Vein Density Research Articles

Leaf vascular architecture in temperate dicotyledons: correlations and link to functional traits.

Using 227 dicotyledonous species in temperate region, we found the relationships among densities of different-order veins, creating diversity of leaf vascular architectures. Dicotyledonous angiosperms commonly possess a hierarchical leaf vascular system, wherein veins of different orders have different functions. Minor vein spacing determines leaf hydraulic efficiency, whereas the major veins provide mechanical support. However, there is limited information on the coordination between these vein orders across species, limiting our understanding of how diversity in vein architecture is arrayed. We aimed to examine the (1) relationships between vein densities at two spatial scales (lower- vs. higher-order veins and among minor veins) and (2) relationships of vein densities with plant functional traits. We studied ten traits related to vein densities and three functional traits (leaf dry mass per area [LMA], leaf longevity [LL], and adult plant height [Hadult]) for 227 phylogenetically diverse plant species that occur in temperate regions and examined the vein-vein and vein-functional traits relationships across species. The densities of lower- and higher-order veins were positively correlated across species. The minor vein density was positively correlated with the densities of both areoles and free-ending veins, and vascular networks with higher minor vein density tended to have a lower ratio of free-ending veins to areoles across species. Neither densities of lower- nor higher-order veins were related to LMA and LL. On the other hand, the densities of veins and areoles tended to be positively correlated with Hadult. These results suggest that densities of different-order veins are developmentally coordinated across dicotyledonous angiosperms and form the independent axis in resource use strategies based on the leaf economics spectrum.

Genome duplication effects on functional traits and fitness are genetic context and species dependent: studies of synthetic polyploid Fragaria.

Divergence in functional traits and adaptive responses to environmental change underlies the ecological advantage of polyploid plants in the wild. While established polyploids may benefit from combined outcomes of genome doubling, hybridization, and polyploidy-enabled adaptive evolution, whether genome doubling alone can drive ecological divergence or whether the outcome is genetically variable remains less clear. Using synthetic, colchicine-induced, autotetraploid (4x) plants derived from self-pollinated diploid (2x) seeds, and their colchicine-treated but unconverted diploid (2x.nc) full sibs from two diploid wild strawberry taxa (Fragaria vesca subsp. vesca and F. vesca subsp. bracteata), we examined the effects of genome doubling on functional traits, heat stress tolerance, and fitness components across taxa and maternal families (i.e., genetic families) within taxa. Comparisons between 2x and 2x.nc plants indicated a negligible effect of colchicine treatment on functional traits. Genome doubling increased stomatal length and decreased stomatal density, specific leaf area, and leaf vein density, recapitulating patterns observed in wild polyploid Fragaria. Trichome density, heat stress tolerance, and relative growth rate were not significantly affected by genome doubling. Although clonal reproduction was reduced in response to genome doubling, this effect was strongly genetic-family dependent. The results suggest that genome doubling during incipient speciation alone can generate ecological divergence and variation among genetic lineages. This response potentially allows for rapid short-term evolutionary adaptation and fuels genomic diversity and independent origins of polyploidy.

On the road to C4 rice: advances and perspectives.

SummaryThe international C4 rice consortium aims to introduce into rice a high capacity photosynthetic mechanism, the C4 pathway, to increase yield. The C4 pathway is characterised by a complex combination of biochemical and anatomical specialisation that ensures high CO2 partial pressure at RuBisCO sites in bundle sheath (BS) cells. Here we report an update of the progress of the C4 rice project. Since its inception in 2008 there has been an exponential growth in synthetic biology and molecular tools. Golden Gate cloning and synthetic promoter systems have facilitated gene building block approaches allowing multiple enzymes and metabolite transporters to be assembled and expressed from single gene constructs. Photosynthetic functionalisation of the BS in rice remains an important step and there has been some success overexpressing transcription factors in the cytokinin signalling network which influence chloroplast volume. The C4 rice project has rejuvenated the research interest in C4 photosynthesis. Comparative anatomical studies now point to critical features essential for the design. So far little attention has been paid to the energetics. C4 photosynthesis has a greater ATP requirement, which is met by increased cyclic electron transport in BS cells. We hypothesise that changes in energy statues may drive this increased capacity for cyclic electron flow without the need for further modification. Although increasing vein density will ultimately be necessary for high efficiency C4 rice, our modelling shows that small amounts of C4 photosynthesis introduced around existing veins could already provide benefits of increased photosynthesis on the road to C4 rice.

Comparative analysis of leaf vein density in Sri Lankan traditional rice varieties

The C3 photosynthetic pathway of rice is less efficient than the C4 pathway. The possibility of conversion from C3 to C4 pathways in rice is currently under experiment. In plants undergoing such a transition, higher leaf-vein densities (LVD), and development of Kranz anatomy is expected to be present at an initial stage. High LVD could exist among traditional rice and those could be used as a starting point towards developing C4 rice. In the present study, LVD (estimated by average vein length between, two large longitudinal veins (LLV), two small longitudinal veins (SLV), and the vein length per unit area (TLV)) of 23 Sri Lankan rice accessions were analysed by performing a one-way ANOVA, with mean separation using Duncan’s multiple range test. Among the tested varieties LLV, SLV, and TLV were found to be significantly (p<0.05) different among accessions. Based on the mean separation, the highest LLV was shown by Thanthiribalan, and the lowest by Dewareddhiri, Mahasuduwee, Suwadel and five other accessions. The highest SLV was reported in three accessions and the lowest was in Mahasuduwee, Suwadel and Mahakuruwee. The highest TLV was reported in Mahasuduwee, Suwadel and Mahakuruwee and the lowest in IR 64. Unlike TLV estimation, SLV can be measured directly. Given that TLV and SLV are negatively correlated (r=-0.9183) a low SLV will be a suitable parameter to select for high TLV. The accessions, Mahasuduwee, Suwadel and Mahakuruwee carried a higher LVD (lower SLV and LLV leading to higher TLV) and can be recommended as candidates for studying C3 to C4 photosynthetic pathway conversion in rice.

Adjustments of leaf traits and whole plant leaf area for balancing water supply and demand in Robinia pseudoacacia under different precipitation conditions on the Loess Plateau

The adjustments of plant traits for balancing water supply and demand are critical for keeping the survival of forests under drought stress. In this study, we aimed to determine the long-term adjustments of leaf traits and whole plant leaf area (PLA) in Robinia pseudoacacia trees under different precipitation conditions, and to provide physiological information for modelling. We characterized the temporal changes of plant traits with simulated different precipitation conditions using three levels of water supply in a controlled growth chamber. The results indicated that increasing transpiration with R. pseudoacacia growth leaded to a decline in soil moisture under each precipitation conditions. As drought progressed, leaves exhibited a coordinated increase in vein and stomatal densities, higher drought tolerance by increasing cell wall elasticity, and higher water storage capacitance. After 60 days, leaf traits were similar among the treatments while PLA decreased considerably with decreasing water supply. The field observation along a precipitation gradient indicated that PLA decreased by 64% as mean annual precipitation declined from 645.9 mm to 421.9 mm, while leaf traits did not exhibit marked differences among different sites. The variation in PLA along the precipitation gradient could be well estimated with the optimal PLA calculated by long-term simulations of soil water balance. In summary, increasing transpiration with plant growth induced similar patterns of soil desiccation under different precipitation conditions, which further resulted in the convergence in leaf traits. The adjustment of PLA achieved an optimal value to maximize plant growth and to prevent severe drought stress by balancing the water supply and demand. These results provided a way to fill the gap between experiments and modelling studies for large-scale predictions of plant traits, and should be helpful for the sustainable management of plantation forests in the Loess Plateau.

Variation in leaf anatomical traits relates to the evolution of C4 photosynthesis in Tribuloideae (Zygophyllaceae)

Tribuloideae (Zygophyllaceae, Zygophyllales) is a warm-climate clade of mostly creeping herbs with an uncertain number of C4 species from at least two genera, raising the possibility of multiple C4 origins within this lineage. To delineate C3 and C4 distributions within Tribuloideae, we conducted a phylogenetic analysis using four genetic markers from 78 accessions of Tribuloideae. δ13C values from 68 Tribuloideae members detected 42 C4 species in the genera Kallstroemia, Tribulopis and Tribulus, and no C4 in Balanites, Neoluederitzia, and Sisyndite. All Kallstroemia are C4, while Tribulopis and Tribulus include C3 species. Two independent C4 origins are supported, one in Tribulus and a second in Kallstroemia; both lineages are NADP-ME subtypes. The C4Tribulopis clade occurs in a conflicting position that suggests a hybrid origin between ancestral Kallstroemia and C3Tribulopis/Tribulus species. Anatomical assessment did not show enhanced vein density in C3 Tribuloideae, however, relative bundle sheath area is greater in C3 clades closely related to the C4 lineages, supporting a hypothesis that bundle sheath enhancement in C3 Tribuloideae facilitated C4 evolution.

Drought-induced anatomical modifications of barley (Hordeum vulgare L.) leaves: An allometric perspective

Xeromorphism is a set of structural traits facilitating plant functioning under the conditions of water deficit. While leaf xeromorphic traits have been widely described in a variety of species, much less is known about the ability of plants to acclimate to drought by plastically modifying their leaf structure. We hypothesized that such modification would recapitulate the xeromophic syndrome.We conducted a greenhouse experiment in which a genetically and phenotypically diverse population of barley (Hordeum vulgare L.) cultivars and hybrid lines were subjected to controlled drought followed by re-watering. Leaves produced after the onset of drought were sampled for determination of lamina length and 18 anatomical traits of adaxial epidermis and central transverse lamina sections.Across all studied genotypes, mean leaf length, width, and dimensions of all internal structures were reduced by drought, whereas the density of veins, stomata, and trichomes increased. However, since anatomical traits were commonly correlated with leaf length and following drought the leaves became shorter, we statistically controlled for the leaf size-related variation. Although leaf shortening explained much anatomical response to drought, several traits exhibited additional, leaf-length independent modification. For example, vein and stomatal density increased and xylem area and vessel diameter decreased to a greater extent than expected from leaf size reduction.These results confirm the occurrence of modest facultative xeromorphism in barley but also emphasize the need to use allometric analysis to uncouple the true plasticity of traits from changes attributable to altered plant and organ size.

Effects of major vein blockage and aquaporin inhibition on leaf hydraulics and stomatal conductance.

The density and architecture of leaf veins determine the network and efficiency of water transport within laminae and resultant leaf gas exchange and vary widely among plant species. Leaf hydraulic conductance (Kleaf) can be regulated by vein architecture in conjunction with the water channel protein aquaporin. However, our understanding of how leaf veins and aquaporins affect leaf hydraulics and stomatal conductance (gs) remains poor. By inducing blockage of the major veins and inhibition of aquaporin activity using HgCl2, we examined the effects of major veins and aquaporins on Kleaf and gs in species with different venation types. A vine species, with thick first-order veins and low vein density, displayed a rapidly declined gs with high leaf water potential in response to vein blockage and a greatly reduced Kleaf and gs in response to aquaporin inhibition, suggesting that leaf aquaporins are involved in isohydric/anisohydric stomatal behaviour. Across species, the decline in Kleaf and gs due to aquaporin inhibition increased linearly with decreasing major vein density, possibly indicating that a trade-off function between vein architecture (apoplastic pathway) and aquaporin activity (cell-to-cell pathway) affects leaf hydraulics.

Potassium mediates coordination of leaf photosynthesis and hydraulic conductance by modifications of leaf anatomy.

Typical symptoms of potassium deficiency, characterized as chlorosis or withered necrosis, occur concomitantly with downregulated photosynthesis and impaired leaf water transport. However, the prominent limitations and mechanisms underlying the concerted decreases of leaf photosynthesis and hydraulic conductance are poorly understood. Monocots and dicots were investigated based on responses of photosynthesis and hydraulic conductance and their components and the correlated anatomical determinants to potassium deficiency. We found a conserved pattern in which leaf photosynthesis and hydraulic conductance concurrently decreased under potassium starvation. However, monocots and dicots showed two different hydraulic-redesign strategies: Dicots tended to show a decreased minor vein density, whereas monocots reduced the size of the bundle sheath and its extensions, rather than the minor vein density; both of these strategies may restrain xylem and outside-xylem hydraulic conductance. Additionally, potassium-deprived leaves developed with fewer mesophyll cell-to-cell connections, leading to a reduced area being available for liquid-phase flow. Further quantitative analysis revealed that mesophyll conductance to CO2 and outside-xylem hydraulic resistance were the major contributors to photosynthetic limitation and increased hydraulic resistance, at more than 50% and 60%, respectively. These results emphasize the importance of potassium in the coordinated regulation of leaf photosynthesis and hydraulic conductance through modifications of leaf anatomy.

Trait acclimation of the clonal fern Selliguea griffithiana to forest epiphytic and terrestrial habitats

AbstractAlthough epiphytic habitats are more stressful and heterogeneous than terrestrial habitats, how facultative epiphytes acclimate to such contrasting environments has been poorly understood. Our study focused on the variation of functional traits between epiphytic and terrestrial individuals of Selliguea griffithiana, and provided considerable functional acclimation of this species to such contrasting environments. We sampled ramets of S. griffithiana from epiphytic and terrestrial habitats of a subtropical montane moist forest, SW China. Morphological and anatomical traits, photosynthesis, biomass and ramet density of S. griffithiana were measured and it was found that these traits differed significantly between the two habitats. Frond length, stipe length, spacer length (interramet distance), stomatal density, vein density, maximal chlorophyll fluorescence and relative chlorophyll content of fronds, and biomass per ramet were all lower in epiphytic habitat than those in terrestrial habitat, whereas frond thickness and ramet density were higher in the former. Photosynthetic light–response curves revealed a higher carbon assimilation capability of individuals in terrestrial habitat than in epiphytic habitat, whereas cumulative water loss curves showed a lower water loss rate in the latter. The findings demonstrate acclimation of S. griffithiana to both habitats, that is, epiphytic ramets can mitigate water scarcity at some cost of a reduced photosynthetic capacity, whereas terrestrial ramets can afford to improve the light capture to a higher photosynthetic capacity without any water stresses.

Leaf structural and hydraulic adjustment with respect to air humidity and canopy position in silver birch (Betula pendula).

Climate change scenarios predict an increase in air temperature and precipitation in northern temperate regions of Europe by the end of the century. Increasing atmospheric humidity inevitably resulting from more frequent rainfall events reduces water flux through vegetation, influencing plants' structure and functioning. We investigated the extent to which artificially elevated air humidity affects the anatomical structure of the vascular system and hydraulic conductance of leaves in Betula pendula. A field experiment was carried out at the Free Air Humidity Manipulation (FAHM) site with a mean increase in relative air humidity (RH) by 7% over the ambient level across the growing period. Leaf hydraulic properties were determined with a high-pressure flow meter; changes in leaf anatomical structure were studied by means of conventional light microscopy and digital image processing techniques. Leaf development under elevated RH reduced leaf-blade hydraulic conductance and petiole conductivity and had a weak effect on leaf vascular traits (vessel diameters decreased), but had no significant influence on stomatal traits or tissue proportions in laminae. Both hydraulic traits and relevant anatomical characteristics demonstrated pronounced trends with respect to leaf location in the canopy-they increased from crown base to top. Stomatal traits were positively correlated with several petiole and leaf midrib vascular traits. The reduction in leaf hydraulic conductance in response to increasing air humidity is primarily attributable to reduced vessel size, while higher hydraulic efficiency of upper-crown foliage is associated with vertical trends in the size of vascular bundles, vessel number and vein density. Although we observed co-ordinated adjustment of vascular and hydraulic traits, the reduced leaf hydraulic efficiency could lead to an imbalance between hydraulic supply and transpiration demand under the extreme environmental conditions likely to become more frequent in light of global climate change.

Hydraulic and Photosynthetic Traits Vary with Successional Status of Woody Plants on the Loess Plateau

Research highlights: Water transport and CO2 diffusion are two important processes that determine the CO2 assimilation efficiency in leaves. The integration of leaf economic and hydraulic traits will help to present a more comprehensive view of the succession of woody plants in arid regions. However, studies on hydraulic traits of plants from different successional stages are still rare compared to that on economic traits in arid regions. Materials and methods: We selected 31 species from shrub stage, pioneer tree stage and late successional stage on the Loess Plateau, and measured five economic traits and five hydraulic traits of these species. Results: We found species from the pioneer tree stage exhibited "fast-growing" characteristics with high maximum net photosynthesis rate (Pmax) and vein density (VD). Species from the late successional stage exhibited "slow-growing" characteristics with low Pmax and VD. Economic traits showed no significant differences among the three stages except for Pmax. Hydraulic traits, such as VD, leaf area to sapwood area ratio and vessel frequency, exhibited significant differences among different stages. Conclusions: Hydraulics may play an important role in the succession of woody plants in arid regions. Hydraulic traits and Pmax, should be combined to investigate succession of woody plants in future studies. The "fast-growing" characteristics of pioneer trees and "slow-growing" characteristics of late successional trees may induce the succession of woody plants.

Precipitation has dominant influences on the variation of plant hydraulics of the native Castanopsis fargesii (Fagaceae) in subtropical China

Understanding the roles of climate and intraspecific phylogeny in affecting the variation of plant hydraulics can provide insights into species distribution in different habitats. In the present study, we quantified ten functional traits characterizing branch and leaf hydraulic architecture of Castanopsis fargesii from 12 populations along a precipitation gradient (1120–1690 mm y−1), covering an 1800-km-long west-center-east transect in the subtropical region of China. We also conducted phylogenetic analyses to test the role of intraspecific phylogeny in affecting the variation of hydraulic architecture. We found that, with decreasing precipitation, branch vessel density remained unchanged while hydraulically weighted vessel diameter (Dh) declined by 31.9%, leading to a 74.3% reduction in theoretical hydraulic conductance (Kth). In parallel, leaf vein density (VD) and stomatal pore area index (SPI) declined by 14.6% and 29.9%, respectively. Leaf turgor loss point also declined significantly from −1.51 to −2.29 MPa along the precipitation gradient. In addition, functional traits related to hydraulic efficiency (i.e. Kth, Dh, VD and SPI) were positively correlated, whereas both trait variation and trait-trait correlations were not significantly affected by intraspecific phylogeny, as indicated by the values of Blomberg’s K < 1 and the consistency between principle component analysis and phylogenetic principle component analysis. We conclude that, hydraulic architectures of branch and leaf in C. fargesii varied remarkably under the primary influence of precipitation, suggesting that this subtropical tree species has a high degree of plasticity in terms of hydraulic adjustment, allowing it to cope with shifts in precipitation under future climate change.

Bundle sheath extensions affect leaf structural and physiological plasticity in response to irradiance

Coordination between structural and physiological traits is key to plants' responses to environmental fluctuations. In heterobaric leaves, bundle sheath extensions (BSEs) increase photosynthetic performance (light-saturated rates of photosynthesis, Amax ) and water transport capacity (leaf hydraulic conductance, Kleaf ). However, it is not clear how BSEs affect these and other leaf developmental and physiological parameters in response to environmental conditions. The obscuravenosa (obv) mutation, found in many commercial tomato varieties, leads to absence of BSEs. We examined structural and physiological traits of tomato heterobaric and homobaric (obv) near-isogenic lines grown at two different irradiance levels. Kleaf , minor vein density, and stomatal pore area index decreased with shading in heterobaric but not in homobaric leaves, which show similarly lower values in both conditions. Homobaric plants, on the other hand, showed increased Amax , leaf intercellular air spaces, and mesophyll surface area exposed to intercellular airspace (Smes ) in comparison with heterobaric plants when both were grown in the shade. BSEs further affected carbon isotope discrimination, a proxy for long-term water-use efficiency. BSEs confer plasticity in traits related to leaf structure and function in response to irradiance levels and might act as a hub integrating leaf structure, photosynthetic function, and water supply and demand.

NO LARGE BIAS WITHIN SPECIES BETWEEN THE RECONSTRUCTED AREAS OF COMPLETE AND FRAGMENTED FOSSIL LEAVES

Research Article| January 21, 2019 NO LARGE BIAS WITHIN SPECIES BETWEEN THE RECONSTRUCTED AREAS OF COMPLETE AND FRAGMENTED FOSSIL LEAVES ERIC R. HAGEN; ERIC R. HAGEN 1Wesleyan University, Department of Earth and Environmental Sciences, Middletown, Connecticut 06459, USA Search for other works by this author on: GSW Google Scholar DANA L. ROYER; DANA L. ROYER 1Wesleyan University, Department of Earth and Environmental Sciences, Middletown, Connecticut 06459, USA Search for other works by this author on: GSW Google Scholar RYAN A. MOYE; RYAN A. MOYE 1Wesleyan University, Department of Earth and Environmental Sciences, Middletown, Connecticut 06459, USA Search for other works by this author on: GSW Google Scholar KIRK R. JOHNSON KIRK R. JOHNSON 2Smithsonian Institution, National Museum of Natural History, Washington, D.C. 20013, USA Search for other works by this author on: GSW Google Scholar Author and Article Information ERIC R. HAGEN 1Wesleyan University, Department of Earth and Environmental Sciences, Middletown, Connecticut 06459, USA DANA L. ROYER 1Wesleyan University, Department of Earth and Environmental Sciences, Middletown, Connecticut 06459, USA RYAN A. MOYE 1Wesleyan University, Department of Earth and Environmental Sciences, Middletown, Connecticut 06459, USA KIRK R. JOHNSON 2Smithsonian Institution, National Museum of Natural History, Washington, D.C. 20013, USA email: ehagen@wesleyan.edu Publisher: SEPM Society for Sedimentary Geology First Online: 21 Jan 2019 Online Issn: 1938-5323 Print Issn: 0883-1351 Copyright © 2019, SEPM (Society for Sedimentary Geology) PALAIOS (2019) 34 (1): 43–48. https://doi.org/10.2110/palo.2018.091 Article history First Online: 21 Jan 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ERIC R. HAGEN, DANA L. ROYER, RYAN A. MOYE, KIRK R. JOHNSON; NO LARGE BIAS WITHIN SPECIES BETWEEN THE RECONSTRUCTED AREAS OF COMPLETE AND FRAGMENTED FOSSIL LEAVES. PALAIOS 2019;; 34 (1): 43–48. doi: https://doi.org/10.2110/palo.2018.091 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyPALAIOS Search Advanced Search Abstract Taphonomic processes may filter in a biased manner the tiny fraction of leaves preserved as fossils. A common perception is that large leaves are underrepresented; this is based both on intuition (large leaves are more likely to break apart) and some observations of extant vegetation. Characterizing leaf area correctly is critical for reconstructing climate and for studying evolutionary and biogeographic patterns. In extant dicotyledonous angiosperms, leaf area generally scales with the inverse of second-order vein density. This scaling offers the potential to test if fossil leaf fragments were derived from leaves that were larger than complete (or nearly complete) fossil leaves of the same species. Here we test vein scaling on 573 complete leaves from the latest Cretaceous Hell Creek Formation and earliest Paleocene Fort Union Formation in the Williston Basin of western North and South Dakota. We find a strong scaling similar to extant vegetation, with a somewhat shallower slope (1.67 vs. 2.04) and lower r2 (0.64 vs. 0.80). We apply these two scalings to 41 species-site pairs from the Williston Basin that are each represented by complete (n = 355) and fragmented (n = 387) leaves. With both scalings, the reconstructed leaf areas of fragments are on average 10% larger (±36% 1σ) than their complete companions. This small but noisy signal means that the underrepresentation of large leaves, as captured by our study design, is probably not critical for most fossil applications. Comparing directly the reconstructed areas of complete and fragmented leaves appears reasonable, thus expanding the usefulness of fossil leaf fragments. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Quantification of Leaf Phloem Anatomical Features with Microscopy.

Measurements of vein density and foliar minor vein phloem cell numbers, minor vein phloem cell sizes, and transfer cell wall ingrowths provide quantitative proxies for the leaf's capacities to load and export photosynthates. While overall infrastructural capacity for sugar loading and sugar export correlated positively and closely with photosynthetic capacity, the specific targets of the adjustment of minor vein organization varied with phloem-loading mechanism, plant life-cycle characteristics, and environmental growth conditions. Among apoplastic loaders, for which sugar loading into the phloem depends on cell membrane-spanning transport proteins, variation in minor vein density, phloem cell number, and level of cell wall ingrowth (when present) were consistently associated with photosynthetic capacity. Among active symplastic loaders, for which sugar loading into the phloem depends on cytosolic enzymes, variation in vein density and phloem cell size were consistently associated with photosynthetic capacity. All of these anatomical features were also subject to acclimatory adjustment depending on species and environmental conditions, with increased levels of these features supporting higher rates of photosynthesis. We present a procedure for the preparation of leaf tissue for minor vein analysis, using both light and transmission electron microscopy, that facilitates quantification of not only phloem features but also xylem features that provide proxies for foliar water import capacity.

Extended differentiation of veins and stomata is essential forthe expansion of large leaves in Rheum rhabarbarum.

The densities of veins and stomata govern leaf water supply and gas exchange. They are coordinated to avoid overproduction of either veins or stomata. In many species, where leaf area is greater at low light, this coordination is primarily achieved through differential cell expansion, resulting in lower stomatal and vein density in larger leaves. This mechanism would, however, create highly inefficient leaves in species in which leaf area is greater at high light. Here we investigate the role of cell expansion and differentiation as regulators of vein and stomatal density in Rheum rhabarbarum, which produces large leaves under high light. Rheum rhabarbarum plants were grown under full sunlight and 7% of full sunlight. Leaf area, stomatal density, and vein density were measured from leaves harvested at different intervals. Leaves of R. rhabarbarum expanded at high light were six times larger than leaves expanded at low light, yet vein and stomatal densities were similar. In high light-expanded leaves, minor veins were continuously initiated as the leaves expanded, while an extended period of stomatal initiation, compared to leaves expanded at low light, occurred early in leaf development. We demonstrate that R. rhabarbarum adjusts the initiation of stomata and minor veins at high light, allowing for the production of larger leaves uncoupled from lower vein and stomatal densities. We also present evidence for an independent control of vein and stomatal initiation, suggesting that this adjustment must involve some unknown developmental mechanism.

Screening of Mutants Related to the C4 Photosynthetic Kranz Structure in Foxtail Millet

C4 plants exhibit significantly higher photosynthetic, water and nutrient use efficiency compared with C3 plants. Kranz anatomy is associated with many C4 plants in which bundle sheath cells surround the veins and are themselves surrounded by mesophyll cells. This specialized Kranz anatomy is elucidated as an important contributor to C4 photosynthetic activities in C4 plant. Characterizing the molecular basis of Kranz structure formation has become a key objective for studies of C4 photosynthesis. However, severe mutants that specifically disrupt Kranz anatomy have not been identified. In this study, we detected 549 stable ethyl methane sulfonate-induced foxtail millet (cultivar Yugu1) mutants related to leaf development and photosynthesis among 2,709 mutants screened (M3/M4 generation). The identified mutants included 52 that had abnormal leaf veins (with abnormal starch accumulation based on iodine staining). Each of the 52 mutants was characterized through an analysis of leaf morphology, and through microscopic observations of leaf tissue sections embedded in resin and paraffin. In total, 14 mutants were identified with abnormal Kranz structures exemplified by small bundle sheath cell size. Additional phenotypes of the mutants included poorly differentiated mesophyll and bundle sheath cells, increased vein density and the absence of chloroplasts in the bundle sheath cells. Kranz structure mutations were accompanied by varying leaf thickness, implying these mutations induced complex effects. We identified mutations related to Kranz structure development in this trial, which may be useful for the mapping and cloning of genes responsible for mediating Kranz structure development.

Getting closer: vein density in C4 leaves.

Contents Summary 1260 I. Introduction 1260 II. Molecular and genetic mechanisms of C4 leaf venation 1262 III. Conclusions and future perspectives 1266 Acknowledgements 1266 References 1266 SUMMARY: C4 grasses are major contributors to the world's food supply. Their highly efficient method of carbon fixation is a unique adaptation that combines close vein spacing and distinct photosynthetic cell types. Despite its importance, the molecular genetic basis of C4 leaf development is still poorly understood. Here we summarize current knowledge of leaf venation and review recent progress in understanding molecular and genetic regulation of vascular patterning events in C4 plants. Evidence points to the interplay of auxin, brassinosteroids, SHORTROOT/SCARECROW and INDETERMINATE DOMAIN transcription factors. Identification and functional characterization of candidate regulators acting early in vascular development will be essential for further progress in understanding the precise regulation of these processes.

Physiologically adaptive plasticity in nutrient resorption efficiency of Avicennia officinalis L. under fluctuating saline environments in the Sundarbans of Bangladesh

Nutrient resorption efficiency is an important nutrient conservation and ecophysiological mechanism of mangroves growing in saline environments. This study investigated the nitrogen, phosphorus, and potassium resorption efficiency of Avicennia officinalis L. growing across a salinity gradient with seasonal variations in the Sundarbans of Bangladesh. Due to decreasing salinity during the monsoon and postmonsoon seasons, the nutrient availability in soil and nutrient resorption efficiency did not vary significantly among the low-salinity, medium-salinity, and high-salinity zones. However, the nutrient availability in the medium-salinity and high-salinity zones was significantly lower than that in the low-salinity zone during the premonsoon season due to increased salinity. Consequently, nutrient resorption efficiency in the medium-salinity and high-salinity zones was significantly higher than that in the low-salinity zone during the premonsoon. Further, leaf vein density of A. officinalis in the medium-salinity and high-salinity zones was significantly higher than that in the low-salinity zone. This modification in vein density was the mechanism for the higher nutrient resorption efficiency of A. officinalis in the medium-salinity and high-salinity zones than that in the low-salinity zone. This plasticity in nutrient resorption efficiency is a physiologically adaptive mechanism that enables A. officinalis to persist in increasingly saline environments due to climate change.