In-vitro germination and growth of lily pollen tubes is affected by protein phosphatase inhibitors

Inhibitors of type-2A protein phosphatase (PPase-2A), calyculin A (cal A) a nd okadaic acid (OA), inhibit pollen grain germination and growth of pollen tubes of Lilium longiflorum Thunb. at nanomolar concentrations. Half-maxim al inhibition of cytoplasmic PPase-2A activity was below 0.1 nM for cal A a nd at 0.7 nM for OA. Other protein phosphatase inhibitors (tautomycin, cype rmethrin, and dephostatin) were less effective. The OA- and cal A-sensitive as well as dephostatin-sensitive PPase activity in the cytoplasm did not c hange during germination and growth of pollen tubes. Addition of cal A and OA disturbed the direction of pollen tube growth and the distribution of cy toplasmic organelles and caused cell wall thickenings as observed by light and electron microscopy. Inhibition of PPase-2A caused multiple effects at the cellular level, cytoskeletal elements being a putative target of PPase- 2A activity.