Polymorphism and Mendelian inheritance of photosystem II 23-kilodalton polypeptide.

Soluble proteins from leaves of Nicotiana glauca Grah., N. langsdorffii Weinm., their reciprocal hybrids and amphiploid hybrid (N. glaucaxN. langsdorffii) were resolved by two-dimensional gel electrophoresis. Among a group of well-resolved polypeptides, in the isoelectric-point range of 5-5.5 and relative-molecular-mass (Mr) range of 18-23 kilodaltons (kDa), species-specific variation was observed. Polypeptides designated "L" and "l" are specific to N. langsdorffii, and "G" and "g" to N. glauca, while "C" is common to both species. Polypeptides "L", "G" and "C" are localized in the chloroplasts and associated with thylakoid membranes. Polypeptide "L" is more acidic than polypeptide "G", and both polypeptides have an Mr of 23 kDa. They were isolated from two-dimensional gels and their first 13 N-terminal amino-acid sequences were determined. These were found to be identical to the 13N-terminal amino acids of the photosystem II (PSII) 23-kDa polypeptide from spinach (T. Jansen et al. (1987) FEBS Lett. 216, 234-240) and, except for one change, to those from pea (R. Wales et al. (1989) Plant Molec. Biol., in press). Polypeptides "G" and "L" cross-react with antiserum against the PSII 23-kDa polypeptide from pea. Therefore, polypeptides "G" and "L" are extrinsic PSII 23-kDa polypeptides. They appear jointly and in equal amounts in the reciprocal hybrids. Since chloroplasts in Nicotiana are maternally inherited, these results demonstrate that polypeptides "G" and "L" are encoded by nuclear genes, are polymorphic variants of the PSII 23-kDa polypeptide, and are inherited in a Mendelian manner.