Response of growth and development of rice cultivars with different cadmium accumulation to removing NO

Objectives  Nitric oxide (NO) is an active signal molecule that can influence plants response to various stress. This study evaluates the regulatory effect of NO on the physiological, biochemical and nitrogen metabolism of rice seedlings under Cd stress.

Methods  Rice cultivars of high and low Cd accumulation (TN1 and Chunjiang 06) were investigated in Cd stress (40 µmol/L) hydroponic trials. The treatments included Cd stress solution (i.e., control), the addition of sodium nitroprusside to increase NO content (Cd+SNP), the addition of CPTIO to remove NO (Cd+CPTIO), and the addition of NR inhibitor to inhibit NO (Cd+TU). Data was collected on NO₃⁻-N distribution, root development, photosynthetic characteristics, and growth of the rice seedlings.

Results  The effects of NO on the rice varieties with high- and low- Cd accumulation was different (P<0.05). 1) The cultivar with high-Cd accumulation recorded low NO₃⁻-N content in the aboveground and underground parts of the rice seedlings, however, no inhibition effect was found in the biomass and N uptake of the seedlings in response to NO regulation in Cd+SNP treatment. Cd+CPTIO treatment increased growth, N accumulation, and N use efficiency of rice seedling ( P<0.05). The addition and elimination of NO significantly reduced the Cd contents in the aboveground and underground parts of rice seedlings. 2) The treatments (Cd+SNP, Cd+CPTIO and Cd+TU) had no significant effect on seedling growth, N uptake of the low-Cd accumulation cultivar.

Conclusions  The rice cultivar with high Cd accumulation is sensitive to NO regulation but not the cultivar with low Cd accumulation. For the high Cd rice cultivar, removing NO inhibits the absorption and movement of Cd from the root to the shoot, but promotes the absorption and utilization of N and the growth of seedlings. The effect of inhibiting nitrate reductase activity concerning the alleviation of Cd stress to promote seedling growth was instability. For the low Cd accumulation rice cultivar, the elimination of NO has a certain effect on alleviating Cd absorption. However, this effect is less important than the Cd rejection of gene itself. Therefore, removing NO could be considered a useful way of alleviating Cd stress in high-Cd accumulated rice cultivars.