Effects of O3 on the stomatal behaviour of Egyptian varieties of radish (Raphanus sativus L. cv. Baladey) and turnip (Brassica rapa 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 O₃decreased 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.