Light-induced changes in the distribution of the 36000-Mr polypeptide of NADPH-protochlorophyllide oxidoreductase within different cellular compartments of barley (Hordeum vulgare L.) : II. Localization by immunogold labelling in ultrathin sections.

The cellular distribution of the 36000-Mr polypeptide of NADPH-protochlorophyllide oxidoreductase has been determined in ultrathin sections of barley leaves by the method of immunogold labelling. In leaves of etiolated seedlings a large portion of the immunoreactive protein was localized within the prolamellar body. However, approximately one third of the total immunoreactive protein was present outside the plastid in the area of the plasmalemma. During illumination of etiolated seedlings the two polypeptide populations were differentially affected by light. While the concentration of the plastid-localized immunoreactive protein rapidly decreased and was hardly detectable after 16 h of continuous white-light treatment, the concentration of the extraplastidic polypeptide did not decline significantly during this illumination period. A similar distribution pattern of the immunoreactive polypeptide was also found in maize and rye. The chlorophyll-deficient barley mutant xantha-l(81) contained the immunoreactive 36000-Mr polypeptide, even though the prolamellar body was not detectable in etioplasts of this mutant. All of the immunoreactive polypeptide was localized outside the plastid in the area of the plasmalemma. Despite the apparent absence of the enzyme protein from the plastid, dark-grown mutant plants contained the same relative concentration of mRNA activity for the NADPH-protochlorophyllide oxidoreductase, which declined rapidly during illumination, as in wild-type plants. The antigenic properties and the apparent molecular weight of the plastid-localized NADPH-protochlorophyllide oxidoreductase and the 36000-Mr immunoreactive polypeptide outside the plastid were so similar as to indicate that the two proteins may be of common origin.