Effects of copper on the growth, photosynthesis and nutrient concentrations of Phaseolus plants

Abstract

Bean plants (Phaseolus vulgaris L. var. Zargana Kavala) were grown under conditions of increasing Cu concentrations in the growth medium (0.5-160.5 μM). Generally, the Cu concentrations between 0.5-1.5 μM were deficient, 1.5-10.5 μM were optimal, and 10.5-160.5 μM were toxic to plant growth. The Cu toxicity was associated with marked increases in plant tissue Cu concentrations. Under the Cu-deficient and optimal growth conditions, Cu was located primarily in the leaves. Under Cu toxicity, it was primarily sequestered in the roots. With increasing Cu in the growth medium, there was a positive correlation between Cu concentrations in the roots, stems and leaves, Ca in the roots, and K and Mg in the leaves. In contrast, Ca concentrations in the leaves and stems showed a negative correlation. The chlorophyll (Chl) concentration increased with increasing leaf Cu concentration, however, the Chl a/b ratio decreased. Since with an increasing leaf Cu concentration the leaf area decreased more markedly than the leaf dry mass, the net photosynthetic rate (P(N)) per leaf area increased and per dry mass decreased. The increase in P(N) per leaf area was almost entirely accounted for by the increase in Chl concentration. The initial Chl fluorescence (F0) increased with increasing leaf Cu concentration. The ratio of variable to maximum fluorescence (F(v)/F(m)) under Cu toxicity decreased. The half-time for the rise from F0 to F(m) (t(1/2)) remained relatively unchanged with increasing leaf Cu concentration. Therefore the Cu-stress caused a small decrease in the efficiency of photosystem 2 photochemistry, but its primary effect was on growth.