Comparative analysis of the action of cytokinin and light on the growth of rye leaves.

In etiolated rye seedlings (Secale cereale L.) the cytokinin supply controls leaf growth. Dry weight and total amino-nitrogen, protein, total nucleic acid, DNA, and rRNA levels were similarly lowered in leaves depleted of their endogenous cytokinin supply by early excision of the seedling roots and increased by 70-100% after the addition of kinetin. The proportion of cytoplasmic ribosomes bound as polyribosomes was only slightly increased from 40% in cytokinin-deficient to 50% in kinetin-treated darkgrown leaves. White light increased the polyribosome proportion to 61%. In cytokinin-supplied leaves uptake and accumulation of L-[(3)H]leucine were greater than in cytokinin-deficient leaves. Under all conditions of cytokinin supply the same proportion of the total amino nitrogen content (80%) was present as protein nitrogen and virtually, the same percentage (60%) of the total uptake of L-[(3)H]leucine was incorporated into protein in dark-grown leaves. In light, significantly higher proportions of the amino nitrogen content and of the L-[(3)H]leucine uptake were incorporated into protein. The results suggest that the accumulation of substrate is a main cytokinin-controlled step determining the growth of the leaves.