| Heavy metals Al, Cd and Hg pollution seriously influence plants growth and development. The influence on the growth and DNA damage of two different seedling stages (2-day-old and 12-day-old seedlings) of the main field crop wheat (Triticum aestivum cv. Xiaoyan No.22) exposed to different concentrations of A13+ (from 0.1 to 50mmol.L-1) , Cd2+ (from 0.05 to 10mmol.L-1) and Hg2+ (from 0.001 to 1.0mmol.L-1) was investigated using electrophoresis gel et al methods. We studied the influence on the wheat growth by mensurating different parameters, such as the growth amount of the seedling and roots, the increscent amount of roots number, the fresh, dry weight of the above-ground part and roots. The damage to wheat treated with A13+, Cd2+ and Hg2+ by using the extractible amount of DNA of leafs and roots, hyperchromic effect and electrophoresis gel method was studied. Meanwhile, we preliminarily discussed the damage mechanisms of A13+, Cd2+ and Hg2+ in plants, and hope to establish academic groundwork of further studies of heavy metals damage mechanism in plants. The main conclusions of investigation as follows:1.Al3+, Cd2+and Hg2+ have obviously toxic effects on 2-day-old and 12-day-old seedling wheats. They can prominently decrease the seedlings root length, root number, the fresh weight, dry weight of the overground part and roots and inhibit the increasement of the seedlings height. They can lead to DNA damage of leafs and roots (including the decreasement of the extractible DNA amount, inducing DNA interchain crosslinking and DNA fragmentation). DNA damage is earlier a little than the growth inhibition in seedlings, which may be the indirect factor of seedlings growth inhibition.2. When exposed to the same ion concentration and same time of exposure, the sequence of toxic effect on wheat seedlings treated with heavy metals is Cd2+> Hg2+ >A13+, and the roots are harmed more seriously than leafs, which probably relates to roots direct contacts with ions. After exposure Id in no less than 1.0mmol.L-1Cd2+, 10mmol.L-1 A13+and 2d in no less than 1.0mmol.L-1 Hg2+, seedlings leafs increasingly show apochlorotic, and the whole plant inclines to senescence.3. The inductive effects of apoptosis in the leafs and roots of two-seedling-stage wheats exposed to different A13+, Cd2+ and Hg2+ concentrations and times of exposureare different. Exposure 2d to 0.1 and 1.0mmol.L~1Al3+, 3d to 0.05mmol.L-1Cd2+ and 0.1m mol.L-1Hg2+ all can induce apoptosis of 2-day-old-seedling leafs. Exposure 3d to 0.001 and 0.01mmol.L~1Hg2+, 2d to 0.1mmol.L~1Cd2+ can induce apoptosis of 2-day-old-seedling roots, DNA ladder can be obviously observed on electrophoresis map. Exposure to 0.1, 1.0mmol.L-1Al3+, 0.05, 0.1mmol.L-1Cd2+ and 0.001, 0.01 and 0.1mmol.L-1Hg2+ probably can enhance apoptosis of the 12-day-old-seedling roots. The further increasment of inos concentrations can induce DNA fragmentation of leafs and roots, DNA become smear bands in agarose gel.4.The reactions of two-seedling-stage wheats treated with heavy metals are obviously different, the 2-day-old seedling is more sensitive to heavy metals than the 12-day-old seedling. Exposure 2d to no less than 0.1mmol.L~1Hg2+, LOmmol.L-1Al3+ and 0.05mmol.L-1Cd2+ can prominently inhibit the 2-day-old-seedling growth. And 1d treatment with no less than 0.001mmol-L"1Hg2+, 0.1mmol-L~1Al3+ and 0.05mmol.L-1 Cd2+ can lead to serious DNA damage of leafs and roots of it including the decre-asement of DNA extractible amount (that is DNA and proteins crosslinking) and inducing DNA interchain crosslinking. As to 1 2-day-old-seedling, exposure 2d and 3d to no less than 1.0mmol.L-1Al3+, 1d to 0.1mmol.L-1Hg2+ and 0.1mmol.L-1 Cd2+ can obviously inhibit its growth. And exposure 1d to no less than 0.1mmol.L-1 A13+, 0.05m mol.L~1Cd2+ and 0.01mmol.L-1Hg2+ can prominently decrease the amount of extractible DNA, and 2d to no less than 0.1mmol.L-1Hg2+, 3d to 0.05m mol.L-1Cd2+, and to 10mmol.L-1Al3+ can lead to DNA interchain crosslinking of leafs and roots of it.5. The toxic effects on wheat exposed to th...
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