Sugar and Ion Content in Leaf Tissues of Several Drought Tolerant Plants under Water Stress

Abstract

Soluble sugars and dominant anions and cations were measured in turgescent and air-dry leaves of desiccation-tolerant South African grasses.The species investigated can lose up to 95% water without suffering damage.A drought sensitive species whose leaves did not survice drying served as control. Turgid leaves of the grasses contained little soluble sugar compared with dry leaves.Leaves of the tolerant species showed the largest increase in sugar content on drying.Starch concentrations decrease simultaneously with increases in sugar levels during drying.In contrast to leaves of the tolerant grasses, leaves of other resurrection plants ( Ceterach , Polypodiaceae, and Craterostigma , Scrophulariaceae) already had a higher sugar content when turgid.Content of soluble sugars increased less during drying in these species than in grasses.Content of the grasses of nitrate, chloride, sulphate, and malate varied considerably in the grasses.Correlation of desiccation- tolerance with individual ions could not be detected. However, the ratio of soluble sugars to inorganic anions exhibited correlation to desiccationtolerance.Under water stress this ratio increased much less in the sensitive species than in the tolerant grasses investigated.When sensitive membrane systems are dehydrated high ratios of membrane-compatible sugars to chaotropic ions (e.g.nitrate or chloride) are known to protect them from damage during dehydration.It is concluded that increases in the above ratio during drying protect membranes against chaotropic inactivation and thereby contribute to desiccation- tolerance.