Plant–Water Relations of Kidney Bean Plants Treated with NaCl and Foliarly Applied Glycinebetaine

Salinity is at present one of the most serious environmental problems influencing crop growth. It has been extensively demonstrated that salinity affects several physiological processes in the plant, including the plant–water relations of most salt‐sensitive crops species. In this study, the effects of salinity on the plant–water relations of kidney bean ( Phaseolus vulgaris L.) and the possibility that foliarly applied glycinebetaine improves these water relations are examined. Kidney bean plants were grown in a greenhouse and treated with 0, 30, 50 and 100 m M NaCl, combined with 0, 10 and 30 m M glycinebetaine in foliar applications. Increased salinity levels decreased stomatal conductance, photosynthetic rate, transpiration and leaf relative water content in the 30, 50 and 100 m M treatments relative to the control treatment. Glycinebetaine applications of 10 m M increased stomatal conductance at 50 m M NaCl, ameliorating significantly the effect of salinity on water relations through increases in the leaf relative water content. At 100 m M NaCl, 30 m M glycinebetaine applications in particular contributed to osmotic stress, and had an adverse effect on plants. Our experiment suggests that glycinebetaine can be used as an alternative treatment to reduce the effects of salt stress on the water relations of salt‐sensitive plants, but only to limited salinity levels. Furthermore, the improvement in the water status of kidney beans was dose dependent, suggesting that the concentration of glycinebetaine essential for the survival of salt‐sensitive plants is species specific and must be determined individually for each plant species.