Abstract: 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 La3+ 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 La3+,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.

Key words: Ca2+, Oryza sativa, programmed cell death, reactive oxygen species, salt stress