Lanthanum Prevents Salt Stress-induced Programmed Cell Death in Rice Root Tip Cells by Controlling Early Induction Events

In a previous study, a salt stress-induced programmed cell death （PCD） model was established in rice root tip cells. Here, by using Wuyunjing 8th rice seedlings, the effects of lanthanum on salt stress-induced PCD early events were studied. The results indicated that low concentrations （10 μmol/L）, but not high concentrations （100 μmol/L） of LaCl3 could effectively prevent salt stress-induced PCD. Further study demonstrated that in the early stages of salt-induced PCD process, 10 μmol/L of La^3＋ could prevent the increase of cytoplasmic calcium levels, inhibit reactive oxygen species （ROS） production, and enhance the ROS-scavenging enzyme activities such as superoxide dismutases （SOD） and ascorbate peroxidase （APX）. Imidazole （20 mmol/L）, the inhibitor of nicotinamide adenine dinucleotide phosphate-oxidase （NADPH oxidase）, could alleviate the occurrence of PCD obviously, and such alleviation could be enhanced by the addition of La^3＋, indicating the involvement of NADPH oxidase in the salt stress-induced PCD process. Taken together, lanthanum could prevent salt stress-induced PCD occurrence in the rice root tip cells by blocking the calcium influx under stress, which was followed by inhibiting calcium-dependent NADPH oxidase activity to prevent O2^·- production and, enhancing the cytosolic antioxidative enzyme activities to scavenge the reactive oxygen species.