Aspects of the growth and development of the sporangiophore of phycomyces blakesleeanus

Abstract

Chapter I of this study deals with the distribution of cellular components and growth during the differentiation and morphogenesis of the reproductive structure, sporangiophore, of Phycomyces blakesleeanus. A non-uniform distribution of nuclei, mitochondria, nucleic acids, protein and cell wall components throughout the sporangiophore of stage I was found. The above result gave an understanding of (i) the organization of the cytoplasm in the growing region of the sporangiophore (with especial emphasis on the apical region); (ii) the possible importance of a balance between polymer synthesis and hydrolysis in growth regions; (iii) the probable location of wall synthesizing and lysing enzymes. In Chapter II of this investigation, the isolation and development of protoplasts is described. A different capacity for wall production and development from proto plasts released from different region of sporangiophore is described. Protoplasts from the tip region were found to have a great concentration of nucleic acids and protein and also a greater activity in wall production. A correlation between the regeneration of protoplasts and the integrity of the membrane in wall morphogenesis in general is described. In Chapter III the biochemical observation of the distribution and recovery of RNA species and ribosomes during growth and development of the sporangiophore is presented. Isolations and characterizations are described,, The non-uniform distribution of macromolecules was found to be associated with greater recovery of RNA and ribosomal polymers The maintenance of the apical growth was seen to be associated with the location of greater quantities of rRNA, ribosomes and also appeared to be dependent on the existence of preformed mRNA Abnormal production of wall substances was found to be associated with the breakdown of the rRNA and ribosomes fractions. Conclusions reached from this work are that the sub apical region of the sporangiophore contains the necessary components to maintain a high synthetic capacity for proteins and cell wall precursors. This non-uniform distribution of metabolism appeared to be maintained at the expense of other regions; it may well also provide the basis f o r the polar properties and the general behaviour summed up by the term 'apical dominance'.