Effect of increasing zinc levels on Trigonella foenum-graecum growth and photosynthesis activity

Zinc is an indispensable element for the plant growth and the cellular metabolism. However, this mineral element becomes harmful athigh quantities. The effects of high zinc supply on different physiological parameters were investigated in fenugreek. Seedlings were grown in plastic pots filled with inert sand under five ZnSO4 treatments (C: control :1.5 μM Zn; 1mM, 2 mM, 3 mM and 4 mM ZnSO4). Results showed a decrease of 56% to 75% in shoot dry weight and a decrease of 65% to 90% in roots dry weight, relatively to the control. In addition we showed a significant reduction in photosynthetic parameters, with the highest value of CO2 assimilation under 1 mM Zn (3.3 μmol CO2, m-2·s-1) and a lower value under 4 mM Zn (0.5 μmol CO2, m-2·s-1). The concentration of zinc in plant shoot was around two folds the control under 1, 2 and 3 mM Zn and about four folds under the maximal concentration, 4 mM Zn. In roots, we showed a progressive increase of zinc content. Increasing zinc concentration induced a significant decrease of phosphorus concentration in shoot. Fenugreek was mainly affected by zinc excess greater than 1 mM ZnSO4, however at the highest concentration, fenugreek plants exhibited different adaptation strategies