Exogenous ABA induces drought tolerance in upland rice: the role of chloroplast and ABA biosynthesis-related gene expression on photosystem II during PEG stress

Abscisic acid (ABA) plays an important role in regulating photosynthesis under stress. To understand the differential function of exogenous ABA in the regulation of drought tolerance between two rice (Oryza sativa L.) genotypes, upland rice (UR, resistant to drought stress) and lowland rice (LR, susceptible to drought stress), photosynthetic parameters, chlorophyll fluorescence parameters, and the expression of chloroplast and ABA biosynthesis-related genes were investigated under 15 % polyethylene glycol (PEG) and exogenous ABA (60 µM) treatments. In both rice lines, most of the photosynthetic parameters, chlorophyll fluorescence parameters, and chloroplast and ABA biosynthesis-related gene transcript levels were rapidly reduced by PEG stress, with the exception of up-regulated levels of OsPsbA, OsNCED3, OsNCED4, and OsZEP in LR and OsNCED3, OsNCED4, and OsZEP in UR. Moreover, a rapid stress-responsive regulation mechanism was found in UR according to the more rapid and strong up-regulation of three ABA biosynthesis-related genes in UR than in LR. Under PEG stress, exogenous ABA application significantly enhanced the recovery of the net photosynthetic rate (P n), stomatal conductance (G s), and transpiration rate (T r) in UR, with increased expression of OsPsbD1, OsPsbD2, OsNCED2, OsNCED3, OsNCED4, and OsNCED5. These data suggest a role for chloroplast and ABA biosynthesis-related genes in photosystem II (PSII) induction by exogenous ABA in the UR genetic background.