Effects of abscisic acid on photoinhibition in maize plants

Effects of short- and long-term abscisic acid (ABA) treatments on CO2 assimilation, PSII photochemistry, and the xanthophyll cycle were investigated in maize plants during exposure to high light (1500 mumol m(-2) s(-1)). Under non-photoinhibitory condition, both short- and long-term ABA treatments showed no effects on PSII photochemistry and carboxylation efficiency but induced a similar decrease in CO2 assimilation and stomatal conductance. The pool size of the xanthophyll cycle was increased in long-term ABA-treated plants but not in short-term ABA-treated plants. When exposed to high light, there was a significant decrease in the maximal efficiency of PSII photochemistry (Fv/Fm). However, such a decrease was less in long-term ABA-treated plants but greater in short-term ABA-treated plants than in control plants. There was no difference in Fv/Fm between control and short-term ABA-treated plants after exposure to high light for longer time, e.g. 60 min. Similar results were observed in the actual PSII efficiency, photochemical quenching, CO2 assimilation and carboxylation efficiency. The xanthophyll cycle pigment contents and non-photochemical quenching (NPQ) were significantly higher but malondialdehyde content was lower in long-term ABA-treated plants than in control plants. However, there were no significant differences in the xanthophyll cycle pigment contents, NPQ and malondialdehyde content between control and short-term ABA-treated plants. The results suggest that short-term ABA treatment had no effect on photoinhibition or even induced aggravated photoinhibition, while long-term ABA treatment led to increased resistance to photoinhibition, which was associated with higher CO2 assimilation capacity and enhanced xanthophyll cycle. (C) 2003 Elsevier Ireland Ltd. All rights reserved.