Developmental Alternatives Of Symbiotic Nostoc Punctiforme In Response To Its Plant Partner Anthoceros Punctatus

Abstract

In species of certain filamentous cyanobacterial genera of the orders Nostocales and Stigonematales, such as Nostoc, vegetative cells can mature in four developmental directions (Table 1). (i) The cells can divide upon reaching a critical size and perpetuate the vegetative growth cycle, (ii) The cells can divide uncoupled from biomass increase and DNA replication to form motile hormogonium filaments, (iii) Some, or all, cells can differentiate into perennating akinetes. (iv) A few cells (typically less than 10%) can differentiate into nitrogen-fixing heterocysts. Entry into a specific developmental state is initiated by environmental conditions that are presumed to be sensed by distinct signal cascade systems resulting in differential gene expression.