Differential expression of 1-aminocyclopropane-1-carboxylate synthase genes during orchid flower senescence induced by the protein phosphatase inhibitor okadaic acid

Applying 10 pmol of okadaic acid (OA), a specific inhibitor of type 1 or ty pe 2A serine/threonine protein phosphatases, to the orchid (Phalaenopsis sp ecies) stigma induced a dramatic increase in ethylene production and an acc elerated senescence of the whole flower. Aminoethoxyvinylglycine or silver thiosulfate, inhibitors of ethylene biosynthesis or action, respectively, e ffectively inhibited the OA-induced ethylene production and retarded flower senescence, suggesting that the protein phosphatase inhibitor induced orch id flower senescence through an ethylene-mediated signaling pathway. OA tre atment induced a differential expression pattern for the 1-aminocyclopropan e-1-carboxylic acid synthase multigene family. Accumulation of Phal-ACS1 tr anscript in the stigma, labelum, and ovary induced by OA were higher than t hose induced by pollination as determined by "semiquantitative" reverse tra nscriptase-polymerase chain reaction. In contrast, the transcript levels of Phal-ACS2 and Phal-ACS3 induced by OA were much lower than those induced b y pollination. Staurosporine, a protein kinase inhibitor, on the other hand , inhibited the OA-induced Phal-ACS1 expression in the stigma and delayed f lower senescence. Our results suggest that a hyper-phosphorylation status o f an unidentified protein(s) is involved in up-regulating the expression of Phal-ACS1 gene resulting in increased ethylene production and accelerated the senescence process of orchid flower.