Amelioration of Plant Drought Stress by Plant Growth-Promoting Bacteria

Plant growth-promoting bacteria (PGPB) that contain the enzyme (1-aminocyclopropane-1-carboxylate) ACC deaminase protect a variety of plants against damage from various biotic and abiotic stresses. Here, the ability of bacterial strains Pseudomonas sp. UW4 (a rhizospheric PGPB) and Pseudomonas fluorescens YsS6 (an endophytic PGPB) and their respective (1-aminocyclopropane-1-carboxylate) ACC deaminase minus mutants, to ameliorate the effects of drought stress on canola (Brassica campestris) seedlings was assessed. Initially, biochemical assays were used to estimate the levels of a number of the plant growth-promoting activities encoded within each of the four above-mentioned strains. These activities include: ACC deaminase activity, indole-3-acetic acid (IAA) production, siderophore synthesis and the trehalose concentration produced. Subsequently, the effect of the four bacterial strains on canola seedlings grown in the greenhouse in potting soil and subjected to different levels of drought stress (0, 6, 8, and 10 days) was measured. In all experiments, measurements were taken of shoot fresh weight, shoot dry weight, shoot protein concentration, leaf chlorophyll concentration, and shoot trehalose concentration. The results are discussed in terms of a previously developed model of PGPB functioning in the facilitation of plant growth