Biology subjects

Zait, Y.

Publications and source records attributed to Zait, Y..

6 recordsLinked to original sources

bioRxiv2026

β-Carbonic anhydrase SlβCA4 is required for normal growth, carbon assimilation and stomatal plasticity in tomato

{beta}-Carbonic anhydrases ({beta}CAs) catalyze the reversible interconversion of CO2 and bicarbonate and contribute to plant carbon metabolism and environmental responses. However, the physiological functions of individual {beta}CA isoforms in crops remain poorly understood. Here, we investigated two chloroplast-localized {beta}CAs, Sl{beta}CA1 and Sl{beta}CA4, in tomato (Solanum lycopersicum). We combined subcellular localization, CRISPR/Cas9 mutagenesis, grafting, leaf gas-exchange measurements, and controlled environmental treatments to examine their roles in growth, photosynthesis, and stomatal developmental plasticity. Both proteins localized to chloroplasts but their disruption resulted in markedly different phenotypes. While Sl{beta}CA1 mutants showed largely normal growth and photosynthesis, Sl{beta}CA4 mutants exhibited severe root and shoot growth defects. Grafting mutant shoots onto wild-type rootstocks partially restored vegetative growth, indicating that impaired root function contributes to the growth defects. Sl{beta}CA4 mutants also showed reduced CO2 assimilation and stomatal conductance, while electron transport remained largely unaffected. Elevated CO2 partially improved leaflet growth but did not restore plant height or root elongation. Furthermore, unlike wild-type plants, Sl{beta}CA4 mutants failed to increase stomatal index in response to elevated temperature. These findings reveal distinct physiological roles for chloroplast-localized {beta}CAs in tomato and identify Sl{beta}CA4 as an important contributor to plant growth, photosynthesis, and temperature-dependent stomatal developmental plasticity.

plant biology↗

bioRxiv2026

Stem photosynthesis from wild Prunus arabica enhances growth, advances bloom and increases yield in cultivated almond

Rising winter temperatures threaten deciduous fruit tree productivity by depleting carbohydrate reserves during dormancy. This study investigated Stem Photosynthetic Capacity (SPC), a rare adaptive trait from wild Prunus arabica, as a mechanism to enhance almond carbon economy. Using extreme segregating groups from the F1 population (P. dulcis X P. arabica), we evaluated physiological performance through high-resolution lysimetric and multi-year orchard monitoring. High-SPC [SPC(+)] genotypes maintained significantly greater stem CO2 assimilation and transpiration during leafless periods compared to low-SPC [SPC(-)] progenies. Over five successive seasons, SPC(+) trees exhibited a 33.3% increase in trunk secondary growth and reached 10% bloom approximately 8 days earlier. Most importantly, the SPC(+) group achieved a 4.6-fold increase in mean kernel yield when compared to SPC(-) group. These findings demonstrate that SPC provides a flexible, supplementary winter carbon source that directly supports both vegetative and reproductive development. Integrating SPC into commercial almond breeding programs may offer a valuable strategy to improve climate resilience and help sustain yields under warming conditions. HighlightIntegrating stem photosynthesis into commercial almond hybrids provides a winter carbon source that advances blooming, expands trunk growth by [~]33%, and increases kernel yields by more than 4.5-fold.

Plant Biology↗

bioRxiv2025

Tomato drought-responsive transcription factor TINY1 suppresses embryonic growth

Dehydration-Responsive Element-Binding (DREB) transcription factors play an important role in plant responses to drought. DREB subfamily A4, contains a sub-group named TINY. Previous studies in Arabidopsis suggest that TINYs suppress plant growth and mediate abscisic acid (ABA)-induced stomatal closure. In this study, we investigated the function of the tomato drought-induced TINY1. Under drought conditions, tiny1 mutant lost turgor and wilted more rapidly than control M82 plants. However, this sensitivity was attributed to its larger leaf area, rather than intrinsic differences in drought response. Measurements of stomatal conductance, leaf temperature, and osmotic adjustment revealed no significant differences between tiny1 and M82. Furthermore, whole plant daily transpiration of M82 and tiny1 with similar leaf area, showed no differences. Interestingly, the growth-promoting effect of tiny1 was confined to early developmental stages; enhanced embryo growth and hypocotyl elongation, and accelerated emergence of the first true leaves--trait that later contributed to increased leaf area. At later stages, the mutation had no observable impact on growth rate. Our results show increased gibberellin (GA) activity in the mature tiny1 embryo and suggest that TINY1 suppresses embryonic growth by repressing GA biosynthesis through downregulation of GA 20-oxidase 4 (GA20ox4) gene expression.

plant biology↗

bioRxiv2025

Disentangling the stomatal response to transpiration and relative humidity

Stomatal responses to atmospheric conditions are critical for balancing plant CO2 gain with water loss. Yet, the question of whether stomata respond directly to humidity or to the rate of water loss (transpiration) remains unresolved due to the tight coupling between these variables. To decouple them, we manipulated water vapor diffusivity using Helox (21% O2, 79% He), where vapor diffuses 2.33 times faster than in air, and Argox (21% O2, 79% Ar), where it diffuses 0.75 times slower. This allows control of VPD and transpiration independent of one another while maintaining a constant leaf temperature. We investigated the stomatal conductance (gsw) responses to air and Helox in several plant species, including Solanum lycopersicum, Vitis vinifera, and the fern Nephrolepis exaltata. In addition, we tested the Commelina communis, with coupled gas exchange and real-time imaging of stomatal aperture in intact leaves. In all angiosperms tested, we observed that stomatal closing was triggered exclusively by reductions in RH rather than by transpiration increases. When transpiration increased, but relative humidity remained constant, we detected an increase in gsw without a following decrease in the experimental time span. Exposure to Argox without altering RH reduced transpiration, likely enabling restoration of epidermal turgor and inducing passive mechanical closure. However, the rate of stomatal closure under reduced RH was 2.35 times faster than that observed under Argox, suggesting that passive turgor-driven responses cannot fully explain the kinetics or extent of closure under dry air. This work provides direct experimental evidence for humidity-driven stomatal closure.

plant biology↗

bioRxiv2023

Wind speed affects the rate and kinetics of stomatal conductance

Understanding the relationship between wind speed and gas exchange in plants is a longstanding challenge. Our aim was to investigate the impact of wind speed on maximum rates of gas exchange and the kinetics of stomatal responses. We conducted experiments using an infrared gas analyzer equipped with a controlled leaf fan, enabling precise control of the boundary layer conductance. We first showed that the chamber was adequately mixed even at extremely low fan speeds (down to 200 rpm, equivalent to a wind speed of 0.0005 m s-1) and evaluated the link between fan speed, wind speed, and boundary layer conductance. We observed that higher wind speeds led to increased gas exchange of both water vapor and CO2 in Arabidopsis, presumably due to its effect on transpiration and the consequential reduction in epidermal pressure that led to stomatal opening. We documented that stomatal opening in response to light was three times faster at a fan speed of 10000 rpm (wind speed of 2 m s-1) compared with 500 rpm (0.25 m s-1) in Vicia faba, while the latter exhibited an opening rate that was similar to those of epidermal peels. The increase of stomatal conductance under high wind was observed in four species under field conditions. Our findings demonstrate the importance of the size of the boundary layer on determining maximum rates of gas exchange and the kinetics of gas exchange responses to environmental changes.

plant biology↗

bioRxiv2018

Long-term acclimation to different stress types: revealing tradeoffs between mesophyll and stomatal conductance

Ziziphus spina-christi, a thermophilic tree, became more abundant in the Mediterranean, presumably due to increased winter temperatures. In order to predict the plant acclimation to future climate changes, we attempted to understand which factors underlie photosynthetic stress acclimation.\n\nStress acclimation to three major long-term abiotic stresses (drought, salinity and temperature) was investigated by measuring growth, gas exchange, chlorophyll fluorescence and leaf structure. We developed a stress index that allowed to precisely define stress level, enabling a comparison between stress types. For each stress, photosynthesis-limiting factors were compared: stomatal conductance (gs), mesophyll conductance (gm) and maximum capacity for Rubisco carboxylation (Vcmax).\n\nPhotosynthesis under all stresses was limited mostly by gs and gm (80-90%); whereas biochemistry (Vcmax) made a minor contribution (10-20%). The relative contribution of gs and gm on photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline in gs, while intolerance to low temperatures was driven by decline in gm. Low mesophyll-imposed limitation was the best predictor of abiotic stress tolerance.\n\nThe results demonstrate how warming climate benefits thermophilic species. Moreover, current work gives methodology for stress studies, and defines the main factors underlying the plant response to climate change.\n\nHighlightWe have compared the photosynthesis limitation resulting from long-term acclimation to three major a-biotic stresses (drought, salinity and temperature) to understand which limiting-factor are dominant under each type of stress.

plant biology↗