Calcium Channel Activity during Pollen Tube Growth and Reorientation

Area of Science:

• Plant reproductive biology
• Cellular signaling
• Ion channel biophysics

Background:

• Cytosolic free calcium ([Ca2+]c) increase precedes pollen tube growth inhibition and reorientation.
• Calcium (Ca2+) is implicated in signaling these crucial plant reproductive processes.

Purpose of the Study:

• To develop and apply a novel method for measuring Ca2+ channel activity in living pollen tubes.
• To investigate the spatial and temporal dynamics of Ca2+ channel activity during growth reorientation.

Main Methods:

• Utilized a novel technique involving extracellular Mn2+ to quench Indo-1 fluorescence at the isosbestic point.
• Measured Ca2+ channel activity in pollen tubes subjected to electrical fields and ionophoretic microinjection.
• Correlated Ca2+ channel activity with cytosolic free calcium ([Ca2+]c) dynamics using fluorescence ratio imaging.

Main Results:

• Observed and quantified tip-focused gradients in Ca2+ channel activity and [Ca2+]c in growing and reorienting pollen tubes.
• Found very low Ca2+ channel activity and absent [Ca2+]c gradients in non-growing pollen tubes.
• Demonstrated that growth reorienting treatments induce plasma membrane depolarization, suggesting voltage-gated Ca2+ channel activation.

Conclusions:

• Ca2+ influx through channels is critical for pollen tube growth reorientation.
• Spatial and temporal gradients of Ca2+ channel activity and [Ca2+]c are key regulatory mechanisms.
• Voltage-gated Ca2+ channels are likely involved in mediating the response to growth reorienting stimuli.