Effect of carbonic anhydrase-containing endophytic bacteria on growth and physiological attributes of wheat under water-deficit conditions

Drought is one of the major limitations to agricultural productivity, suppressing plant growth and yield of food crops throughout the world particularly in arid and semiarid regions. Drought-tolerant carbonic anhydrase (CA; EC 4.2.1.1)-containing endophytic bacteria may improve plant growth under stressed conditions. In the present study, effect of drought-tolerant CA-containing endophytic bacteria on growth and physiology of wheat under water-deficit conditions was studied. One hundred and fifty isolates were isolated from wheat plants and screened for their ability to tolerate polyethylene glycol (PEG) 6000-induced water-deficit stress (−0.31 to −3.20 MPa). Fifty isolates exhibiting intrinsic ability to tolerate stress were further screened for CA activity. Ten drought-tolerant isolates with higher CA activity were evaluated for improving wheat growth under water-deficit conditions (−0.04, −1.09, −1.23 MPa). Results showed that PEG-mediated water-deficit stress significantly reduced growth of wheat. However, inoculation with isolates WR2, WS11 and WL19 significantly enhanced seedling growth by improving maximum root length, shoot length, root and shoot dry weight under non-stressed as well as stressed conditions. These isolates were identified by 16S rRNA as Bacillus marisflavi (WR2) Bacillus thuringiensis (WS11) and Bacillus subtilis (WL19). Isolate WL19 also improved chlorophyll content, photosynthetic rate, CA activity and relative water content compared to uninoculated control plants. Overall, our findings suggest that endophytic bacterial isolates WR2, WS11 and WL19 with CA activity can enhance photosynthesis and biomass of wheat seedlings under water-deficit conditions.

Abbreviations: CA: Carbonic anhydrase; PEG: Polyethylene glycol; CO₂: Carbon dioxide; HCO^3–: Bicarbonate; TSA: Tryptic Soy Agar; LB: Luria Bertani; A: CO₂ assimilation rate; E: Transpiration rate; g_s: Stomatal conductance; C_i: Substomatal CO₂ concentration; RWC: Relative water content; EL: Electrolyte leakage