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Several experiments have been performed during the last few decades to evaluate the responses of plants to enhanced solar UV radiation (UV-R) that may occur because of stratospheric ozone depletion. The objective of this study was to evaluate the effects of UV radiation on some anatomical and ultrastructural aspects of pepper plants (Capsicum longum L) in the greenhouse. Pepper plants were grown in a uniform environment and after 35 days they were exposed to UV-A and UV-C radiation for 15 and 8 days, respectively. The results indicated that the changes in root growth was not significant but the growth of shoot decreased in UV-R exposed plants and this reduction was significant in UV-C exposed plants. Leaf area was also reduced in UV-R exposed plants and this reduction was significant in UV-C exposed plants. The root diameter was not affected under UV treatment, but the stem diameter and leaf thickness were significantly increased in both UV-A and UV-C treatments. The number and size of stomata were also increased in UV-R exposed plants. At the ultrastructural level, it was found that the thylakoids of chloroplast were dilated and starch reduction was observed. UV treatment resulted in the formation of crystalline inclusion in the peroxisomes of the mesophyll cells. Formation of these crystals may be due to the increased activity of catalase, which is an antioxidant enzyme. The study shows that pepper plants are sensitive to UV-R and this finding provides insight into the structural and ultrastructural changes during UV exposure, and indicates the sensitivity of these plants to UV-C more than UV-A radiation.

Keywords: UV-A, UV-C, Capsicum longum, Structure, Ultrastructure, Chloroplast

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