The germination of foxtail millet seeds and the physiological and biochemical indexes of its seedlings in responses to lead stress

【Objective】To investigate the effects of heavy metal lead(Pb)on the germination of foxtail millet seeds and the physio-biochemical characteristics of its seedlings so as provide a theoretical basis for the safe production and quality assurance of this type of special rainfed cereal under the background of Pb pollution.【Method】A pot experiment was conducted using foxtail millet cultivar Jingu 21 as the experimental material to investigate its seed germination and seedling physio-biochemical indexes as influenced by five exogenous Pb concentrations(50,100,250,500,1000 mg/kg). Soil without added Pb was used as the control(CK,0 mg/kg).【Result】The germination energy,germination ratio and germination indexes of Jingu 21 were inhibited with increasing Pb concentrations,the relative germination rate of foxtail millet seeds under Pb treatment of 1000 mg/kg was only 52.5% compared with CK. The contents of chlorophyll increased firstly,and then decreased with increasing Pb concentrations,and all of these kinds of chlorophyll contents were significantly higher than those in the CK(P<0.05,the same below). When Pb concentration was 500 mg/kg,the chlorophyll a,chlorophyll b and chlorophyll a+b contents reached the maximum,which increased by 58.3%,69.5% and 64.3% respectively compared with CK. As Pb concentration increased,peroxidase(POD)activity,Plasma membrane permeability, malondialdehyde(MDA)content and proline content in leaves of Jingu 21 seedlings increased significantly,among with POD activity was especially sensitive to stress of high Pb concentration. Soluble protein content increased first and then decreased with increa-sing Pb concentrations. When Pb concentration was 500 mg/kg,the soluble protein content reached the highest,which was 54.1% higher than that of CK. When Pb concentration was 1000 mg/kg,soluble protein content decreased sharply,which was 14.9% lower than that of CK. The correlation analysis showed that the germination potential,germination rate and germination index of foxtail millet were negatively correlated with Pb concentrations. The POD activity,plasma membrane permeability,MDA content and proline content were positively correlated with Pb concentration(P<0.01). The average relative value of resistance index(sensitivity)at different Pb concentrations was in the order POD activity>plasma membrane permeabilyty>proline content>MDA content>soluble protein content.【Conclusion】Millet is affected by Pb stress during both germination and the seedling stage. Within a certain concentration range,foxtail millet can alleviate the damage caused by Pb stress by adjusting its own physiological and biochemical indexes.