Abscisic acid promotes plant acclimation to the combination of salinity and high light stress.

Plants encounter combinations of different abiotic stresses such as salinity (S) and high light (HL). These environmental conditions have a detrimental effect on plant growth and development, posing a threat to agricultural production. Metabolic changes play a crucial role in enabling plants to adapt to fluctuations in their environment. Furthermore, hormones such as abscisic acid (ABA), jasmonic acid (JA) and salicylic acid (SA) have been previously identified as regulators of plant responses to different abiotic stresses. Here we studied the response of Arabidopsis wild type (Col and Ler) plants and mutants impaired in hormone biosynthesis (aba2-11 and aba1-1 in ABA, aos in JA and sid2 in SA) to the combination of S and HL (S + HL). Our findings showed that aba2-11 plants displayed reduced growth, impaired photosystem II (PSII) function, increased leaf damage, and decreased survival compared to Col when subjected to stress combination. However, aos and sid2 mutants did not display significant changes in response to S + HL compared to Col, indicating a key role for ABA in promoting plant tolerance to S + HL and suggesting a marginal role for JA and SA in this process. In addition, we revealed differences in the metabolic response of plants to S + HL compared to S or HL. The analysis of altered metabolic pathways under S + HL suggested that the accumulation of flavonoids is ABA-dependent, whereas the accumulation of branched-chain amino acids (BCAAs) and proline is ABA-independent. Therefore, our study uncovered a key function for ABA in regulating the accumulation of different flavonoids in plants during S + HL.