The Effects of Copper Supply and Shading on Retranslocation of Copper from Mature Wheat Leaves

Plants of Gamenya wheat (Triticum aestivum L.) were grown in pots of a Cu-deficient sand at two levels of Cu (deficient and sufficient), and harvested on days 13, 22, 28 and 38. In 50 per cent of the pots in each Cu treatment, the oldest leaf and leaf 2 of the main stem were shaded when they reached full expansion. The Cu content of the oldest leaf of Cu-sufficient, unshaded plants was high at day 13 and declined rapidly to day 38. That of Cu-deficient, unshaded plants was initially relatively low and declined much more slowly, so that at day 38 it resembled that of Cu-sufficient plants. Shading the oldest leaf accelerated the loss of its Cu in both Cu-deficient and Cu-sufficient plants. The effects of shading and of Cu supply on the loss of Cu from the oldest leaf paralleled their effects on the loss of N and chlorophyll. The results suggest that most of the Cu in the oldest leaf does not move out until the leaf senesces. In Cu-deficient plants retention of Cu by old green leaves accentuated Cu deficiency. The release of Cu, resulting from shading the old leaves of Cu-deficient plants, stimulated the growth of new leaves. In Cu-sufficient plants, shading depressed growth.