Fine-tuning of the cytoplasmic Ca2+ concentration is essential for pollen tube growth.

Pollen tube growth is crucial for the delivery of sperm cells to the ovule during flowering plant reproduction. Previous in vitro imaging of Lilium longiflorum and Nicotiana tabacum has shown that growing pollen tubes exhibit a tip-focused Ca(2+) concentration ([Ca(2+)]) gradient and regular oscillations of the cytosolic [Ca(2+)] ([Ca(2+)](cyt)) in the tip region. Whether this [Ca(2+)] gradient and/or [Ca(2+)](cyt) oscillations are present as the tube grows through the stigma (in vivo condition), however, is still not clear.