Abstract
UV-B radiation at moderate levels causes impairment of photosynthesis (1). At lower levels of UV-B, gene expression is altered, so as to cause decreased levels of mRNAs for photosynthetic genes or genes for chloroplast-localised defence enzymes (2). The abundance of transcripts for extraplastidic defence proteins, such as those involved in flavonoid biosynthesis (3) and scavenging of reactive oxygen species (4), increase. These increased mRNA levels indicate that no serious damage has been caused to the transcriptional machinery by the UV-B (5). Whether or not the UV-B radiation has deleterious effects on translation has so far not been shown. However, a small but significant drop in total cellular RNA occurs during UV-B exposure (A. Strid, unpublished), which most probably reflects a certain decrease in the number of cytoplasmic ribosomes. In this study, we have examined the effect of two different levels of UV-B radiation on the abundance and integrity of the two major ribosomal RNAs of the chloroplast, 23S and 16S. As a comparison the mRNA levels for other chloroplastic and extraplastidic proteins were examined.
Published Version
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