Effects of Na₂CO₃ stress on photosynthesis and antioxidative enzymes in endophyte infected and non-infected rice.

Endophyte infected and uninfected seedlings of rice (Oryza sativa L.) were subjected to five different levels of Na(2)CO(3) for 2 weeks. Under both Na(2)CO(3) stress as well as no stress, endophyte-infected plants were higher for above-ground dry weight and shoot length, but lower for root length compared to non-infected controls, and there was no significant difference for below-ground dry weight. Chlorophylls and carotenoid contents, net photosynetic rate, transpiration rate, catalase and peroxidase activities increased, but malondialdehyde content declined in the infected plants compared to non-infected controls under Na(2)CO(3) stress. Compared to non-infected controls, water use efficiency, stomatal conductance, chlorophyll fluorescence parameters (F(v)/F(m), F(v)/F(o)) and superoxide dismutase activity in infected plants increased under high concentrations of Na(2)CO(3) while there was no significant difference under low concentrations of Na(2)CO(3). Endophyte infection was concluded to be beneficial to the growth and antioxidative mechanisms in Oryza sativa under Na(2)CO(3) stress.