Biochemical and ultrastructural changes in leaves of potato plants grown under supplementary UV-B radiation

As tolerance to UV-B radiation involves many mechanisms, changes in several parameters associated to plant protection against UV-B radiation were studied in leaves of potato plants, exposed to this radiation. UV-B exposure increased constitutive flavonoids and two new types were induced. Chlorophyll amount, as well as, total protein content, was slightly decreased. However, the synthesis of a 34 kDa polypeptide was induced. Leaf area diminished, leaf dry weight and leaf thickness increased, but the gross anatomy was not changed, neither was the structural integrity of the cells. All sub-cellular structures maintained their integrity although some changes were detected. In guard cells, the fractional volume of both plastids and starch was reduced, whereas thylakoids increased. The appearance of paracrystalline inclusions in peroxisomes in both epidermal and palisade cells was conspicuous. The fractional volume of both starch and chloroplasts in palisade cells decreased. The activity of the antioxidant enzymes catalase, ascorbate peroxidase and guaiacol peroxidase increased associated with the induction of a new catalase isoform and three new guaiacol isoperoxidases. Our results show that potato plants activate several defence systems, altogether contributing to the preservation of cell structural integrity, suggesting that this encompassing defence response enables plants to cope with UV-B aggression. (C) 2004 Elsevier Ireland Ltd. All rights reserved.