Amelioration of short-term drought stress during different growth stages in Brassica juncea by rhizobacteria mediated maintenance of ROS homeostasis.

ABSTRACT

In the present investigation, the role of rhizobacteria in alleviating the deleterious effects of drought on mustard was assessed. The plants were exposed to short-term water shortages, during the vegetative and reproductive growth stages. Drought stress in both stages had a negative effect on growth, physiological, and biochemical parameters of mustard. Both the root and shoot biomass were significantly reduced in plants exposed to drought, but rhizobacterial inoculation resulted in better plant biomass than uninoculated plants. The ameliorative effects of inoculation were also indicated by improved relative water content, membrane stability index, total chlorophyll content, and photosynthetic parameters. Similarly, inoculation resulted in enhanced activity of antioxidative enzymes superoxide dismutase (SOD), ascorbate peroxidase, and catalase in both stages of growth which possibly increased stress tolerance by maintaining reactive oxygen species (ROS) homeostasis. There was a significant reduction in the accumulation of H2 O2 , proline and total soluble sugar in rhizobacteria treated plants under drought, suggesting that the treated plants did not encounter much stress and could maintain better plant health than uninoculated plants. Expression analysis of the BjP5CSB and BjFeSOD genes was conducted during both the growth stages. Expression of the BjP5CSB gene was significantly down-regulated in inoculated plants under drought, while BjFeSOD gene transcript levels were upregulated. The vegetative stage was more responsive to rhizobacterial inoculations than the reproductive stage under drought. Principal component analysis indicated a differential response by the two growth stages to inoculation. Hence, results indicate that these rhizobacteria reduce the negative impacts of drought in mustard by maintaining ROS homeostasis.