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

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Abstract
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-[3H]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-[3H]leucine was incorporated into protein in dark-grown leaves. In light, significantly higher proportions of the amino nitrogen content and of the L-[3H]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.

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