Biogenesis of petunia and carnation corolla chloroplasts: changes in the abundance of nuclear and plastid‐encoded photosynthesis‐specific gene products during flower development

To study the biogenesis of the photosynthetic apparatus in corollas, as well as compositional differences between corolla and leaf chloroplasts, the levels of 12 nuclear‐ and plastid‐encoded thylakoid and stromal components were analyzed by western blotting using heterologous antisera. Relative levels of the thylakoid polypeptides analyzed in petunia (Petunia hybrida cv. Hit Parade Rosa) and carnation (Dianthus caryophyllus cv. White Sim) corollas increased, per unit chlorophyll, in parallel to corolla development, peaking at the mature stage in both flower types, with the exception of subunit V of the photosystem I (PSI) core complex, which continued to accumulate even after anthesis. The photosystem II (PSII) major light‐harvesting chlorophyll a/b protein accumulated in corollas to a level, per unit chlorophyll, similar to that in leaves in both petunia and carnation plants. Components of the cytochrome b₆/f complex were found to accumulate to higher levels in corolla chloroplasts than in leaves. The opposite trend was found for components of the PSI core complex, as well as for the stromally located small and large subunits of ribulose‐1,5‐bisphosphate carboxylase, which accumulated in corollas to levels ca 2. 5 times lower than their respective levels in leaves. The latter subunits accumulated coordinately in corollas of both plant types during flower development. Data obtained from immunological studies were correlated with those at the mRNA level. Nothern blotting revealed that, in petunia corollas, the steady‐state transcript level of genes coding for the small subunit of ribulose‐l,5‐bisphosphate carboxylase was identical to that of genes coding for the major light‐harvesting chlorophyll a/b protein. Levels of both transcripts, as well as those of plastid‐encoded genes for the PSII reaction center's Dl and D2, were ca two‐thirds of their respective levels in leaves. In contrast, the level of transcript for the large subunit of ribulose‐1,5‐bisphosphate carboxylase was reduced 5‐fold in petunia corollas, as compared to leaves.