We have seen in the previous chapter that planar growth of the protonema in blue light is due to a change in the orientation of the plane of division of the terminal cell from transverse to oblique or longitudinal. This response to blue light may be the microscopically visible manifestation of a sequence of complex biochemical processes in the cell subsequent to the photochemical reaction. These processes are initiated by the transcription of a particular set of polysomal mRNA which moves into the cytoplasm to direct the synthesis of new proteins. The general view is that the pattern of nucleic acid and protein synthesis in the protonema might provide the operational criterion for gene transcription during planar growth. We will use this as a frame of reference for discussion in this chapter on the reprogramming of the cellular machinery of the gametophyte during photomorphogenesis. The approach chosen here is to introduce the various facets of earlier investigations and to focus on those concepts which have received renewed experimental attention in recent years. This subject is also considered in the reviews of Miller (1968a), DeMaggio and Raghavan (1973), and Raghavan (1974c).

Protein synthesis

A change in the rate synthesis of enzymatic, regulatory and structural proteins is the basic attribute of an organism embarking on a specific mode of growth.