Comparative Phloem Mobility of Nickel in Nonsenescent Plants

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Abstract
63Ni 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 ÷% 86Rb transported) for 63Ni in peas was 2.12 and in geranium 0.25. The value for the phloem mobile 86Rb was 1.00. By contrast, the comparative mobility of 45Ca, 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 63Ni 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.