Stb6 mediates stomatal immunity, photosynthetic functionality, and the antioxidant system during the Zymoseptoria tritici-wheat interaction.

This study offers new perspectives on the biochemical and physiological changes that occur in wheat following a gene-for-gene interaction with the fungal pathogen Zymoseptoria tritici. The Z. tritici isolate IPO323, carries AvrStb6, while ΔAvrStb6#33, lacks AvrStb6. The wheat cultivar (cv.) Shafir, bears the corresponding resistance gene Stb6. Inoculation of cv. Shafir with these isolates results in two contrasted phenotypes, offering a unique opportunity to study the immune response caused by the recognition of AvrStb6 by Stb6. We employed a variety of methodologies to dissect the physiological and biochemical events altered in cv. Shafir, as a result of the AvrStb6-Stb6 interaction. Comparative analysis of stomatal conductance demonstrated that AvrStb6-Stb6 mediates transient stomatal closures to restrict the penetration of Zymoseptoria tritici. Tracking photosynthetic functionality through chlorophyll fluorescence imaging analysis demonstrated that AvrStb6-Stb6 retains the functionality of photosynthesis apparatus by promoting Non-Photochemical Quenching (NPQ). Furthermore, the PlantCV image analysis tool was used to compare the H2O2 accumulation and incidence of cell death (2, 4, 8, 12, 16, and 21 dpi), over Z. tritici infection. Finally, our research shows that the AvrStb6-Stb6 interaction coordinates the expression and activity of antioxidant enzymes, both enzymatic and non-enzymatic, to counteract oxidative stress. In conclusion, the Stb6-AvrStb6 interaction in the Z. tritici-wheat pathosystem triggers transient stomatal closure and maintains photosynthesis while regulating oxidative stress.

Elevated light intensity compensates for nitrogen deficiency during chrysanthemum growth by improving water and nitrogen use efficiency.

Identifying environmental factors that improve plant growth and development under nitrogen (N) constraint is essential for sustainable greenhouse production. In the present study, the role of light intensity and N concentrations on the biomass partitioning and physiology of chrysanthemum was investigated. Four light intensities [75, 150, 300, and 600 µmol m-2 s-1 photosynthetic photon flux density (PPFD)] and three N concentrations (5, 10, and 15 mM N L-1) were used. Vegetative and generative growth traits were improved by increase in PPFD and N concentration. High N supply reduced stomatal size and gs in plants under lowest PPFD. Under low PPFD, the share of biomass allocated to leaves and stem was higher than that of flower and roots while in plants grown under high PPFD, the share of biomass allocated to flower and root outweighed that of allocated to leaves and stem. As well, positive effects of high PPFD on chlorophyll content, photosynthesis, water use efficiency (WUE), Nitrogen use efficiency (NUE) were observed in N-deficient plants. Furthermore, photosynthetic functionality improved by raise in PPFD. In conclusion, high PPFD reduced the adverse effects of N deficiency by improving photosynthesis and stomatal functionality, NUE, WUE, and directing biomass partitioning toward the floral organs.

The regulatory role of γ-aminobutyric acid in chickpea plants depends on drought tolerance and water scarcity level.

γ-Aminobutyric acid (GABA) is a non-protein amino acid with multifunctional roles in dynamic plant responses. To determine the effects of exogenous GABA application (0, 25 and 50 µM) on drought response, two chickpea cultivars with contrasting tolerance to water deficit were examined. Plants were exposed to four irrigation levels (irrigation to 100, 60, 40 and 20% field capacity). Water deficit decreased growth, chlorophyll content, and photosynthetic efficiency. It increased electrolyte leakage and lipid peroxidation owing to both higher ROS accumulation and lower antioxidant enzyme activity. These negative effects of water deficit and the alleviating role of GABA application were more prominent in the sensitive, as compared to the tolerant cultivar. Water deficit also increased proline and GABA contents more in the tolerant cultivar, whereas their content was more enhanced by GABA application in the sensitive one. This may confer an additional level of regulation that results in better alleviation of drought damage in tolerant chickpea cultivars. In conclusion, the stimulatory effect of GABA on growth and physiological modulation depends on both the water stress severity and the cultivar sensitivity to it, implying a probable unknown GABA-related mechanism established by tolerant chickpea cultivars; a lost or not gained mechanism in susceptible ones.

Synergistic Effects of Melatonin and Gamma-Aminobutyric Acid on Protection of Photosynthesis System in Response to Multiple Abiotic Stressors.

GABA (gamma-aminobutyric acid) and melatonin are endogenous compounds that enhance plant responses to abiotic stresses. The response of Vicia faba to different stressors (salinity (NaCl), poly ethylene glycol (PEG), and sulfur dioxide (SO2)) was studied after priming with sole application of GABA and melatonin or their co-application (GABA + melatonin). Both melatonin and GABA and their co-application increased leaf area, number of flowers, shoot dry and fresh weight, and total biomass. Plants treated with GABA, melatonin, and GABA + melatonin developed larger stomata with wider aperture compared to the stomata of control plants. The functionality of the photosynthetic system was improved in primed plants. To investigate the photosynthetic functionality in details, the leaf samples of primed plants were exposed to different stressors, including SO2, PEG, and NaCl. The maximum quantum yield of photosystem II (PS II) was higher in the leaf samples of primed plants, while the non-photochemical quenching (NPQ) of primed plants was decreased when leaf samples were exposed to the stressors. Correlation analysis showed the association of initial PIabs with post-stress FV/FM and NPQ. Stressors attenuated the association of initial PIabs with both FV/FM and NPQ, while priming plants with GABA, melatonin, or GABA + melatonin minimized the effect of stressors by attenuating these correlations. In conclusion, priming plants with both GABA and melatonin improved growth and photosynthetic performance of Vicia faba and mitigated the effects of abiotic stressors on the photosynthetic performance.

γ-Aminobutyric acid confers cadmium tolerance in maize plants by concerted regulation of polyamine metabolism and antioxidant defense systems.

Gamma-Aminobutyric acid (GABA) accumulates in plants following exposure to heavy metals. To investigate the role of GABA in cadmium (Cd) tolerance and elucidate the underlying mechanisms, GABA (0, 25 and 50 µM) was applied to Cd-treated maize plants. Vegetative growth parameters were improved in both Cd-treated and control plants due to GABA application. Cd uptake and translocation were considerably inhibited by GABA. Antioxidant enzyme activity was enhanced in plants subjected to Cd. Concurrently GABA caused further increases in catalase and superoxide dismutase activities, which led to a significant reduction in hydrogen peroxide, superoxide anion and malondealdehyde contents under stress conditions. Polyamine biosynthesis-responsive genes, namely ornithine decarboxylase and spermidine synthase, were induced by GABA in plants grown under Cd shock. GABA suppressed polyamine oxidase, a gene related to polyamine catabolism, when plants were exposed to Cd. Consequently, different forms of polyamines were elevated in Cd-exposed plants following GABA application. The maximum quantum efficiency of photosystem II (Fv/Fm) was decreased by Cd-exposed plants, but was completely restored by GABA to the same value in the control. These results suggest a multifaceted contribution of GABA, through regulation of Cd uptake, production of reactive oxygen species and polyamine metabolism, in response to Cd stress.