Phytochrome in etiolated annual rye : II. Distribution of photoreversible phytochrome in the coleoptile and primary leaf.

Phytochrome per fresh weight in the apical 0.5 cm of the 1.5-cm coleoptile was twice that in the basal 0.5 cm; phytochrome per dry weight and phytochrome per DNA did not vary significantly from the base to the apex. Ratios of phytochrome to fresh or dry weight in the 6-cm coleoptile were nearly constant in the basal 5 cm, but increased in the two apical 0.5-cm sections. Phytochrome per DNA in the 6-cm coleoptile did not vary significantly in the apical 4 cm, but decreased by one-half in the basal 2 cm.In the 5-cm first leaf, phytochrome per fresh or dry weight was greatest in the basal 0.5 cm (zone of cell division). Phytochrome per DNA in the leaf decreased from apex to base; the phytochrome per DNA in the basal 0.5 cm (zone of cell division) was one-third as high as in the apical 0.5 cm.Pytochrome per cell was greater in all parts of the 6-cm coleoptile compared to the 1.5-cm coleoptile, although no cell division had occurred during this elongation. Phytochrome per cell was higher in the sections of the first leaf wihch were growing primarily by cell expansion rather than by cell division. Phytochrome expressed per unit dry weight was more constant than any of the other parameters studied.It was concluded (1) that the phytochrome content of all coleoptile cells is the same at any given age (length); (2) that the phytochrome content of all nondividing leaf cells is equal at any given age (but lower than that of coleoptile cells); (3) that the phytochrome content of all cells increases in direct proportion to their expansion (increase in dry weight).