated. Creso is a short-strawed cultivar carrying the Gai 1 gene which influences both plant height and insensitivity to applied GA₃. Cell division, as measured by mitotic index, was similar in darkness, continuous red light and dichromatic irradiation (far-red plus red), while lower mitotic rates were observed under continuous far-red light: this indicates that the response of cell division is modulated by a high-irradiance reaction of phytochrome in both cultivars. The two cultivars showed different responses to blue light. In Cappelli, blue light and dichromatic irradiation (blue plus red) gave lower mitotic indices than the dark control, indicating the action of a specific blue-light-absorbing photoreceptor, whereas in Creso the response kinetics to all light regimes which included blue light were more complex. On the basis also of the results obtained with GA₃ application in Cappelli, it appears that (i) the hormonal treatment is able to change the pattern of mitotic index only in the presence of the action of a blue-light receptor and (ii) the different responses of the two cultivars could be the result of different endogenous hormonal levels. The importance of the observations in relation to the data for first-leaf longitudinal growth reported in a previous paper (Baroncelli et al. 1984, Planta 160, 298–304) is discussed.Abbreviations BL blue light - D darkness - FR far-red light - GA gibberellin - GA₃ gibberellic acid - m.i. mitotic index - Norflurazon 4-chloro-5-(methylamino)-2-(,,,-trifluoro-m-totyl-3(2H)) pyridazinone - R red light - WL white light - phytochrome photoequilibrium     

Tagetitoxin affects plastid development in seedling leaves of wheat

Ultrastructural and biochemical approaches were used to investigate the mode of action of tagetitoxin, a nonhost-specific phytotoxin produced by Pseudomonas syringae pv. tagetis (Hellmers) Young, Dye and Wilkie, which causes chlorosis in developing — but not mature — leaves. Tagetitoxin has no effect on the growth rate or morphology of developing leaves of wheat (Triticum aestivum L.) seedlings. Its cytological effects are limited to plastid aberrations; in both light-and dark-grown leaves treated with toxin, internal plastid membranes fail to develop normally and plastid ribosomes are absent, whereas mitochondrial and cytoplasmic ribosomes are unaffected. The activity of a plastid stromal enzyme, ribulose-1,5-bisphosphate carboxylase (RuBPCase, EC 4.1.1.39), which is co-coded by nuclear and chloroplast genes, is markedly lower in extracts of both light-and dark-grown toxin-treated leaves, whereas the activity of another stromal enzyme, NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-G-3P-DH, EC 1.2.1.13), which is coded only by the nuclear genome, is significantly lower in extracts of light-grown, but not of dark-grown, treated leaves. The mitochondrial enzymes fumarase (EC 4.2.1.2) and cytochrome-c oxidase (EC 1.9.3.1) are unaffected by toxin in dark-grown leaves, but fumarase activity is reduced in light-grown ones. Four peroxisomal enzyme activities are lowered by toxin treatment in both light- and dark-grown leaves. Light- and dark-grown, toxintreated leaves contain about 50% and 75%, respectively, of the total protein of untreated leaves. There are threefold and twofold increases in free amino acids in light-grown and dark-grown treated leaves, respectively. In general, the effects of tagetitoxin are more extensive and exaggerated in light-grown than in dark-grown leaves. We conclude that tagetitoxin interferes primarily with a light-independent aspect of chloroplast-specific metabolism which is important in plastid biogenesis.Abbreviations NADP-G-3-DH NADP-glyceraldehyde-3-phosphate dehydrogenase - PLB prolamellar body - RuBP-Case ribulose-1,5-bisphosphate carboxylase - SADH shikimic acid dehydrogenase     

Seed development in Pisum

The Ih and lh _i alleles have been shown previously to reduce the level of endogenous gibberellin A₁ (GA₁) in shoots of pea (Pisum sativum L.), resulting in a dwarf phenotype compared with the wild type, cv. Torsdag (Lh). In addition, plants homozygous for the lh ⁱ allele have reduced seed yield compared with Lh (tall, wild type) and lh (dwarf) plants. In this paper we show that the lh ⁱ mutation is expressed in developing seeds and pods. Comparison of GA levels in young shoots and developing seeds of genotypes lh and lh ⁱ demonstrates that the relative severity of the two mutations varies in different tissues. Homozygous h ⁱ seeds have reduced GA levels, weigh less, and are less likely to develop to maturity when compared with Lh seeds. However, fertilization of lh ⁱ plants with Lh pollen increases seed GA levels, seed weight and seed survival, indicating that an increase in seed GA levels due to the presence of the Lh allele can restore normal seed growth. Pods developing on self-pollinated lh ⁱ plants are shorter than pods on Lh (wild type) plants, although this may be an indirect effect of the increased seed abortion of lh _i plants. Based on these results we suggest that endogenous GAs play an important role in the development of seeds of P. sativum L.Abbreviations GA_(n) gibberellin A_n We wish to thank Katherine McPherson, Peter Newman, Leigh Johnson and Peter Bobbi for technical assistance, Professor L. Mander (ANU, Canberra) and Professor B.O. Phinney (UCLA, USA) for labelled GA standards, and the Australian Research Council for financial support.     

Determination for inflorescence development is a stable state,separable from determination for flower development in Pisum sativum L. buds

Terminal meristems of Pisum sativum (garden pea) transit from vegetative to inflorescence development, and begin producing floral axillary meristems. Determination for inflorescence development was assessed by culturing excised buds and meristems. The first node of floral initiation (NFI) for bud expiants developing in culture and for adventitious shoots forming on cultured meristems was compared with the NFI of intact control buds. When terminal buds having eight leaf primordia were excised from plants of different ages (i.e., number of unfolded leaves) and cultured on 6-benzylaminopurine and kinetin-supplemented medium, the NFI was a function of the age of the source plant. By age 3, all terminal buds were determined for inflorescence development. Determination occurred at least eight nodes before the first axillary flower was initiated. Thus, the axillary meristems contributing to the inflorescence had not formed at the time the bud was explanted. Similar results were obtained for cultured axillary buds. In addition, meristems excised without leaf primordia from axillary buds three nodes above the cotyledons of age-3 plants gave rise to adventitious buds with an NFI of 8.3 ±0.3 nodes. In contrast seed-derived plants had an NFI of 16.5 ±0.2. Thus cells within the meristem were determined for inflorescence development. These findings indicate that determination for inflorescence development in P. sativum is a stable developmental state, separable from determination for flower development, and occurring prior to initiation of the inflorescence at the level of meristems.     

The source of gibberellins in the parthenocarpic development of ovaries on topped pea plants

The role and source of gibberellins (GAs) involved in the development of parthenocarpic fruits of Pisum sativum L. has been investigated. Gibberellins applied to the leaf adjacent to an emasculated ovary induced parthenocarpic fruit development on intact plants. The application of gibberellic acid (GA₃) had to be done within 1 d of anthesis to be fully effective and the response was concentration-dependent. Gibberellin A₁ and GA₃ worked equally well and GA₂₀ was less efficient. [³H]Gibberellin A₁ applied to the leaf accumulated in the ovary and the accumulation was related to the growth response. These experiments show that GA applied to the leaf in high enough concentration is translocated to the ovary. Emasculated ovaries on decapitated pea plants develop without application of growth hormones. When [³H] GA₁ was applied to the leaf adjacent to the ovary a substantial amount of radioactivity accumulated in the growing shoot of intact plants. In decapitated plants, however, this radioactivity was mainly found in the ovary. There it caused growth proportional to the accumulation of CA₁. Application of LAB 150978, an inhibitor of GA biosynthesis, to decapitated plants inhibited parthenocarpic fruit development and this inhibition was counteracted by the application of GA₃ (either to the fruit, or the leaf adjacent to the ovary, or through the lower cut end of the stem). All evidence taken together supports the view that parthenocarpic pea fruit development on topped plants depends on the import of gibberellins or their precursors, probably from the vegetative aerial parts of the plant.Abbreviations FW flesh weight - GA_n gibberellin A_n - HPLC high-performance liquid chromatography     

Cuticle development and ultrastructure: evidence for a procuticle of high osmium affinity

Transmission electron microscopy was used to investigate the development and ultrastructure of the cuticles of the bladder primordium and other parts of Utricularia, the stem of Cuscuta gronovii, and the leaves of Athanasia parviflora. In all materials investigated, except the apical meristem of Cassytha pubescens, the first-formed cuticle, named the procuticle, was very electron dense and apparently amorphous in texture. Later, the procuticle changed its ultrastructural appearance: in all species having a procuticle it lost much of its electron density. Simultaneously, it developed into a lamellar structure in U. lateriflora and Cuscuta, and became part of a lamellar cuticle proper. In U. sandersonii and Athanasia the procuticle generally remained without visible structure. The velum of the pavement epithelium of Utricularia is considered to be a slightly modified procuticle which has become loosened from the epithelial cells and stretched.     

Chloroplast development and the synthesis of chlorophyll and protochlorophyllide in Zostera transferred to darkness

Intact plants and isolated leaves of Zostera capricornii Martens ex Aschers were transferred from daylight to darkness. Substantial amounts of chloropyll a and b continued to accumulate in immature and mature tissue in the same ratio as in the light and were incorporated into chlorophyll-protein complexes in the thylakoids. A small amount of protochlorophyllide also accumulated in immature tissue in the dark. Proplastids and immature chloroplasts continued to develop into mature chloroplasts in the dark in the normal manner but prolamellar bodies, which are a conspicuous feature of immature chloroplasts, took longer to disperse than in the light. Protochlorophyllide accumulation and prolamellar-body formation were not correlated. The results indicate that Zostera has a genetic capacity for dark chlorophyll synthesis which is expressed in immature and mature leaf tissue and enables this plant to continue synthesising chlorophyll and assembling chloroplasts at night.Abbreviations Chl chlorophyll - T_o time of transfer to darkness     

Spatial distribution of growth rates and of epidermal cell lengths in the elongation zone during leaf development in Lolium perenne L.

Relative elemental growth rates (REGR) and lengths of epidermal cells along the elongation zone of Lolium perenne L. leaves were determined at four developmental stages ranging from shortly after emergence of the leaf tip to shortly before cessation of leaf growth. Plants were grown at constant light and temperature. At all developmental stages the length of epidermal cells in the elongation zone of both the blade and sheath increased from 12 m at the leaf base to about 550 m at the distal end of the elongation zone, whereas the length of epidermal cells within the joint region only increased from 12 to 40 m. Throughout the developmental stages elongation was confined to the basal 20 to 30 mm of the leaf with maximum REGR occurring near the center of the elongation zone. Leaf elongation rate (LER) and the spatial distributions of REGR and epidermal cell lengths were steady to a first approximation between emergence of the leaf tip and transition from blade to sheath growth. Elongation of epidermal cells in the sheath started immediately after the onset of elongation of the most proximal blade epidermal cells. During transition from blade to sheath growth the length of the blade and sheath portion of the elongation zone decreased and increased, respectively, with the total length of the elongation zone and the spatial distribution of REGR staying near constant, with exception of the joint region which elongated little during displacement through the elongation zone. Leaf elongation rate decreased rapidly during the phase when only the sheath was growing. This was associated with decreasing REGR and only a small decrease in the length of the elongation zone. Data on the spatial distributions of growth rates and of epidermal cell lengths during blade elongation were used to derive the temporal pattern of epidermal cell elongation. These data demonstrate that the elongation rate of an epidermal cell increased for days and that cessation of epidermal cell elongation was an abrupt event with cell elongation rate declining from maximum to zero within less than 10 h.Abbreviations LER leaf elongation rate - REGR relative elemental growth rates