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Using a polyclonal antibody (P23) generated against the human platelet integrin αIIbβ3 and a FITC-conjugate secondary antibody, fluorescence is observed at the surface of protoplasts isolated from Arabidopsis thaliana and Rubus fruticosus. Arabidopsis thaliana cells grown in suspension culture containing P23 and glycylarginylglycylaspartylserine (GRGDS), a synthetic peptide containing the RGD sequence found in many extracellular matrix adhesive proteins demonstrated aberrant cell wall/plasma membrane interactions and organization. When glycoproteins from these plants, purified on a concanavalin A Sepharose 4B, were subjected to SDS/PAGE and Western blotting, under reduced and non-reduced conditions, immunoblots probed with P23 revealed bands in both species. A shift in electrophoretic mobility is observed to different apparent molecular mass when no reducing agent is present. When purified by immunoaffinity chromatography on anti-αIIbβ3 Sepharose or Sepharose linked to the synthetic peptide D-Arg-Gly-Asp-Trp, the major antigenic components detected migrate at 30 kDa and 60 kDa in the first experiment and 60 kDa in the second one. Only the 60-kDa component is immunodetected with antibodies specific for either the β3 platelet chain or the αIIb polypeptide, suggesting the presence of two polypeptides co-migrating. To address more precisely the structure of this complex in plants, competition assays were performed. A significant inhibition is observed with CS3 a monoclonal antibody that interacts with the complexed form αIIbβ3 but not the dissociated subunits. Further structural similarities with the animal αIIbβ3 complex is demonstrated with Western blotting detection after plant glycoproteins immunoprecipitation with CS3 in absence or presence of 5 mM EDTA to dissociate the complex. We also present data on the characterization of a polyclonal antibody, named AcAt2, raised against Arabidopsis glycocoproteins... [ABSTRACT FROM AUTHOR]

The plastid terminal oxidase (PTOX) is a plastoquinol oxidase whose absence in tomato (Solanum lycopersicum) results in the ghost (gh) phenotype characterized by variegated leaves (with green and bleached sectors) and by carotenoid-deficient ripe fruit. We show that PTOX deficiency leads to photobleaching in cotyledons exposed to high light primarily as a consequence of reduced ability to synthesize carotenoids in the gh mutant, which is consistent with the known role of PTOX as a phytoene desaturase cofactor. In contrast, when entirely green adult leaves from gh were produced and submitted to photobleaching high light conditions, no evidence for a deficiency in carotenoid biosynthesis was obtained. Rather, consistent evidence indicates that the absence of PTOX renders the tomato leaf photosynthetic apparatus more sensitive to light via a disturbance of the plastoquinone redox status. Although gh fruit are normally bleached (most likely as a consequence of a deficiency in carotenoid biosynthesis at an early developmental stage), green adult fruit could be obtained and submitted to photobleaching high light conditions. Again, our data suggest a role of PTOX in the regulation of photosynthetic electron transport in adult green fruit, rather than a role principally devoted to carotenoid biosynthesis. In contrast, ripening fruit are primarily dependent on PTOX and on plastid integrity for carotenoid desaturation. In summary, our data show a dual role for PTOX. Its activity is necessary for efficient carotenoid desaturation in some organs at some developmental stages, but not all, suggesting the existence of a PTOX-independent pathway for plastoquinol reoxidation in association with phytoene desaturase. As a second role, PTOX is implicated in a chiororespiratory mechanism in green tissues. [ABSTRACT FROM AUTHOR]