| Popis: |
The declining thickness of the stratospheric ozone layer has resulted in increased UV-B radiation (280–320 nm) reaching the Earth’s surface. Severe deleterious effects have been induced in plants by UV-B radiation. Exposure of plants to UV-B radiation can lead to alterations in growth and development, transpiration and photosynthetic capacity. Inhibitory effects of UV-B radiation have been observed at different levels of the photosynthetic process; the photosynthetic machinery can be damaged directly or indirectly by exposure to UV-B radiation. However, to date there is no consensus on the primary site of attack of UV-B radiation. In vivo, one of the major candidates is Rubisco, it the activity and content of which are affected directly (1,2). One in vivo study revealed a large decrease in CO2 assimilation without a significant decrease in PSII photochemistry (3). Despite this, has been demonstrated inhibition on the reducing or oxidizing side of PSII (4). Plants growing under supplementary UV-B light are able to synthetize flavonoids in the epidermal cells, these protecting the lower levels of the leaves (5) from the penetration of UV-B radiation. In the present study, the functional and structural aspects of photosynthesis were compared in leaves acclimated or non-acclimated to UV-B radiation. |
