CONCENTRATIONS OF INORGANIC AND ORGANIC SOLUTES IN EXTRACTS FROM INDIVIDUAL EPIDERMAL, MESOPHYLL AND BUNDLE-SHEATH CELLS OF BARLEY LEAVES

The distribution of solutes between epidermal, mesophyll and bundle-sh eath cells in barley (Hordeum vulgare L. cv. Klaxon) leaves was studie d by analysing extracts obtained from single cells with a modified pre ssure probe. Activity of the cytoplasmic marker enzyme, malate dehydro genase, revealed that epidermal cell extracts were completely vacuolar in origin, but extracts from mesophyll cells also contained cytoplasm ic constituents. The extracts were analysed for osmolality and the con centrations of K, Na, Ca, Cl, P, S, NO3-, sugars and total amino acids . Epidermal and mesophyll cell extracts had similar osmolalities but t hese varied between 420 and 565 mosmol - kg-1 depending on the leaf de velopmental stage; the osmolality of bundle-sheath extracts was approx imately 100 mosmol . kg-1 lower. Under the growth conditions used, K a nd NO3- were found in all three cell types and their concentrations ge nerally ranged between 180 and 230 mM. In contrast, Ca was almost rest ricted to epidermal cells, where it increased to 70 mM during leaf age ing. Phosphorus was only detectable (greater-than-or-equal-to 5 mM) in extracts from mesophyll and bundle-sheath cells, while Cl concentrati ons were highest in epidermal and lowest in mesophyll cell extracts. T he concentrations of sugars and amino acids were close to the detectio n limit (approx. 2 mM) in epidermal cells but mesophyll cells containe d total sugar (glucose, fructose and sucrose) of up to 78 mM and total amino-acid concentrations of up to 13.5 mM. Concentrations in bundle- sheath cells were intermediate between those in the epidermis and meso phyll.