POLLINATION-INDUCED SENESCENCE IN PHALAENOPSIS PETALS - RELATIONSHIP OF ETHYLENE SENSITIVITY TO ACTIVITY OF GTP-BINDING PROTEINS AND PROTEIN-PHOSPHORYLATION

Treatments of cut phalaenopsis (Phalaenopsis hybrid, cv. 'Herbert Hage r') flowers with cholera toxin or guanosine-5-0-(3-thiotriphospbate), compounds that modulate GTP-binding protein activity, increased the se nsitivity of the flowers to ethylene. Guanosine-5-0-(2-thiodiphosphate ) which does not affect the activity of GTP-binding proteins, had no a ffect on the sensitivity to ethylene. Western blot analysis of microso mal proteins, revealed that a peptide with a molecular mass of ca 42 k Da cross-reacts with antibodies against a well-conserved amino acid se quence (G(alpha-common) peptide) of mammalian G-proteins. Calcium ions , known co-factors of protein kinases, also increased the sensitivity of the flowers to ethylene, while EGTA, a chelator of calcium, decreas ed it. Phorbol 12-myrisate 13-acetate, a phorbol ester, had no effect on the sensitivity to ethylene. Protein phosphorylation in petal micro somal membranes was doubled in the presence of calcium ions, but was u naffected by phorbol ester. Ten h after pollination, at the peak of et hylene sensitivity, a significant increase of ca 20% was measured in t he binding of GTP to the membranes. Protein phosphorylation in flowers increased significantly following pollination, with a single peptide of ca 30 kDa most heavily phosphorylated. These observations may indic ate a direct involvement of GTP-binding proteins, and protein phosphor ylation, two major components of the cellular signal transduction path way, in the regulation of pollination induced ethylene sensitivity in phalaenopsis petals.