Abscisic acid enhances alkaline stress tolerance in grapevines: Physiological and transcriptional profiling

Abstract

Abscisic acid (ABA) is a crucial signaling regulator governing plant growth and survival during adverse conditions. However, the mechanism by which ABA mediates grapevine tolerance to alkali stress has not yet been elucidated. Here, we investigated the role of ABA in regulating physiological characteristics and transcriptome of grapevines under alkali stress through the application of exogenous ABA and fluridone (an ABA biosynthesis inhibitor). The results revealed that alkali stress led to significant reductions in the net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), transpiration rate (Tr), chlorophyll content, the maximum quantum yields of primary photochemistry of PSII (Fv/Fm), nonphotochemical quenching (NPQ), which were greatly alleviated by exogenous ABA (50 and 100 μM) application. Specifically, the application of exogenous ABA (50 μM) increased Pn, chlorophyll content and Fv/Fm by 28.39 %, 30.45 % and 17.29 %, respectively, compared with alkali stress alone. Furthermore, exogenous ABA treatment reduced alkali stress-induced superoxide anions (O2∙−) and hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage, as well as higher proline content and activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). Additionally, exogenous ABA (50 μM) decreased O2∙−, H2O2, MDA, electrolyte leakage by 38.64 %, 28.16 %, 39.29 % and 39.42 %, respectively, respect to alkali stress alone. Moreover, exogenous ABA reduced the Na+, increased K+ and K+/Na+ ratio, as well as the phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI) activities and flavonoid content, and increased zeaxanthin epoxidase (ZEP) and 9-cis-epoxy carotenoid dioxygenase (NCED) activities and endogenous ABA levels in alkali stress-treated grapevines. Exogenous ABA (50 μM) increased flavonoid content and endogenous ABA content by 74.03 % and 20.84 %, compared with alkali stress alone, respectively. Conversely, exogenous fluridone exacerbated alkali stress-induced physiological damage in grapevine plants. Transcriptome analysis revealed that exogenous ABA (50 μM) and fluridone significantly induced the ‘Plant hormone signal transduction (ko04075)’, the ‘MAPK signaling pathway-plant (ko04016)’, ‘ABC transporters (ko02010)’, ‘Photosynthesis-antenna proteins (ko00196)’, ‘Flavonoid biosynthesis (ko00941)’, ‘Phenylpropanoid biosynthesis (ko00940)’ and other biological pathways and key gene involved in chlorophyll metabolism and ion transport. In conclusion, ABA markedly enhanced grapevines tolerance to alkali stress by modulating key biological pathways and physiological characteristics.