To investigate the role of
nitrogen (N) metabolism in the adaptation of photosynthesis to
water stress in rice, a hydroponic experiment supplying with low N (0.72 mM), moderate N (2.86 mM), and high N (7.15 mM) followed by 150 g⋅L-1 PEG-6000 induced
water stress was conducted in a rainout shelter.
Water stress induced stomatal limitation to photosynthesis at low N, but no significant effect was observed at moderate and high N. Non-photochemical quenching was higher at moderate and high N. In contrast, relative excessive energy at PSII level (EXC) was declined with increasing N level.
Malondialdehyde and
hydrogen peroxide (H2O2) contents were in parallel with EXC.
Water stress decreased
catalase and
ascorbate peroxidase activities at low N, resulting in increased H2O2 content and severer
membrane lipid peroxidation; whereas the activities of antioxidative
enzymes were increased at high N. In accordance with photosynthetic rate and antioxidative
enzymes,
water stress decreased the activities of key
enzymes involving in N metabolism such as
glutamate synthase and
glutamate dehydrogenase, and photorespiratory key
enzyme glycolate oxidase at low N. Concurrently,
water stress increased
nitrate content significantly at low N, but decreased
nitrate content at moderate and high N. Contrary to
nitrate,
water stress increased
proline content at moderate and high N. Our results suggest that N metabolism appears to be associated with the tolerance of photosynthesis to
water stress in rice via affecting CO2 diffusion,
antioxidant capacity, and osmotic adjustment.