EFFECTS OF COPPER ON THE GROWTH, PHOTOSYNTHESIS AND NUTRIENT CONCENTRATIONS OF PHASEOLUS PLANTS

Bean plants (Phaseolus vulgaris L. var. Zargana Kavala) were grown und er conditions of increasing Cu concentrations in the growth medium (0. 5-160.5 mu M). Generally, the Cu concentrations between 0.5-1.5 mu M w ere deficient, 1.5-10.5 mu M were optimal, and 10.5-160.5 mu M were to xic to plant growth. The Cu toxicity was associated with marked increa ses in plant tissue Cu concentrations. Under the Cu-deficient and opti mal growth conditions, Cu was located primarily in the leaves. Under C u 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) concentrat ion increased with increasing leaf Cu concentration, however, the Chl a/b ratio decreased. Since with an increasing leaf Cu concentration th e leaf area decreased more markedly than the leaf dry mass, the net ph otosynthetic rate (P-N) per leaf area increased and per dry mass decre ased. The increase in P-N per leaf area was almost entirely accounted for by the increase in Chl concentration. The initial Chl fluorescence (F-0) increased with increasing leaf Cu concentration. The ratio of v ariable to maximum fluorescence (F-v/F-m) under Cu toxicity decreased. The half-time for the rise from F-0 to F-m (t(1/2)) remained relative ly unchanged with increasing leaf Cu concentration. Therefore the Cu-s tress caused a small decrease in the efficiency of photosystem 2 photo chemistry, but its primary effect was on growth.