An interconnection between tip-focused Ca and anion homeostasis controls pollen tube growth.

Plant reproduction is the basis for economically relevant food production. It relies on pollen tube (PTs) growth into the female flower organs for successful fertilization. The high cytosolic Ca concentration ([Ca]) at the PT tip is sensed by Ca-dependent protein kinases (CPKs) that in turn activate R- and S-type anion channels to control polar growth.

Tip-localized Ca -permeable channels control pollen tube growth via kinase-dependent R- and S-type anion channel regulation.

Pollen tubes (PTs) are characterized by having tip-focused cytosolic calcium ion (Ca ) concentration ([Ca ] ) gradients, which are believed to control PT growth. However, the mechanisms by which the apical [Ca ] orchestrates PT growth are not well understood. Here, we aimed to identify these mechanisms by combining reverse genetics, cell biology, electrophysiology, and live-cell Ca and anion imaging.

Pollen tube NAD(P)H oxidases act as a speed control to dampen growth rate oscillations during polarized cell growth.

Reactive oxygen species (ROS) produced by NAD(P)H oxidases play a central role in plant stress responses and development. To better understand the function of NAD(P)H oxidases in plant development, we characterized the Arabidopsis thaliana NAD(P)H oxidases RBOHH and RBOHJ. Both proteins were specifically expressed in pollen and dynamically targeted to distinct and overlapping plasma membrane domains at the pollen tube tip.

Pollen tube growth regulation by free anions depends on the interaction between the anion channel SLAH3 and calcium-dependent protein kinases CPK2 and CPK20.

Apical growth in pollen tubes (PTs) is associated with the presence of tip-focused ion gradients and fluxes, implying polar localization or regulation of the underlying transporters. The molecular identity and regulation of anion transporters in PTs is unknown. Here we report a negative gradient of cytosolic anion concentration focused on the tip, in negative correlation with the cytosolic Ca(2+) concentration.