Effect of copper on growth in cucumber plants (Cucumis sativus) and its relationships with carbohydrate accumulation and changes in ion contents

Twenty-day-old cucumber plants were Submitted to copper stress during 5 days. Leaf expansion rather than dry weight accumulation was the first target of copper inhibition. Despite of a higher copper accumulation in the second leaf (SL) rather than in the first (FL), photosynthesis decrease was more pronounced in the latter. Since leaf expansion declined, leaves became a weak sink and this might account for the observed accumulation of carbohydrates in leaves. This accumulation could induce a feedback inhibition of photosynthesis. The significant accumulation of starch and sucrose did not occur in roots and seemed to be confined to leaves. Copper was sequestered primarily in the roots. The ion distribution (calcium, potassium and magnesium) between roots and leaves of cucumber plants suggested that the uptake and the upward translocation of these ions Could be altered by copper excess. The decrease in potassium content may have played a crucial role in the inhibition of leaf expansion. Moreover, in leaves, the observed decline of magnesium content could contribute to the reduction in net assimilation rate and to the accumulation of assimilates in leaves. (C) 2004 Elsevier Ireland Ltd. All rights reserved.