The Movement of Zinc through Excised Stems of Seedlings of Pinus radiata D. Don.

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Abstract
Radioactive Zn solns were drawn through 10 cm stem sections excised from seedlings of P. radiata to determine the location and quantity of 65Zn remaining in the stems and the concn of 65Zn in the exudate. Zinc was removed from solns passing through the excised stems by processes which appeared to be non-metabolic because cooling the inflow solns did not decrease the proportion of Zn removed and non-specific because Ca competed with Zn for ‘exchange sites’. The formation of anionic or uncharged complexes between Zn and EDTA, or citrate resulted in more Zn passing through the excised stems. Consistent with the greater stability of Zn-EDTA complexes more Zn passed through stems treated with EDTA than with citrate. Decreasing the pH of solns containing Zn, Ca and potassium citrate increased the amount of Zn deposited in the basal (inflow) end of the stems, probably by decreasing the amount of Zn bound to citrate. Increasing the conen of Zn in test solns containing Zn, Ca and potassium citrate did not change the distribution of 65Zn in the stems as the capacity of the stems to remove Zn from soln was large enough to remove all the free Zn in all the solns

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