The specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) in crude extracts of leaves from euploid, amphiploid and alloplasmic lines of wheat fell into high or low categories (3.75 or 2.70 μmol·mg−1·min−1, 30°C). For the alloplasmic lines, where the same hexaploid nuclear genome was substituted into different cytoplasms, the specific activity of RuBPCase was consistent with the type of cytoplasm (high for the B and S cytoplasms and low for the A and D cytoplasms). There was no evidence from the euploid and amphiploid lines that small subunits encoded in different nuclear genomes influenced the specific activity. High specific activity was conferred by possession of the chloroplast genome of the B-type cytoplasm which encodes the large subunit of RuBPCase. All lines with a cytoplasm derived from the Sitopsis section of wheat, with the exception ofAegilops longissimaandA. speltoides18940, had RuBPCase with high specific activity. In contrast with the euploid lines ofA. longissima, the alloplasmic line containingA. longissimacytoplasm from a different source had RuBPCase with high specific activity. The difference in specific activity found here in-vitro was not apparent in-vivo when leaf gas exchange was m
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