Genetic variability in the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase and its small subunit mRNA in pea.

The amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) was studied during greening in 12Pisum sativum L. genotypes. The proportion of mRNA coding for the small subunit of Rubisco (SSU mRNA) was also monitored by hybridization with a cDNA (complementary DNA) probe from one of the nuclear genes coding for SSU (rbcS). Both the SSU mRNA and Rubisco (in g·FW)(-1)) contents rapidly increased in all genotypes on illumination of dark-grown seedlings. Natural genetic variability was found in the amounts of SSU mRNA, Rubisco· (g FW)(-1), total RNA·(g FW)(-1) and mRNA·(μg total RNA)(-1). Differences among genotypes in SSU mRNA were apparently the result of differences in the rate of light-induced accumulation of therbcS gene transcripts. Genotype means for SSU mRNA and Rubisco· (g FW)(-1) amounts during greening were significantly correlated (r=0.788;P<0.01). This indicates a relationship between genetic differences in the rate of light-induced accumulation of therbcS gene transcripts and the Rubisco amount, and establishes a link between natural genetic variability at the molecular and the physiological levels. Genotypic variability in SSU mRNA during greening was also positively correlated to the Rubisco content per unit leaf area in fully greened leaves. Although Southern-blot analysis indicated that there was also natural genetic variability in the copy number of therbcS genes, this difference in copy number could not account for the differences in SSU mRNA production.