Exogenous GABA alleviates alkaline stress in Malus hupehensis by regulating the accumulation of organic acids

Alkaline stress affects the apple production in northwestern China. Here, Malus hupehensis was used as a material to study the influence of exogenous gamma-aminobutyric acid (GABA) application on seedlings under alkaline stress in hydroponics. 0.5 mM GABA was identified as the most suitable concentration to alleviate alkaline stress. Compared with the control, exogenous GABA significantly increased biomass, root growth, and scavenging activities of reactive oxygen species in apple seedlings under alkaline stress. In addition, the photosynthetic characteristics and total chlorophyll concentration increased remarkably in response to GABA application. Exogenous GABA also significantly increased the contents of malate, citric acid, and succinate by promoting the GABA shunt. Furthermore, the activities of malate dehydrogenase, citrate synthase, isocitrate dehydrogenase, and aconitase increased in response to GABA application. These results are important to indicate the use of exogenous substances to improve the resistance of apples to alkaline stress.