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Plastids from red and green fruits of the bell pepper, Capsicum annuum L., var. Emerald Giant, were examined for the presence of chromoplast-specific transcripts. Plastid DNA fragments produced by the restriction endonuclease PvuII were individually cut into small pieces, resolved on agarose gels, blotted, and probed with labelled cDNAs prepared from total chloroplast or chromoplast RNA. Although many chloroplast transcripts were detected at high levels in the red fruits, we saw no consistent evidence of chromoplast-specific transcripts. In order to increase the signal-to-noise ratio, chromoplast cDNA probes were absorbed with an excess of chloroplast RNAs. We also examined in greater detail regions of the plastid genome thought to contain unidentified open reading frames. None of the Southern blots provided unambiguous evidence of chromoplast-specific transcripts. Taken together with other data, these results make it unlikely, but do not exclude the possibility that plastid genes contribute to chromoplast development.

Chloroplasts and chromoplasts were isolated from green and red fruits, respectively, of the bell pepper, Capsicum annuum var. Emerald giant. A comparison of the restriction patterns of DNAs isolated from these plastids was made using single and double digests by SacI, PvuII, PstI, and SalI and found to be indistinguishable. It is inferred therefore that the conversion of chloroplasts to chromoplasts in Capsicum annuum does not involve any large rearrangements of the plastid chromosome. A restriction map of Capsicum annuum plastid DNA was constructed using the same restriction enzymes in single digests and in all possible pair combinations. Overlapping restriction fragments were identified by digesting each product of a single digest with each of the other three enzymes. The resulting restriction map is similar to that of chloroplast DNA from other members of the Solanaceae with respect to most restriction sites. The genome size corresponds to 143 kbp. The locations of 24 genes, coding for ribosomal RNAs and for proteins of Photosystem I (PSI), Photosystem II (PSII), ATP synthase, cytochromes, the large subunit of ribulose-1,5-bisphosphate carboxylase-oxygenase (E.C. 4.1.1.29) (RuBPC), and ribosomal proteins were determined by probing Southern blots of Capsicum chloroplast DNA with probes of genes from spinach and tobacco. The gene locations are completely conserved with respect to those of other members of the Solanaceae and the majority of higher land plants.