Effects of O₃ on the stomatal behaviour of Egyptian varieties of radish <i>(Raphanus sativus</i> L. cv. Baladey) and turnip <i>(Brassica rapa</i> L. cv. Sultani)

Abstract

The effects of O₂ (80 nl 1^-1 ) on the photosynthetic rate (A) and stormatal conductance (g) of Egyptian varieties of radish (Raphanus sativus L. ev. Baladey) and turnip (Brassica rapa L. ev. Sultani) were examined. Exposure to O₃ decreased A in both species, while gs was increased in radish and decreased in turnip. The effect of different concentrations of O₃ , (50, 100, 150 nl l^-1 on radish was examined and it was found that A decreased, while g, increased, with increasing concentrations of O₃ . Scanning electron microscopy (SEM) of fumigated leaves showed that the increase in g_s in radish resulted from the collapse of epidermal cells. Counts of the percentage of stomata which were fully open demonstrated that 80 nl 1^-1 O₃ caused an increase of 18% in radish and a decrease of 14% in turnip. The proportion of opened stomata was found to increase with increasing O₃ concentration in radish.