Localized Apical Increases of Cytosolic Free Calcium Control Pollen Tube Orientation

Area of Science:

• Plant Biology
• Cell Biology
• Biophysics

Background:

• Pollen tube growth requires precise directional changes to reach the ovule.
• Cytosolic free calcium ([Ca2+]c) influences pollen tube orientation, but its precise spatial role was unclear.

Purpose of the Study:

• To spatially resolve the role of calcium in directing pollen tube growth.
• To identify the specific domain within the pollen tube responsible for orienting growth.

Main Methods:

• Combined ion imaging, confocal microscopy, and localized photoactivation of caged calcium compounds (nitr-5, diazo-2).
• Manipulated [Ca2+]c in distinct pollen tube regions.
• Applied localized ionophore (A23187) and channel blocker (GdCl3) gradients.

Main Results:

• Asymmetric [Ca2+]c increases at the apex directed growth towards the stimulated side.
• Decreased [Ca2+]c promoted bending away from the affected region.
• Distal [Ca2+]c changes induced random reorientation, communicated via calcium waves.
• Localized apical [Ca2+]c manipulation precisely controlled growth direction.

Conclusions:

• Localized cytosolic free calcium ([Ca2+]c) changes in the pollen tube apex are the primary regulators of growth direction.
• Asymmetric calcium influx through tip channels likely drives directional growth.
• Distal calcium events can influence tip growth but require communication to the apex.