Effects Of Sulfate And Cadmium Interaction On Growth And Physiological Characteristics And Cadmium Content In Pakchoi (Brassica Chinensis L.)

Different varieties of Brassica chinensis L. were used with hydroponic experiments andpot experiments under different concentrations of cadmium and sulfate treated in this study.The absorption and accumulation of Cd of different varieties of Brassica chinensis L.wasstudied. Moreover, the antioxidant system and ascorbate-glutathione cycle were alsoinvestigated to study the effect of Cd to the growth of Brassica chinensis L. The main resultsof this research are as follows:1．A series of hydroponics experiments were performed to investigate effects of sulfuron ascorbate （AsA）-glutathione （GSH） cycle and the content of phytochelatins （PCs） inpakchoi （Brassica chinensis L.） leaves under cadmium （Cd） stress. The results showed thatapplication of moderate level of sulfur decreased the contents of peroxide （H₂O₂） andmalondialdehyde （MDA）, but increased key enzyme activities and antioxidant content ofAsA-GSH cycle in pakchoi leaves. Under low Cd stress (5μmol·L^-3), the content of H₂O₂were significantly decreased and the content of MDA fell first then rose withincreasing concentration of sulfur, while PCs content and the activity of glutathione reductase（GR） were raised. Along with the increase of the sulfur concentration, other key enzymesactivities, such as ascorbate peroxidase （APX）, dehydroascorbate reductase （DHAR） andmonodehydroascorbate reductase （MDHAR） in AsA-GSH cycle and the content of AsAincreased at the beginning, reaching to the peak in the3mmol·L^-3sulfur level. Under high Cdstress (50μmol·L^-3), the contents of H₂O₂and MDA decreased first then increased, while thekey enzymes activities and antioxidant content of AsA-GSH cycle showed an oppositetendency, and many of them reached to the peak in the2mmol·L^-3sulfur level. The resultsindicated that application of moderate level of sulfur could maintain the efficiencymetabolism of AsA-GSH cycle during the stress period, increase the synthesis of PCs andkeep the regenerative capacity of antioxidant substances and heavy metal chelating ability.Although sulfur plays an important role in reducing Cd toxicity, overhigh concentration ofSO₄^2-could cause toxicity of salt stress and thus affect its Cd toxicity relief.2．The current study investigated the remediation effects of exogenous sulfur (0,90 mg·kg^-3) on growth inhibition and oxidative stress and cadmium uptake and accumulationunder cadmium (0,1,5,10mg·kg^-3)stress of two pakchios with different resistance tocadmium in pot experiment. Compared with the control, the growth inhibition effect on cAikangqing is not significant under1mg·kg^-3cadmium. The content of chlorophyll, O.–2andMDA changed little in leaves of Aikangqing. Aikangqing can maintain a high antioxidantenzyme activities under1mg·kg^-3cadmium.10mg·kg^-3cadmium induced O.–2, MDA,and Cdcontent increased significantly in both pakchios leaves. Plant growth was significantlyinhibited under higher cadmium stress. Addition of S to Cd-treated two pakchios showeddecrease in O.–2, MDA, and Cd content in leaves and restoration of growth and antioxidantenzymes activities, but increased root Cd content. Exogenous sulfur can reduce the toxicity ofCd through protecting activities of antioxidant enzymes. Cadmium stress and cadmium sulfurinteraction were significantly increased phytochelatins （PCs） content of two pakchios, and theincreasing of Aikangqing is greater than the increasing of Qibaoqing. These results confirmthat an adequate supply of sulfur in the soil, can protect the activity of antioxidant enzymes,enhanced antioxidant capacity, inhibiting the transport of cadmium to reduce the toxicity ofcadmium, effectively improve the resistance of pakchios and protected the growth ofpakchios.