Ultraviolet-B stimulates grana formation in chloroplasts in the African desert plant Dimorphotheca pluvialis

Chloroplasts isolated from a plant species, Dimorphotheca pluvialis Moench (Asteraceae), grown under visible light without supplementary UV-B radiatio n, have poor grana development. The dominant components in the membrane org anizations are doublets and triplets of stroma lamellae. However, such chlo roplasts possess the capacity for electron transfer through the whole photo synthetic chain, based on the measurement of the reduction of ferredoxin. T he chloroplasts isolated from D. pluvialis plants grown under visible light in combination with supplementary UV-B radiation have much greater membran e stacking in the thylakoid organization when compared with those grown wit hout supplementary UV-B. The changes in the membrane organization induced b y UV-B are also reflected in photochemical activity: oxygen-evolving phopto system II (PSII) activity is increased in UV-B chloroplasts compared with c hloroplasts grown without UV-B, On this basis, it is concluded that the dyn amic relation between the granal stacks and the stroma lamellae in the chlo roplasts is closely related to the strategy by which plants are able to cop e with a variety of environments and to optimize the photosynthetic machine ry for the environmental conditions. The increase in membrane stacking in D . pluvialis, induced by supplementary UV-B radiation during plant growth, s uggests that UV-B may be an essential factor for the development of membran e stacking in chloroplasts of higher plants. The mechanism of action of UV- B in this process is discussed. (C) 1999 Elsevier Science S.A. All rights r eserved.