TRANSPIRATION, ESSENTIAL OIL GLANDS, EPICUTICULAR WAX AND MORPHOLOGY OF THYMUS-VULGARIS ARE INFLUENCED BY LIGHT-INTENSITY AND WATER-SUPPLY

Plants of two clonal selections of thyme (Thymus vulgaris) were grown under natural light and natural light supplememted by a PPF of 200 mu mol m(-2)s(-1) provided by high pressure sodium lamps at 90%, 70% and 50% substrate water content in a greenhouse. Stomatal and cuticular tr anspiration, essential oil glands, epicuticular wax, and morphological traits were measured. Both stomatal transpiration and cuticular trans piration decreased under supplemental light and at low substrate water content. The time for which the stomata remained open or partially op en was longer for plants developed under supplemental light at low sub strate water content compared with variants grown under natural light and higher soil water content. The number of essential oil glands was significantly higher for plants grown under supplemental light (31 for 'Laval 1' and 27/2.27 mu m(2) for 'Laval 2') compared with natural li ght (23 for 'Laval 1' and 19/2.27 mu m(2) for 'Laval 2') grown plants. The lower the substrate water content, the higher the epicuticular wa x load. The epicuticular wax concentration under supplemental light va ried between 171 and 214 mg m(-2) for 'Laval 1', and 169 and 208 mg m( -2) for 'Laval 2', while under natural light, this value fluctuated be tween 128 and 163 mg m(-2) for 'Laval 1', and 114 and 146 mg m(-2) for 'Laval 2'. Plants grown under supplemental light developed upright er ect shoots with increased tillers, branches, thicker and glossy leaves that were aesthetically more appealing, while plants under natural li ght had a prostrate type of growth with thinner, broader leaves of sli ghtly pale green colour.