Individual members of the light-harvesting complex II chlorophyll a/b-binding protein gene family in pea (Pisum sativum) show differential responses to ultraviolet-B radiation.

Light-harvesting complex II chlorophyll a/b-binding protein (Lhcb) mRNA levels are differentially affected by ultraviolet-B radiation (UV-B, 280-320 nm) at different stages of development of pea (Pisum sativum L. cv. Feltham first) seedlings. Addition of UV-B radiation to the light periods of diurnal cycles of white light resulted in reduction of total Lhcb mRNAs in green leaves but a transient increase in etiolated buds. The aims of this study were to determine the stage during de-etiolation at which supplementary UV-B began to inhibit Lhcb gene expression, and to determine whether differential regulation of individual Lhcb genes could explain the differential response to supplementary UV-B at different developmental stages. All seven Lhcb mRNAs were shown to increase in etiolated buds transferred to a diurnal cycle with supplementary UV-B during the light periods, but were greatly reduced in green leaves given the same treatment. Therefore, the different responses of total Lhcb mRNA levels to UV-B radiation in green leaves and etiolated buds are not primarily due to the expression of different members of the Lhcb gene family at different developmental stages. However, the Lhcb genes could be divided into two groups based on their sensitivities to UV-B. Transcripts from the three genes, Lhcb1*2, Lhcb1*3 and Lhcb1*5, which were undetectable in dark-grown etiolated buds, exhibited stronger responses to supplementary UV-B in green leaves than the four genes, Lhcb1*1, Lhcb1*4, Lhcb2*1 and Lhcb3*1, which showed low levels of initial transcript accumulation in dark-grown etiolated buds. The effect of UV-B on Lhcb mRNA levels were, however, correlated with chlorophyll content, suggesting that the developmental stage of chloroplasts may be important in determining the responses of the Lhcb genes to supplementary UV-B radiation in pea seedlings. [ABSTRACT FROM AUTHOR]