Interveinal Distance Research Articles

Biochemical and Structural Diversification of C4 Photosynthesis in Tribe Zoysieae (Poaceae).

C4 photosynthesis has evolved independently multiple times in grass lineages with nine anatomical and three biochemical subtypes. Chloridoideae represents one of the separate events and contains species of two biochemical subtypes, NAD-ME and PEP-CK. Assessment of C4 photosynthesis diversification is limited by species sampling. In this study, the biochemical subtypes together with anatomical leaf traits were analyzed in 19 species to reveal the evolutionary scenario for diversification of C4 photosynthesis in tribe Zoysieae (Chloridoideae). The effect of habitat on anatomical and biochemical diversification was also evaluated. The results for the 19 species studied indicate that 11 species have only NAD-ME as a decarboxylating enzyme, while eight species belong to the PEP-CK subtype. Leaf anatomy corresponds to the biochemical subtype. Analysis of Zoysieae phylogeny indicates multiple switches between PEP-CK and NAD-ME photosynthetic subtypes, with PEP-CK most likely as the ancestral subtype, and with multiple independent PEP-CK decarboxylase losses and its secondary acquisition. A strong correlation was detected between C4 biochemical subtypes studied and habitat annual precipitation wherein NAD-ME species are confined to drier habitats, while PEP-CK species prefer humid areas. Structural adaptations to arid climate include increases in leaf thickness and interveinal distance. Our analysis suggests that multiple loss of PEP-CK decarboxylase could have been driven by climate aridization followed by continued adaptive changes in leaf anatomy.

Screening of advanced sugarcane genotypes against rust mite

In the screening trial, among the nineteen sugarcane genotypes screened for the reaction to sugarcane rust mite, Abacarus sacchari, only 2 genotypes (009-64 and 0961-07) harboured >1 mites /2 cm2 leaf area while remaining all the genotypes harboured <2 mites/2 cm2 leaf area for the entire crop duration. Morphological characters of genotypes revealed that interveinal distance, leaf area and trichome density were found to influence the A. sacchari negatively. The genotype with high phenol and lower amount of total sugar, reducing sugar, crude protein was found with the lower level of incidence of mites. The study on the role of leaf nutrient on the mite population revealed that genotype with higher potassium content and lower nitrogen levels were found with the minimum incidence of A. sacchari.

Estimating Genetic Variability and Diversity for Vein Density, Photosynthesis and Yield in Rice Genotypes

Understanding the physiological and leaf anatomical traits having positive association with higher yields is critical to utilize these traits effectively in breeding programs for yield improvements in stable food crops. In rice, this would help in improving the productivity to feed the ever growing population. Therefore, the experiment was conducted to evaluate the variability and diversity of ninety-nine rice genotypes for photosynthesis, vein-related characters, and yield. The field trial was carried out in a wetland in Tamil Nadu Agricultural University, Coimbatore during Rabi, 2020. To investigate the genetic variability, efforts were made to estimate the percent of genotypic and phenotypic variation, heritability, and genetic advance likewise genetic diversity was estimated for twelve traits using Mahalanobis (D2) statistics. Analysis variance elucidates the existence of significant variation among the genotypes for all the twelve characters studied. The difference between GCV and PCV was narrow for all the characters studied which shows these characters are less influenced by environmental factors. The highest GVC and PCV was observed in yield and biomass simultaneously the high heritability in broad sense along with high genetic advance as percent mean was estimated in biomass, photosynthetic rate, yield, interveinal distance between major vein, leaf width, total number of veins, and total number of minor veins. These characters are considered to be inherent in nature and selection for improving these traits may be effective in the genetic improvement program. Based on the D2 value ninety-nine genotypes were diversified into five clusters in which Cluster II is the largest containing 37 genotypes followed by cluster I. The highest inter-cluster distance was estimated between cluster II and cluster IV whereas the highest intracluster distance was observed in cluster V indicating that genotypes in this cluster are highly diversified. Subsequently, the higher cluster means of most of the characters including vein characters, leaf width, and photosynthetic rate along with optimum yield and biomass fell in cluster II. Whereas in cluster IV the highest cluster means for biomass and yield was recorded. The traits biomass, yield, photosynthetic rate, interveinal distance between major veins, the total number of minor vein is the major contributors of total divergence in this population. Based on the trait contribution percentage for genetic diversity and genetic distance this study suggests that the genotypes from cluster II and cluster IV can be selected as parents for genetic improvement programs. Hence, information on the nature and degree of divergence in this population would help the plant breeder in the selection and hybridization procedure for choosing the right type of parents to improve vein characters, photosynthetic rate, yield, and biomass.

Coordination of stomata and vein patterns with leaf width underpins water-use efficiency in a C4 crop.

Despite its importance for crop water use and productivity, especially in drought-affected environments, the underlying mechanisms of variation in intrinsic water-use efficiency (iWUE = net photosynthesis/stomatal conductance for water vapour, gsw ) are not well understood, especially in C4 plants. Recently, we discovered that leaf width (LW) correlated negatively with iWUE and positively with gsw across several C4 grasses. Here, we confirmed these relationships within 48 field-grown genotypes differing in LW in Sorghum bicolor, a C4 crop adapted to dry and hot conditions. We measured leaf gas exchange and modelled leaf energy balance three times a day, alongside anatomical traits as potential predictors of iWUE. LW correlated negatively with iWUE and stomatal density, but positively with gsw , interveinal distance of longitudinal veins, and the percentage of stomatal aperture relative to maximum. Energy balance modelling showed that wider leaves needed to open their stomata more to generate a more negative leaf-to-air temperature difference, especially at midday when air temperatures exceeded 40°C. These results highlight the important role that LW plays in shaping iWUE through coordination of vein and stomatal traits and by affecting stomatal aperture. Therefore, LW could be used as a predictor of higher iWUE among sorghum genotypes.

Closer vein spacing by ectopic expression of nucleotide-binding and leucine-rich repeat proteins in rice leaves

Key messageElevated expression of nucleotide-binding and leucine-rich repeat proteins led to closer vein spacing and higher vein density in rice leaves.To feed the growing global population and mitigate the negative effects of climate change, there is a need to improve the photosynthetic capacity and efficiency of major crops such as rice to enhance grain yield potential. Alterations in internal leaf morphology and cellular architecture are needed to underpin some of these improvements. One of the targets is to generate a “Kranz-like” anatomy in leaves that includes decreased interveinal spacing close to that in C4 plant species. As C4 photosynthesis has evolved from C3 photosynthesis independently in multiple lineages, the genes required to facilitate C4 may already be present in the rice genome. The Taiwan Rice Insertional Mutants (TRIM) population offers the advantage of gain-of-function phenotype trapping, which accelerates the identification of rice gene function. In the present study, we screened the TRIM population to determine the extent to which genetic plasticity can alter vein density (VD) in rice. Close vein spacing mutant 1 (CVS1), identified from a VD screening of approximately 17,000 TRIM lines, conferred heritable high leaf VD. Increased vein number in CVS1 was confirmed to be associated with activated expression of two nucleotide-binding and leucine-rich repeat (NB-LRR) proteins. Overexpression of the two NB-LRR genes individually in rice recapitulates the high VD phenotype, due mainly to reduced interveinal mesophyll cell (M cell) number, length, bulliform cell size and thus interveinal distance. Our studies demonstrate that the trait of high VD in rice can be achieved by elevated expression of NB-LRR proteins limited to no yield penalty.

Grasviq: an image analysis framework for automatically quantifying vein number and morphology in grass leaves.

Beyond facilitating transport and providing mechanical support to the leaf, veins have important roles in the performance and productivity of plants and the ecosystem. In recent decades, computational image analysis has accelerated the extraction and quantification of vein traits, benefiting fields of research from agriculture to climatology. However, most of the existing leaf vein image analysis programs have been developed for the reticulate venation found in dicots. Despite the agroeconomic importance of cereal grass crops, like Oryza sativa (rice) and Zea mays (maize), a dedicated image analysis program for the parallel venation found in monocots has yet to be developed. To address the need for an image-based vein phenotyping tool for model and agronomic grass species, we developed the grass vein image quantification (grasviq) framework. Designed specifically for parallel venation, this framework automatically segments and quantifies vein patterns from images of cleared leaf pieces using classical computer vision techniques. Using image data sets from maize inbred lines and auxin biosynthesis and transport mutants in maize, we demonstrate the utility of grasviq for quantifying important vein traits, including vein density, vein width and interveinal distance. Furthermore, we show that the framework can resolve quantitative differences and identify vein patterning defects, which is advantageous for genetic experiments and mutant screens. We report that grasviq can perform high-throughput vein quantification, with precision on a par with that of manual quantification. Therefore, we envision that grasviq will be adopted for vein phenomics in maize and other grass species.

Plant ontogenetic changes in vein and stomatal traits and their relationship with economic traits in leaves of three Mediterranean oaks

Abstract Aims We compared vein and stomatal traits of seedlings and adults of three Mediterranean Quercus species. Previous work suggests that gas-exchange rates tend to be higher at the seedling stage than in adults. Our objective was to determine whether vein and stomatal traits vary throughout whole-plant ontogeny in parallel with the changes in gas-exchange rates. We addressed the following alternative hypotheses: hypothesis 1—seedlings show higher vein and stomatal densities than adults; and hypothesis 2—seedlings have lower investments in vascular tissues to reduce construction costs. Methods Ten specimens from each growth stage were randomly sampled for each species in a location in central-western Spain. We measured mean stomatal and vein traits (size and number of stomata per unit of leaf area, vein density, vein volume, vein to epidermis distance), leaf mass per area and lamina thickness. Important Findings Minor vein density and vein volume per area increased with tree age, which seems inconsistent with the ontogenetic trends in gas-exchange rates. This discrepancy is in support of our hypothesis 2, and it suggests that, at the seedling stage, reducing investments in vascular tissues in benefit of maximizing growth rates is a priority. Larger interveinal distances in seedlings were compensated by smaller vein to epidermis distances. The thin leaves of the seedlings may thus constitute as a necessary trait for achieving shorter path length distances for the transport of water to evaporation sites without the need for a strong investment in costly vascular tissues.

Plasticity of Leaf Hydraulic Conductance in Maize in Response to Varying Nitrogen and Water Supplies

The availabilities of nitrogen (N) and water are two important environmental factors affecting crop growth and productivity in the dryland farming, how they affected leaf water transport capabilities, a bottleneck of whole-plant water transport, was seldom studied. So, the effects of different N and water supplies on leaf hydraulic conductance (Kleaf) in maize (Zea mays L.) were studied by a pot experiment, Kleaf, leaf gas exchange, vein traits and other physio-anatomical traits were measured. We found Kleaf was strongly coupled to leaf gas exchange (net photosynthetic rate, Pn, and stomatal conductance, gs) and whole-plant performance under varying N and water supplies. Long-term N supply had a greater impact than irrigation on Kleaf, Pn and gs due to the type and duration of stress, and the N and water treatments did not interact with these physiological parameters. Kleaf was related positively with the xylem conduit diameter of large longitudinal veins, the proportion of minor-vein length and interveinal distance of large and intermediate longitudinal veins, and negatively with the density of the major veins, and the interveinal distance of the transverse veins. The higher Kleaf under ambient N and water supply was also associated with larger leaf area, leaf mass per area and N content per leaf area and with an improved status of leaf water, which partly enhanced the vein traits responsible for the higher Kleaf. These results are helpful to understand leaf hydraulic strategy in adapting to long-term resource deficiency.

Flag leaf vein traits and their correlation with photosynthesis and grain yield in wheat genotypes of differing ploidy

Leaf venation and coupled physiological function of wild plants co-evolve during the natural selection. How artificial selection affects leaf vein traits and coordinated physiological functions of main crops are largely unknown. This study examined the changes of leaf vein traits and their correlation with gas exchange of flag leaves and yield in eight wheat genotypes of differing ploidy under the same growing conditions. The results indicate that flag leaf vein density (VLA), major-vein density (VLAmajor), and minor-vein density (VLAminor) decreased whereas the proportion of minor-vein length and interveinal distance between small longitudinal veins (IVD) increased during the polyploidization process, and the major advance occurred from the period from diploids to tetraploids. The VLA, VLAmajor, and VLAminor were closely coordinated with maximum net photosynthetic rate (PN) and photosynthetic N use efficiency (PNUE), but not with stomatal conductance. The proportion of minor-vein length and IVD were negatively related with PN and PNUE but positively related with N content per area (Narea) during wheat evolution. A higher proportion of minor-vein length and IVD, and a lower VLAmajor in flag leaves along with a larger Narea were largely responsible for the increased yield in modern cultivars. The decreased redundancy of leaf vein density and increased minor-vein proportion in modern cultivars can confer a yield advantage during wheat evolution.

DNA content equivalence in haploid and diploid maize leaves

Main conclusionThe qPCR assay developed to differentiate haploid and diploid maize leaf samples was unsuccessful due to DNA content difference. Haploid cells are packed more closely together with less cellular expansion.Increased ploidy content (> 2 N) directly correlates with increased cell size in plants, but few studies have examined cell morphology in plants with reduced ploidy (i.e., haploids). To pioneer a scalable new ploidy test, we compared DNA content and cellular morphology of haploid and diploid maize leaves. The amount of genomic DNA recovered from standardized leaf-punch samples was equivalent between these two ploidy types, while both epidermal and mesophyll cell types were smaller in haploid plants. Pavement cells had a substantially smaller size than mesophyll cells, and this effect was more pronounced in the abaxial epidermis. Interveinal distance and guard cell size were significantly reduced in haploids, but the cell percentage comprising stomata did not change. These results confirm the direct correlation between ploidy content and cell size in plants, and suggest that reduced cell expansion predominantly explains DNA content equivalence between haploid and diploid samples, confounding efforts to develop a haploid detection method using DNA content.

Stomatal conductance responses to evaporative demand conferred by rice drought-yield quantitative trait locus qDTY12.1.

Rice quantitative trait locus (QTL) qDTY12.1 is a major-effect drought yield QTL that was identified from a cross of Vandana (recipient parent) and Way Rarem (donor parent) through breeding efforts to improve rice yield under upland drought stress conditions. The two main physiological effects previously observed to be related to the presence of qDTY12.1 were (i) increased lateral root growth, and (ii) increased transpiration efficiency. Since relatively more progress has thus far been made on characterising the lateral root growth response related to qDTY12.1, the present study focussed on characterising how qDTY12.1 confers higher transpiration efficiency under upland drought stress in the Vandana background. In a series of field experiments in which stomatal conductance was measured across different times of day in four qDTY12.1 near isogenic lines (NILs), the NILs and Way Rarem showed consistently higher stomatal conductance than Vandana under conditions of low vapour pressure deficit (VPD) and low photosynthetically active radiation (PAR), and consistently lower stomatal conductance than Vandana under high VPD and high PAR. Leaf δ18O was higher in the qDTY12.1 NIL than in Vandana, and although this trend was previously observed for leaf δ13C it appeared to be more consistent across measurement dates and treatments for leaf δ18O. The qDTY12.1 NILs and Way Rarem tended to show greater large vein to small vein interveinal distance and mesophyll area than Vandana, also consistent across treatments. In terms of aquaporin-related plant hydraulics, variation among NILs in terms of aquaporin inhibition of root hydraulic conductivity (Lpr) was observed, with the highest-yielding NIL showing a lack of Lpr inhibition similar to Way Rarem. The results reported here suggest that the effects of qDTY12.1 are in response not only to soil moisture, but also to atmospheric conditions. An interaction among multiple mechanisms including leaf anatomy and aquaporin function appear to confer the transpiration efficiency effect of qDTY12.1.

Bundle sheath chloroplast volume can house sufficient Rubisco to avoid limiting C4 photosynthesis during chilling.

C4 leaves confine Rubisco to bundle sheath cells. Thus, the size of bundle sheath compartments and the total volume of chloroplasts within them limit the space available for Rubisco. Rubisco activity limits photosynthesis at low temperatures. C3 plants counter this limitation by increasing leaf Rubisco content, yet few C4 species do the same. Because C3 plants usually outperform C4 plants in chilling environments, it has been suggested that there is insufficient chloroplast volume available in the bundle sheath of C4 leaves to allow such an increase in Rubisco at low temperatures. We investigated this potential limitation by measuring bundle sheath and mesophyll compartment volumes and chloroplast contents, as well as leaf thickness and inter-veinal distance, in three C4 Andropogoneae grasses: two crops (Zea mays and Saccharum officinarum) and a wild, chilling-tolerant grass (Miscanthus × giganteus). A wild C4 Paniceae grass (Alloteropsis semialata) was also included. Despite significant structural differences between species, there was no evidence of increased bundle sheath chloroplast volume per leaf area available to the chilling-tolerant species, relative to the chilling-sensitive ones. Maximal theoretical photosynthetic capacity of the leaf far exceeded the photosynthetic rates achieved even at low temperatures. C4 bundle sheath cells therefore have the chloroplast volume to house sufficient Rubisco to avoid limiting C4 photosynthesis during chilling.

Physiological analysis of C3 rice [Oryza sativa (L.)] and C4 millet [Setaria italica (L.)] to identify photosynthetically efficient plants

The study was undertaken with the aim of developing a reliable and rapid screening protocol to identify crop plants with higher photosynthetic efficiencies. The vascular architecture and physiological functions of the leaves of C3 and C4 photosynthetic genetic model systems were compared. Vein densities, leaf chlorophyll index, Chlorophyll a fluorescence and gas exchange parameters were correlated with photosynthetic efficiency to develop an efficient protocol. The photosynthetic rates of Setaria italica were almost double when compared with the C3 plants. The higher photosynthetic efficiency of Setaria italica was supported by high photosynthetic rates coupled with moderate to high stomatal conductance and low transpiration rates. Setaria italica showed a significant increase in PSII efficiency as the growth progressed, while no significant changes in Fv/Fm values were observed in Oryza sativa genotypes. The distribution of SPAD index values among the rice genotypes during the entire growth period did not exceed 34.35. Setaria italica genotypes exhibited a denser arrangement of SLV’s, almost three times higher than Oryza sativa, with an interveinal distance of 0.317–0.329 mm. Denser networks of small longitudinal veins, higher SPAD indices and PSII efficiency were key traits to look for photosynthetic efficiency in crop plants.

Variations in physiological, biochemical, and structural traits of photosynthesis and resource use efficiency in maize and teosintes (NADP-ME-type C4)

C4 plants show higher photosynthetic capacity and resource use efficiency than C3 plants. However, the genetic variations of these traits and their regulatory factors in C4 plants still remain to be resolved. We investigated physiological, biochemical, and structural traits involved in photosynthesis and photosynthetic water and nitrogen use efficiencies (PWUE and PNUE) in 22 maize lines and four teosinte lines from various regions of the world. Net photosynthetic rate (PN) ranged from 32.1 to 46.5 μmol m−2 s−1. PN was positively correlated with stomatal conductance, transpiration rate, and chlorophyll, nitrogen and soluble protein contents of leaves, but not with specific leaf weight. PN was positively correlated with the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and the C4-acid decarboxylases, NADP-malic enzyme and phosphoenolpyruvate carboxykinase, but not with the activity of phosphoenolpyruvate carboxylase. Leaf structural traits (stomatal parameters, leaf thickness, and interveinal distance) were not correlated with PN. These data suggest that physiological and biochemical traits are involved in the genetic variation of PN, but structural traits are not directly involved. PWUE is in the lower class of values reported for C4 plants, whereas PNUE is in the highest class of values reported for C4 plants. PNUE was negatively correlated with leaf nitrogen content but not significantly correlated with PN. PWUE was not correlated with δ13C values of leaves, indicating difficulty in using δ13C values as an indicator of PWUE of maize. In general, teosinte lines showed lower PN but higher PWUE than maize lines.

Adaptive variation in vein placement underpins diversity in a major Neotropical plant radiation

Vein placement has been hypothesised to control leaf hydraulic properties, but the ecophysiological significance of variation in vein placement in the angiosperms has remained poorly understood. The highly diverse Neotropical Bromeliaceae offers an excellent system for exploring understudied relationships between leaf vein placement, physiological functions, and species ecology. To test key hypotheses regarding the links between vein placement, functional type divergences, and ecological diversity in the Bromeliaceae, I characterised the ratio of interveinal distance (IVD) to vein-epidermis distance (VED) in 376 species, representing all major functional types and 10% of the species diversity in the family, as well as bioclimatic properties and key leaf traits for subsets of species. There were significant differences in vein placement parameters in species of contrasting functional type, habitat association, and bioclimatic distribution. In many C3 tank-epiphytes, a greater ratio between interveinal distance and the depth of veins within the mesophyll reflects optimisation for resource foraging in shady, humid habitats. In succulent terrestrials, overinvestment in veins probably facilitates rapid recharge of water storage tissue, as well as restricting water loss. These results highlight how divergences in vein placement relate to distinctive ecophysiological strategies between and within bromeliad functional types, and provide timely insights into how structural–functional innovation has impacted the evolution of ecological diversity in a major radiation of tropical herbaceous angiosperms.

Studies on anatomical characters indicating C_3 and C_4 photosynthetic metabolism in the genus Boerhavia L. (Nyctaginaceae)

The C_3 and C_4 photosynthetic pathways in dicotyledons were investigated with the four species of Boerhavia occurring in Nigeria using light microscopy. The study is not yet well reported on dicotyledons as done for monocotyledons. The features cross-examined were stomata index, stomata size, inter-stomatal distance, stomatal density, interveinal distance, intercellular air spaces, leaf thickness, mesophyll thickness, Kranz tissue, one cell distant count criterion, maximum lateral cell count criterion, vein density and vein distance. Based on these features, these species (B. erecta, B. coccinea and B. repens) were grouped into C_4 while B. diffusa was grouped as a C_3 plant. In particular, interveinal distance less than 166μm and maximum lateral count ranging 2 to 6 will help in grouping C_4 dicotyledons species while those that were greater than these values are useful in grouping C_3 and plants.

Variations in structural, biochemical, and physiological traits of photosynthesis and resource use efficiency in Amaranthus species (NAD-ME-type C4)

C4 plants show higher photosynthetic capacity and productivity than C3 plants owing to a CO2-concentrating mechanism in leaves, which reduces photorespiration. However, which traits regulate the photosynthetic capacity of C4 plants remains unclear. We investigated structural, biochemical, and physiological traits associated with photosynthesis and resource use efficiency in 20 accessions of 12 species of Amaranthus, NAD-malic enzyme-type C4 dicots. Net photosynthetic rate (PN) ranged from 19.7 to 40.5 μmol m−2 s−1. PN was positively correlated with stomatal conductance and nitrogen and chlorophyll contents of leaves and was weakly positively correlated with specific leaf weight. PN was also positively correlated with the activity of the C3 enzyme ribulose-1,5-bisphoshate carboxylase/oxygenase, but not with the activities of the C4 enzymes phosphoenolpyruvate carboxylase and NAD-malic enzyme. Structural traits of leaves (stomatal density, guard cell length, leaf thickness, interveinal distance, sizes of mesophyll and bundle sheath cells and the area ratio between these cells) were not significantly correlated with PN. These data suggest that some of the biochemical and physiological traits are involved in interspecific PN variation, whereas structural traits are not directly involved. Photosynthetic nitrogen use efficiency ranged between 260 and 458 μmol mol−1 N s−1. Photosynthetic water use efficiency ranged between 5.6 and 10.4 mmol mol−1. When these data were compared with previously published data of C4 grasses, it is suggested that common mechanisms may determine the variations in resource use efficiency in grasses and this dicot group.

Leaf anatomical characters in relation to the C3 and C4 photosynthetic pathway in Cyperus (Cyperaceae)

Leaf anatomical characters of twelve species from the genus Cyperus, a genus known to contain species with both C3 and C4 plants, have been investigated. We investigated and established the usefulness of all‐inclusive functional leaf anatomical characters for identifying the photosynthetic pathways of these species. The species investigated were C. articulatus L., C. compressus L., C. difformis L., C. dilatatus Schum. & Thonn., C. distans L., C. esculentus L., C. haspan L., C. imbricatus Retz., C. iria L., C. rotundus L., C. sphacelatus Rottb. and C. tenuiculmis (Boeck.) Hooper, collected from locations in southwestern Nigeria. Standard anatomical procedures for examining epidermal and cross sections of leaves were employed. Our data suggested that a combination of characters, such as the occurrence of Kranz tissue, maximum cell distant count, maximum lateral cell count, interveinal distance, and to some extent leaf and mesophyll thickness, provide a reliable basis for the assessment of the photosynthetic pathways of the investigated species as compared to the isolated characters used previously. The study indicate that C. difformis and C. haspan are C3 species while the rest follow the C4 photosynthetic pathway. A salient feature of this study is the identification of C. dilatatus as belonging to the C4 group.

Leaf hydraulic conductance is coordinated with leaf morpho-anatomical traits and nitrogen status in the genus Oryza.

Leaf hydraulic conductance (K leaf) is a major determinant of photosynthetic rate in plants. Previous work has assessed the relationships between leaf morpho-anatomical traits and K leaf with woody species, but there has been very little focus on cereal crops. The genus Oryza, which includes rice (Oryza sativa) and wild species (such as O. rufipogon cv. Griff), is ideal material for identifying leaf features associated with K leaf and gas exchange. Leaf morpho-anatomical traits, K leaf, leaf N content per leaf area, and CO2 diffusion efficiency were investigated in 11 Oryza cultivars. K leaf was positively correlated with leaf thickness and related traits, and therefore positively correlated with leaf mass per area and leaf N content per leaf area, and negatively with inter-veinal distance. K leaf was also positively correlated with leaf area and its related traits, and therefore negatively correlated with the proportion of minor vein length per area. In addition, coordination between K leaf and CO2 diffusion conductance in leaves was observed. We conclude that leaf morpho-anatomical traits and N content per leaf area strongly influence K leaf. Our results suggest that more detailed anatomical and structural studies are needed to elucidate the impacts of leaf feature traits on K leaf and gas exchange in grasses.

Environmental and genetic variation in leaf anatomy among populations ofAndropogon gerardii(Poaceae) along a precipitation gradient

Phenotypes of two Andropogon gerardii subspecies, big bluestem and sand bluestem, vary throughout the prairie ecosystem of North America. This study sought to determine the role of genetics and environment in driving adaptive variation of leaf structure in big bluestem and sand bluestem. • Four populations of big bluestem and one population of sand bluestem were planted in common gardens at four sites across a precipitation gradient from western Kansas to southern Illinois. Internal leaf structure and trichome density of A. gerardii were examined by light microscopy to separate genetic and environmentally controlled traits. Leaf thickness, midrib thickness, bulliform cells, interveinal distance, vein size, and trichome density were quantified. • At all planting sites, sand bluestem and the xeric population of A. gerardii had thicker leaves and fewer bulliform cells compared with mesic populations. Environment and genetic source population were both influential for leaf anatomy. Leaves from plants grown in mesic sites (Carbondale, Illinois and Manhattan, Kansas) had thicker midribs, larger veins, fewer trichomes, and a greater proportion of bulliform cells compared to plants grown in drier sites (Colby and Hays, Kansas). • Water availability has driven adaptive variation in leaf structure in populations of A. gerardii, particularly between sand bluestem and big bluestem. Genetically based differences in leaves of A. gerardii indicate adaptive variation and evolutionary forces differentiating sand bluestem from big bluestem. Environmental responses of A. gerardii leaves suggest an ability to adjust to drought, even in populations adapted to mesic home environments.