Cl – Efflux Triggers a Growth Spurt

Abstract

Pollen tube growth is a polarized process whereby cytoplasmic streaming, vesicle delivery, and the cytoskeleton are organized to allow vectorial growth at the apical end of the tube. Pollen tube growth is also pulsatile, occuring in oscillatory bursts. Oscillations in Ca 2+ , H + , and K + concentrations all occur in pollen tubes; however, these are out of phase with the growth cycle, and their peak increases are delayed as compared to growth. Zonia et al. measured Cl – efflux in the apical region of tobacco pollen tubes while monitoring tube growth and found that the efflux of Cl – oscillated in phase with growth. If Cl – channels were blocked pharmacologically, the tubes swelled, Cl – efflux oscillations were abolished, growth ceased, and with certain inhibitors cytoplasmic streaming was abolished. Inositol(3,4,5,6)polyphosphate [I(3,4,5,6)P 4 ] may be an endogenous regulator of Cl – efflux channels, because microinjection or extracellular application of this polyphosphate, but not of I(1,3,4,5)P 4 or I(1,3,4,5,6)P 5 , also blocked pollen tube growth and induced tube swelling. The effect of I(3,4,5,6)P 4 on Cl – efflux oscillations was more complex, with some tubes exhibiting inhibition of the oscillations and some tubes showing an increased amplitude and altered periodicity. Attempts to correlate Cl – efflux with vesicle movement and pollen tube growth suggested that changes in Cl – efflux may be a signal regulating growth, so that when Cl – efflux through the apex of the tube is high, the vesicles stream toward the top and growth occurs. L. Zonia, S. Cordeiro, J. Tupý, J. Feijó, Oscillatory chloride efflux at the pollen tube apex has a role in growth and cell volume regulation and is targeted by Inositol 3,4,5,6-Tetrakisphosphate. Plant Cell 14 , 2233-2249 (2002). [Abstract] [Full Text]