title: Calcium Channel Activity during Pollen Tube Growth and Reorientation.
abstract: We have shown previously that the inhibition of pollen tube growth and its subsequent reorientation in Agapanthus umbellatus are preceded by an increase in cytosolic free calcium ([Ca2+]c), suggesting a role for Ca2+ in signaling these processes. In this study, a novel procedure was used to measure Ca2+ channel activity in living pollen tubes subjected to various growth reorienting treatments (electrical fields and ionophoretic microinjection). The method involves adding extracellular Mn2+ to quench the fluorescence of intracellular Indo-1 at its ca2+-insensitive wavelength (isosbestic point). The spatial and temporal kinetics of Ca2+ channel activity correlated well with measurements of [Ca2+]c dynamics obtained by fluorescence ratio imaging of Indo-1. Tip-focused gradients in Ca2+ channel activity and [Ca2+]c were observed and quantified in growing pollen tubes and in swollen pollen tubes before reoriented growth. In nongrowing pollen tubes, Ca2+ channel activity was very low and [Ca2+]c gradients were absent. Measurements of membrane potential indicated that the growth reorienting treatments induced a depolarization of the plasma membrane, suggesting that voltage-gated Ca2+ channels might be activated.
authors.affiliation: Departamento de Biologia Vegetal, Faculdade de Ciencias de Lisboa, R. Ernesto de Vasconcelos, Bloco C2, 1700 Lisbon, Portugal.
authors.forename: R.
authors.initials: R
authors.lastname: Malho
authors.forename: N. D.
authors.initials: ND
authors.lastname: Read
authors.forename: A. J.
authors.initials: AJ
authors.lastname: Trewavas
authors.forename: M. S.
authors.initials: MS
authors.lastname: Pais