Alleviation of the effect of environmental stresses using co-inoculation of mungbean by<i>Bradyrhizobium</i>and rhizobacteria containing stress-induced ACC deaminase enzyme

Abstract

Ethylene is synthesized at accelerated rate in response to stress conditions, and regarded as a stress hormone that inhibits overall plant growth. Apparently, the amount of ethylene can be reduced by using silver thiosulfate (STS) or bacteria containing 1-amino-cyclopropane-1-carboxylate (ACC) deaminase. In this study, we examined whether different concentrations of STS differently prevent legume growth under various environment stress conditions, and whether co-inoculation of mungbean (Vigna radiata (L.) R. Wilczek) by Bradyrhizobium and rhizobacteria containing ACC deaminase also alleviates legume stress. Mungbean is one of the most responsive plants among tested legume species, and different varieties of mungbean also respond differently to STS. Stress conditions and inappropriate concentrations of STS affect plant growth and symbiosis, while a suitable concentration of STS supports plant growth under stress conditions. Three isolates of bacteria containing ACC deaminase, Enterobacter sp. ACC1, Enterobacter sp. ACC2, and Chryseobacterium sp. ACC3, were selected according to their ACC deaminase activity and resistance abilities to high temperature, drought, and salt stress conditions. Interestingly, the gene encoding ACC deaminase, acdS, of selected ACC deaminase bacteria was highly induced when the cell culture was exposed to stress conditions. It coincided with co-inoculation of plants by Bradyrhizobium and rhizobacteria containing ACC deaminase. This co-inoculation obviously alleviated the stress of plants growing under stress conditions. These results revealed the role of bacteria containing ACC deaminase that can adjust its expression of ACC deaminase to different levels of stress conditions, which will be useful in agriculture under global warming.