Abstract：Plant-growth promoting rhizobacterium (PGPR) Bacillus cereus AR156 is a potential bio-pesticide. In order to study the mechanism of drought tolerance in tomato (Lycopersicon esculentum) induced by B. cereus AR156, we tested relative water content, malondialdehyde(MDA) content, relative electrical conductivity and chlorophyll content of leaves and recovery intension of roots, the antioxidant enzymes activities and the expression of cytosolic ascorbate peroxidase gene (cAPX), monodehydroascorbate reductase gene (MDHAR) and ribulose-1, 5-bisphosphate carboxy/oxygenase(Rubisco) small subunit gene(rbcS) under drought stress condition. Results showed that after treated with culture supernate of AR156, relative water content of leaves was 82% comparing to control group, increased by 44%, recovery intension of roots was 0.336 mg/g/h, increased by 100%, chlorophyll a, chlorophyll b and total chlorophyll were increased by 16%, 20% and 20.2%, respectively, and the expression of rbcS maintained a stable high level, besides MDA content was 2.2×10-3 μmol/g FW, decreased by 21.4%, relative electrical conductivity was 56.0%, decreased by 28.2%, compared with control treatment. What's more, the activities of superoxide dismutase(SOD), peroxidase(POD) and hydrogen peroxidase(CAT) were increased markedly after applying with the culture supernate of AR156, and the expression of cAPX and MDHAR were up-regulated at anaphase of drought stress. Moreover the survival rate of tomato 24 h after re-watering were increased markedly, compared with control group. These results suggested that the culture supernate of AR156 increased drought tolerance of tomatoes by protecting plant cell, maintaining photosynthetic efficiency and increasing some of peroxidases activities. This made a contribution to the studies on the mechanism of systemic tolerance induced by PGPR. These results demonstrate the primary mechanism of drought torelance in tomato induced by AR156, and also provide theoretical basis for the application of AR156 as a good drought tolerance biological inducer.
