A Systems Approach to Uncover the Effects of the PGPR Pseudomonas koreensis on the Level of Drought Stress Tolerance in Helianthus Annuus

Abstract

Drought is one of the major production-limiting factors to agriculture and it has been predicted to increase in frequency, duration and intensity due to global climate change. The lack of water induces stomatal closure in plants, therefore decreasing levels of photosynthesis and the plant's ability to acquire nutrients1. Further decreases in plant growth include increased levels of abscisic acid, ethylene and reactive oxygen species1. Plants can tolerate drought by increasing the production of phenolic compounds, proline and soluble sugars1. Plant-growth-promoting-rhizobacteria (PGPR) can improve the plants’ tolerance to many abiotic and biotic stresses, including drought stress. PGPR improve water retention and soil aggregation around the plant's roots2. Some PGPR have the enzyme 1-aminocyclopropane-1-carboxylic-acid (ACC)-deaminase2,3; can increase the availability of phosphorous and iron through phosphatase enzymes3 and siderophore production2; and can produce indole-3-acetic acid (IAA)3. In order to study the effects of PGPR on drought tolerance in plants I will firstly measure the germination index of uninoculated and inoculated H. annuus seeds. The biochemical assays performed on P. koreensis include: phosphatase activity, ACC-deaminase activity, chitinase activity and the production of IAA and siderophores. For the drought-experiments, I will have uninoculated and inoculated controls (i.e. no drought stress) and uninoculated and inoculated treatments (i.e. with an appropriate drought stress). In all cases I will be measuring leaf area, leaf water content, chlorophyll fluorescence and electrolyte leakage; and I will also measure recovery and regrowth after the end of the drought stress. I will also be quantifying the levels of soluble sugars, phenolic acids, proline and superoxide in both leaf and root tissues. Preliminary results show that P. koreensis can produce 103.5±3.84 μM deferoxamine mesylate equivalent/OD540 (mean±SD) and 169.2±37.0 μg/ml/OD580 IAA. P. koreensis has an acidic phosphatase activity of 9.30±0.53 milliunits/OD580 and an alkaline phosphatase activity of 3.59±0.10 milliunits/OD580.

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