Comparative Studies of the Thylakoid Proteins of Mesophyll and Bundle Sheath Plastids of Zea mays

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  • RPRoderic B. Park
    Roderic B. Park
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Abstract
The proteins from both grana and stroma lamellae of maize (Z. mays) mesophyll plastids and from maize bundle sheath plastid membranes were compared by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels using a discontinuous buffer system. Peptide differences between grana and stroma lamellae were essentially quantitative and not qualitative. Bundle sheath plastid membrane peptides more closely resemble those of the ultrastructurally similar stroma lamellae. Bundle sheath membranes contained several peptides not apparent in the stroma lamellae. The unappressed membranes (stroma lamellae and bundle sheath plastid membranes) were enriched in heavy (60-40 kilodaltons) peptides and depleted in light (31-20 kilodaltons) peptides as compared to stacked grana membranes. The heavier peptides were tentatively identified as subunits of chloroplast coupling factor. These peptides in unappressed membranes were much more resistant to removal by washing with EDTA (under conditions of low ionic strength) than they were in granal membranes. Ribulose-1,5-diphosphate carboxylase was identified on the gels and was localized exclusively in the bundle sheath cells. Sodium dodecyl sulfate electrophoresis is a simple method to test for the localization of carboxylase in various C4 plastid fractions.

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