Fine structure, carbohydrates and photosynthetic pigments of sugar maize leaves under UV-B radiation

Leaves of Zea mays were subjected to different scenarios of ultraviolet-B r adiation in a sun simulator to determine the cellular vitality at the micro scopic level and the contents of carbohydrates and photosynthetic pigments. The results show that the leaf morphology and fine structure of sugar maiz e leaves are only slightly affected by UV cut-off wavelengths down to 288 n m. At a microscopic level: a number (about one third) of epidermal cells, p redominantly below leaf tips, are affected by supplemental UV-B. They showe d partially collapsed or deformed cell walls and membranes. Underneath dama ged epidermal cells, a slight enlargement of intercellular space could be o bserved. However, other cell components including thylakoid membranes and t he epicuticular wax layer on the adaxial leaf surface remained unaffected. The leaf dry weight was not influenced by enhanced UV-B. The amount and str ucture of starch grains in leaf chloroplasts did not differ between UV trea tments. There was no clear impact of enhanced UV-B on sucrose content. Carb ohydrate partitioning was more significantly influenced by leaf exposure th an by UV treatment. Only glucose was decreased under high UV-B. Changes in photosynthetic pigments were limited to a slight destructive effect of UV-B on chlorophyll b. The results presented in this study may be interpreted t hat sugar maize leaves have adapted efficiently to cope with supplemental U V-B radiation. Changes in epidermal cell layer due to their shield function may indicate that this remarkable resistance against enhanced UV-B radiati on is not unlimited. (C) 2000 Elsevier Science B.V. All rights reserved.