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

Abstract

Leaves of Zea mays were subjected to different scenarios of ultraviolet-B radiation in a sun simulator to determine the cellular vitality at the microscopic level and the contents of carbohydrates and photosynthetic pigments. The results show that the leaf morphology and fine structure of sugar maize leaves are only slightly affected by UV cut-off wavelengths down to 288 nm. At a microscopic level, a number (about one third) of epidermal cells, predominantly below leaf tips, are affected by supplemental UV-B. They showed partially collapsed or deformed cell walls and membranes. Underneath damaged epidermal cells, a slight enlargement of intercellular space could be observed. However, other cell components including thylakoid membranes and the epicuticular wax layer on the adaxial leaf surface remained unaffected. The leaf dry weight was not influenced by enhanced UV-B. The amount and structure of starch grains in leaf chloroplasts did not differ between UV treatments. There was no clear impact of enhanced UV-B on sucrose content. Carbohydrate partitioning was more significantly influenced by leaf exposure than 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 that sugar maize leaves have adapted efficiently to cope with supplemental UV-B radiation. Changes in epidermal cell layer due to their shield function may indicate that this remarkable resistance against enhanced UV-B radiation is not unlimited.