Comparative Phloem mobility of nickel in nonsenescent plants.

(63)Ni was applied to nonsenescent source leaves and found to be transported to sink tissues in pea (Pisum sativum L.) and geranium plants (Pelargonium zonale L.). The comparative mobilities (percent tracer transported out of source leaf /% (86)Rb transported) for (63)Ni in peas was 2.12 and in geranium 0.25. The value for the phloem mobile (86)Rb was 1.00. By contrast, the comparative mobility of (45)Ca, which is relatively immobile in the phloem, was low (0.05 in peas, 0.00 in geranium). Interruption of the phloem pathway between source and sink leaves by steam girdling almost completely inhibited (63)Ni accumulation in the sink leaves of both species. We conclude that Ni is transported from nonsenescent source leaves to sink tissues via the phloem of leguminous and nonleguminous plants.