Rapid spatiotemporal patterning of cytosolic Ca2+ underlies flagellar excision in Chlamydomonas reinhardtii

Abstract

Ca2+-dependent signalling processes are implicated in many aspects of flagella function in the green alga, Chlamydomonas. In this study, we examine the spatiotemporal dynamics of cytosolic Ca2+ ([Ca2+]cyt) in single Chlamydomonas cells during the process of flagellar excision, using biolistically loaded calcium-responsive dyes. Acid-induced deflagellation occurred in parallel with a single transient elevation in whole-cell [Ca2+]cyt, which was absent in the acid deflagellation-deficient adf1 mutant. Deflagellation could also be induced by elevated external Ca2+ ([Ca2+]ext), which promoted very rapid spiking of [Ca2+]cyt across the whole cell and in the flagella. We also detected very rapid apically localised Ca2+ signalling events with an approximate duration of 500 msec. Ninety-seven per cent of deflagellation events coincided with a rapid elevation in [Ca2+]cyt in the apical region of the cell, either in the form of a whole cell or an apically localised increase, indicating that [Ca2+]cyt elevations in the apical region play an underlying role in deflagellation. Our data indicate that elevated [Ca2+]ext acts to disrupt Ca2+ homeostasis which induces deflagellation by both Adf1-dependent and Adf1-independent mechanisms. Elevated [Ca2+]ext also results in further [Ca2+]cyt elevations after the main period of whole cell spiking which are very strongly associated with deflagellation, exhibit a high degree of apical localisation and are largely absent in the adf1 mutant. We propose that these later elevations may act as specific signals for deflagellation.

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