Optimisation of approaches to study plant-microbe interactions under drought stress

Abstract

Food insecurity is a rising concern in the present era, with agriculture facing potentially severe limitations due to environmental changes. The greatest of these limitations, is the effect of drought induced water stress on crops. The use of plant growth promoting bacteria (PGPR) has however, been shown to significantly improve plant growth, productivity, and tolerance and resistance mechanisms. This study focussed on optimising approaches for the study of plant-microbe interactions under drought stressed and unstressed conditions. Physiological, biochemical and metabolomic approaches were optimised in this study. This was achieved by using Helianthus annuus and Pseudomonas koreensis. There were four sampling treatments which included: a control set of plants that was neither stressed nor inoculated (C), an inoculated, unstressed set (I), an inoculated and water stressed set (IS), and an uninoculated set, water stressed set (S). The physiological measurements conducted included height and leaf area, both of which were found to be significantly larger in the inoculated treatments. Biochemical analyses included ROS, phenolic acids and proline assays. Both phenolic acids and proline were significantly upregulated in inoculated plants, which was likely in response to a ROS spike. The uninoculated, stressed subset showed severe deterioration, with some plants dying. This result, in comparison with responses observed in stressed, inoculated plants further demonstrated the tolerance mechanisms elicited by the PGPR in plants under drought stress. The metabolite extraction and sampling technique optimised in this study, showed a high technical reproducibility for leaf and biofilm extraction methods. Leaf and biofilm metabolites appeared to have larger metabolite peak areas in inoculated plants. Metabolite extraction was however, less successful for root samples. It can be concluded that the overall health and drought tolerance of H. annuus plants were enhanced significantly, compared to uninoculated plants. The use of various experimental approaches and techniques in this study enabled a systems interpretation of plant-microbe interactions under drought stress. However, further studies are required for a better understanding of biochemical and metabolite pathways that are exclusively associated with tolerance mechanisms, which can be done using metabolite techniques optimized in this study.