EPIDERMAL SOLUTE CONCENTRATIONS AND OSMOLALITY IN BARLEY LEAVES STUDIED AT THE SINGLE-CELL LEVEL - CHANGES ALONG THE LEAF BLADE, DURING LEAF AGING AND NACL STRESS

The solute relations of the upper epidermis of the third leaf of barle y (Hordeum vulgare L. cv. Klaxon) were studied by analysing vacuolar s aps extracted from individual cells. Their osmolality (nanolitre osmom etry) and the concentrations of K, Na, Ca, Cl, P, S (energy dispersive X-ray analysis) and NO3- (microfluorometry) were measured. All of the osmotically important solutes were accounted for. These were K+, NO3- , Cl-, and Ca2+. The concentration of each solute varied along the lea f blade and changed with leaf age. Calcium in particular increased dur ing leaf ageing, exceeding concentrations of 50 mM. Plants starved of Ca2+ during this period accumulated epidermal K+ instead of Ca2+. Leaf ageing was accompanied by an increase in epidermal osmolalities by ab out 100 mosmol . kg-1. When compared to the bulk leaf extract, epiderm al cell extracts exhibited significantly higher concentrations of NO3- , Cl and Ca2+, similar concentrations of K+ and Na+, and lower concent rations of P. In plants subjected to various levels of NaCl stress (up to 200 mM), epidermal concentrations of Cl- always exceeded those of the bulk extract, while Na+ concentrations were similar. Epidermal cel ls osmotically adjusted to the increase in the external salt concentra tion.