CA2-HYBRIDA POLLEN TUBES( CHANNELS CONTROL THE RAPID EXPANSIONS IN PULSATING GROWTH OF PETUNIA)

Pollen tubes exhibit a rip-focused gradient of the cytosolic Ca2+ conc entration, which is presumably governed by the activity of Ca2+ channe ls in the plasma membrane. The putative role of Ca2+ as a signalling f actor in pulsating growth of Petunia hybrida pollen tubes was examined . The application of inorganic Ca2+ channel inhibitors La3+ and Gd3+ c aused the pulsating pollen tubes to abandon their rhythm and continue growth with rather steady rates. This effect was reversible upon remov al of these ions. The organic inhibitors of Ca2+ channels nifedipine a nd verapamil caused the arrest of overall pollen tube growth at higher concentrations, whereas intermediate concentrations caused a slowdown of pulse frequency, but not the inhibition of pulses. This leads to t he hypothesis, that the activity of a certain group of Ca2+ channels, which is sensitive to La3+ and Gd3+ would be responsible for the contr ol of pulsating growth. Another group of Ca2+ channels, which is sensi tive to organic inhibitors, would be required for pollen tube growth i n general and provide the basic Ca2+ influx, but would nor be directly involved in the growth oscillations. Based on these findings a hypoth etical model for the mechanism that controls pulsating growth in polle n tubes is proposed.