Abstract:

The effects of salt stress on photosynthesis, Mehler-peroxidase reaction (MPR) and the susceptibility of PSⅡ to photoinhibition were investigated in Rumex K-1 leaves. Salt stress resulted in dramatic decrease in photosynthesis, but had no significant effect on maximal photochemistry of PSⅡ (Fv/Fm). During photosynthetic induction, a considerable electron flow was transported to oxygen in MPR both in control and salt-stressed leaves. Under steady state photosynthesis, enhanced electron flow to oxygen in MPR was observed only in salt-stressed leaves. The enhanced MPR in salt-stressed leave was accompanied by enhanced activities of scavenging enzymes, i.e. superoxidase dismutase (SOD) and ascor-bate peroxidase (APX). In the presence of saturating CO₂, decreasing oxygen concentration from 21% to 2% did not affect the susceptibility to photoinhibition in control leaves, but largely increased the suscep-tibility to photoinhibition in salt-stressed leaves. Based on these results, it is concluded that the enhanced MPR in salt-stressed Rumex leaves serves as a sink to drain the excess electrons off the electron chain and thus mitigates photoinhibition.

Key words: Rumex , salt stress, photoinhibition, Mehler-peroxidase reaction, chlorophyll fluorescence