During sexual reproduction in flowering plants, cellular interactions guide the growth of the pollen tube from the stigma to the embryo sac where fertilisation occurs. The cytoplasmic Ca2+ concentration ([Ca2+]cyt) regulates pollen tube growth, but does it also regulate pollen tube guidance and reception? On p. , Seiji Takayama and colleagues investigate Ca2+ dynamics during fertilisation by expressing a Ca2+ sensor in Arabidopsis pollen tubes and synergid cells (cells in the ovule that guide the pollen tube). During semi-in vivo fertilisation, they report, pollen tubes turn towards wild-type ovules but not towards ovules in which pollen tube guidance has been genetically disrupted. Notably, [Ca2+]cyt is higher in turning pollen tube tips than in non-turning tips. Moreover, [Ca2+]cyt oscillation in the synergid cells, which reaches a maximum at pollen tube rupture, begins only upon pollen tube arrival. These results suggest that signals from the synergid cells induce Ca2+ oscillations in the pollen tube and vice versa, and that these oscillations are involved in pollen tube guidance and reception.
