Investigation was carried out to find whether enhanced ultraviolet radiation influences the Malva parviflora L., Plantago major L., Rumex vesicarius L. and Sismbrium erysimoids Desf. of some annual desert plants. The seeds were grown in plastic pots equally filled with a pre-sieved normal sandy soil for 1 month. The planted pots from each species were randomly divided into equal groups (three groups). Plants of the first group exposed to white-light tubes (400-700 nm) 60 w and UV (365 nm) 8 w tubes. The second group was exposed to white-light tubes (400-700 nm) 60 w and UV (302 nm) 8 w tubes. The third group was exposed to white-light tubes (400-700 nm) 60 w and UV (254 nm) 8 w tubes, respectively, for six days. The results indicated that the chlorophyll contents were affected by enhanced UV radiation. The chlorophyll a, b, and total contents were decreased compared with the control values and reduced with the enhanced UV radiation, but the carotenoid was increased compared with the control and also reduced with the enhanced UV radiation. So, the contents of chlorophylls varied considerably. M. parviflora showed the highest constitutive levels of accumulated chlorophyll a, b, and total chlorophyll (0.463, 0.307 and 0.774 mg g(-1) f w) among the investigated plant species. P. major showed the lowest constitutive levels of the chloroplast pigments, 0.0036, 0.0038 and 0.0075 mg g(-1) f w for chlorophyll a, b, and total chlorophyll at UV-365 nm, respectively. The protein content was decreased significantly in both root and shoot systems compared with the control values but, it was increased with increasing wave lengths of UV-radiation of all tested plants. R. vesicarius showed the highest protein contents among the investigated plants; its content was 3.8 mg g(-1) f w at UV-365 nm in shoot system. On the other hand, decreasing ultraviolet wave length induced a highly significant increase in the level of proline in both root and shoot of all tested plants. From the results obtained, it is suggested that proline can protect cells against damage induced by ultraviolet radiation. Statistically, the variations of the studied metabolic activities were significant due to UV radiation treatment in shoot and root system of all investigated plant species.

The present investigation studied the effectiveness of ozone (O 3 ) concentrations on epidermal cells of pepper (Capsicum frutescens L.) leaves and its response to ascorbic acid (AS). The plants were grown at two sites in Riyadh, King Saud University (KSU) Campus, and the second industrial city (SIC) under an average of 42.33 and 138.66 ppb of O 3 . Two groups grown at KSU site as a control; one of them was treated with tap water (TW) and the other was treated with TW+AS, while the remaining two groups were transferred to SIC site, treated as described previously. Treatment with 300 mg/L AS was performed once every 15 days until the end of the experiment. The plants grown under separately high concentrations of O 3 and AS increased the stomatal numbers, dimensions and cell dimensions in both upper and lower epidermises of leaves in comparison to control plant leaves. Treatment with O 3 +AS significantly increased the length of the upper and lower epidermal cells, while it decreased the cell widths in comparison to plants grown under only O 3 . The AS might have a mitigating effect on the impacts of O 3 on leaf epidermal cells of the pepper plant particularly, with respect to cell width.