Effects of Cd on photosynthesis and growth of safflower (Carthamus tinctorius L.) genotypes

Abstract

Heavy metals such as cadmium (Cd) may affect different physiological functions in plants. We carried out a hydroponic experiment under greenhouse conditions in order to evaluate the effect of Cd on photosynthetic and physiological parameters of safflower. The responses of six safflower genotypes (Nebraska-10, 2811, Kouseh, S149, C111, and K12) to four concentrations of CdCl2 (0, 1.5, 3, and 4.5 mg L−1) were examined. Mean shoot and root dry masses of safflower plants were reduced by nearly 57% after the treatment by 4.5 mg(CdCl2) L−1. Contrary to the mean proline content, which increased by 121%, the mean total leaf area per plant, net photosynthetic rate, stomatal conductance to the CO2, leaf chlorophyll a, b, and (a+b), carotenoid content, and quantum efficiency of PSII decreased by 84.4, 50.5, 50.0, 31.6, 32.2, 31.8, 32.9, and 11.2%, respectively, at the presence of 4.5 mg(CdCl2) L−1. The mean Cd concentration in shoots and roots of safflower genotypes exhibited 52- and 157-fold increase, respectively, due to the addition of 4.5 mg(CdCl2) L−1 to the growing media. The mean malondialdehyde content was enhanced by 110% with the increasing CdCl2 concentration, indicating the occurrence of a considerable lipid peroxidation in the plant tissues. Even though the membrane stability index was adversely affected by the application of 1.5 mg(CdCl2) L−1, the decrease ranged from 45 to 62% when plants were treated with 4.5 mg(CdCl2) L−1. Genotype Nebraska-10 seemed to be different from the remaining genotypes in response to the 4.5 mg(CdCl2) L−1; its net photosynthetic rate tended to be the greatest and the Cd concentration in shoots and roots was the lowest among genotypes studied. This study proved Cd-induced decline in growth, photosynthesis, and physiological functions of safflower.