Role of cytosolic free calcium in the reorientation of pollen tube growth

Authors

  • Rui Malhó,

    1. Departamento de Biologia Vegetal, Faculdade de Ciéncias de Lisboa, R. Ernesto de Vasconcelos, Bloco C2, 1700 Lisboa, Portugal
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  • Nick D. Read,

    Corresponding author
    1. Molecular Signalling Group, Institute of Cell and Molecular Biology, University of Edinburgh, Rutherford Building, Edinburgh EH9 3JH, UK
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  • M. Salomé Pais,

    1. Departamento de Biologia Vegetal, Faculdade de Ciéncias de Lisboa, R. Ernesto de Vasconcelos, Bloco C2, 1700 Lisboa, Portugal
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  • Anthony J. Trewavas

    1. Molecular Signalling Group, Institute of Cell and Molecular Biology, University of Edinburgh, Rutherford Building, Edinburgh EH9 3JH, UK
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*For correspondence (fax + 44 31 6505392).

Summary

Growing pollen tubes of Agapanthus umbellatus exhibited a tip-to-base gradient in cytosolic free calcium ([Ca2+]c). Although this gradient is believed to be involved in pollen tube growth, its role in specifying reorientation is unknown. The direction of pollen tube growth could be modified by iontophoretic micro-injection, electrical fields (EFs) or photolysis of caged Ca2+. Iontophoretic injection resulted in a temporary cessation of growth, an increase in [Ca2+]c and, upon recovery, reoriented growth. Weak EFs also elevated [Ca2+]c, reduced growth rates and resulted in the reorientation of pollen tubes towards the cathode. Treatment with very low concentrations of the Ca2+-channel blocker lanthanum chloride, prior to exposure to an EF, inhibited both the increase in [Ca2+]c and reorientation whilst only slightly affecting growth rates. The responses of growth inhibition and reorientation were mimicked when [Ca2+]c was artificially elevated by photoactivating caged Ca2+ (Nitr-5). Our data suggest that [Ca2+]c is part of a transduction mechanism which enables growing pollen tubes to successfully reorient to directional signals in the style and thus accomplish eventual fertilization of the egg.

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