Role of calcium in short-term responses of bean plants to osmotic or saline shocks

Abstract

Summary When analyzing the causes of plant growth depression under saline conditions, a distinction can be made between specific and osmotic effects produced by ions. In an attempt to study the role of Ca 2+ on both osmotic and specific effects on plant growth, bean seedlings ( Phaseolus vulgaris L. cv. Contender) were stressed with either 80 mmol/L NaCl or 12% (w/w) PEG (isosmotic concentrations) in the presence of low (0.5 mmol/L) or high (5 mmol/L) Ca 2+ concentrations. Leaf growth inhibition was observed 2.5 h after the beginning of the treatments and was not restored to the initial steady-state rate levels except for saline treatment with 5 mmol/L Ca 2+ several hours later. The growth inhibition was accompanied by a reduction of the root water content and modification of the ionic absorption by the roots. Upon NaCl or PEG stresses, malate and most amino acids reached a maximum 3–12 h after the initiation of the osmotic shock, and were then restored to values observed for control plants. In addition, PEG-treated plants showed an increase of metabolite concentration at longer times (12 to 50 h, with a maximum at 31 h). Supplemental Ca 2+ in salinized plants increased Cl − in the leaves, decreased Na + and prevented the synthesis of organic metabolites, restoring the initial steady-state growth rate of control plants. Under PEG shock, Ca 2+ induced an increase of essential nutrients, such as K + , and slightly reduced the synthesis of organic metabolites. Plants growing under PEG stress need to increase energetically expensive metabolical process(es) that could account for the stoppage of plant growth observed during the time period studied.