Biology subjects

Ghannoum, O.

Publications and source records attributed to Ghannoum, O..

6 recordsLinked to original sources

bioRxiv2023

Mesophyll-specific overexpressing of SvHXK6 gene improves water use efficiency without yield loss in C4 Setaria viridis

Hexokinases (HXK) were the first sugar signalling proteins identified in plants and are well known for their feedback regulation of photosynthetic gene expression. In some C3 plants, HXKs have been found to regulate stomatal function. However, the role of HXK in C4 photosynthesis, which is inherently more water use efficient than C3 metabolism, remains poorly understood. Here, we report on the first tissue-specific modification of HXK in a C4 plant. SvHXK6 was expressed in the model C4 grass Setaria viridis under the control of the ZmPEPC promoter (ZmPEPCpro), which directs expression in the leaf mesophyll tissue. Three S. viridis transgenic lines with increased abundance of SvHXK6 transcripts in the leaf tissue showed significant reduction in stomatal conductance with minimal effects on leaf CO2 assimilation rate. Consequently, the transgenic lines had higher leaf-level water use efficiency relative to the control (wild-type and null) plants. Overexpression of SvHXK6 had no effect on shoot biomass or seed yield of the S. viridis plants. Our study shows conserved function of HXK in regulating stomatal conductance in a C4 grass, demonstrating possible widespread utility in improving water use efficiency in C4 as well as C3 species.

plant biology↗

bioRxiv2022

An energy-saving glasshouse film reduces seasonal, and cultivar dependent Capsicum yield due to light limited photosynthesis

Glasshouse films can be used to reduce energy costs by limiting non-productive heat-generating radiation, but the impact on yield of greenhouse horticultural crops remains unknown. The effects of energy-saving film ULR-80 (referred to as Smart Glass; SG) designed to block long wavelength light that generates heat also reduced photosynthetically active radiation (PAR) consequently affecting crop morphology, photosynthesis, leaf pigments, and yield of two hydroponically grown capsicum (Capsicum annuum L.) cultivars (Red and Orange). The crops were grown in four high-tech glasshouse bays over two seasons of similar daily light integrals (DLI) during ascending (Autumn) and descending (Summer) photoperiods. The Red cultivar exhibited higher photosynthetic rates (light saturated - Asat and maximal - Amax) and yield than the Orange cultivar in control but displayed stronger reductions in modelled photosynthetic rates at growth light and yield in SG without changes in photosynthetic capacity. Foliar pigment ratios of chlorophyll a/b and carotenoid: chlorophyll remained unaffected by the SG during both seasons indicating that chloroplast homeostasis was similar between SG and control. The seasonal differences in photosynthetic pigments and xanthophyll de-epoxidation state (DPS) revealed that cultivars were able to sense the SG-altered light environment during the ascending, but not descending photoperiod. The descending photoperiod correlated with a lower daily light level and a substantial yield reduction of 29 % and 13 % in Red and Orange cultivars, respectively. Thus, SG-induced higher reductions in yield during the descending photoperiod indicate that SG may be more beneficial for capsicum crops planted during Autumn with an ascending photoperiod. HighlightsO_LIA potential energy saving SG film limited net photosynthesis of capsicum C_LIO_LIThe SG film reduced yield of two capsicum cultivars that can be mitigated by planting during the low light growth season with a shorter photoperiod C_LIO_LISG reduced genotype-dependent capsicum yield was associated with alterations in the level of foliar pigments required for photoprotection under adverse light conditions C_LI

plant biology↗

bioRxiv2022

Anatomical drivers of stomatal conductance in sorghum lines with different leaf widths grown under different temperatures

O_LIImprovements in leaf water use efficiency (iWUE) can maintain crop productivity in water limited environments under rising temperatures. We investigated the leaf anatomical traits which underpin our recently identified link between leaf width (LW) and iWUE. C_LIO_LITen sorghum lines with varying LW were grown under three temperatures to expand the range of variation of both LW and gas exchange rates. Leaf gas exchange, surface morphology and cross-sectional anatomy were measured and analysed using structural equations modelling. C_LIO_LINarrower leaves had lower stomatal conductance (gs) and higher iWUE across growth temperatures. They also had smaller intercellular airspaces, stomatal size, percentage of open stomatal aperture relative to maximum, hydraulic pathway, mesophyll thickness, and leaf mass per area. Structural modelling revealed a developmental association among leaf anatomical traits that underpinned gs variation in sorghum. C_LIO_LIGrowing temperature and LW both impacted leaf gas exchange rates, but only LW directly impacted leaf anatomy. Wider leaves may be more productive under well-watered conditions, but consume more water for growth and development, which is detrimental under water stress. C_LI HighlightCoordination between leaf width and leaf anatomy underpins stomatal conductance variation in sorghum grown under different temperatures.

plant biology↗

bioRxiv2021

Heat stress prevented the biomass and yield stimulation caused by elevated CO2 in two well-watered wheat cultivars

To investigate the interactive effects of elevated CO2 and heat stress (HS), we grew two contrasting wheat cultivars, early-maturing Scout and high-tillering Yitpi, under non-limiting water and nutrients at ambient (aCO2, 450 ppm) or elevated (eCO2, 650 ppm) CO2 and 22{degrees}C in the glasshouse. Plants were exposed to two 3-day HS cycles at the vegetative (38.1{degrees}C) and/or flowering (33.5{degrees}C) stage. At aCO2, both wheat cultivars showed similar responses of photosynthesis and mesophyll conductance to temperature and produced similar grain yield. Relative to aCO2, eCO2 enhanced photosynthesis rate and reduced stomatal conductance and maximal carboxylation rate (Vcmax). During HS, high temperature stimulated photosynthesis at eCO2 in both cultivars, while eCO2 stimulated photosynthesis in Scout. Electron transport rate (Jmax) was unaffected by any treatment. eCO2 equally enhanced biomass and grain yield of both cultivars in control, but not HS, plants. HS reduced biomass and yield of Scout at eCO2. Yitpi, the cultivar with higher grain nitrogen, underwent a trade-off between grain yield and nitrogen. In conclusion, eCO2 improved photosynthesis of control and HS wheat, and improved biomass and grain yield of control plants only. Under well-watered conditions, HS was not detrimental to photosynthesis or growth but precluded a yield response to eCO2. Key messageHigh temperatures increased photosynthetic rates only at eCO2 and photosynthesis was upregulated after recovery from heat stress at eCO2 in Scout suggesting that eCO2 increased optimum temperature of photosynthesis.

physiology↗

bioRxiv2021

Intrinsic water use efficiency depends on stomatal aperture rather than stomatal density in C3 and C4 grasses grown at glacial CO2 and low light

We investigated how stomatal morphology and physiology control intrinsic leaf water use efficiency (iWUE) in grasses. Two C3 and six C4 grasses were grown at ambient (400 {micro}l L-1) or glacial CO2 (180 {micro}l L-1) and high (1000 {micro}mol m-2 s-1) or low light intensity (200 {micro}mol m-2 s-1). C4 grasses tended to have higher iWUE and CO2 assimilation rates, and lower stomatal conductance (gs), operational stomatal aperture (aop) and guard cell K+ influx rate relative to C3 grasses, while stomatal size (SS) and stomatal density (SD) did not vary according to the photosynthetic type. Overall, iWUE and gs depended most on aop and density of open stomata. In turn, aop correlated with K+ influx, stomatal opening speed on transition to high light and SS. Species with higher SD had smaller and faster-opening stomata. Although C4 grasses operated with lower gs and aop at ambient CO2, they showed a greater potential to open stomata relative to maximal stomatal conductance (gmax), indicating heightened stomatal sensitivity and control. We uncover novel links between aop, gs, iWUE and K+ influx amongst grasses and differential K+ influx responses of C4 guard cells to low light, revealing molecular targets for breeding crops with high iWUE. HighlightsAcross C3 and six C4 grasses, intrinsic water use efficiency was strongly associated with stomatal conductance, operational stomatal aperture, guard cell K+ influx and stomatal opening speed on transition to high light.

plant biology↗

bioRxiv2020

Smart Film Impacts Stomatal Sensitivity of Greenhouse Capsicum Through Altered Light

Optical films that alter light transmittance may reduce energy consumption in high-tech greenhouses, but their impact on crop physiology remains unclear. We compared the stomatal responses of capsicum plants grown hydroponically under control glass (70% diffuse light) or smart glass (SG) film ULR-80, which blocked >99% of ultraviolet light and 19% of photosynthetically active radiation (PAR). SG had no significant effects on steady-state (gs) or maximal (gmax) stomatal conductance. In contrast, SG reduced stomatal pore size and sensitivity to exogenous ABA thereby increasing rates of leaf water loss, guard cell K+ and Cl- efflux, and Ca2+ influx. The transition between low (100 mol m-2 s-1) and high (1500 mol m-2 s-1) PAR induced faster stomatal closing and opening rates in SG relative to control plants. The fraction of blue light (0% or 10%) did not affect gs, but induced stomatal oscillations in SG plants. Increased expression of stomatal closure and photoreceptor genes in epidermal peels of SG plants is consistent with fast stomatal responses to light changes. In conclusion, light intensity was more critical than spectral quality for optimal stomatal responses of capsicum under SG, and re-engineering of the SG should maximize PAR transmission to maintain a better stomatal development. HighlightsO_LICapsicum plants grown under SG film exhibit decreased stomatal pore area, higher water loss and reduced ABA-sensitivity. C_LIO_LISG-grown plants have faster rates of stomatal closing and opening in response to light intensity changes. C_LIO_LISG increases efflux of K+ and Cl- and influx of Ca2+ of guard cells. C_LIO_LISG upregulated the expression of key genes involved in stomatal regulation and light sensing. C_LI

plant biology↗