EFFECTS OF O-3 ON THE STOMATAL BEHAVIOR OF EGYPTIAN VARIETIES OF RADISH (RAPHANUS-SATIVUS L CV BALADEY) AND TURNIP (BRASSICA-RAPA L CV SULTANI)

The effects of O-3 (80 nl l(-1)) on the photosynthetic rate (A) and st omatal conductance (g(s)) of Egyptian varieties of radish (Raphanus sa tivus L. cv. Baladey) and turnip (Brassica rapa L. cv. Sultani) were e xamined. Exposure to O, decreased A in both species, while gs was incr eased in radish and decreased in turnip. The effect of different conce ntrations of O-3 (50, 100, 150 nl l(-1)) on radish was examined and it was found that A decreased, while g(s) increased, with increasing con centrations of O-3. Scanning electron microscopy (SEM) of fumigated le aves showed that the increase in gs in radish resulted from the collap se of epidermal cells. Counts of the percentage of stomata which were fully open demonstrated that 80 nl l(-1) O-3 caused an increase of 18% in radish and a decrease of 14% in turnip. The proportion of opened s tomata was found to increase with increasing O-3 concentration in radi sh.