Participation of actin filaments, myosin and phosphatidylinositol 3-kinase in the formation and polarisation of tetraspore germ tube of Gelidium floridanum (Rhodophyta, Florideophyceae).

Abstract

This study aimed to examine the evidence of direct interaction among actin, myosin and phosphatidylinositol 3-kinase (PI3K) in the polarisation and formation of the tetraspore germ tube of Gelidium floridanum. After release, tetraspores were exposed to cytochalasin B, latrunculin B, LY294002 and BDM for a period of 6h. In control samples, formation of the germ tube occurred after the experimental period, with cellulose formation and elongated chloroplasts moving through the tube region in the presence of F-actin. In the presence of cytochalasin B, an inhibitor of F-actin, latrunculin B, an inhibitor of G-actin, and BDM, a myosin inhibitor, tetraspores showed no formation of the germ tube or cellulose. Spherical-shaped chloroplasts were observed in the central region with a few F-actin filaments in the periphery of the cytoplasm. Tetraspores treated with LY294002, a PI3K inhibitor, showed no formation of the tube at the highest concentrations. Polarisation of cytoplasmic contents did not occur, only cellulose formation. It was concluded that F-actin directs the cell wall components and contributes to the maintenance of chloroplast shape and elongation during germ tube formation. PI3K plays a fundamental role in signalling for the asymmetric polarisation of F-actin. Thus, F-actin regulates the polarisation and germination processes of tetraspores of G.floridanum.