3 - Origin, function and development of the spore wall in early land plants

Abstract

This chapter explores the current understanding of the origin of the spore wall, the function(s) of the spore wall in early land plants, and mode of spore wall formation in early land plants. The embryophytes are one of the major kingdoms of eukaryotice life. The sporopollenin wall surrounding charophycean zygotes and embryophyte spores/pollen grains is homologous, and the spore/pollen wall is an embryophyte synapomorphy that evolved as an adaptive response to the invasion of the land. It is considered that the primary function of the spore/pollen wall involves protection in the harsh subaerial environment. Regarding spore wall development, ultrastructural studies have demonstrated that structural elements present in the spore walls of extant plants can be recognized in the fossil spores of early land plants, suggesting that spore wall development was similar in extant and ancient land plants. Studies of molecular genetics of spore wall formation are in their infancy but have the potential to solve many unanswered questions regarding spore wall homologies and developmental processes—particularly when such studies are commenced on more “primitive” land plants and their extant sister group.