The co-ordinated synthesis of the subunits of ribulose bisphosphate carboxylase in a wheat line with alien cytoplasm

Abstract

The large subunit of ribulose bisphosphate carboxylase (RUBPC) is encoded and synthesized in the chloroplast [1,2] whereas the small subunit is encoded in the nucleus and synthesized as a higher M, precursor in the cytoplasm [3,4]. The synthesis of these subunits is closely co-ordinated during early cellular development in normally-grown first leaves of wheat, with changes in the synthesis of the 2 subunits and their translatable mRNAs occurring simultaneously [S]. Whether this co-ordination in the synthesis of the subunits of RUBPC is the result of inherent developmental patterns in the expression of the 2 subunit genes, or whether there is a signal co-ordinating their synthesis as in the hypothesis that the SSU acts as a positive control signal on the synthesis of the LSU [6,7], needs to be answered. To elucidate the pattern of control we have examined the cellular co-ordination of the synthesis of LSU and SSU of RUBPC in a wheat line in which a nucleus has been introduced into an alien plastid and cytoplasmic background. Several wheat lines with alien cytoplasms were available but all except the one chosen for these experiments appeared to undergo normal leaf development. The chosen wheat line has the nuclear genetic component from the hexaploid wheat Triticum aestivum cv. Chinese Spring and the cytoplasm from a diploid wheat Aegilops umbellulata. There is no transfer of plastids