Concanavalin A-mediated agglutination of plant plastids

Cucumber (Cucumis sativus L.) and pear (Pyrus domestica Medik.) fruit proplastids, and pea (Pisum sativum L., cv. Meteor) leaf chloroplasts, extracted by osmotic rupture of protoplasts isolated after degradation of the cell walls by cellulase and pectinase, agglutinated in the presence of Con A. Agglutination of cucumber proplastids was inhibited by anti-Con A and by methyl α D-gluco/manno pyranosides but not by methyl α D-galactopyranoside. Fluorescein isothiocyanate-conjugated Con A (FITC-Con A) rendered agglutinated clumps fluorescent. If cellulase was omitted from the macerating medium, Con A-mediated agglutination did not occur even if proplatids were subsequently incubated with cellulase. Proplastids and chloroplasts extracted by conventional mechanical disruption methods were not agglutinated by Con A and did not acquire fluorescence with FITC-Con A. However, cucumber proplastids so extracted could be agglutinated by Con A if incubated with cellulase after preparation.