The effects of copper and nitrogen supply on the retranslocation of copper in four cultivars of wheat

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Abstract
The retranslocation of copper and nitrogen was studied in four cultivars of wheat grown in pots of a copper-deficient sand from Lancelin, W.A. Plants were grown at two levels of nitrogen and three levels of copper, and harvested three times during growth and at maturity. Plants grown at low copper were severely copper-deficient and yielded no grain. At low nitrogen, plants at marginal copper gave similar grain yields to plants at high copper. Application of high nitrogen at marginal copper either had little effect or depressed grain yield. Application of high nitrogen at high copper gave a strong positive interaction producing maximal grain yield in each cultivar. Low copper supply delayed yellowing and the decline in copper and nitrogen content of the oldest leaf of each cultivar. Application of high nitrogen further delayed yellowing of the oldest leaf and loss of its copper and nitrogen. Probably the copper content of the oldest leaf does not decline until the leaf begins to senesce. Senesced leaves retain low concentrations of copper and nitrogen. It is suggested that at marginal copper, copper retention by senesced vegetation limits the retranslocation of copper from vegetation to grain. Susceptibility to copper deficiency differed markedly with stage of growth and with cultivar. At marginal copper and high nitrogen, copper deficiency almost eliminated the grain yield of Argentine IX, but had relatively small effects on Gamenya, Olympic, and Petit Rojo. The higher susceptibility of grain production in Argentine IX to copper deficiency was not related to its copper content in whole tops or to its grain protein concentration. The susceptibility may have resulted from the ability of this cultivar to form large numbers of tillers which competed with the developing grain for retranslocated copper.