Studies On The Injurious Mechanisms Of CD～(2+) And ZN～(2+) Stress On Tomato

In this paper, a solution culture experiment was carried out to study the injurious mechanisms of Cd~2+ and Zn~2+ stress on tomato (Lycopersicom esculentum, Mill.). The results showed as follows:Cd~2+ and Zn~2+ affected germination of tomato seedings. Low concentration promoted sprouting potential. Cd~2+ and Zn~2+ ( 2.0 mmol/L ) remarkably inhibited the sprouting potential, sprouting ratio and the root elongation. The inhibition was in the order of root elongation > sprouting potential > sprouting ratio.Cd~2+( 0.001 mmol/L ~ 0.1 mmol/L) and Zn~2+ ( 0.01 mmol/L ~ 1.0 mmol/L) could inhibit plant height and biomass accumulation and decrease the value of Chlorophyll a, Chlorophyll b, Chlorophyll a+b and Chlorophyll a/b of leaves. Under high concentration, leaves expressed sap green, other indicators increased, instead, except chlorophyll a/b ratio, but remained lower than the control. The chlorophylla fluorescence parameters of tomato leaf were changed obviously under Cd~2+ and Zn~2+ stress. With the increase in concentration of Cd~2+ and Zn~2+, the ratio of the variable to maximal fluorescence (Fv/Fm) decreased, which was notable relativity with concentration.Malondialdehyde (MDA) content in roots and leases was enhanced. The activities of Superoxide dismutase (SOD, EC 1.15.1.1), Peroxidase (POD, EC 1.11.1.7), Ascorbate peroxidase (APX, EC 1.11.1.11) and Catalase (CAT, EC 1.11.1.6) were induced to rise. The activities of enzymes changed obviously under high concentration. The activities of SOD and CAT in leaves were higher than that in roots. But the activity of POD was contrary, and the change of POD in leaves was higher than that of SOD, APX and CAT. The increased activities of enzymes played an important role in resistingCd~2+ and Zn~2+ toxicity on tomato seedlings. Unenzymatic antioxidant such as GSH content increased, and content in leaves was higher than that in roots.With the increase in concentration of heavy metal, soluble protein synthesize in leaves and roots was inhibited, and the content decreased. The content in leaves was higher than that in roots, and was even more inhibited obviously. The water content of stems and leaves of tomato declined significantly under high concentrations stress (Cd ~2+ and Zn~2+ concentrations in nutrient solution were respectively 0.1 mmol/L and 1.0 mmol/L). With increasing of Cd~2+ and Zn~2+ concentrations, contents of proline and GSH increased, but soluble sugar content increased when Cd~2+ concentration was 0.1 mmol/L and Zn~2+ concentrations were 0.1 mmol/L and 1.0 mmol/L. According to the results of the experiment, the author discussed the role of soluble sugar, proline and GSH in roots and leaves of tomato seedlings under Cd~2+ and Zn~2+ stress.The dynamic change of ascorbate-glutathione (ASA-GSH) cycle metabolism in roots and leaves of tomato seedlings under 0.05mmol/L Cd~2+ stress and recovery was studied. Under stress malonaldehyde (MDA) content in roots and leaves increased, ascorbate peroxidase activity rose at the begining of three days and then decreased, glutathione reductase (GR, EC ;1.6.4.2) activity decreased on the first day and then increased, the content of ascrobate (AsA) and glutathione (GSH) increased and the increase in roots was higher than that of leaves. After recovery the MDA content in leaves declined to the control level, while the MDA content in roots duratively increased. The activities of APX and GR and the content of AsA and GSH could recover, which were higher than control. GSH contents in roots duratively maintain high level. There were defferences between the resumptive extent of parameters of leaves and roots. According to the results of the experiment, the author discussed the role of AsA-GSH cycle metabolization during the stressed and resuming period.Cd~2+, Zn~2+ could affect tomato quality. With the increase in concentration of heavy metal, the content of solubility solid matter, vitamin c, and soluble sugar changed unobviously, but expressed drop in the mass. On the contrary, organic acid increased and difference between treatments were...