[Effects of Burkholderia sp. Y4 on Cadmium Damage and Uptake in Rice Seedlings]

In order to investigate the effects of Burkholderia sp. Y4 on rice seedlings under cadmium (Cd) stress, seed germination and vermiculite culture experiments were conducted using low Cd-accumulation xiangzaoxian 24 (X24) and high Cd-accumulation Tyou 705 (T705) varieties. The effects of Burkholderia sp. Y4 on rice growth, oxidative damage caused by Cd, and Cd accumulation were studied. Additionally, the Cd²⁺ flux rates in the elongation zone of rice roots under Burkholderia sp. Y4 application were detected using non-invasive micro-test technology. Burkholderia sp. Y4 alleviated the inhibition effect of Cd on rice seed germination by 13.8%. After inoculation with Burkholderia sp. Y4 for 7 d, the length of rice roots and buds increased by 83.3% and 12.2%, and their dry weight increased by 56.8% and 12.5%, respectively; those in the 10 d Y4 inoculation group increased by 28.6% and 20.0% in length and by 113.2% and 46.0% in dry weight, respectively. Burkholderia sp. Y4 inoculation also alleviated rice oxidative stress damage caused by Cd. The application of strain Y4 significantly reduced the content of the oxidative damage product malondialdehyde (MDA) in the shoots and roots of rice seedlings by 21.5% and 16.9%, respectively. Under Burkholderia sp. Y4 inoculation, the significant changes in antioxidant enzyme SOD and CAT activities caused by Cd stress disappeared in rice roots; those in shoots also decreased from 176.9% and 74.8% to 53.3% and 21.5%, respectively. Conversely, Burkholderia sp. Y4 inhibited Cd uptake by rice seedlings with different genotypes, including the low Cd-accumulation variety X24 and high Cd-accumulation variety T705. The root application of strain Y4 significantly reduced Cd accumulation in the shoots and roots of rice seedlings by 79.2% and 62.7% in T705 and by 57.3% and 24.1% in X24, respectively. The Cd²⁺ flux rate of high Cd-accumulation variety T705 was significantly higher than that of low Cd-accumulation variety X24. Under Burkholderia sp. Y4 inoculation, the yellow membrane was formed on the root surface of rice seedlings, and the Cd²⁺ flux rate in the elongation zone of T705 and X24 roots decreased by 36.0% and 35.0% in 3-day-old seedlings, as well as by 44.6% and 24.9% in 10-day-old seedlings, respectively. In conclusion, Burkholderia sp. Y4 inoculation inhibited the toxic effects of Cd on rice seedling growth through alleviating oxidative stress and damage caused by Cd. Furthermore, the root application of Burkholderia sp. Y4 effectively decreased the Cd²⁺ flux rate in the elongation zone of roots to inhibit the Cd uptake and accumulation in roots and shoots of rice seedlings. This study provides theoretical basis and data support for the application of Burkholderia sp. Y4 as a Cd-reducing and growth-promoting agent for rice in contaminated farmland.