Non-photochemical quenching triggered by abscisic acid mitigates the inhibition of photosynthesis in rice under drought

Abstract

Abscisic acid (ABA) plays a key role in drought. Non-photochemical quenching (NPQ), as a photoprotective mechanism, also plays an important role in different adversities. Although this mechanism is relatively understood, the relationship between ABA synthesis and NPQ induction under drought remains poorly defined. To understand the role of ABA in the mechanism underlying the photosynthetic response to drought, two rice cultivars with different chlorophyll contents were exposed to drought and exogenous ABA. Drought significantly stimulated the accumulation of endogenous ABA in leaf, and the application of exogenous ABA under drought further stimulated it through the up-regulated expression of the genes encoding 9′-cis-epoxycarotenoid dioxygenase. The application of exogenous ABA triggered higher NPQ under drought, especially in Zhefu802. The expression of PsbS1 was significantly increased by drought, while the expression of PsbS1 was further up-regulated by spraying ABA under drought. However, the high zeaxanthin content was not further up-regulated by spraying ABA under drought. These results indicated that ABA increased the expression of PsbS1 and further triggered NPQ as a strategy to decrease the overexcitation of the photosynthetic apparatus in rice. This phenomenon was validated by slowing the decrease of the net photosynthetic rate under the application of exogenous ABA in the two rice cultivars. Except for the regulation of photoprotection, exogenous ABA significantly decreased the malondialdehyde level in Zhefu802 and the H₂O₂ level in Fgl. In conclusion, exogenous ABA significantly increases endogenous ABA and then triggers NPQ to mitigate the inhibition of photosynthesis in drought.