Effect of elevated temperatures on heat shock protein and ribulose-1,5-bisphosphate carboxylase gene expression in Brassica napus

Abstract

Leaf segments of Brassica napus were exposed to 22, 35, 38, or 40 °C for up to 4 h. Analysis of radiolabeled proteins by two-dimensional sodium dodecyl sulfate – polyacrylamide gel electrophoresis and fluorography revealed two major groups of heat shock proteins (HSPs). One group comprised HSPs 70, 76, and 87, with (pIs) isoelectric points ranging from 5.7 to 6.1, whereas the second group had molecular masses ranging from 23 to 16 kilodaltons (kDa) and pIs from 5.6 to 6.9. Immunoblot analysis using antibodies directed against the large (RLSU) and small (RSSU) subunits of ribulose-1,5-bisphosphate carboxylase (RUBISCO) showed that increasing temperatures from 35 to 38° or 40 °C for the duration of thermal stress (i.e., from 1 to 5 h) did not affect levels of the RSSU (15 kDa), whereas levels of the RLSU (52 kDa) fell sharply. Nevertheless, the activity of RUBISCO was not adversely affected at 38 °C for periods of up to 5 h. Northern blot analysis revealed that the increase observed in HSP 70 synthesis during heat shock may be transcriptionally regulated, but the decrease in the RLSU was not accompanied by a corresponding reduction in levels of its mRNA.Key words: Brassica, heat shock, ribulose-1,5-bisphosphate carboxylase, gene expression.