Accumulation of osmolytes and osmotic adjustment in water-stressed wheat (Triticum aestivum) and maize (Zea mays) as affected by calcium and its antagonists

Maize (Zea mays) and wheat (Triticum aestivum) were water stressed for 4 days at early vegetative growth (15-day-old) using PEG-6000 (-1.0 MPa), in the presence of 1 mM CaSO4, 50 muM Verapamil (VP; calcium channel blocker); 50 muM Trifluoperazine (TFP; calmodulin antagonist) and then put to recovery in order to investigate the changes in osmoregulation in plants having C-3 and C-4 metabolism. Accumulation of proline (Pro) and quaternary ammonium compounds (QAC's), activities of pyrroline-5-carboxylate reductase (P5CR), proline dehydrogenase (PDH), water potential (psi(w)), osmotic adjustment (OA), relative elongation rate (RER) and electrolyte leakage (EL) were examined during stress and recovery. Maize had significantly higher accumulation of Pro while wheat showed relatively more accumulation of QAC's. The activities of P5CR and PO were also significantly higher in maize than wheat. Maize shoots under stress showed higher psi(w) OA, RER and less EL than wheat shoots. Upon recovery from stress, maize regained its growth and water potential faster than wheat. Ca2+ elevated the accumulation of osmolytes in both the plants but OA was less sensitive to it. In the presence of Ca2+ wheat showed significantly more accumulation of osmolytes, higher psi(w), RER than maize. Ca2+ inhibitors partially reversed the effects of calcium indicating its involvement in governing solute accumulation. The differential sensitivity of maize and wheat towards water stress may be related to variation in endogenous calcium expression and its function. (C) 2003 Elsevier B.V. All rights reserved.