Xylem Vessel Size Research Articles

Small Stomates and Xylem Vessels Associated With Freeze Tolerance in Winter Barley

ABSTRACTFreeze tolerance is a complex agronomic trait that is difficult to evaluate in the field because of year‐to‐year variation in weather. Discovering plant characteristics closely related to freeze tolerance would enable more effective selection for this important trait. To explore possible physiological mechanisms and search for useful characteristics related to freeze tolerance in winter barley, we conducted field and growth chamber experiments with seven freeze‐tolerant and seven freeze‐susceptible genotypes that exhibited contrasting winter survival in preliminary field screenings. In a 2‐year field experiment, malondialdehyde, proline and water‐soluble carbohydrate concentrations were measured during cold acclimation and deacclimation to investigate differences in osmoregulation and membrane stability between freeze‐tolerant and freeze‐sensitive genotypes. All parameters varied by sampling year, and significant differences between freeze tolerance groups were found mainly during cold deacclimation in the spring. In growth chamber experiments, the size of xylem vessels and stomates was measured with and without cold acclimation. Freeze‐tolerant genotypes had smaller xylem vessels and stomates than freeze‐sensitive genotypes with and without cold acclimation, and small stomatal length was associated with a small xylem vessel area. Thus, it may be possible to improve freeze tolerance in winter barley by selecting smaller xylem and stomate cells. This study also validated germplasms of winter barley with differential freeze tolerance for future projects on breeding for improving winter hardiness and on plant physiology and genetics in response to freezing stress.

Influence of IAA and ABA on maize stem vessel diameter and stress resistance in variable environments.

The plasticity of the xylem and its associated hydraulic properties play crucial roles in plant acclimation to environmental changes, with vessel diameter (Dv) being the most functionally prominent trait. While the effects of external environmental factors on xylem formation and Dv are not fully understood, the endogenous hormones indole-3-acetic acid (IAA) and abscisic acid (ABA) are known to play significant signalling roles under stress conditions. This study investigates how these hormones impact Dv under various environmental changes. Experiments were conducted in maize plants subjected to drought, soil salinity, and high CO2 concentration treatments. We found that drought and soil salinity significantly reduced Dv at the same stem internode, while an elevated CO2 concentration can mitigate this decrease in Dv. Remarkably, significant negative correlations were observed between Dv and the contents of IAA and ABA when considering the different treatments. Moreover, appropriate foliar application of either IAA or ABA on well-watered and stressed plants led to a decrease in Dv, while the application of corresponding inhibitors resulted in an increase in Dv. This finding underscores the causal relationship between Dv and the levels of both IAA and ABA, offering a promising approach to manipulating xylem vessel size.

ОБОСНОВАНИЕ ПРИМЕНЕНИЯ ЭЛЕМЕНТА КАПЕЛЬНОГО ПОЛИВА ДЛЯ ОПТИМИЗАЦИИ ГИДРОТРОФИЧЕСКОГО РЕЖИМА ДЫНИ В УСЛОВИЯХ ЗАЩИЩЕННОГО ГРУНТА

The aim of the study is to investigate the possibilities of using drip irrigation to optimize the hydrotrophic regime of melon in protected ground conditions. The object of the study is the melon crop of the F1 Polidor variety. The study was carried out in 2021–2023 at the enterprise of OJSC Vysokovsky Greenhouse Plant (Kostroma Region) under the adopted technology for growing F1 Polidor melon (control – drip irrigation) and using an additional element of the GTK drip irrigation system (experiment). The experiment was carried out on an area of 200 m2 (the size of the survey site is 25 m2) in accordance with the approved methods. Hydrotrophic capsules were installed when planting seedlings in the ground at the rate of 1 hydrocapsule per 2 plants, while 2 capillaries of the automated irrigation system were mounted in the lid. The frequency and level of water and nutrient solutions supply were programmed in accordance with the requirements of the biology of the crop and were carried out centrally. The experiment was repeated 4 times. Optimization of the water and nutrient supply regime for melons contributed to the development of a powerful root system with a positively changed anatomical and morphological (increase in root system weight by 125.7 g/plant, decrease in the number of root hairs and increase in the size of xylem vessels to 0.32 mm) and functional structure (101 % more working adsorbing surface of roots), increasing the physiological activity of above-ground organs in terms of photosynthetic productivity to 0.99 mgC/dm2/h and reducing water losses by 3.4 %/h/plant, which affected the formation of additional melon production of 8.9 t/ha with high accumulation of sugars (16.4 %) and vitamin C (8.9 mg%). Reducing the costs of additional water consumption will have a positive effect on the cost of production and on the economy of the enterprise as a whole. In greenhouse conditions, a favorable climate will be created for the working personnel, the amount of weeding will be reduced, and the risk of allergic reactions to mold spores will be reduced.

Natural variation of maize root hydraulic architecture underlies highly diverse water uptake capacities.

Plant water uptake is determined by the root system architecture and its hydraulic capacity, which together define the root hydraulic architecture. The current research aims at understanding the water uptake capacities of maize (Zea mays), a model organism and major crop. We explored the genetic variations within a collection of 224 maize inbred Dent lines and successively defined core genotype subsets to access multiple architectural, anatomical, and hydraulic parameters in the primary root (PR) and seminal roots (SR) of hydroponically grown seedlings. We found 9-, 3.5-, and 12.4-fold genotypic differences for root hydraulics (Lpr), PR size, and lateral root size, respectively, that shaped wide and independent variations of root structure and function. Within genotypes, PR and SR showed similarities in hydraulics and, to a lesser extent, in anatomy. They had comparable aquaporin activity profiles that, however, could not be explained by aquaporin expression levels. Genotypic variations in the size and number of late meta xylem vessels were positively correlated with Lpr. Inverse modeling further revealed dramatic genotypic differences in the xylem conductance profile. Thus, tremendous natural variation of maize root hydraulic architecture underlies a high diversity of water uptake strategies and paves the way to quantitative genetic dissection of its elementary traits.

Cas9/gRNA-Mediated Mutations in PtrFLA40 and PtrFLA45 Reveal Redundant Roles in Modulating Wood Cell Size and SCW Synthesis in Poplar

Fasciclin-like arabinogalactan proteins (FLAs) play an important role in plant development and adaptation to the environment. However, the roles of FLAs in wood formation remain poorly understood. Here, we identified a total of 50 PtrFLA genes in poplar. They were classified into four groups: A to D, among which group A was the largest group with 28 members clustered into four branches. Most PtrFLAs of group A were dominantly expressed in developing xylem based on microarray and RT-qPCR data. The roles of PtrFLA40 and PtrFLA45 in group A were investigated via the Cas9/gRNA-induced mutation lines. Loss of PtrFLA40 and PtrFLA45 increased stem length and diameter in ptrfla40ptrfla45 double mutants, but not in ptrfla40 or ptrfla45 single mutants. Further, our findings indicated that the ptrfla40ptrfla45 mutants enlarged the cell size of xylem fibers and vessels, suggesting a negative modulation in stem xylem cell size. In addition, wood lignin content in the ptrfla40fla45 mutants was increased by nearly 9%, and the lignin biosynthesis-related genes were significantly up-regulated in the ptrfla40fla45 mutants, in agreement with the increase in wood lignin content. Overall, Cas9/gRNA-mediated mutations in PtrFLA40 and PtrFLA45 reveal redundant roles in modulating wood cell size and secondary cell wall (SCW) synthesis in poplar.

Kiwifruit Adaptation to Rising Vapor Pressure Deficit Increases the Risk of Kiwifruit Decline Syndrome Occurrence

Kiwifruit has, for a long time, been widely affected by a syndrome named “kiwifruit decline syndrome” (KiDS). Several environmental factors have already been investigated looking for the possible origin of this syndrome. Recently, a possible role of climate change has been proposed, highlighting the influence of high air and soil temperature. In this work, the role of rising vapor pressure deficit (VPD) was also investigated in an experimental orchard in which several agronomic practices were examined in order to find strategies to face KiDS occurrence in crops. Stomatal control in response to rising VPD showed to be lacking, and root xylem vessel size and number modifications were observed as an adaptation to water stress; then, a scarce prospect of success facing sudden and strong weather events related to climate change can be expected in this plant. None of the agronomic strategies tested, that were focused on the soil quality improvement and on prevention of desiccation, avoided the KiDS occurrence. Agronomic management should move to new practices focused on orchard climate control.

Trading water for carbon in the future: Effects of elevated CO2 and warming on leaf hydraulic traits in a semiarid grassland.

The effects of climate change on plants and ecosystems are mediated by plant hydraulic traits, including interspecific and intraspecific variability of trait phenotypes. Yet, integrative and realistic studies of hydraulic traits and climate change are rare. In a semiarid grassland, we assessed the response of several plant hydraulic traits to elevated CO2 (+200 ppm) and warming (+1.5 to 3°C; day to night). For leaves of five dominant species (three graminoids and two forbs), and in replicated plots exposed to 7 years of elevated CO2, warming, or ambient climate, we measured: stomatal density and size, xylem vessel size, turgor loss point, and water potential (pre‐dawn). Interspecific differences in hydraulic traits were larger than intraspecific shifts induced by elevated CO2 and/or warming. Effects of elevated CO2 were greater than effects of warming, and interactions between treatments were weak or not detected. The forbs showed little phenotypic plasticity. The graminoids had leaf water potentials and turgor loss points that were 10% to 50% less negative under elevated CO2; thus, climate change might cause these species to adjust their drought resistance strategy away from tolerance and toward avoidance. The C4 grass also reduced allocation of leaf area to stomata under elevated CO2, which helps explain observations of higher soil moisture. The shifts in hydraulic traits under elevated CO2 were not, however, simply due to higher soil moisture. Integration of our results with others' indicates that common species in this grassland are more likely to adjust stomatal aperture in response to near‐term climate change, rather than anatomical traits; this contrasts with apparent effects of changing CO2 on plant anatomy over evolutionary time. Future studies should assess how plant responses to drought may be constrained by the apparent shift from tolerance (via low turgor loss point) to avoidance (via stomatal regulation and/or access to deeper soil moisture).

Physiological and Structural Responses to Prolonged Water Deficit in Young Trees of Two Olive Cultivars.

This study aimed to characterize the physiological and structural responses of potted one-year-old olive trees belonging to two olive cultivars—‘Nocellara del Belice’ and ‘Cerasuola’—exposed to prolonged drought under greenhouse conditions. Two irrigation treatments based on evapotranspiration (ET) were imposed for 69 days, i.e., well-watered (WW, 100% ET) and drought-stressed (DS, 10–30% ET). Leaf stomatal conductance (gs), stem water potential (Ψstem), transpiration (E), photosynthetic capacity (Amax), water use efficiency (WUE), stem (Kstem) and root (Kroot) hydraulic conductance, trunk diameter variations (TDV), and leaf patch attenuated pressure fluctuations (pp, a proxy of the inverse of leaf turgor pressure) were measured in WW and DS trees at different stages of the experiment. Leaf gs did not significantly differ between cultivars under DS, whereas differences in Ψstem only became significant at the end of prolonged drought, when ‘Nocellara del Belice’ experienced Ψstem < −4 MPa. ‘Cerasuola’ trees expressed the best WUE under drought, although they were more susceptible to photoinhibition under optimal plant water status. Both cultivars tended to increase their Kstem at the end of the drought period. A marked reduction in Kroot occurred in ‘Cerasuola’ plants after prolonged drought; however, a similar mechanism was not observed in ‘Nocellara del Belice’. The ratio between Kstem and Kroot exponentially increased towards the end of the prolonged drought period in both cultivars, but more markedly in ‘Cerasuola’. TDV and pp trends suggested that ‘Cerasuola’ plants keep better plant water status under severe drought compared to ‘Nocellara del Belice’ by maintaining high leaf turgor and reduced trunk diameter fluctuations. These responses may be related to reduced cell wall elasticity and xylem vessel size and/or wall thickness—drought avoidance mechanisms. The Kstem/Kroot ratio can serve as an indicator of drought stress avoidance mechanisms to compare genotype-specific responses to drought stress.

Water deficit responses of field-grown Pinot noir mediated by rootstock genotypes in a cool climate region

Under the global warming scenario, water scarcity is expected to intensify in most grape-growing regions. The use of drought-tolerant rootstocks is considered a useful tool to mitigate the negative effects of soil water deficit on vine functioning. Differences in leaf gas exchange, plant water status, specific hydraulic conductivity in petioles (Kpetiole), xylem vessel size and vegetative vigour of field-grown Pinot noir grafted onto five rootstocks (3309C, 101-14 MGt, Kober 5BB, Riparia Gloire de Montpellier, 41B MGt) were investigated during one season under water deficit in Switzerland. The water deficit was imposed by installing waterproof and non-reflecting plastic sheets on the soil from March to harvest (September) to avoid rainfall infiltration. Rootstocks had stronger effects on vine water status than on gas exchanges. During the grape ripening stage, vines grafted onto 41B MGt and 101-14 MGt were characterised by more severe water stress as shown by the lowest values of pre-dawn leaf (Ψpd), stem water potential (Ψstem) and water stress integral (SΨ), whereas 3309C and Kober 5BB rootstocks induced milder effects. Significant differences in photosynthesis (A), stomatal conductance (gs) and transpiration (E) were only observed between vines grafted onto 41B MGt and 3309C at later stages of ripening. Changes induced by rootstocks in shoot vigour, Kpetiole and the number and size of xylem vessels in petioles and stems were correlated to differential responses of Pinot noir to water deficit. The increased vegetative vigour induced by 3309C and Kober 5BB was associated with the highest Kpetiole, xylem vessel size and a good plant water status of Pinot noir under low soil water availability. Kober 5BB induced the highest yield, probably due to the better vine water status, whereas vines grafted onto 41B MGt showed the lowest malic acid content and yeast assimilable nitrogen in berries.

Lianas and Trees From a Seasonally Dry and a Wet Tropical Forest Did Not Differ in Embolism Resistance but Did Differ in Xylem Anatomical Traits in the Dry Forest

One of the most prominent changes in neotropical forests has been the increase in abundance and size of lianas. Studies suggest that lianas have more acquisitive strategies than trees, which could allow them to take advantage of water more effectively when it is available in water-limited forests, but few studies compared across growth form (i.e., lianas vs. trees) and forest type (i.e., wet vs. seasonally dry). We measured hydraulic and anatomical traits of co-occurring lianas and trees that convey drought resistance (xylem embolism resistance and intervessel pit membranes) and water transport capacity (xylem vessel diameter and density) in a seasonally dry and a wet evergreen tropical forest to address: (1) Are there differences between vulnerability to embolisms (P50—water potential at 50% loss of hydraulic conductivity) and hydraulic safety margins (HSM) across growth form and forest type? (2) How do vessel diameter and density vary across growth form and forest type? (3) Are there differences in xylem intervessel pit membrane thickness across growth form and forest type and does it predict xylem embolism vulnerability in trees and lianas? We examined hydraulic and xylem anatomical traits of 32 species—eight lianas and eight trees in each forest type. We found no difference in P50and HSMs between lianas and trees and between the wetter and drier forest. Dry forest lianas had 81% greater maximum vessel diameter and 125% greater range in vessel diameter sizes than dry forest trees but, there was no significant difference between life forms in the wet forest. Dry forest species had 50% greater vessel density and 30% greater maximum pit membrane thickness than wet forest ones. Maximum pit membrane thickness was correlated to P50and HSMs. The main difference between lianas and trees occurred in the dry forest, where lianas had larger maximum xylem vessel size than trees, implying that they have proportionally greater hydraulic conductive capacity than the trees in seasonal forests.

Analyses of Xylem Vessel Size on Grapevine Cultivars and Relationship with Incidence of Esca Disease, a Threat to Grape Quality

Esca disease is one of the most important grapevine trunk diseases. It seriously reduces the quality and quantity of grapevine production, and results in a shorter vineyard lifespan. Previous studies have suggested that wide xylem vessel diameter favours development on grapevine of Phaeomoniella chlamydospora, one of the fungi involved in esca, thus affecting disease susceptibility. In this study, cultivars mainly originated from European countries, 27 white-berried and 24 red-berried grapevine cultivars, were grown in the same experimental vineyard and were analysed for xylem vessel sizes (as diameter and frequency) for correlation with esca incidence. In this study, the cultivars showed significant differences in the xylem vessel parameters. However, no relationship was detected between vessel size and esca incidence in the field. Overall, white-berried cultivars showed wider vessel diameters than red-berried cultivars. The relationship between xylem vessel size in the red-berried and white-berried cultivars and incidence of esca symptoms is discussed. We suggest that vessel anatomy profiles can provide useful information for further investigations on grapevine genotype structure–esca incidence relationships.

Maternal drought stress on Persian oak (Quercus brantii Lindl.) affects susceptibility to single and combined drought and biotic stress in offspring

Zagros woodlands in Iran are threatened by the decline of Persian oak (Quercus brantii) trees. Although the main cause of tree mortality is drought stress, bacterial pathogens such as Brenneria goodwinii also contribute to tree dieback. Maternal effects were studied in a drought-affected environment. We investigated if the susceptibility of Q. brantii seedlings to single and combined B. goodwinii and drought stresses depends on the health status of mother trees. Plants were grown from seeds collected from non-stressed healthy and drought-stressed unhealthy trees. Root weight and belowground to aboveground weight ratios were significantly higher in offspring of unhealthy mother trees, suggesting that drought stress regulated the performance of Q. brantii in the subsequent generation. Brenneria goodwinii followed by drought had synergistic negative effects on seedlings (reduced plant growth, reduced xylem vessel size and reduced relative water content of tissues) and induced more injury (reduced leaf chlorophyll content and increased root electrolyte leakage) in offspring of unhealthy trees. Increased adaptation to drought in plants germinating from drought-stressed trees was observed and the effects persisted over the vegetative period, after the plants were rewatered. The results provide a first evidence of transgenerational plasticity in response to drought stress in trees. It is concluded that the health status of trees influences the response of offspring to combined stress.

Floodwater Depth Causes Different Physiological Responses During Post-flooding in Willows.

Willows are widely planted in areas under risk of flooding. The physiological responses of willows to flooding have been characterized, but little is known about their responses during the post-flooding period. After the end of the stress episode, plants may modify some traits to compensate for the biomass loss during flooding. The aim of this work was to analyze the post-flooding physiological responses of willow under two different depths of stagnant floodwater. Cuttings of Salix matsudana NZ692 clone were planted in pots in a greenhouse. The experiment started when the plants were 2 months old with the following treatments: Control plants (watered to field capacity); plants partially flooded 10 cm above soil level (F10) and plants partially flooded 40 cm above soil level (F40). The flooding episode lasted 35 days and was followed by a recovery period of 28 days (post-flooding period). After the flooding period, height, diameter and total biomass were higher in F10, while F40 plants showed an increase in plant adventitious root production and leaf nitrogen content. During the post-flooding period, the photosynthetic rate, nitrogen, chlorophyll and soluble sugar contents were significantly higher in leaves of F40 than in Control and F10 treatments. Stomatal conductance and specific leaf area were higher in the previously flooded plants compared to Control treatment. Plants from F10 treatments showed a higher growth in height, root-to-shoot ratio, and carbon isotope discrimination than F40, while the opposite occurred for growth in diameter, vessel size and leaf area. We conclude that depth of floodwater not only causes different responses during flooding, but that its effects are also present in the post-flooding recovery period, affecting the growth and physiology of willows once the stress episode has ended. Even when flooding impacted growth negatively in F40, in the post-flooding period these plants compensated by increasing the photosynthetic rate, plant leaf area and xylem vessel size. Willows endurance to flooding is the result of both responses during flooding, and plastic responses during post-flooding.

Factors contributing to ice nucleation and sequential freezing of leaves in wheat

Main conclusionAnatomical, metabolic and microbial factors were identified that contribute to sequential freezing in wheat leaves and likely contribute to supercooling in the youngest leaves and potentially meristematic regions.Infrared thermography (IR) has been used to observe wheat leaves freezing independently and in an age-related sequence with older leaves freezing first. To determine mechanisms that might explain this sequence of freezing several analytical approaches were used: (1) The size of xylem vessels, in proximity to where freezing initiated, was measured to see if capillary freezing point depression explained sequential freezing. The sequence of freezing in the four youngest leaves was correlated, with the largest vessels freezing first. (2) Carbohydrate and amino acids were analyzed to determine if solute concentrations as well as interactions with membranes explained the freezing sequence. Sucrose was highly correlated to the freezing sequence for all leaves suggesting a prominent role for this sugar as compared to other simple sugars and fructans. Among individual free amino acids proline and serine were correlated to the freezing sequence, with younger leaves having the highest concentrations. (3) Microflora within and on leaf surfaces were determined to measure potential freezing initiation. Levels of bacteria and fungi were correlated to the freezing sequence for all leaves, and species or genera associated with high ice nucleation activity were absent in younger leaves. Moisture content and transcript expression of ice binding proteins were also measured. As expected, our results show that no single mechanism explains the freezing sequence observed via infrared analyses. While these multiple mechanisms are operative at different levels according to the leaf age, they seem to converge when it comes to the protection of vital meristematic tissues. This provides potential phenotypic characters that could be used by breeders to develop more winter-hardy genotypes.

Rootstock–Scion Hydraulic Balance Influenced Scion Vigor and Yield Efficiency of Malus domestica cv. Honeycrisp on Eight Rootstocks

Rootstocks with internal hydraulic limitations can effectively restrict scion growth, influence crop load, and improve yield efficiency in apple production. The characteristics of xylem vessels in rootstock and scion play essential roles in determining the hydraulic properties of the grafted tree; however, much remains unknown for commonly available rootstocks. In this study, we extracted secondary xylem using an increment borer from living Honeycrisp scion (Malus domestica cv. ‘Honeycrisp’), and two Malling rootstocks, one Budagovsky rootstock, and five Geneva rootstocks. The size and density of xylem vessels in rootstocks and scions were analyzed in relation to trunk cross-section area (TCSA), tree–water relations, and fruit dry matter of 2019, as well as with cumulative yield efficiency during 2014–2019. Honeycrisp scion exceeded most of the rootstocks in cross-section size and density of vessel elements. Scion vigor and cumulative yield were positively correlated with TCSA and total vessel cross-section area (VCSA) of the rootstock, with G.202 being the highest, and B.9 being the lowest with small xylem vessels in high density. In the rootstocks with the highest cumulative yield efficiency, the rootstock/scion ratio in VCSA was equal to or slightly higher than 1. Lower scion vessel density in G.214 was associated with lower fruit dry matter weight, more restricted water relations, and worsened leaf chlorosis. G.935 with larger rootstock vessels led to both high yield and high yield efficiency. This suggested that higher scion vessel density and larger rootstock vessel size can be advantageous characteristics for early-stage evaluation.

Vascular Connections Into the Grape Berry: The Link of Structural Investment to Seededness.

Vascular bundles in the grape pedicel and berry contain the conduits, phloem and xylem, for transport of water, sugar, nutrients and signals into and through the grape berry and play a critical role in berry growth and composition. Here, we assess the vascular anatomy within the proximal region of the berry. Guided using a 3D berry model generated by micro-CT, differential staining of transverse sections of berries and receptacles was followed by fluorescent microscopy. Morphometric and vascular characteristics were analyzed within the central proximal region (brush zone, a fibrous extension from the pedicel vascular system into the berry) of the seeded cultivars Shiraz and Sauvignon Blanc, as well as the stenospermocarpic cultivars Ruby Seedless and Flame Seedless. Observations revealed a change in vascular arrangement from the receptacle into the berry brush zone and differences in xylem element size as well as xylem and phloem area relationships. Xylem anatomical and derived hydraulic parameters, as well as total tissue area of xylem and phloem varied between cultivars and in receptacle and berry components. Variation in vascular growth between grape pedicels and berries was independent of seededness. Differences in receptacle xylem vessel size and distribution could contribute to cultivar-dependent xylem backflow constraint.

Heritability of Anatomical Characteristics in Cherry Interspecific Hybrids

The aim of this study was to assess the stem anatomical structure of divergent cherry germplasm and estimate genetic variation and heritability as well as hybrid enhancement for anatomical traits of cherry interspecific hybrids. Plant material included 18 cherry genotypes representing seven species and species hybrids. Analyses included detailed anatomical investigations of 1- and 2-year-old stems’ macro and micro cross-sectional characteristics, theoretical hydraulic conductance calculations, as well as estimations of genotypic and phenotypic variances, coefficients of variation, broad sense heritability, hybrid enhancement, and potence ratio. Average vessel lumen areas and percentages of vessels belonging to different size classes exhibited moderate to high heritability (more than 60%). In contrast, macro-anatomical characteristics—cambial-induced secondary thickening and production of secondary wood (xylem) and secondary cortex (phloem), appeared to be more environmentally sensitive. The high heritability of xylem vessel properties and low heritability of cross-sectional traits, along with previous knowledge regarding cambial-induced secondary thickening observed in the same germplasm, could be used to inform parentage choice for rootstock breeding crosses. The results support the hypothesis that xylem vessel size is primarily under genetic control and exhibits different degrees of dominance—partial (very close to better parent), full, and overdominance. It is presumed that the MSU rootstocks ‘Cass’ and ‘Clare’, followed by ‘Benzie’ and ‘Lake’ would have the greatest size-controlling effect on grafted cherry varieties, while Prunus maackii, the P. maackii × ‘Montmorency’ hybrid , and ‘Montmorency’ × ‘Colt’ hybrid would act as invigorating rootstocks. Our findings suggest that future hybrids between Prunus cerasus and Prunus fruticosa, the ‘weaker’ parental species characterized by smaller vessels, would result in rootstock candidates with better size-controlling effect, while crossings between P. fruticosa and Prunus mahaleb should have well-balanced vessel lumen areas and cambial activity, which is a prerequisite for successful adaptation to changing environmental conditions.

Survival Strategies in Khavi Grass [Cymbopogon jwarancusa (Jones) Schult.] Colonizing Hot Hypersaline and Arid Environments

Deserts are generally prone to a number of ecological hazards which act as agents for the development of particularly a very diverse group of grasses, which can resist to salt stress through multiple morpho-anatomical and physio-biochemical mechanisms. Of such grasses, Cymbopogon jwarancusa is found inhabiting different saline patches of the Cholistan desert, so its different populations were selected from five saline habitats [least saline Derawar Fort (DF); moderately saline Trawaywala Toba (TW) and Bailahwala Dahar (BD), and high saline Ladam Sir (LS) and Pati Sir (PS)] and tested for their salt tolerance mechanism. Differentially adapted populations of this grass showed specific modifications in terms of anatomical features, mainly increased sclerification in both external hypodermis and internal endodermis, cortical layers, and increased size of xylem vessels with increase in salinity of the habitat. Increased endodermal thickness may control radial movement of water in roots. The reduction in leaf area is found to be the principal strategy that makes C. jwarancusa promising to attenuate the effects of the reduced availability of water under saline stress. Thick epidermis with dense cuticle and large bulliform cells area can be particularly considered as an important adaptation of this grass against physiological drought. Moreover, increased density of trichomes is found critical for checking undue water loss through the leaf surface and increase in these tissues at high salinity level may indicate that this species has better adapted to saline habitat.

PGPR-induced OsASR6 improves plant growth and yield by altering root auxin sensitivity and the xylem structure in transgenic Arabidopsis thaliana

Plant-growth-promoting rhizobacteria (PGPR) improve plant growth by altering the root architecture, although the mechanisms underlying this alteration have yet to be unravelled. Through microarray analysis of PGPR-treated rice roots, a large number of differentially regulated genes were identified. Ectopic expression of one of these genes, OsASR6 (ABA STRESS RIPENING6), had a remarkable effect on plant growth in Arabidopsis. Transgenic lines over-expressing OsASR6 had larger leaves, taller inflorescence bolts and greater numbers of siliques and seeds. The most prominent effect was observed in root growth, with the root biomass increasing four-fold compared with the shoot biomass increase of 1.7-fold. Transgenic OsASR6 over-expressing plants showed higher conductance, transpiration and photosynthesis rates, leading to an ˜30% higher seed yield compared with the control. Interestingly, OsASR6 expression led to alterations in the xylem structure, an increase in the xylem vessel size and altered lignification, which correlated with higher conductance. OsASR6 is activated by auxin and, in turn, increases auxin responses and root auxin sensitivity, as observed by the increased expression of auxin-responsive genes, such as SAUR32 and PINOID, and the key auxin transcription factor, ARF5. Collectively, these phenomena led to an increased root density. The effects of OsASR6 expression largely mimic the beneficial effects of PGPRs in rice, indicating that OsASR6 activation may be a key factor governing PGPR-mediated changes in rice. OsASR6 is a potential candidate for the manipulation of rice for improved productivity.

Changes in Anatomical Features and Protein Pattern of Sunflower Partially Resistant and Susceptible Lines During Infection By Virulence Factors of Sclerotinia Sclerotiorum

Helianthus annuus L. as an oil seed crop is widely grown throughout the world. One of the most destructive diseases of sunflower is stem rot caused by Sclerotinia sclerotiorum. Oxalic acid is the major virulence factor of this necrotrophic pathogen. It is important to further investigate plant responses to this non-specific toxin. The basal stems of sunflower partially resistant and susceptible lines were treated with 40 mM OA (pH 3.7) of fungus culture filtrate and samples were collected at 24, 48 and 72 hours post treatment. SDS-PAGE protein pattern and total soluble protein were determined in both lines after treatment. In SDS-PAGE protein pattern new protein bands appeared in both lines after treatment. These observations suggest induction of stress-related proteins upon culture filtrate treatment. The identities of these new proteins need to be more clarify in future investigations. The changes in xylem morphology and degree of lignification of both lines was studied by light microscopy and microtome sectioning techniques after treatment with S. sclerotiorum culture filtrate. Anatomical investigations revealed changes in xylem diameter and xylem lignification of treated lines at various time points. More lignin deposition in xylem vessels of partially resistant line has been observed after treatment. In addition, the size of xylem vessels in partially resistant line has been sharply decreased upon pathogen filtrate treatment. The results of this study will help us gain a more complete understanding of resistance mechanisms to this cosmopolitan and devastating pathogen.