Plant Physiology and Biochemistry | Gansu Agricultural University and other researchers reveal that exogenous γ-aminobutyric acid (GABA) alleviates the combined stress of low temperature and low light in peppers by regulating photosynthetic performance and antioxidant systems.
Low temperature and low light combined stress is a major limiting factor in winter and spring production of greenhouse-grown peppers in Northwest China. Gamma-aminobutyric acid (GABA), as a key signaling metabolite, plays an important role in plant stress responses, but its function in peppers’ response to low temperature and low light stress remains unclear. Recently, a research team from Gansu Agricultural University and other institutions systematically revealed the physiological and molecular mechanisms by which exogenous spraying of GABA alleviates low temperature and low light stress in pepper seedlings by restoring photosynthetic performance, regulating the antioxidant defense system, and endogenous GABA metabolism. The relevant research results, titled “Foliar application of exogenous gamma-aminobutyric acid alleviates the detrimental effects of combined low-temperature and low-light stress in pepper (Capsicum annuum L.)”, were published in the academic journal Plant Physiology and Biochemistry.
This study used ‘Hangjiao 2’ pepper seedlings as material, setting up a normal temperature and light control and a low temperature and low light stress treatment (10℃/5℃ day/night, 100 μmol·m⁻²·s⁻¹ PPFD), while simultaneously applying different concentrations (0-125 mmol·L⁻¹) of exogenous GABA via foliar spraying. The results showed that the 75 mmol·L⁻¹ GABA treatment had the most balanced and comprehensive stress-relieving effect. Compared with the simple stress treatment, at this concentration, the plant height, stem diameter, and aboveground and belowground biomass of pepper seedlings were significantly restored; leaf wilting symptoms were significantly reduced.
At the photosynthetic physiological level, exogenous GABA significantly increased the content of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids in leaves; enhanced net photosynthetic rate, stomatal conductance, and transpiration rate; and reduced intercellular CO₂ concentration. Chlorophyll fluorescence parameter analysis showed that GABA treatment increased Fv/Fm, qP, qN, Y(II), and ETR, while decreasing 1-qP and (1-qP)/NPQ, indicating the recovery of PSII photochemical efficiency and non-photochemical quenching capacity. OJIP curves and JIP-test analysis further demonstrated that GABA treatment restored the electron transport capacity of the PSII receptor side under low-temperature and low-light stress.
At the oxidative stress level, exogenous GABA significantly reduced hydrogen peroxide and superoxide anion content and malondialdehyde levels, while increasing superoxide dismutase and peroxidase activities, while catalase activity showed a decreasing trend. Soluble sugar and soluble protein contents decreased significantly after GABA treatment, reflecting a reduction in osmotic regulation requirements after stress relief; while proline content continuously increased with increasing GABA concentration, possibly related to the exogenous GABA carbon skeleton entering the tricarboxylic acid cycle and promoting glutamate synthesis.
At the molecular level, exogenous GABA treatment promoted the accumulation of endogenous GABA, upregulated the expression of key GABA catabolism genes CaGABA-T1, CaGABA-T2, and CaSSADH, and downregulated the expression of synthesis genes CaGAD1 and CaGAD2, indicating that exogenous GABA may regulate endogenous GABA homeostasis through feedback inhibition. Furthermore, GABA treatment also regulated the expression of cold-response genes CaCBF1A, CaCBF1B, and CaF-BOX.
Principal component analysis and correlation analysis revealed close correlations among endogenous GABA content, photosynthetic parameters, chlorophyll fluorescence parameters, and antioxidant enzyme gene expression, collectively forming a regulatory network for GABA to alleviate low-temperature and low-light stress.
In summary, this study systematically elucidates for the first time the physiological and molecular mechanisms by which exogenous GABA alleviates combined low-temperature and low-light stress in pepper seedlings through the synergistic regulation of photosynthetic performance, antioxidant defense systems, and GABA metabolic pathways. 75 mmol·L⁻¹ GABA was determined to be the optimal application concentration. This study provides a theoretical basis and technical reference for the stress-resistant cultivation of greenhouse peppers during the winter and spring seasons.
