Effect of exogenous iron on photosynthesis, quality, and
accumulation of cadmium in different varieties of tomato

【Objectives】In soils simulated with cadmium (Cd) pollution, different levels of exogenous Fe were added and their influences on the chemical forms of cadmium (Cd)and the Cd accumulation in tomato were studied to provide a theoretical base for tomato safe production.【Methods】 Pot experiments were carried out to investigate the influence of different iron levels(0,200 and 400 μmol/L, FeSO4·7H2O) on the plant growth,the activities of antioxidant enzymes,the accumulation and chemical forms of cadmium(Cd)in tomato when exposed to Cd(10 mg/kg). 【Results】 The exogenous Fe increased the dry weights of roots, stems, leaves, fruits as well as the total dry matter, which increased by 20.4%-48.6%,13.3%-56.0%, 16.0%-63.1%, 9.8%-16.5% and 21.6%-40.3% respectively. The dry weights of plant parts and whole plant were increased first, and then decreased with increasing of Fe levels. Comparing the two tested tomato cultivars, ‘4641’ had stronger resistance to Cd, ‘Yufen 109’ was more sensitive to Fe. The Pn, Gs and Tr values in tomato leaves of both the cultivars were high with moderate Fe (200 μmol/L) application, and low with excess Fe (400 μmol/L); compared to the control, the Pn, Gs and Tr of ‘4641’ were increased by 8%, 11% and 2.9% and these of ‘Yufen 109’ were increased by 28.7%, 15.5% and 18.8%, while concentration of intercellular carbon dioxide (Ci) decreased with the application of Fe. Both photosynthesis and transpiration of ‘4641’ were stronger than those of ‘Yufen 109’. The contents of nitrate in fruits of both the cultivars and sugar in ‘Yufen 109’ increased after Fe application, while amino acid in ‘Yufen 109’decreased compared to the control, and the increase of nitrate 18.1%-22.2% and2.3%-22.0%. In addition, high Fe application (400 μmol/L) facilitated the biological synthesis of Vc in fruit increased by 8.2% and 13.2%. Cadmium was mainly existed in the fractions of residual Cd and hydrochloric acid-extractable Cd in fruits, which were low activity form and accounting for 70.8% of the total. Deionized water extractable Cd (FW) and ethanol extractable Cd (FE) were high activity form with only 11.8% of the total Cd. Toxic effects of Cd on Tomato were effectively inhibited by spraying Fe. Foliar application of different levels of Fe reduced the concentrations of all Cd forms compared to the control. Cadmium was mostly accumulated in leaves and stems with the concentrations of Cd in the order of leaves toots stem fruits with foliar Fe. Spraying Fe could reduce the concentration of Cd in tomato leaves, roots, stems and fruits with a ranges of 7.1%-21.9%, 35.6%-50.4%, 13.0%-37.0% and 2.8%-8.2%, respectively. Cadmium concentrations of all plants parts decreased with foliar Fe application compared to the control, while displayed an upward trend when excessive Fe applied. The Cd accumulation of leaves, stems and fruits and total accumulation of ‘4641’ were higher than those of ‘Yufen 109’. It showed that planting ‘4641’ in Cd contaminated soil had greater risk. 【Conclusions】 Appropriate Fe could promote photosynthesis and transpiration of the tomato leaves and increase the dry weights of each part of the tomato plants. Toxic effects of Cd on tomato plants and the concentration of Cd in each part could be decreased by applying the appropriate concentration of Fe.