Ma. Messerli et al., Periodic increases in elongation rate precede increases in cytosolic Ca2+ during pollen tube growth, DEVELOP BIO, 222(1), 2000, pp. 84-98
Pollen tubes grown in vitro require an intracellular tip-high gradient of C
a2+ in order to elongate. Moreover, after about 2 h in vitro both the tip C
a2+ and the elongation rate of lily tubes begin to oscillate regularly with
large amplitudes, This raises the question of the phase relation between t
hese two oscillations. Previous studies lacked the temporal resolution to a
ccurately establish this relationship. We have studied these oscillations w
ith a newly developed, high temporal resolution system and the complementar
y use of both luminescent and fluorescent calcium reporters. We hereby show
that the periodic increases in elongation rate during oscillatory growth o
f Lilium longiflorum pollen tubes clearly precede those in subtip calcium a
nd do so by 4.1 +/- 0.2 s out of average periods of 38.7 +/- 1.8 s. Also, b
y collecting images of the light output of aequorin, we find that the magni
tude of the [Ca2+] at the tip oscillates between 3 and 10 mu M, which is co
nsiderably greater than that reported by fluorescent indicators. We propose
an explanatory model that features cyclic growth and secretion in which gr
owth oscillations give rise to secretion that is essential for the subseque
nt growth oscillation, We also critically compile data on L. longiflorum st
ylar growth rates, which show little variation from in vitro rates of polle
n tubes grown in optimal medium. (C) 2000 Academic Press.