Effect of ABA on Photosynthesis and Chlorophyll Fluorescence in Emmenopterys henri Oliv. under High Light

Abstract: The effect of exogenous abscisic acid (ABA) on photosynthesis in Emmenopterys henryi Oliv. under high light (HL) was investigated. HL resulted in reduction of chlorophyll content, net photosynthetic rate (P), stomatal conductance (g), transpiration rate (Tr), instantaneous carboxylation efficiency (ICE) whereas increase of intercellular CO concentration (Ci), which returned more or less after removal of HL. Application of ABA alleviated the decrease of chlorophyll content, P and ICE under HL and promoted the recovery of them after removal of HL while further depressed g, Tr and Ci induced by HL and delayed the recovery of them. HL resulted in reduction of the maximal efficiency of PSII photochemistry (F/F), the PSII potential activity (F/F), photochemical quenching (qP), the actual quantum yield of PSII (Y(II)), the proportion of heat dissipation (NPQ), the regulated-energy dissipation (Y(NPQ)) and the electron transport rate (rETR (II)) while significant increase of unregulated energy dissipation (Y(NO)), which were alleviated by ABA pretreatment. The recovery of F/F, F/F, qP, Y(II), NPQ, Y(NPQ) and rETR (II) after relieve of HL were advanced by ABA pretreatment. These results suggest that ABA pretreatment alleviated the adverse effect of HL on photosynthesis in E. henryi during HL and enhanced its recovery by alleviating chlorophyll degradation, improving ICE, promoting repair of PSII reaction center, allocating more energy to photochemical reaction, maintaining electron transport activity. Anthocyanin accumulation induced by HL was inhibited by ABA pretreatment. The role of anthocyanin in the protection function of ABA under HL remain to be further explored.