DIURNAL PATTERN OF LEAF EXTENSION IN SALIX-VIMINALIS RELATES TO THE DIFFERENCE IN LEAF TURGOR BEFORE AND AFTER STRESS-RELAXATION

Diurnal variations in leaf extension and turgor relaxation were measur ed in young willow leaves (Salix viminalis L.). Turgor relaxation was calculated from measurements of xylem water potential and osmotic pote ntial of whole, detached leaves that were incubated, without loss of w ater, under controlled conditions. There were clear diurnal variations in leaf extension and in leaf turgor relaxation and the diurnal patte rn of the difference in leaf turgor before and after relaxation was in phase with that of leaf extension. The extent to which leaf turgor af ter relaxation may be related to threshold turgors for growth and the possible importance of leaf turgor during leaf extension are discussed .