|
Résumé :
|
The solute relations of the upper epidermis of the third leaf of barley (Hordeum vulgare L. cv. Klaxon) were studied by analysing vacuolar saps extracted from individual cells. Their osmolality (nanolitre osmometry) 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 leaf blade and changed with leaf age. Calcium in particular increased during 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 about 100 mosmol . kg-1. When compared to the bulk leaf extract, epidermal cell extracts exhibited significantly higher concentrations of NO3-, Cl and Ca2+, similar concentrations of K+ and Na+, and lower concentrations of P. In plants subjected to various levels of NaCl stress (up to 200 mM), epidermal concentrations of Clalways exceeded those of the bulk extract, while Na+ concentrations were similar. Epidermal cells osmotically adjusted to the increase in the external salt concentration.
|
