Effects of Pseudomonas aeruginosa on root activity and leaf physiological characteristics in rice (Oryza sativa L.) seedling under cadmium stress

Abstract

To reveal the physiological effects of rice alleviated by cadmium-tolerant Pseudomonas aeruginosa under cadmium stress condition, the influences of bacterial strian on the root vigor and leaf physiological characteristics were analyzed under a set of hydroponic experiments involving adding bacteria suspension, empty carrier, microbial inoculum with 20 μmol·L-1 Cd. Cadmium-free treatment as control. The results showed that the root vigor was significantly inhibited, leaf photosynthetic rate decreased, and the contents of soluble protein, flavonoid and total phenols in rice leaves were reduced, while the contents of malondialdehyde (MDA) and superoxide anion(O2-·) increased significantly under cadmium stress condition. Compared with cadmium treatment, root vigors of rice were increased by 36.1%-42.5% and 49.4%-53.0% respectively in bacteria suspension and microbial inoculum additions, net photosynthetic rates in leaves were increased by 118.5%-147.1% and 137.6%-156.9%, and the contents of soluble protein were increased by 37.0%-49.3% and 37.7%-72.6%, respectively. For the bacteria suspension treatment, the activities of SOD, POD and CAT in leaves were increased by 25.8%-36.6%, 40.9%-55.9%, 24.0%-29.2%, and the activities of SOD, POD and CAT in leaves under microbial inoculum treatment were increased by 36.9%-42.6%, 82.7%-92.6% and 43.3%-52.2%, respectively, with the stimulative effects on antioxidation enzymes in rice leaves being higher than those of bacteria suspension. Compared with cadmium treatment, the contents of MDA and O2-· in rice leaves were reduced by 44.8%-54.7%, 29.4%-41.9% and 9.9%-10.2%, 3.0%-7.1% in microbial inoculum and bacteria suspension treatments, respectively. In contrast, the contents of flavonoids and total phenols were increased by 125.4%-135.7%, 100.8%-119.4% and 139.4%-146.7%, 115.0%-134.7%, respectively. In summary, P. aeruginosa and the microbial inoculum could promote rice seedling growth by improving root vigor and photosynthetic rate, as well as the contents of flavonoids and total phenols, which led to the fact that P. aeruginosa could significantly alleviate the stress of cadmium on rice.