Biology subjects

Moshelion, M.

Publications and source records attributed to Moshelion, M..

29 records · Page 2Linked to original sources

bioRxiv2022

On the biological constraints that limit the productivity of rain-fed annual crops

Efforts to cope with hunger by breeding highly productive annual crops for rain-fed agriculture in stochastic-rainfall environments have had only minor success, which we attribute to biological constraints that limit the crops yields. We use optimization modelling to interpret experimentally measured transpiration trajectories of wild barley plants following a rain event: the plants first maximized biomass accumulation by employing their maximal transpiration rate, then switched to their minimal transpiration rate to ensure survival until maturity. Thus, breeding plants with lower minimal transpiration rates combined with higher water-use efficiency and maximal transpiration rates could increase expected yields. However, our experimental results indicate that biological constraints impose tradeoffs among maximal and minimal transpiration rates and water-use efficiency. A proposed breeding methodology identifies less biologically constrained cultivar candidates.

plant biology↗

bioRxiv2022

Diurnal stomatal apertures and density ratios affect whole-canopy stomatal conductance, water-use efficiency and yield

Key physiological traits of crop plants, such as transpiration, stomatal conductance, and photosynthesis are highly related to plant productivity. However, these traits are typically studied under steady-state conditions or modeled using only a few measured data points which do not reflect the dynamic behavior of the plant in response to field conditions. In this work, we hypothesized that the plastic behavior of whole-plant water balance regulation, as previously observed in tomato WT, was partially lost in the breeding process due to selective pressure towards productivity. We also hypothesized that this plastic behavior would be observed in some members of the tomato introgression lines (ILs) population, which was created by crossing the WT and M82 lines, particularly in ILs that demonstrate improved drought response. To overcome the steady-state bottleneck, and to test our hypothesis we used a gravimetric functional-phenotyping platform and a reverse-phenotyping method to examine the dynamic whole-plant water-regulation responses of tomato ILs and compared those responses with several years of yield performance in commercial fields. Indeed, our study enabled us to identify high plasticity in a few ideotypic ILs. We found that ideotype lines with highly plastic stomatal conductance and high abaxial-adaxial stomatal density ratios had stomatal apertures that peaked early in the day, even under water-deficit conditions. These traits resulted in dynamic daily water-use efficiency, along with rapid recovery of transpiration when irrigation was resumed after a period of imposed drought. Abaxial stomatal density was also found to be strongly correlated with the expression of the stomatal-development genes SPCH and ZEP. This study demonstrates how a reverse functional phenotyping approach based on field yield data, continuous and simultaneous whole-plant water-balance measurements and anatomical examination of individual leaves can help us to understand and identify dynamic and complex yield-related physiological traits.

plant biology↗

bioRxiv2021

Stress is basic: ABA alkalinizes both the xylem sap and the cytosol of Arabidopsis vascular bundle sheath cellsby inhibiting their P-type H+-ATPaseand stimulating their V-type H+-ATPase

BACKGROUND AND HYPOTHESIS* Under water deprivation, in many perennial species, the stress hormone, ABA, appears in the xylem sap in the shoot (including leaf) veins and the xylem sap pH (pHEXT) increases. This study aimed to test the hypothesis that ABA is the signal for an altered proton balance of the leaf-vein-enwrapping bundle sheath cells (BSCs). METHODS* Plant Material. We used a few Arabidopsis thaliana (L.) Heynh. genotypes: wildtype (WT) of two accessions, Landsberg erecta (Ler) and Columbia (Col), and a few mutants and transformants in these backgrounds. * H+-Pumps activities. We monitored ABA effects on the H+-pump activities in the BSCs cytosol-delimiting membranes (plasma membrane and tonoplast) by monitoring the cytosol and the xylem pH, and the membrane potential (EM), by imaging the fluorescence of pH- and membrane potential (EM)-reporting probes: (a) the BSCs pHEXT - with the ratiometric fluorescent dye FITC-dextran petiole-fed into detached leaves in unbuffered xylem perfusion solution (XPS), (b) the BSCs pHCYT - with the ratiometric dye SNARF1 loaded into BSCs isolated protoplasts, and (c) the BSCs EM - with the ratiometric dye di- 8-ANEPPS. RESULTS* ABA increased the pHEXT; this response was abolished in an abi1-1 mutant with impaired signaling via a PP2C (ABI1) and in an aha2-4 mutant with knocked-down AHA2; * ABA depolarized the WT BSCs; * ABA increased pHCYT irrespective of AHA2 activity (i.e., whether or not AHA was inhibited by vanadate, or in the aha2-4 mutant); * The ABA-induced cytosol alkalinization was abolished in the absence of VHA activity (i.e., when VHA was inhibited by bafilomycin A1, or in the vha-a2 vha-a3 double mutant with inactive VHA); * All these results resemble the ABA effect on GCs; * In contrast to GCs, AHA2 and not AHA1 is the ABA major target in BSCs; * Blue light (BL) enabled the response of the BSCs VHA to ABA; * The ABA- and BL-signaling pathways acting on both BSCs pumps, AHA2 and VHA, are likely to be BSCs autonomous, based on (a) the presence in the BSCs of many genes of the ABA- and BL-signaling pathways and (b) ABA responses (depolarization and pHCYT elevation) demonstrated under BL in isolated protoplasts. SIGNIFICANCE STATEMENTWe reveal here an alkalinizing effect of the plant drought-stress hormone ABA on the pH on both sides of the plasmalemma of the vein-enwrapping bundle sheath cells (BSCs), due to ABA inhibition of the BSCs AHA2, the plasmalemma H+- ATPase and stimulation of VHA, their vacuolar H+-ATPase. Since pH affects the BSCs selective regulation of solute and water fluxes into the leaf, these H+- pumps may be attractive targets for manipulations aiming to improve plant drought response.

plant biology↗

bioRxiv2021

Predicting tomato field-yield using continuous monitoring of young tomato water status

To address the challenge of predicting tomato yields in the field, we used whole-plant functional phenotyping to evaluate water relations under well-irrigated and drought conditions. The genotypes tested are known to exhibit variability in their yields in wet and dry fields. The examined lines included two lines with recessive mutations that affect carotenoid biosynthesis, zeta z2083 and tangerine t3406, both isogenic to the processing tomato variety M82. The two mutant lines were reciprocally grafted onto M82, and multiple physiological characteristics were measured continuously, before, during and after drought treatment in the greenhouse. A comparative analysis of greenhouse and field yields showed that the whole-canopy stomatal conductance (gsc) in the morning and cumulative transpiration (CT) were strongly correlated with field measurements of total yield (TY: r2 = 0.9 and 0.77, respectively) and plant vegetative weight (PW: r2 = 0.6 and 0.94, respectively). Furthermore, the minimum CT during drought and the rate of recovery when irrigation was resumed were both found to predict resilience.

physiology↗

bioRxiv2021

Flagellin triggers mesophyll dehydration: An early PTI defense against bacterial establishment in intercellular spaces

Plants have evolved various mechanisms to defend themselves against pathogens. Many pathogens induce the formation of water-soaked lesions during early infection under conditions of high atmospheric humidity. These water-soaked spots are caused by the disruption of the plasma membrane or cell wall integrity due to various activities of effector proteins during infection. We hypothesized that bacterial PAMP-flagellin plays a role in modulating the cell-membrane permeability that controls the availability of water in the apoplast, to prevent bacterial establishment on the cell wall during the early stages of the PAMP-triggered immunity (PTI) response. Our results revealed that the conductivity of hydraulic pathways in the leaf was reduced in response to flagellin22 (flg22). The cellular osmotic water permeability (Pf) of both mesophyll cells and bundlesheath cells was dramatically reduced in response to flg22 treatment. Moreover, the whole-leaf hydraulic conductance (Kleaf) was also reduced in response to flg22 treatment. The fact that the Pf of mesophyll cells of an aquaporin (AQP) mutant was not affected by the flg22 treatment suggests the involvement of AQP channels in the flg22-induced Pf reduction signal transduction pathway. We conclude that the binding of flagellin to their receptors elicits signals to close AQPs, consequently reducing the water content of the cell wall and intercellular spaces and leading to a more negative water potential. This serves as an early PTI response to pathogen attack, which, in turn, might decrease the rate of bacterial growth and establishment in the apoplast. Significance statementWe report that the membrane osmotic water permeability of both leaf mesophyll and vascular bundle-sheath cells is reduced in response to treatment with flagellin22. We suggest that this mechanism for cell dehydration may serve as an apoplastic defense response, to limit the chances of bacterial pathogens becoming established on the walls of leaf mesophyll cells.

plant biology↗

bioRxiv2020

A High Throughput Gravimetric Phenotyping Platform for Real Time Physiological Screening of Plant Environment Dynamic Responses

Food security for the growing global population is a major concern. The data provided by genomic tools far exceeds the supply of phenotypic data, creating a knowledge gap. To meet the challenge of improving crops to feed the growing global population, this gap must be bridged. Physiological traits are considered key functional traits in the context of responsiveness or sensitivity to environmental conditions. Many recently introduced high-throughput phenotyping techniques are based on remote sensing or imaging and are capable of directly measuring morphological traits, but measure physiological parameters only indirectly. This paper describes a method for direct physiological phenotyping that has several advantages for the functional phenotyping of plant-environment interactions. It aims to help users overcome the many challenges encountered in the use of load-cell gravimetric systems and pot experiments. The suggested techniques will enable users to distinguish between soil weight, plant weight and soil water content, providing a method for continuous and simultaneous measurement of dynamic soil, plant and atmosphere conditions, alongside key physiological traits. This method allows researchers to closely mimic field stress scenarios while taking into consideration the environments effect on the plants physiology. This method also minimizes pot effects, which are one of the major problems in pre-field phenotyping. It includes a feedback fertigation system that enables a truly randomized experimental design with a field-like plant density. This system detects the soil-water content limiting threshold ({theta}) and allows for the translation of data into knowledge through the use of a real-time analytic tool and an online statistical resource. This method for the rapid and direct measurement of the physiological responses of multiple plants to a dynamic environment has great potential for use in screening for beneficial traits associated with responses to abiotic stress, in the context of pre-field breeding and crop improvement. SUMMARYThis high-throughput, whole-plant water relations gravimetric phenotyping method enables direct and simultaneous real-time measurements and analysis of multiple yield-related physiological traits involved in dynamic plant-environment interactions.

plant biology↗

bioRxiv2019

Out of the blue; Phototropins of the leaf vascular bundle sheath mediate the blue light regulation of the leaf hydraulic conductance

The Arabidopsis leaf veins bundle sheath cells (BSCs) - a selective barrier to water and solutes entering the mesophyll - increase the leaf radial hydraulic conductance (Kleaf) by acidifying the xylem sap by their plasma membrane H+-ATPase, AHA2. Based on this and on the BSCs expression of PHOT1 and PHOT2, and the known blue-light (BL)-induced Kleaf increase, we hypothesized that, resembling the guard cells, BL perception by the BSCs phots activates its H+-ATPase, which, consequently, upregulates Kleaf. Indeed, under BL, the Kleaf of the knockout mutant lines phot1-5, phot2-1, phot1-5phot2-1, and aha2-4 was lower than that of the WT. BSC-only-directed complementation of phot1-5 or aha2-4 by PHOT1 or AHA2, respectively, restored the BL-induced Kleaf increase. BSC-specific silencing of PHOT1 or PHOT2 prevented such Kleaf increase. A xylem-fed kinase inhibitor (tyrphostin 9) replicated this also in WT plants. White light - ineffective in the phot1-5 mutant - acidified the xylem sap (relative to darkness) in WT and in the PHOT1-complemented phot1-5. These results, supported by BL increase of BSC protoplasts water permeability and cytosolic pH and their hyperpolarization by BL, identify the BSCs as a second phot-controlled water conductance element in leaves, in series with stomatal conductance. Through both, BL regulates the leaf water balance. One-Sentence summaryBlue light regulates the leaf hydraulic conductance via the bundle-sheath cells blue light PHOT receptors which, via an autonomous signaling pathway, activate the BSCs AHA2 H+-pump.

plant biology↗

bioRxiv2019

A High-Throughput Physiological Functional Phenotyping System for Time- and Cost-Effective Screening of Potential Biostimulants

The improvement of crop productivity under abiotic stress is one of the biggest challenges faced by the agricultural scientific community. Despite extensive research, the research-to-commercial transfer rate of abiotic stress-resistant crops remains very low. This is mainly due to the complexity of genotype{square}x{square}environment interactions and in particular, the ability to quantify the dynamic plant physiological response profile to a dynamic environment.\n\nMost existing phenotyping facilities collect information using robotics and automated image acquisition and analysis. However, their ability to directly measure the physiological properties of the whole plant is limited. We demonstrate a high-throughput functional phenotyping system (HFPS) that enables comparing plants dynamic responses to different ambient conditions in dynamic environments due to its direct and simultaneous measurement of yield-related physiological traits of plants under several treatments. The system is designed as one-to-one (1:1) plant-[sensors+controller] units, i.e., each individual plant has its own personalized sensor, controller and irrigation valves that enable (i) monitoring water-relation kinetics of each plant-environment response throughout the plants life cycle with high spatiotemporal resolution, (ii) a truly randomized experimental design due to multiple independent treatment scenarios for every plant, and (iii) reduction of artificial ambient perturbations due to the immobility of the plants or other objects. In addition, we propose two new resilience-quantifying-related traits that can also be phenotyped using the HFPS: transpiration recovery rate and night water reabsorption.\n\nWe use the HFPS to screen the effects of two commercial biostimulants (a seaweed extract--ICL-SW, and a metabolite formula--ICL-NewFo1) on Capsicum annuum under different irrigation regimes. Biostimulants are considered an alternative approach to improving crop productivity. However, their complex mode of action necessitates cost-effective pre-field phenotyping. The combination of two types of treatment (biostimulants and drought) enabled us to evaluate the precision and resolution of the system in investigating the effect of biostimulants on drought tolerance. We analyze and discuss plant behavior at different stages, and assess the penalty and trade-off between productivity and survivability. In this test case, we suggest a protocol for the screening of biostimulants physiological mechanisms of action.

plant biology↗

bioRxiv2018

Vascular bundle sheath and mesophyll regulation of leaf water balance in response to chitin

Plants can detect pathogen invasion by sensing pathogen-associated molecular patterns (PAMPs). This sensing process leads to the induction of defense responses. Most PAMP mechanisms of action have been described in the guard cells. Here, we describe the effects of chitin, a PAMP found in fungal cell walls, on the cellular osmotic water permeability (Pf) of the leaf vascular bundle-sheath (BS) and mesophyll cells and its subsequent effect on leaf hydraulic conductance (Kleaf).\n\nThe BS is a parenchymatic tissue that tightly encases the vascular system. BS cells have been shown to control Kleaf through changes in their Pf, for example, in response to ABA. It was recently reported that, in Arabidopsis, the chitin receptors chitin elicitor receptor kinase 1 (CERK1) and LYSINE MOTIF RECEPTOR KINASE 5 (LYK5) are highly expressed in the BS, as well as the neighboring mesophyll. Therefore, we studied the possible impact of chitin on these cells.\n\nOur results revealed that both BS cells and mesophyll cells exhibit a sharp decrease in Pf in response to chitin treatment. In addition, xylem-fed chitin decreased Kleaf and led to stomatal closure. However, an Atlyk5 mutant showed none of these responses. Complimenting AtLYK5 specifically in the BS cells (using the SCARECROW promoter) and transient expresion in mesophyll cells each resulted in a response to chitin that was similar to that observed in the wild type. These results suggest that BS and mesophyll cells each play a role in the perception of apoplastic chitin and in initiating chitin-triggered immunity.\n\nSignificance StatementPAMP perception by plant receptors triggers various defense responses important for plant immunity. Here we provide new insights into a topic that has received a great deal of previous attention, revealing that a chitin immune response is present in additional leaf tissues other than the stomata. Chitin perception by the bundle sheath cells enwrapping the whole leaf vascular system decrease its cellular osmotic permeability and leaf hydraulic conductance. This in turn, leads to hydraulic signals being sent to the stomata and regulates whole-leaf water balance in response to chitin application and, perhaps, during fungal infection. Emphasizing the dynamic role of the BS in chitin-sensing and water balance regulation.

plant biology↗

bioRxiv2017

Bundle-sheath cells are internal leaf "water valves" controlled via xylem acidification by H+-ATPase

O_LIThe leaf vascular bundle sheath cells (BSCs) that tightly envelop the leaf veins, are a selective and dynamic barrier to xylem-sap water and solutes radially entering the mesophyll cells. Under normal conditions, xylem-sap pH of <6 is presumably important for driving and regulating the transmembranal solute transport. Having discovered recently a differentially high expression of a BSCs proton pump, AHA2, we now test the hypothesis that it regulates this pH and leaf radial water fluxes. C_LIO_LIWe monitored the xylem-sap pH in the veins of detached leaves of WT Arabidopsis, AHA mutants, and aha2 mutants complemented with AHA2 gene solely in BSCs. We tested an AHA inhibitor and stimulator, and different pH buffers. We monitored their impact on the xylem-sap pH and the whole leaf hydraulic conductance (Kleaf), and the effect of pH on the water osmotic permeability (Pf) of isolated BSCs protoplasts. C_LIO_LIOur results demonstrated that AHA2 is necessary for xylem-sap acidification, and in turn, for elevating Kleaf. Conversely, knocking out AHA2 alkalinized the xylem-sap. Also, elevating xylem sap pH to 7.5 reduced Kleaf and elevating external pH to 7.5 decreased the BSCs Pf. C_LIO_LIAll these demonstrate a causative link between AHA2 activity in BSCs and leaf radial water conductance. C_LI One-sentence summaryBundle-sheath cells can control the leaf hydraulic conductance by proton-pump-regulated xylem sap pH

plant biology↗

bioRxiv2017

Role of guard-cell ABA in determining maximal stomatal aperture and prompt vapor-pressure-deficit response

Abscisic acid (ABA) is known to be involved in stomatal closure. However, its role in stomatal response to rapid increases in the vapor pressure deficit (VPD) is unclear. To study this issue, we generated guard cell (GC)-specific ABA-insensitive Arabidopsis plants (GC-specific abi1-1; GCabi). Under normal conditions, the stomatal conductance (gs) and apertures of GCabi plants were greater than those of control plants. This supports GC ABA role as limiting maximal stomatal aperture under non-stressful conditions. When there was a rapid increase in VPD (0.15 to 1 kPa), the gs and stomatal apertures of GCabi decreased in a manner similar that observed in the WT control, but different from that observed in WT plants treated with fusicoccin. Low VPD increased the size of the stomatal apertures of the WT, but not of GCabi. We conclude that GC ABA does not play a significant role in the initial, rapid stomatal closure that occurs in response to an increase in VPD, but is important for stomatal adaptation to ambient VPD. We propose a biphasic angiosperm VPD-sensing model that includes an initial passive-hydraulic, ABA-independent phase and a subsequent ABA-dependent steady-state phase in which stomatal behavior is optimized for ambient VPD conditions.\n\nHighlightGuard-cell ABA does not play a significant role in the immediate closure of stomata following an increase in the VPD, but is important for stomatal adaptation to ambient VPD.

plant biology↗