The action of a range of supplementary ultraviolet (UV) wavelengths on photosynthesis in Brassica napus L. in the natural environment: effects on PS II, CO(2) assimilation and level of chloroplast proteins.

The effects of different wavebands of UV radiation on photosynthesis and the expression and abundance of photosynthetic proteins in oilseed rape (Brassica napus L. cv. Rebel) were investigated. Plants were grown outdoors under natural radiation (52 degrees N, 0 degrees E) supplemented with six wavebands of UV radiation (0.4 Wm(-2)) between 313 nm and 356 nm. A control treatment was centred at 343 nm. Exposure to supplementary UV-A radiation (320-400 nm) had no significant effects, however UV-B radiation, centred at 313 nm, caused a marked reduction in photosynthesis. This decrease was related to a reduction in the initial carboxylation velocity of Rubisco which was further correlated with a large reduction in the expression and abundance of both large and small subunits of Rubisco. These results indicate a molecular mechanism behind UV-B induced reductions in photosynthesis per unit area in plants grown under field conditions.