WATER STRESS-INDUCED DIURNAL-VARIATIONS IN LEAF WATER RELATIONS, STOMATAL CONDUCTANCE, SOLUBLE SUGARS, LIPIDS AND ESSENTIAL OIL CONTENT OF ORIGANUM-MAJORANA L

Diurnal changes in relative water content, water relations, stomatal conductance, soluble sugars and total lipid content were measured on potted plants of Origanum majorana L. under soil moisture deficit. Much of the drought tolerance of Origanum is due to the ability of leaves to maintain turgor potentials at levels conducive to growth and stomatal conductance. Diurnally, leaf turgor was maintained through decreasing leaf solute potential. Solute accumulation was observed, even though relative water content (RWC) was found to be higher than 60%. Combined data, of RWC and PSI-leaf measurements, indicated that leaves of plants experienced in soil water content (SWC) almost-equal-to 1.5% required less water to recover from water stress than leaves of plants experienced in SWC almost-equal-to 15%. Essential oil content, total lipids and leaf dry weight were increased as soil moisture deficit was increased. Since leaf elongation was retarded by water stress, it is suggested that dividing cells failed to subsequently enlarge because of the water stress.