Plant Growth Regulation 24: 185–191, 1998. 185 c 1998 Kluwer Academic Publishers. Printed in the Netherlands. Contents of sugars in leaves of drying desiccation tolerant flowering plants, particularly grasses H.R. Ghasempour 1 , D.F. Gaff 2 , R.P.W. Williams 3 & R.D. Gianello 3 1 Biology Department, Razi University, Kermanshah 67147, Iran; 2 Department of Ecology Evolutionary Biology, Monash University, Clayton 3168, Australia; 3 Department of Biochemistry, Monash University, Clayton 3168, Australia Key words: desiccation tolerance, grass, raffinose, resurrection plant, sucrose, sugars, trehalose Abstract Sugar complements were analysed in extracts from leaves of desiccation tolerant species in the angiosperm families Cyperaceae, Gesneriaceae, Liliaceae, Poaceae and Velloziaceae. Total sugar content was higher in live air-dry leaves of all desiccation tolerant species (except the grass Eragrostiella nardoides; 22 moles/g dw) than in the dead air-dry leaves of the desiccation sensitive grass Sporobolus pyramidalis (36 moles/g dw). Sucrose contents rose to high levels (40–98 moles/g dw) in live air-dry leaves of all species (except the grass Eragrostiella nardoides in which it rose to only 11 moles/g dw) to become the predominant sugar. Glucose and/or fructose contents frequently were lower after leaf drying but usually these were the sugars of next highest contents in live air-dry leaves. Contents of raffinose (that has been postulated to reduce sucrose crystallization) rose to c. 10% of sucrose contents in air-dry leaves of most desiccation tolerant species (but only c. 4% in Tripogon jacquemontii) compared with c. 2% of sucrose contents in the sensitive grass S. pyramidalis. Trehalose (a rare sugar in seed- plants) was present in all but one desiccation tolerant species (Xerophyta villosa) but only in minor amounts. The results are consistent with the views that sugars play a protective role during drying of desiccation tolerant plants in general but that other factors are also involved indesiccation tolerance, that in desiccation tolerant angiospermae sucrose is generally the predominant protective sugar and that raffinose and trehalose may supplement the role of sucrose. Abbreviations: dw = dry weight; PDT = protoplasmic drought tolerance; RH = relative humidity; RWC = relative water content 1. Introduction Hypotheses of protoplasmic drought tolerance (PDT) attribute important roles to sugars in plant tissue Webb [28] offered the water-substitution hypothesis in which he proposed that sugars, sugar alcohols and amines would H-bond to macromolecules, thereby substituting for the arrays of water molecules normally bound to the macromolecules and stablizing the latter’s native conformation. The membrane-protection hypothesis was postu- lated by [19] who found that high ion concentration damaged cell membranes in vitro and that addition of sugars (particularly glucose, but also sucrose and raffi- nose at 0.01–0.2 M) protected isolated chloroplasts and to some extent mitochondria against chaotropic effects of high ion concentrations. A sufficiently high ratio of sugar concentration to ion concentration protected the chloroplasts’ ability for photophosphorylation against the influence of salt during freezing. High sugar concentrations that are developed in desiccation tolerant embryos during seed maturation have been postulated to produce in drying cells a transition to a vitreous phase [31], a phase which is