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Salt stress induces significant loss in crop yield worldwide. Although the growth‐stimulating effects of micronutrient nanoparticles (NPs) application under salinity have been studied, the molecular and biochemical mechanisms underlying these effects are poorly understood. The large size of maize leaf growth zones provides an ideal model system to sample and investigate the molecular and physiological bases of growth at subzonal resolution. Using kinematic analysis, our study indicated that salinity at 150 mM inhibited maize leaf growth by decreasing cell division and expansion in the meristem and elongation zones. Consistently, salinity downregulated cell cycle gene expression (wee1, mcm4, and cyclin‐B2‐4). B2O3 NP (BNP) mitigated the stress‐induced growth inhibition by reducing the decrease in cell division and expansion. BNP also enhanced the photosynthesis‐related parameters. Simultaneously, chlorophyll, phosphoenolpyruvate carboxylase and ribulose‐1,5‐bisphosphate carboxylase/oxygenase were stimulated in the mature zone. Concomitant with growth stimulation by BNP, mineral homeostasis, particularly for B and Ca, was monitored. BNP reduced oxidative stress (e.g., lessened H2O2 generation along the leaf zones and reduced lipid peroxidation in the mature zone) induced by salinity. This resulted from better maintenance of the redox status, that is, increased the glutathione‐ascorbate cycle in the meristem and elongation zones, and flavonoids and tocopherol levels in the mature zone. Our study has important implications for assessing the salinity stress impact mitigated by BNP on maize growth, providing a basis to improve the resilience of crop species under salinity stress conditions. [ABSTRACT FROM AUTHOR]

BASIC PENTACYSTEINE (BPCs) transcription factors are important regulators of plant growth and development. However, the regulatory mechanism of BPC2 in roots remains unclear. In our previous study, we created Csbpc2 cucumber mutants by the CRISPR/Cas9 system, and our studies on the phenotype of Csbpc2 mutants showed that the root growth was inhibited compared with wide‐type (WT). Moreover, the surface area, volume and number of roots decreased significantly, with root system architecture changing from dichotomous branching to herringbone branching. Compared with WT, the leaf growth of the Csbpc2 mutants was not affected. However, the palisade and spongy tissue were significantly thinner, which was not beneficial for photosynthesis. The metabolome of root exudates showed that compared with WT, amino acids and their derivatives were significantly decreased, and the enriched pathways were mainly regulated by amino acids and their derivatives, indicating that knockout of CsBPC2 mainly affected the amino acid content in root exudates. Importantly, transcriptome analysis showed that knockout of CsBPC2 mainly affected root gene expression. Knockout of CsBPC2 significantly reduced the gene expression of gibberellins synthesis. However, the expression of genes related to amino acid synthesis, nitrogen fixation and PSII‐related photosynthesis increased significantly, which may be due to the effect of knocking out CsBPC2 on gibberellins synthesis, resulting in the inhibition of seedling growth, thus forming negative feedback regulation. Generally, we showed for the first time that BPC2 is a key regulator gene of root growth and development, laying the foundation for future mechanisms of BPC2 regulation in roots. [ABSTRACT FROM AUTHOR]

Expansins are cell‐wall loosening proteins involved in plant cell expansion and elongation. Objectives of this study were to identify expansins related to leaf elongation in a perennial grass species and determine the relationship between the expression of expansin genes and leaf elongation. A total of 20 expansin genes were identified in tall fescue (Festuca arundinacea), out of which nine genes belonged to the EXPA‐ and 11 to the EXPB subfamily. Two genotypes ("TF007" and "TF116") with different growth rates were used to determine the correlation between expansins and leaf growth. Among the 20 expansins, 16 were differentially expressed in the leaf growth zone in "TF007" and "TF116." The further analysis of gene expression in different leaf segments of "TF007" and "TF116" revealed that the expression level of FaEXPB16 was positively correlated with leaf elongation rate, and "TF007" had a higher leaf elongation rate than "TF116" due to the greater expression level of FaEXPB16. FaEXPA7 exhibited significantly higher expression level in leaves of the rapid‐growing genotypes than the slow‐growing genotypes, suggesting that FaEXPA7 acts as a positive regulator for leaf elongation. FaEXPA7 also exhibited its highest expression level in the cell division zone located in the leaf base. FaEXPB3, FaEXPB4‐2, and FaEXPB11‐2 showed a negative correlation with the leaf elongation rate in "TF007" and "TF116" and were highly expressed in leaves of the slow‐growing genotypes. As promoting or repressing factors for leaf growth, these five expansins could be used as candidate genes in developing the rapid or slow‐growing perennial grass species. [ABSTRACT FROM AUTHOR]

The study aimed to test whether night‐time transpiration provides any potential benefit to wheat plants which are subjected to salt stress. Hydroponically grown wheat plants were grown at four levels of salt stress (50, 100, 150, and 200 mM NaCl) for 5–8 days prior to harvest (day 14–18). Salt stress caused large decreases in transpiration and leaf elongation rates during day and night. The quantitative relation between the diurnal use of water for transpiration and leaf growth was comparatively little affected by salt. Night‐time transpirational water loss occurred predominantly through stomata in support of respiration. Diurnal gas exchange and leaf growth were functionally linked to each other through the provision of resources (carbon, energy) and an increase in leaf surface area. Diurnal rates of water use associated with leaf cell expansive growth were highly correlated with the water potential of the xylem, which was dominated by the tension component. The tissue‐specific expression level of nine candidate aquaporin genes in elongating and mature leaf tissue was little affected by salt stress or day/night changes. Growing plants under conditions of reduced night‐time transpirational water loss by increasing the relative humidity (RH) during the night to 95% had little effect on the growth response to salt stress, nor was the accumulation of Na+ and Cl− in shoot tissue altered. We conclude that night‐time gas exchange supports the growth in leaf area over a 24 h day/night period. Night‐time transpirational water loss neither decreases nor increases the tolerance to salt stress in wheat. [ABSTRACT FROM AUTHOR]

The contribution of hydrogen sulphide (H2S) to salicylic acid (SA) induced lead (Pb) stress tolerance modulated by the ascorbate‐glutathione (AsA‐GSH) cycle was examined in pepper (Capsicum annuum L.) plants. One week after germination, pepper seedlings were sprayed with 0.5 mM SA once a day for a week. Thereafter, seedlings were grown under control (no Pb) or Pb stress (Pb‐S treatment consisting of 0.1 mM PbCl2) for a further 2 weeks. Lead stress reduced plant growth and leaf water status as well as the activities of dehydroascorbate reductase and monodehydroascorbate reductase. However, lead stress elevated leaf Pb, the proline contents, oxidative stress, activities of glutathione reductase and ascorbate peroxidase, as well as the endogenous H2S content. Supplements of SA resulted in improvements in growth parameters, biomass, leaf water status and AsA‐GSH cycle‐related enzyme activities, as well as increasing the H2S content. The positive effect of SA was further enhanced when sodium hydrosulphide was added. However, 0.1 mM hypotaurine (HT) treatment reversed the beneficial effect of SA by reducing the plant H2S content. Application of NaHS in combination with SA + HT suppressed the adverse effect of HT mainly by restoring the plant H2S content, suggesting that higher H2S content, induced by exogenous SA supply, resulted in elevated regulation of the AsA‐GSH cycle. [ABSTRACT FROM AUTHOR]

The leaf is the main photosynthetic organ in plants, such as bamboo. Leaves from bamboo are used as a food additive. However, according to our investigation, to date there have been no reports concerning the leaf development of bamboo. By measuring over 7500 parenchymal cells, we discovered that the linear leaf growth of Pseudosasa japonica could be divided into three growth sections. The first one is a roughly 1‐cm long division zone (DZ), containing about 1580 cells, located at the bottom of the leaf; the second one is an about 3‐cm long elongation zone (EZ), with ~1905 cells, located above the DZ; and the last is a mature zone (MZ) in which cell elongation is completed. The cell production rate of the DZ was 25.33–35.81 cells per hour, with an average of 29.73; and the cell division rate was ~0.45 cells per cell every 24 h. PacBio and Illumina transcriptome sequencing found 21 933 unigenes expressed in these zones. Further analysis revealed a dynamic transcriptome, with transcripts for cell division in the DZ changing to transcripts for cell elongation, photosynthetic development, secondary metabolism, stress resistance, and nutrition transport toward the leaf distal. Those transcriptome transformations correlated well with the changes of relative water content, biomass accumulation, and cellulose crystal degree and were supported by quantitative polymerase chain reaction data. These results revealed a developmental gradient of the bamboo linear growth leaf, which offers a foundation to elucidate and engineer leaf development in bamboo, an economically valuable plant. [ABSTRACT FROM AUTHOR]

To copy with highly heterogeneous light environment, plants can regulate photosynthesis locally and systemically, thus, maximizing the photosynthesis of individual plants. Therefore, we speculated that local weak light may induce the improvement of photosynthesis in adjacent illuminated leaves in plants. In order to test this hypothesis, maize seedlings were partially shaded, and gas exchange, chlorophyll a fluorescence and biochemical analysis were carefully assessed. It was shown that local shading exacerbated the declines in the photosynthetic rates, chlorophyll contents, electron transport and carbon assimilation‐related enzyme activities in shaded leaves as plants growth progressed. While, the decreases of these parameters in adjacent illuminated leaves of shaded plants were considerably alleviated compared to the corresponding leaves of control plants. Obviously, the photosynthesis in adjacent illuminated leaves in shaded plants was improved by local shading, and the improvement in adjacent lower leaves was larger than that in adjacent upper ones. As growth progressed, local shading induced higher abscisic acid contents in shaded leaves, but it alleviated the increase in the abscisic acid contents in adjacent leaves in shaded plants. Moreover, the difference in sugar content between shaded leaves and adjacent illuminated ones was gradually increased. Consequently, local weak light suppressed the photosynthesis in shaded leaves, while it markedly improved the photosynthesis of adjacent illuminated ones. Sugar gradient between shaded leaves and adjacent illuminated ones might play a key role in photosynthetic regulation of adjacent illuminated leaves. [ABSTRACT FROM AUTHOR]

Ethylene is considered one of the most important plant hormones orchestrating plant responses to flooding stress. However, ethylene may induce deleterious effects on plants, especially when produced at high rates in response to stress. In this paper, we explored the effect of attenuated ethylene sensitivity in the Never ripe (Nr) mutant on leaf photosynthetic capacity of flooded tomato plants. We found out that reduced ethylene perception in Nr plants was associated with a more efficient photochemical and non‐photochemical radiative energy dissipation capability in response to flooding. The data correlated with the retention of chlorophyll and carotenoids content in flooded Nr leaves. Moreover, leaf area and specific leaf area were higher in Nr, indicating that ethylene would exert a negative role in leaf growth and expansion under flooded conditions. Although stomatal conductance was hampered in flooded Nr plants, carboxylation activity was not affected by flooding in the mutant, suggesting that ethylene is responsible for inducing non‐stomatal limitations to photosynthetic CO2 uptake. Upregulation of several cysteine protease genes and high protease activity led to Rubisco protein loss in response to ethylene under flooding. Reduction of Rubisco content would, at least in part, account for the reduction of its carboxylation efficiency in response to ethylene in flooded plants. Therefore, besides its role as a trigger of many adaptive responses, perception of ethylene entails limitations in light and dark photosynthetic reactions by speeding up the senescence process that leads to a progressive disassembly of the photosynthetic machinery in leaves of flooded tomato plants. [ABSTRACT FROM AUTHOR]

Carbon dioxide concentration (CO2) and light intensity are known to play important roles in plant growth and carbon assimilation. Nevertheless, the underlying physiological mechanisms have not yet been fully explored. Tomato seedlings (Solanum lycopersicum Mill. cv. Jingpeng No. 1) were exposed to two levels of CO2 and three levels of light intensity and the effects on growth, leaf gas exchange and water use efficiency were investigated. Elevated CO2 and increased light intensity promoted growth, dry matter accumulation and pigment concentration and together the seedling health index. Elevated CO2 had no significant effect on leaf nitrogen content but did significantly upregulate Calvin cycle enzyme activity. Increased CO2 and light intensity promoted photosynthesis, both on a leaf‐area basis and on a chlorophyll basis. Increased CO2 also increased light‐saturated maximum photosynthetic rate, apparent quantum efficiency and carboxylation efficiency and, together with increased light intensity, it raised photosynthetic capacity. However, increased CO2 reduced transpiration and water consumption across different levels of light intensity, thus significantly increasing both leaf‐level and plant‐level water use efficiency. Among the range of treatments imposed, the combination of increased CO2 (800 µmol CO2 mol−1) and high light intensity (400 µmol m−2 s−1) resulted in optimal growth and carbon assimilation. We conclude that the combination of increased CO2 and increased light intensity worked synergistically to promote growth, photosynthetic capacity and water use efficiency by upregulation of pigment concentration, Calvin cycle enzyme activity, light energy use and CO2 fixation. Increased CO2 also lowered transpiration and hence water usage. [ABSTRACT FROM AUTHOR]

The SPORULATION 11 (SPO11) proteins are among eukaryotic the topoisomerase VIA (Topo VIA) homologs involved in modulating various important biological processes, such as growth, development and stress response via endoreduplication in plants, but the underlying mechanism response to stress remains largely unknown under salt treatment. Here, we attempted to characterize a homolog of TOP VIA in upland cotton (Gossypium hirsutum L.), designated as GhSPO11‐3. The silencing of GhSPO11‐3 in cotton plants resulted in a dwarf phenotype with a failure of cell endoreduplication and a phase shift in the ploidy levels. The GhSPO11‐3‐silenced plants also showed substantial changes including accumulated malondialdehyde, significantly reduced chlorophyll and proline contents and decreased antioxidative enzyme activity after salt treatment. In addition, transgenic Arabidopsis lines overexpressing GhSPO11‐3 accelerated both leaf and root growth with cell expansion and endopolyploidy. Both leaf stomatal density and aperture were markedly decreased, and the transgenic Arabidopsis lines were more tolerant with expression of stress‐responsive genes under salinity stress. Furthermore, consistent with the reduced reactive oxygen species (ROS), the expression of ROS scavenging‐related genes was largely reinforced, and antioxidant enzyme activities were accordingly significantly enhanced in transgenic Arabidopsis lines under salt stress. In general, these results indicated that GhSPO11‐3 likely respond to salt stress by positively regulating root growth, stomatal response, ROS production and the expression of stress‐related genes to cope with adverse conditions in plants. [ABSTRACT FROM AUTHOR]

Respiration processes are well recognized as fundamental for the plant carbon balance, but little attention has been paid to the relationships among respiration rates, environment and genetic variability. This can be of particular interest to understand the differences in net carbon balances in crops as grapevines. Night respiration (Rn) and its associated growth (Rg) and maintenance (Rm) components were evaluated during leaf expansion in two grapevine cultivars (Tempranillo cv. and Garnacha cv.) that differ in their plant growth pattern and carbon balance. Simultaneously, leaf traits as leaf mass area, nitrogen (N) and carbon (C) content were evaluated in order to relate to the respiratory processes and the leaf growth. The results showed the differences in respiration rates associated with the leaf expansion pattern. Tempranillo developed leaves with higher leaf area and lower dry weight per leaf unit than Garnacha. Although differences between cultivars were observed in terms of growth costs in expanding leaves, the maintenance costs were similar for both cultivars. Also, a significant linear regression was found between respiration rates and N content in expanding and mature leaves. The results indicate that differences in structure and nitrogen content of expanding leaves may lead to respiratory differences between cultivars. These results also demonstrate the importance of respiratory cost components in carbon balance calculations in grapevines. [ABSTRACT FROM AUTHOR]

Drought can result in severely decreased leaf area development, which impacts plant growth and yield. However, rarely is leaf emergence or leaf expansion separated to resolve the relative sensitivity to water-deficit of these two processes. Experiments were undertaken to impose drought over approximately 2 weeks for eight cowpea (Vigna unguiculata) genotypes grown in pots under controlled environmental conditions. Daily measures of phyllochron index (PI, leaf emergence) and leaf area increase (leaf expansion) were obtained. Each of these measures was referenced against volumetric soil water content, i.e. fraction transpirable soil water. Although there was no clear difference between leaf emergence and leaf expansion in sensitivity to drying soil, both processes were more sensitive to soil drying than plant transpiration rate. Genotypic differences in the soil water content at the initiation of the decline in PI were identified. However, no consistent difference in sensitivity to water-deficit in leaf expansion was found. The difference in leaf emergence among genotypes in sensitivity to soil drying can now be exploited to provide guidance for plant improvement and crop yield increase. [ABSTRACT FROM AUTHOR]

Structural variation in the stroma-grana (SG) arrangement of the thylakoid membranes, such as changes in the thickness of the grana stacks and in the ratio between grana and inter-grana thylakoid, is often observed. Broadly, such alterations are considered acclimation to changes in growth and the environment. However, the relation of thylakoid morphology to plant growth and photosynthesis remains obscure. Here, we report changes in the thylakoid during leaf development under a fixed light condition. Histological studies on the chloroplasts of fresh green Arabidopsis leaves have shown that characteristically shaped thylakoid membranes lacking the inter-grana region, referred to hereafter as isolated-grana (IG), occurred adjacent to highly ordered, large grana layers. This morphology was restored to conventional SG thylakoid membranes with the removal of bolting stems from reproductive plants. Statistical analysis showed a negative correlation between the incidences of IG-type chloroplasts in mesophyll cells and the rates of leaf growth. Fluorescence parameters calculated from pulse-amplitude modulated fluorometry measurements and CO2 assimilation data showed that the IG thylakoids had a photosynthetic ability that was equivalent to that of the SG thylakoids under moderate light. However, clear differences were observed in the chlorophyll a/b ratio. The IG thylakoids were apparently an acclimated phenotype to the internal condition of source leaves. The idea is supported by the fact that the life span of the IG thylakoids increased significantly in the later developing leaves. In conclusion, the heterogeneous state of thylakoid membranes is likely important in maintaining photosynthesis during the reproductive phase of growth. [ABSTRACT FROM AUTHOR]

The NGATHA ( NGA) clade of transcription factors (TFs) forms a small subfamily of four members in Arabidopsis thaliana. NGA genes act redundantly to direct the development of apical tissues in the gynoecium, where they have been shown to be essential for style and stigma specification. In addition, NGA genes have a more general role in controlling lateral organ growth. The four NGA genes in Arabidopsis are expressed in very similar domains, although little is known about the nature of their putative regulators. Here, we have identified a conserved region within the four NGA promoters that we have used as a bait to screen a yeast library, aiming to identify such NGA regulators. Three members of the TCP family of TFs, named after the founding factors TEOSINTE BRANCHED 1, CYCLOIDEA and PROLIFERATING CELL FACTOR 1 AND 2), were recovered from this screening, of which two [ TCP2 and TCP3, members of the CINCINNATA (CIN) family of TCP genes (CIN-TCP) subclade] were shown to activate the NGA3 promoter in planta. We provide evidence that support that CIN-TCP genes are true regulators of NGA gene expression, and that part of the CIN-TCP role in leaf development is mediated by NGA upregulation. Moreover, we have found that this TCP-NGA regulatory interaction is likely conserved in angiosperms, including important crop species, for which the regulation of leaf development is a target for biotechnological improvement. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is considered as an important mechanism for plants to cope with environmental challenges. Leaf growth is one of the first macroscopic processes to be impacted by modification of soil water availability. In this study, we intended to analyze and compare plasticity at different scales. We examined the differential effect of water regime (optimal, moderate water deprivation and recovery) on growth and on the expression of candidate genes in leaves of different growth stages. Candidates were selected to assess components of growth response: abscisic acid signaling, water transport, cell wall modification and stomatal development signaling network. At the tree scale, the four studied poplar hybrids responded similarly to water regime. Meanwhile, leaf growth response was under genotype × environment interaction. Patterns of candidate gene expression enriched our knowledge about their functionality in poplars. For most candidates, transcript levels were strongly structured according to leaf growth performance while response to water regime was clearly dependent on genotype. The use of an index of plasticity revealed that the magnitude of the response was higher for gene expression than for macroscopic traits. In addition, the ranking of poplar genotypes for macroscopic traits well paralleled the one for gene expression. [ABSTRACT FROM AUTHOR]

Transitory starch in cereal plant leaves is synthesized during the day and remobilized at night to provide a carbon source for growth and grain filling, but its mechanistic basis is still poorly understood. The objective of this study is to explore the regulatory mechanism for starch biosynthesis and degradation in plant source organs. Using transmission electron microscopy, we observed that during the day after anthesis, starch granules in mesophyll cells of wheat flag leaves accumulated in chloroplasts and the number of starch granules gradually decreased with wheat leaf growth. During the night, starch granules synthesized in chloroplasts during the day were completely or partially degraded. The transcript levels of 26 starch synthesis-related genes and 16 starch breakdown-related genes were further measured using quantitative real-time reverse transcription polymerase chain reaction. Expression profile analysis revealed that starch metabolism genes were clustered into two groups based on their temporal expression patterns. The genes in the first group were highly expressed and presumed to play crucial roles in starch metabolism. The genes in the other group were not highly expressed in flag leaves and may have minor functions in starch metabolism in leaf tissue. The functions of most of these genes in leaves were further discussed. The starch metabolism-related genes that are predominantly expressed in wheat flag leaves differ from those expressed in wheat grain, indicating that two different pathways for starch metabolism operate in these tissues. This provides specific information on the molecular mechanisms of transitory starch metabolism in higher plants. [ABSTRACT FROM AUTHOR]

Nitrogen (N) limitation reduces leaf growth and photosynthetic rates of maize ( Zea mays), and constrains photosynthate translocation to developing ears. Additionally, the period from about 1 week before to 2 weeks after silking is critical for establishing the reproductive sink capacity necessary to attain maximum yield. To investigate the influence of carbohydrate availability in plants of differing N status, a greenhouse study was performed in which exogenous sucrose (Suc) was infused around the time of silking into maize stems grown under different N regimes. N deficiency significantly reduced leaf area, leaf longevity, leaf chlorophyll content and photosynthetic rate. High N-delayed leaf senescence, particularly of the six uppermost leaves, compared to the other two N treatments. While N application increased ear leaf soluble protein concentration, it did not influence glucose and suc concentrations. Interestingly, ear leaf starch concentration decreased with increasing N application. Infusion of exogenous suc tended to increase non-structural carbohydrate concentrations in the developing ears of all N treatments at silking and 6 days after silking. However, leaf photosynthetic rates were not affected by suc infusion, and suc infusion failed to increase grain yield in any N treatment. The lack of an effect of suc infusion on ear growth and the high ear leaf starch concentration of N-deficient maize, suggest that yield reduction under N deficiency may not be due to insufficient photosynthate availability to the developing ear during silking, and that yield reduction under N deficiency may be determined at an earlier growth stage. [ABSTRACT FROM AUTHOR]

Leaf morphology in the upper canopy of trees tends to be different from that lower down. The effect of long-term water stress on leaf growth and morphology was studied in seedlings of Metasequoia glyptostroboides to understand how tree height might affect leaf morphology in larger trees. Tree height increases water stress on growing leaves through increased hydraulic resistance to water flow and increased gravitational potential, hence we assume that water stress imposed by soil dehydration will have an effect equivalent to stress induced by height. Seedlings were subjected to well-watered and two constant levels of long-term water stress treatments. Drought treatment significantly reduced final needle count, area and mass per area (leaf mass area, LMA) and increased needle density. Needles from water-stressed plants had lower maximum volumetric elastic modulus (εmax), osmotic potential at full turgor (ψπ100) and at zero turgor (ψπ100) than those from well-watered plants. Palisade and spongy mesophyll cell size and upper epidermal cell size decreased significantly in drought treatments. Needle relative growth rate, needle length and cell sizes were linear functions of the daily average water potential at the time of leaf growth (r2 0.88-0.999). We conclude that water stress alone does mimic the direction and magnitude of changes in leaf morphology observed in tall trees. The results are discussed in terms of various models for leaf growth rate. [ABSTRACT FROM AUTHOR]

NAC (NAM, ATAF1,2 and CUC2) proteins, which are plant-specific transcription factors, have crucial roles in plant development, abiotic stress responses, defense and leaf senescence. In this study, an NAC gene was isolated and characterized from the bambooBambusa emeiensis 'Viridiflavus' and tentatively named BeNAC1. Sequence analysis revealed that BeNAC1 belongs to the NAP (NAC-like, activated by APETALA 3/PISTILLATA) subgroup and has a conserved NAC domain in the N-terminus. Transcriptional activation analysis in yeast indicated that BeNAC1 as well as its C-terminus have trans-activation activity. BeNAC1 localized in the nucleus and its transcript level correlated positively with the severity of leaf senescence. Driven by a 1.5-kb upstream fragment of AtNAP, BeNAC1 could rescue the delayed-senescence phenotype of nap. Constitutive overexpression of BeNAC1 resulted in various precocious senescence phenotypes in Arabidopsis. These results collectively indicate that BeNAC1 might play an important regulatory role in leaf senescence in bamboo. [ABSTRACT FROM AUTHOR]

Understanding peroxidase function in plants is difficult because of the lack of substrate specificity, the high number of genes and their diversity in structure. In the present study, the relative expression of 22 genes coding putative peroxidases (E.C 1.11.1.x) in Arabidopsis was studied. The relative expression of AtPrx37 showed a correlation with the cessation of growth in rosette leaves as well as with the growth capacity along the flower stem. Using AtPrx37::GUS construction, its expression was associated with the vascular bundles. Furthermore, the overexpression of AtPrx37 under the control of CaMV 35S promoter rendered a dwarf phenotype with smaller plants and delayed development. The plants overexpressing AtPrx37 also showed an increase in the amount of esterified phenolic material associated with their walls. A role in the growth cessation and phenolic cross-linking during lignin deposition is postulated. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are comprised of approximately 21 nucleotide (nt) RNAs that play important regulatory roles in growth and development by targeting mRNAs for cleavage or translational repression. In Arabidopsis, more than one hundred miRNAs have been identified but the biological functions of only a limited number of them have been determined by molecular genetic analysis. miR396 is a miRNA conserved among the dicot and monocot plants. In Arabidopsis, miR396 has two loci ( MIR396a and MIR396b) and targets six Growth-Regulating Factor ( GRF) genes encoding putative transcription factors with roles in plant leaf growth. Using a northern blot hybridizations approach, we have found that MIR396 is predominantly expressed in leaf and seedling. To further analyze the role of miR396 in the regulation of target genes and leaf growth, we have generated transgenic Arabidopsis plants that constitutively overexpress MIR396a or MIR396b. These transgenic plants have narrow-leaf phenotypes due to reduction in cell number. Ectopic overexpression of MIR396 represses expression of not only six GRF genes but also GIF1 encoding a GRF-interacting transcription coactivator with a role in cell proliferation in leaf. In addition, transgenic MIR396-overexpressing plants have lower densities of stomata and are more tolerant to drought than wild-type plants. These results strongly support the belief that miR396 plays an important role in plant leaf growth and development, most likely by repressing GRF gene expression. [ABSTRACT FROM AUTHOR]

Stratospheric ozone depletion by anthropogenic chlorofluorocarbons has lead to increases in ultraviolet-B radiation (UV-B; 280–320 nm) along the Antarctic Peninsula during the austral spring. We manipulated UV-B levels around plants of Antarctic hair grass (Deschampsia antarctica; Poaceae) and Antarctic pearlwort (Colobanthus quitensis; Caryophyllaceae) for one field season near Palmer Station along the west coast of the Antarctic Peninsula. Treatments involved placing frames over naturally growing plants that either (1) held filters that absorbed most biologically effective radiation (UV-BBE; ‘reduced UV-B’, 22% of ambient UV-BBE levels), (2) held filters that transmitted most UV-BBE (‘near-ambient UV-B’, 87% of ambient UV-BBE levels), or (3) lacked filters (‘ambient UV-B’). Leaves on D. antarctica exposed to near-ambient and ambient UV-B were 16–17% shorter than those exposed to reduced UV-B, and this was associated with shorter epidermal cells at the leaf base and tip. Leaves on C. quitensis exposed to near-ambient and ambient UV-B tended to be shorter (P=0.18) and epidermal cells at the leaf base tended to be smaller than those under reduced UV-B (P<0.10). In order to further explain reductions in leaf length, we examined leaf concentrations of insoluble (cell-wall bound) phenylpropanoids, since it has been proposed that wall-bound phenylpropanoids such as ferulic acid may constrain cell expansion and leaf elongation. In both species, HPLC analysis revealed that ferulic and p-coumaric acid were major components of both insoluble and soluble phenylpropanoids. Although there were no significant differences in concentrations between UV-B treatments, concentrations of insoluble ferulic acid in D. antarctica tended to be higher under ambient and near-ambient UV-B than under reduced UV-B (P=0.17). We also examined bulk-leaf concentrations of soluble (methanol extractable) UV-B-absorbing compounds and found that concentrations were higher in plants exposed to near-ambient and ambient UV-B than in plants exposed to reduced UV-B. We also assessed the UV-B-screening effectiveness of leaves that had developed on plants at the field site with a fiber-optic microprobe. Leaf epidermal transmittance of 300-nm UV-B was 4.0 and 0.6% for D. antarctica and C. quitensis, respectively, which is low compared to grasses and herbaceous dicotyledonous plants found in more temperate climates. While the leaves of Antarctic vascular plants are relatively effective at screening UV-B, levels of UV-B in Antarctica are sufficient to reduce leaf epidermal cell size and leaf elongation in these species, although the mechanisms for these reductions remain unclear. [ABSTRACT FROM AUTHOR]

Various physiological and biochemical characters of a leaf change with stages of its ontogeny. It is likely that the photosynthetic functions of leaves of different ontogeny have different levels of heat tolerance. This study was initiated to analyze the photosynthetic heat tolerance of fully-developed, nearly-developed (more than 2/3 expanded) and developing (10–12 cm visible) leaves of two maize genotypes, F223 and F250. The results indicate that the photosynthetic CO2 assimilation rate (Pn) of developing leaves was less affected by heat stress (42°C in the dark for 90 min) than that of developed leaves. The impaired Pn recovered within 24 h in the developing leaves, while the Pn of developed and nearly-developed leaves did not reach the non-stress level, even after 72 h. The Pn of the developed leaves of genotype F250 was less affected by heat stress than that of genotype F223. After heat stress, the slightly affected Pn of the developing leaf was associated with the almost unchanged photochemical efficiency of photosystem II (Fv/Fm) and the quantum yield of photosystem II electron transport. The chlorophylls a and b were degraded by heat stress; the degradation was pronounced in the developed leaves. As a result of heat stress, the antheraxanthin and zeaxanthin of the xanthophyll cycle accumulated in both the nearly-developed and developed leaves but not in the developing leaves. Injury to the plasma membrane due to heat stress was much less severe in developing leaves than that in the developed leaves. From the physiological characters which we determined it would appear that the Pn functions of the developing leaves are more resistant to heat stress than those of nearly-developed and developed leaves. [ABSTRACT FROM AUTHOR]

Nitrate reductase (EC 1.6.6.1) activity showed circadian rhythmicity in the first leaf of 8-11 days old barley (Hordeum vulgare L. cv. Herta) plants. Circadian rhythms were found using both the in vitro and in vivo method for testing the enzyme activity. When the light intensity was reduced from 65 to 20 W m-2, the amplitude was smaller and the oscillations were damped sooner. In continuous darkness nitrate reductase activity decreased in a two step process. Three different light qualities were tested which all gave the same results. [ABSTRACT FROM AUTHOR]

Growth curves of successive leaves of Populus euramericana (Dode) Guinier 'Robusta' have been determined. With ample supply of water and nutrients the growth of a poplar shoot follows a fixed pattern: an initial logarithmic acceleration phase followed by a stationary phase in which leaves of equal size are produced at a constant rate. Analysis of growth curves of leaves enabled the growth curves of leaf primordia to be predicted. These primordial growth curves are compared to the indirectly determined growth curves of primordia by measuring the lengths of successive leaf primordia in the apex during the stationary phase of growth. The increase in length of successive leaves in the acceleration phase of growth continues for a longer period at high than at low irradiance. The relative growth rates of leaf primordia, leaves and internodes are discussed in terms of shoot growth and phyllotaxis. [ABSTRACT FROM AUTHOR]

Oryza sativa L. (rice) is a salt-sensitive crop species which is relatively ineffective in controlling the influx of sodium and chloride ions to the shoot Nonetheless there is considerable varietal and individual variability in salinity resistance, much of which must derive. Therefore, from differences in the fazes and subsequent effects of saline ions after they have entered the plant The destination of sodium ions within the plant has been investigated, in saline conditions, by examining the time-course of sodium ion concentrations in different leaves of four varieties and breeding lines of rice of differing salinity resistance. Radionuclide tracers were employed to study short term effects and the degree of retranslocation of these sodium ions. Sodium was not distributed uniformly but accumulated in the older leaves before the younger ones. At least some leaves were maintained at sub-lethal salt concentrations in at least the more salt resistant varieties. Radionuclide tracer studies showed that the discontinuous distribution of sodium (from leaf to leaf) is constitutive, and cannot be explained by time of exposure or differential leaf growth rates, and that significant quantities of sodium were not subsequently retranslocated, either within the plant or to the root medium. [ABSTRACT FROM AUTHOR]

The transpiration responses of primary Avena leaves to red and blue light steps were investigated. The response to a red light step was a so-called slow response (with a rise time of about 8 min). The response to a blue light step consisted of both a slow and a rapid response (with a rise time of about 2 min CO2- free air outside the leaf eliminated only the slow response, i. e. in CO2-free air the plant responded to blue light steps but not to red ones. A short exposure of red light prior to a blue light step enhanced the rapid response. The same enhancement of the rapid response could be achieved by means of a temporary pretreatment with CO2-free air. The magnitude of the rapid response was dependent on the blue light if radiance and no threshold effects could be detected. --The experimental results are discussed by means of a model, based on stomatal regulation by ion transport-between the subsidiary cells and the guard cells. It-is suggested that the slow transpiration response is due to CO2-regulation of the stomatal aperture and that the rapid response reflects a, CO2-independent blue light sensitive process which acts directly on the ion transport through the subsidiary and guard cell membranes. [ABSTRACT FROM AUTHOR]

We highlight the novel observation that the responses of maize leaf growth to abscisic acid (ABA) signals can be amplified both by mild water deficits and by nutrient stress. Under our experimental conditions these stresses alone had no effect on leaf growth rate. In most cases leaf growth responses were not attributable to changes in the turgors of growing cells, focusing attention on a regulatory role for cell wall biochemistry. Roles for xyloglucan endotransglycosylase (XET), expansins and peroxidases are discussed. An effect of drought on the activity of expansins seems particularly attractive if xylem sap pH is considered as a chemical signal. We show how changes in xylem sap pH can also modify local accumulation of ABA and thereby modify the apparent sensitivity of guard cells to ABA signals. [ABSTRACT FROM AUTHOR]

When soybean plants are pulsed with [35S]sulphate, label is subsequently redistributed from the roots to the leaves. This confounds studies to measure the redistribution of label from leaves. Accordingly, soybean plants (Glycine max [L.] Merr. cv. Stephens) were grown in 20 µM sulphate and a small portion of the root system (donor root) was pulsed with [35S]sulphate for 24 h. After removing the donor root, the plants were transferred into unlabelled solution, either without sulphate (S20→S0) or with 20 µM sulphate (S20→S20) (intact plants). Also at this time, the expanding leaf (L3) was excised from half of the plants in each treatment (excised plants). Immediately after the pulse, only ca 15% of the label occurred in the roots and ca 40% in the expanding leaf, L3, mostly in the soluble fraction. In intact S20→S20 plants, 35S-label was exported from the soluble fraction of L3, mostly as sulphate, whilst L4 and L5 imported label. Similar responses occurred in S20→S0 plants except that export of label from L3 was more rapid. Excision of L3 from S20→S20 plants inhibited labelling of leaves L4–L6 but not total sulphur, whereas in S20→S0 plants, excision of L3 inhibited the import of both total sulphur and 35S-label in leaves L4, L5 and L6. The data suggest that the soluble fraction of almost fully expanded leaves is an important reserve of sulphur for redistribution to growing leaves. The 35S-label in the root system exhibited fluctuations consistent with its proposed role in the recycling of soluble sulphur from the leaves. [ABSTRACT FROM AUTHOR]

Barley plants (Hordeum vulgare cv. Clipper) were grown in nutrient solution containing 25 μM sulphate and pulsed for 48 h with [35S]sulphate. The plants were then returned to unlabelled 25 μM sulphate and analysed for sulphur and 35S‐label at various times. The sulphur content of each leaf increased to a maximum as it attained full expansion and then decreased by ca 38–50% over the ensuing 30 days. Expanding leaves had the highest specific radioactivity after the pulse but this declined as the leaves expanded. The first leaf to emerge during the chase also had a high specific radioactivity. The data are consistent with the proposal that the sulphur required for early leaf development is derived from a previously formed leaf. 35S‐Labelled sulphur which was delivered to fully expanded leaves did not equilibrate with endogenous sulphur and was selectively re‐exported. In another experiment, barley plants were grown in 5 μM sulphate, pulsed for 48 h with [35S]sulphate and then grown at 0 (S0), 5 (Ss) or 25 μM (S25) unlabelled sulphate. In S25 plants, the sulphur content of both the fully expanded leaves and the expanding leaves increased indicating that the control of sulphur allocation in these plants differed from that in plants grown continuously in 25 μM sulphate and in plants which were grown at 0 or 5 μM sulphate (sub‐optimal for the growth of leaves L7 and L8). The export of 35S‐label from fully expanded leaves during the chase was not influenced by sulphur nutrition. However, the amount of 35S‐label acquired by leaves which formed during the chase increased with sulphur nutrition. In S25 plants these leaves subsequently underwent net loss of label but the analogous leaves of Sn and S5 plants did not. Collectively, the data indicate that, under sulphur limiting conditions, there is no evidence of a mechanism in barley which enhances the mobilization of sulphur from fully expanded leaves to young expanding leaves. [ABSTRACT FROM AUTHOR]

Twenty one-day-old Phaseolus vulgaris ‘Saxa’ plants were cultured in a growth chamber and the plants supplied with either a complete or a Mg-free nutrient solution. From 6 days after transfer to the Mg-free solution, the rate of increase of the area of the second trifoliate leaf was considerably reduced; by day 11 the sucrose concentration in the first trifoliate leaf had increased 6.2-fold at the end of the dark period and 4.6-fold after the light period as compared with the control plants. Corresponding starch concentrations increased 6.6-fold and 2.9-fold respectively. After days 5 to 6 the assimilation rates declined in the first trifoliate leaf of the plants showing deficiency, in comparison with the plants fully supplied with nutrients; respiration increased during darkness. The reduction in net assimilation rate was to a great extent reversible after resupply of magnesium. The reduction of magnesium concentration in the deficient plants was much more marked in the expanding leaves than in the mature primary leaves and roots. Sucrose and starch accumulation did not occur when the first trifoliate leaf was partially shaded, although magnesium concentration, as in the unshaded leaves, was reduced to 13% of that of the control plants. The consequences of magnesium deficiency in the expanding first trifoliate leaf are discussed in terms of the possibility of sink limitation. [ABSTRACT FROM AUTHOR]

UV-B-sensitive (Poinsett) and -insensitive (Ashley) cultivars of cucumber (Cucumis sativus L.) were grown in growth chambers at 600 μmol m-2 s-1 of photosynthetically active radiation provided by metal halide (MH) or high pressure sodium/deluxe (HPS/DX) lamps. Plants were irradiated 15 days from seeding for 6 h per day under 18.2 kJ m-2 day-1 of biologically effective UV-B (UV-BBE) radiation. One of the most pronounced effects of UV-B was a 27 to 78% increase in phenylalanine ammonia-lyase (PAL) activity. UV-B also increased total polyamines. Catalase and superoxide dismutase varied greatly in their response to UV-B. There were no interactive effects on PAL or catalase activity, or total polyamines. There was a UV × PAR source interaction for superoxide dismutase activity. UV-B increased chlorosis and decreased height, dry weight and leaf area. Stem elongation, biomass production, leaf enlargement and chlorosis were greater under HPS/DX lamps than under MH lamps. Chlorosis was greater in Poinsett than in Ashley and in lower leaves than in upper ones. Aside from chlorosis, there were no interactive effects of UV-B. PAR source or cultivar on any of the growth parameters measured, suggesting that the growth response of cucumber seedlings to UV-B is unaffected by PAR source or cultivar. Similarly, except for SOD activity, the biochemical response to UV-B was also not influenced by PAR source or cultivar. [ABSTRACT FROM AUTHOR]

Gas exchange parameters, water relations and Na+/Cl- content were measured on leaves of one-year-old sweet orange (Citrus sinensis [L.] Osbeck cv. Hamlin) seedlings grown at increasing levels of salinity. Different salts (NaCl, KCl and NaNO3) were used to separate the effects of Cl- and Na+ on the investigated parameters. The chloride salts reduced plant dry weight and increased defoliation. Accumulation of Cl- in the leaf tissue caused a sharp reduction in photosynthesis and stomatal conductance. By contrast, these parameters were not affected by leaf Na+ concentrations of up to 478 mM in the tissue water. Leaf water potentials reached values near -1.8 MPa at high NaCl and KCl supplies. This reduction was offset by a decrease in the osmotic potential so that turgor was maintained at or above control values. The changes in osmotic potential were closely correlated with changes in leaf proline concentrations. Addition of Ca2+ (as calcium acetate) increased growth and halved defoliation of salt stressed plants. Furthermore, calcium acetate decreased the concentration of Cl- and Na+ in the leaves, and increased photosynthesis and stomatal conductance. Calcium acetate also counteracted the reductions in leaf water and osmotic potentials induced by salinity. In addition, calcium acetate inhibited the accumulation of proline in the leaves which affected the reduction in osmotic potential. These results indicate that adverse effects of salinity in Citrus leaves are caused by accumulation of chloride. [ABSTRACT FROM AUTHOR]

Barley plants were grown in a nutrient solution containing 25 μM sulphate and the roots were pulsed with [35S]sulphate for 48-h periods at 6 different times between the emergence of leaf 5 (L5) and the emergence of leaf 8 (L8). Growth was continued in unlabelled solution until the emergence of L10. Within the shoot system, sulphur was directed principally into the leaf undergoing expansion. A large proportion of the 35S-label delivered to young expanding leaves (<40% of full expansion) did not occur at the time of the pulse, but subsequently during the ensuing chase indicating slow redistribution of sulphur from another site. During the later stages of leaf expansion (40-100%), most of the sulphur entered the leaf during the pulse, suggesting that sulphur was delivered more directly from the nutrient solution. Up to 75% of the sulphur delivered to L3-L6 at the time they approached or attained full expansion (70-100%) was re-exported. At least some of the sulphur exported from fully expanded leaves was redistributed to developing leaves. [ABSTRACT FROM AUTHOR]

Primary leaves of dark-grown barley (Hordeum vulgare L. cv. Weibull's Ida) unroll in darkness when cut into sections shorter than about 2 cm; the shorter the more unrolling. The unrolling pattern of irradiated leaf sections longer than about 2 cm indicates a polarity in the leaves: the top end of the basal section of a divided leaf unrolls more than the base end of the distal section. Earlier reported findings of a stimulus transmission from irradiated to non-irradiated areas can be fully explained by light-piping and by mechanical, mutual influence between irradiated and non-irradiated areas. [ABSTRACT FROM AUTHOR]

Evidence was obtained by gas chromatography-mass spectrometry and gas chromatography-selected ion monitoring for the presence of gibberellin A20 (GA20), GA1, GA29, GA8 and 2-epiGA29 in vegetative shoots of tall sweet pea, Lathyrus odoratus L. Both tall (genotype L-) and dwarf (genotype II) sweet peas elongated markedly in response to exogenous GA1 attaining similar internode lengths at. the highest dose levels. Likewise internode length in both genotypes, was reduced by application of the GA biosynthesis inhibitor, PP333. The ratio of leaflet length to width was reduced by application of PP333 to tall plants and this effect was reversed by GA1. When applied to plants previously treated with PP333, GA20 promoted internode elongation of L-plants as effectively as GA1, but GA29 was not as effective as GA1 when applied to ll plants. In contrast, GA20 and GA1 were equally effective when applied to the semidwarf lb mutant hut GA-treated Ibib plants did not attain the same internode length as comparable GA-treated Lb-plants. The difference in stature between the tall and dwarf types persisted in dark-grown plants. It is concluded that GA1 may be important for internode elongation and leaf growth in sweet pea. Mutant 1 may influence GA1 synthesis by reducing 3β-hydroxylation of GA20 whereas mutant lb appears to affect GA sensitivity. [ABSTRACT FROM AUTHOR]

Growth analysis techniques are used to test the hypothesis that chilling induces curd (flower) initiation in the cauliflower (Brassica oleracea Botrytis L. cv. Perfection) through inhibiting leaf growth, thereby increasing the availability of growth factors to the stem apex and enabling differentiation of the curd. Effects of chilling on leaf growth and curd induction are compared in juvenile and mature, vegetative plants. Chilling at 5°C reduced dry matter accumulation in the total leaf complement by ca 60% in juvenile plants and 40% in mature plants, compared to control plants growth at 20°C. Juvenile plants showed slower rates of leaf initiation than mature plants. Leaf initiation was retarded by chilling in both plant types with the most marked effect seen in the juvenile plants. This was consistent with dry matter availability to the stem apex limiting differentiation more severely in juvenile plants than in mature plants. The rate of dry matter accumulation in existing leaves, however, was faster in juvenile plants than in mature plants at 20°C. Plants that were juvenile during chilling produced an average of 43 leaves below the curd whereas those that were mature produced 25. Dry matter accumulation in younger leaves was more markedly inhibited by chilling than in older leaves. Chilling also reduced the rate at which enlarging leaves became positionally more remote from the stem apex. Possible roles for such leaves in regulating apical development are considered. [ABSTRACT FROM AUTHOR]

Flowering in Poa pratensis L. cv. Holt and Bromus inermis Leyss. cv. Manchar requires exposure to short days (SD) for primary induction to occur, followed by long days (LD) to allow the inflorescence to develop. Weekly sprays with gibberellic acid (GA3) during primary induction inhibited flower initiation in both P. pratensis and B. inermis. With 10−4M GA3 flowering of P. pratensis was suppressed even after an induction period of 10 weeks. Since both GA3 and non‐inductive LD conditions greatly stimulate leaf elongation, the degree of primary induction was closely negatively correlated with plant height (leaf sheath and blade length) at the end of the induction period. GA3 application or the interpolation of LD during SD induction were most inhibitory during the later middle part of the SD period, whereas they were stimulatory near the beginning or immediately before the SD period. We suggest that changes in the portfolio or levels of endogenous gibberellins mediate photoperiodic control of growth and floral initiation in these plants. However, GA3 sprays could not substitute for LD in causing heading and culm elongation in SD induced plants of the two species. The results are discussed in the light of results with other plants with dual floral induction requirements.

Mineral elements and metabolizable carbohydrates in Citrus leaves [Citrus sinensis (L.) Osbeck cv. Washington navel] have been determined from bud sprouting until the end of the June drop and related to fruitlet growth and abscission. Mineral elements in old leaves decreased during the spring flush of growth and reached minimum values at flower opening, coinciding with a peak in abscission. This was followed by a rapid recovery in potassium and nitrogen to the initial values, with little change afterwards. Old leaves accumulate carbohydrates until flowering, and lose them during post‐anthesis at a constant rate for more than 4 months; this rate of export is unaltered by the presence of a nearby growing fruit. Inflorescence leaves accumulate carbohydrates and mineral elements during post‐anthesis; during the June drop there is an interruption in the accumulation of nitrogen and a net loss of phosphorus, potassium and carbohydrates from these leaves, coinciding with the attainment of the maximum growth rate of the fruit. The two main periods of abscission coincide with minima in the amount of reserves in leaves, suggesting that a limitation in metabolite supply may be the primary cause of drop. There is a closer relationship of the fruit with inflorescence leaves than with old mature ones; however, the regulation of carbohydrate levels in the inflorescence leaves cannot be simply explained in terms of source‐sink relationships with the nearby growing fruit, and the smaller size of inflorescence leaves vs. vegetative ones is not due to the presence of the flower during leaf development. [ABSTRACT FROM AUTHOR]

The photosynthates from leaves from extension shoots may be used either for new growth of the shoot itself, or for growth in other parts of the tree. An attempt has been made to elucidate this problem by determining the content of 14C in long shoots to which 14CO2 was applied either through fully developed leaves at the base, or through very young leaves at the apex. In the case of 14C application at the base, 80 per cent or more of the 14C initially taken up disappears from the shoot, and only a very minor part is translocated upwards in the shoot. When the leaves at the apex are exposed, on the other hand 80 per cent of the 14C absorbed is retained in the leaves and shoot components treated as long as there is still considerable terminal growth taking place, although a small percentage is deposited in the lower parts of the shoot. At the same time, a much higher proportion is incorporated into methanol-insoluble components. As terminal growth decreases, a larger proportion of the 14C activity of the apex leaves also disappears from the shoot. The distribution of activity between the sorbitol, sucrose, glucose and fructose fractions was not significantly different in young and in fully developed leaves. The 14C labelling in the sugar fraction was highest for sorbitol, then sucrose, but decreases with time compared to glucose and fructose. [ABSTRACT FROM AUTHOR]