Physiological Functions Of Sulfate In Response To Cadmium Stress In Millet Seedlings

Millet?Setaria italica L.?is one of the most important coarse food grains for residents in northern China.It is widely planted in arid and semi-arid areas of our country.Because of its short growth period,drought resistance,barren resistance and high photosynthetic efficiency,millet is very suitable for studying the whole genome of Gramineae and C4 photosynthesis model crops.However,millet is only a regional importance of crop in the world,and researchers have done relatively little research on millet.With the successful completion of the sequencing and assembly of the whole genome of millet,and the construction of the whole geneme sequence map,scientific researchers accelerated the research process of molecular mechanism of millet.Sulphur nutrition plays an important role in growth and development of plants.It has been reported in the literature that proper sulfur nutrition can improve the tolerance of plants to cadmium?Cd?toxicity and reduce the injury of Cd toxicity to plants.With the unreasonable discharge of “three wastes” in the industrial production process and the irrigation of farmland with sewage,a large number of containing-Cd fertilizers were applied in agricultural production,which led to the excessive Cd content in the soil of large-scale cultivated land in China,and affected the crops growth and the yield and quality of agricultural works.In this study,millet "Changnong 44" was used as the test materials and millet seedlings were cultured by nutrient solution water and nutrient soil.The effects of sodium sulfate?Na₂SO₄?pretreatment on the physiology of millet seedlings overground tissue under Cd stress and the effects of exogenous sodium sulfate and Cd treatment on the physiology of millet seedlings were mainly studied to study the mechanism of sulfur nutrition in response to Cd toxicity in millet.The results are as follows:?1?Cd toxicity can cause seedlings to show a variety of toxic symptoms,including slow growth and development of plants,chlorosis yellowing of plant leaves,dry tips and other symptoms,which have a certain impact on the growth and development of plants.After Cd stress,the root length and fresh weight of overground parts of millet seedlings decreased significantly,the superoxide anion(O^2-·)rate of formation in overground tissue increased significantly,the content of hydrogen peroxideand?H₂O₂?and malondialdehyde?MDA?increased significantly,the activity of peroxidase?POD?increased significantly,the activity of catalase?CAT?increased slightly,and the content of glutathione?GSH?and cysteine?Cys?increased significantly,and the activities of superoxide dismutase?SOD?,glutathione sulfotransferase?GST?and glutathione peroxidase?GPX?did not change significantly.The results showed that a certain concentration of Cd could induce the increase of reactive oxygen species?ROS?level in millet seedlings,inhibit the growth and development of millet plants.The increase the of antioxidant content and the activation of antioxidant enzymes system were the adaptive responses of millet seedlings to Cd toxicity.?2?Under the condition of water culture,the antioxidant enzymes activitiy and antioxidant substances content in the overground tissues of millet seedlings treated with 0.5 mmol·L^-1 Na₂SO₄ sodium sulfate treated 1day later Cd treatment were different from with the Cd treatment alone.The results showed that After Cd treated 4 days,compared with the Cd treatment alone,Na₂SO₄ treatment 1 day later 50 ?mol·L^-1 Cd treatment the O2-·formation rate in millet seedlings decreased significantly,the CAT activities decreased significantly,GST activities decreased by 23.28%,GPX activities increased by 36.02%;Na₂SO₄ treatment 1 day later 200 ?mol·L^-1Cd treatment SOD?POD and GPX activities increased significantly;With the prolongation of Cd treatment time to 8 days,Na₂SO₄ treatment 1 day later 50?mol·L^-1 Cd treated 8 days,only POD activities increased significantly,Cys content decreased significantly;Na₂SO₄ treatment 1 day later 200 ?mol·L^-1Cd treated 8 days,the content of H2O2 and Cys in seedlings decreasedsignificantly,POD activity decreased significantly.It can be seen that the mitigation effect of 0.5 mmol·L^-1 Na₂SO₄ on Cd toxicity in millet seedlings is related to the concentration and the time of cadmium stress in the environment.sulfate may adapt to Cd toxicity in the millet seedlings by increasing antioxidant enzyme activities and antioxidant substance contents.?3?Under soil culture conditions,0.5 mmol·L^-1 sulfate and Cd combined treatment for 15 days.it was found that compared with the Cd treated alone,the sulfate and 20 ?mol·L^-1 Cd combined treatment group,the content of H2O2 and MDA in millet seedlings were significantly,CAT activity in millet seedlings were increased significantly,Cys content decreased significantly;compared with the Cd alone,sulfate and 100 ?mol·L^-1 Cd combined treatment group,the H2O2 content of increased significantly,the SOD and POD activities in millet seedlings decreased significantly,the content of cysteine increased significantly.The results showed that the 0.5 mmol·L^-1 of sulfate and 20 ?mol·L^-1Cd combined treatment had a certain alleviation effect on the 20 ?mol·L^-1 Cd toxicity in millet seedlings,the 0.5 mmol·L^-1of sulfate and 100 ?mol·L^-1Cd combined treatment had no obvious alleviation effect on the toxicity of 100 ?mol·L^-1 Cd toxicity.