[Photosynthesis and active-oxygen-scavenging enzyme activities in rice varieties with different phosphorus efficiency...

Using six rice varieties with different phosphorus (P) use efficiency as the materials, the photosynthesis and active-oxygen-scavenging enzyme activities of the rice varieties under different P conditions were studied. Under deficient P condition, the photosynthetic rate (Pn) and soluble protein content (pro) were all gradually decreased with the growth process in the six tested varieties. The Pn and pro were always lower under deficient P condition than those under sufficient P condition. The Pn (ranging from 10.06-10.83 micromol CO2 x m(-2) x s(-1)), chlorophyll content (ranging from 3.32-3.56 mg x g(-1) FM) and pro (ranging from 33.08-33.95 mg x g(-1) FM) were all the highest in varieties with high-P efficiency, then in varieties with mid-P efficiency, and the lowest in varieties with low-P efficiency. There were no obvious differences on stomatal conductance (Gs) among the varieties. Meanwhile, the superoxide dismutase (SOD) activities of the tested varieties were all decreased with the process of deficient P stress. The SOD activities were also shown to be the highest in the varieties with high-P efficiency, then in the varieties with mid-P efficiency, and the lowest in the varieties with low-P efficiency under deficient P conditions. The malondialdehyde (MDA) contents in the tested varieties showed a reverse pattern of the SOD activities, with the highest in varieties with low-P efficiency and lowest in varieties with high-P efficiency. There was not an obvious change pattern on POD activity among the tested varieties under different P conditions. Under deficient P condition, the higher SOD activity and lower peroxidation degree of cell membrane system play important roles in improving the photosynthesis of the varieties with high-P efficiency.