Mechanism of S-allyl-L-cysteine Alleviating Cadmium Stress in Seedling Roots and Buds of Rice Seedlings

Abstract

Cd has toxic effects on rice seed germination and plant growth, which may eventually lead to decreased yield and excessive Cd content in rice grains. The potential mechanism of S-allyl-L-cysteine (SAC), a natural sulfur compound derived from garlic extract, in alleviating Cd2+ stress in young roots and buds of rice seedlings was studied by a seed germination experiment. "Zhong zao 35", one of the main rice varieties in Southern China, was selected as the test material. Firstly, the alleviating effect of SAC on Cd2+ stress in rice seedling roots and buds was studied. Following this, the physiological mechanism of Cd2+ stress alleviation by SAC was examined based on the expression of the Cd transporter coding gene using real-time fluorescent quantitative PCR. The results showed that when the Cd2+ stress concentration reached 50 μmol·L-1, the young roots and buds of rice seedlings were significantly inhibited, and when the SAC concentration reached 200 μmol·L-1, Cd2+ stress was significantly alleviated. Compared to a Cd2+ stress treatment group, the total root length, surface area, and volume of young roots was increased by 173.5%, 65.52%, and 37.04%, respectively; CAT and SOD activity in young roots and buds was increased by 212.42% and 110.76%, and 31.41% and 47.31%, respectively; MDA and GSH content was decreased by 43.09% and 34.12%, and 33.97% and 35.74%, respectively; and Cd content was decreased by 35.91% and 28.86%, respectively. The results of quantitative real-time PCR showed that the relative expression levels of OsNramp5 and OsHMA2 were significantly reduced by 33.38% and 34.99% compared with the Cd2+ stress group, respectively. However, the relative expression level of OsHMA3 was significantly increased by 33.96%. From the above experimental results, the main mechanism by which SAC reduces Cd2+ stress in the young roots and buds of rice is via the regulation of Cd transporter-encoding genes, reducing Cd2+ transport to young roots and buds, and increasing transport to vacuoles.