Photosystem II in Guard Cells of Vicia faba: Immunological Detection

Antibodies were raised against individual polypeptides of the oxygen-evolving photosystem II (PSII) complex from mesophyll chloroplasts of Vicia faba (Long Pod). These antibodies were used to probe immunologically for the presence of the main structural components of the PSII complex in guard cell chloroplasts, using both immunofluorescence microscopy and Western blotting. Immunofluorescence of epidermal peels with antibodies raised against the extrinsic 33 kilodalton polypeptide, as well as the 47 and the 44 kilodalton subunits and the light-harvesting chlorophyll a/b protein, resulted in intense fluorescence indicating the presence of these polypeptide components in guard cell chloroplasts. Results obtained with Western blot analysis showed that the relative amounts of the 33 kilodalton and light-harvesting complex protein polypeptides are between 60 and 80% of that found in mesophyll cells (on chlorophyll basis). These results provide evidence for the existence of structural components associated with PSII activity in guard cell similar to those of mesophyll chloroplasts.