TIP LOCALIZED CA2-RATES IN POLLEN TUBES OF LILIUM-LONGIFLORUM( PULSESARE COINCIDENT WITH PEAK PULSATILE GROWTH)

It is known that locally elevated Ca2+ at the growing tips of pollen t ubes is necessary for pollen tube elongation. Here we show that this l ocalized Ca2+ is also temporally regulated and is closely associated w ith pulsatile tip growth. Lilium longiflorum pollen tubes were injecte d with the photoprotein, aequorin, and the Ca2+-dependent light output was detected with a low noise photon-counting system, Ca2+ pulses wit h a mean period of 40 seconds were invariably associated with growth, The pulses were sporadic and of low amplitude for about the first 1.5 hours after germination. With subsequent growth, pulses increased in a mplitude and the period between pulses became more regular, We have lo calized these Ca2+ pulses to the elongating end of the growing tube, T he Ca2+ pulses are asymmetrical, rising more slowly than they fall. We estimate that the Ca2+ concentration at the peak of the pulses reache s nearly 10 mu M The addition of 100 mu M La3+, a Ca2+ channel blocker , extinguished the pulses, An analysis of growth of elongating tubes e stablishes that extension is pulsatile, with a 42 second period betwee n pulses, Calcium imaging, using the fluorescent indicator, Calcium Gr een dextran, shows that calcium pulses are coincident with peak growth rates.