BERBARA, RICARDO1, HENRIQUE FONSECA2, MELVIN DAFT3 Universidade Federal Rural do Rio de Janeiro, Departamento de Solos, Seropedica, Itaguai, RJ, CEP 23851-970, Brazil. 2Universidade de Aveiro, Departamento de Biologia, 3800 Aveiro, Portugal. 3Biological Sciences Department, University of Dundee, Dundee, DD1 4HN, Scotland, UK. - The role of calcium in the germination and germinative hvphal growth of Gigaspora rosea Nicolson and Schenck. The role of lanthanum (calcium blocker), EGTA (calcium chelator) and TFP (calmodulin antagonist) on the spore germination; hyphal growth, branching and gravitropism of Gigaspora rosea Nicolson and Schenck were studied in media with and without calcium. Spore germination was influenced by EGTA and La, although in the former the effect was only significant at the highest level (32mM). Hyphal growth decreased with increasing levels of La, EGTA and TFP. Conversely, higher number of hyphal tips were observed at higher levels of these reagents. Increasing concentrations of La, EGTA and TFP caused mycelia to branch and lose gravitropism. It is proposed that calcium mobilisation within the fungi affect the morphogenesis G. rosea.