Some ultrastructural and physiological studies of Phycomyces Sporangiophores

Abstract

Although the Phycomyces sporangiophore has been the object of numerous physiological investigations little is known of its ultrastructure or of the changes that occur within it during growth and development. This is partly due to the failure of some workers to obtain satisfactory fixation of the sporangiophore for ultrastructural investigations. Investigations were made for suitable fixation procedures which might help to elucidate the fine structure of the sporangiophore during growth and development. Using the fixation procedures developed, long microfilaments lying almost parallel to the long axis of the sporangiophore and closely associated with mitochondria were revealed. These microfilaments probably determine the path along which the mitochondria move and may account for the multistriate streaming of organelles as seen in the phase contrast microscope. Investigations for a discrete gravity receptor proved negative but did reveal an upward displacement of the large central vacuole concurrent with the development of a geotropic curvature. I was not able to find any organelle which might function as a photoreceptor. The ultrastructural changes occurring during the development of the sporangium and germination of the spores are described.