Vegetative nuclear positioning is required for calcium and ROS signaling in Arabidopsis pollen tubes

Efficient transport and delivery of sperm cells (SCs) is vital for angiosperm plant fertility. In , SCs are transported through the growing pollen tube by a connection with the vegetative nucleus (VN). During pollen tube growth, the VN leads the way and maintains a fixed distance from the pollen tube tip, while the SCs lag behind the VN. Upon reception at the ovule, the pollen tube bursts and the SCs are released for fertilization. In pollen tubes of Arabidopsis mutants and , deficient in the outer nuclear membrane component of a plant LINC complex, the SCs precede the VN and the VN falls behind. Subsequently, pollen tubes frequently fail to burst upon reception. In this study, we sought to determine if the pollen tube reception defect observed in and is due to decreased sensitivity to reactive oxygen species (ROS). Here we show that and are hyposensitive to exogenous HO, and that this hyposensitivity is correlated with decreased proximity of the VN to the pollen tube tip. Additionally, we report the first instance of nuclear Ca spikes in growing pollen tubes, which are disrupted in the mutant. In the mutant, nuclear Ca spikes are reduced in response to exogenous ROS, but these spikes are not correlated with pollen tube burst. This study finds that VN proximity to the pollen tube tip is required for both response to exogenous ROS, as well as internal nuclear Ca fluctuations.