Abstract
Apical growth of tobacco pollen tubes is not uniform but exhibits regular growth rate fluctuations with a typical period of 45 seconds. In tobacco, as in lily, calcium signals at the tip show similar periodicity to growth rate, show by the Cameleon calcium reporter (Watahiki et al., 2004). To investigate how this calcium signal might be mediated, a calmodulin domain protein kinase (CDPK or CPK) was isolated from Nicotiana plumbaginifolia. NpCPK17 cDNA was fused with CFP and expressed in growing tubes. Based upon fluorescence Imaging and cell fractionation analysis, pollen NpCPK17 was found to be associated with the plasma membrane and tip-localised vesicle clouds. NpCPK17 possesses myristolylation sites essential for membrane localisation. Distribution of NpCPK17-CFP at the pollen tube tip changed dynamically with a similar frequency to growth fluctuation. These results suggest a mechanism for a possible feedback loop between phosphorylation and tip growth.
