The ions of Pb²⁺, Cu²⁺ are two important environmental pollutants. Pb²⁺ is without biological functions but, once entering into the field, reduces the fertility, inhibits crops root growth, hinders physiological metabolism, damages the nucleolar structure and reduced the fidelity of DNA synthesis. Cu²⁺ is essential element; however, large Cu²⁺ accumulation in crops causes genotoxicity or even crop mortality. This study examined the growth, DNA damage, uptake and accumulation of Pb²⁺ and Cu²⁺ among four genotypes of foxtail millet (Setaria italica(L.)Beauv) seedlings from Shanxi, China using a pot culturing. The foxtail millet seeds were cultured in incubators at 26℃ for germination with no light, then planted in the pots spiked with four different concentration,namely 50, 100, 200, 400(mg/kg of each kind of metal ions), respectively. The growth of roots and shoots, biomass, chlorophyll content, soluble protein content, DNA content, DNA hyperchromicity and the uptake and accumulation were studied after a growing period of 30 days.
The result showed that the average of Pb²⁺ tolerance indexes of D2-8, An 06, Huangmi, Zhaogu were 0.87, 0.81, 0.78 and 0.71, while those of Cu²⁺ were 0.96, 0.97, 0.79 and 0.74 respectively. In the photosynthetic pigment test, the total content of chlorophyll a and b of D2-8, An 06, Huangmi, Zhaogu exposed to 400 mg/kg Pb²⁺ were 33.3%, 52.6%, 37.5%, 49.4% as compared with the control group; while those were 113.5%, 72.3%, 51.9%, 75.6% as compared with control in Cu²⁺ (400 mg/kg) treatment. And the chlorophyll a/b values in foxtail millet of four genotypes were all higher than that of the control group. The content of DNA and the soluble protein decreased with the increasing of Pb²⁺ concentration, showing Cu²⁺ stimulated the DNA and soluble protein synthesis at low concentrations (less than 100 mg/kg), but inhibited at high concentrations (more than 200 mg/kg), respectively. DNA hyperchromicity indicates the disruption of the DNA primary structure, with the trend of initial increased followed by decline in all four foxtail millet seedlings in response to the rising Pb²⁺ and Cu²⁺ concentrations. In addition, the DNA hyperchromicity of Zhaogu and D2-8 were significantly affected by Pb²⁺, so were Zhaogu and Huangmi affected by Cu²⁺. The uptake and accumulation of Pb²⁺ or Cu²⁺ ranks (from high to low): D2-8, zhaogu, An 06, Huangmi. The transportation ability of D2-8 and An 06 from roots to stems and leaves was much better than that of Zhaogu and Huangmi. From the effects on the growth indexes and physiological indices, it was found that the ecophysiological- and geno-toxicities of Pb²⁺ on foxtail millet seedlings was higher than Cu²⁺. The tolerance order of Pb²⁺ was An 06>D2-8>Huangmi>Zhaogu, and the tolerance of Cu²⁺ was D2-8> An 06> Zhaogu >Huangmi.