The Mechanisms Of Physiological Difference Of Arsenic Uptake And Accumulation In Different Cultivars Of Chinese Flowering Cabbage (brassica Parachinensis L.)

Contamination of arsenic?As?in agricultural soils has become increasingly serious,and affects the food safety.Cabbage is widely eaten in the pearl river delta region of China.A novel alternative strategy of screening or breeding low-pollution accumulating crop cultivars has been proposed to ensure the safety of agricultural products.This study focused on the important vegetable-Chinese flowering cabbage?Brassica parachinensis L.?.The two kinds of high and low-As accumulation cultivar cabbages were screened.By comparing the differences of physiological characteristics between low-and high-As cabbages,including tolerance index,As species,antioxidant enzymes,cell ultrastructural,this study revealed the formation mechanism of high-or low-As accumulation cultivar.?1?Screening for high-or low-As accumulation cultivarsThe biomass and As concentrations in 12 cultivars of Chinese flowering cabbage have been studied through pot experiments under different As treatments.Under As stress,great variations were observed in shoots As concentrations among the 12 cultivars,with a range of 0.13 to 2.26mg kg^-1?18.2-fold between the highest and the lowest As accumulators among 12 cultivars?under 15 mg kg^-11 As treatment,and a range of 0.90 to 4.84 mg kg^-1?6.8-fold?under 30 mg kg^-1,respectively.There is a significant negative correlation between shoots As concentration and tolerance index?TI??P<0.01?.In this study,HY49 and JX were selected as low-As accumulation cultivars,and GD and NX45 were screed as high-As accumulation cultivars,respectively.?2?The physiological difference of As in high-and low-As accumulation cultivars.A hydroponic experiment was conducted to investigate various physiological differences?including biomass,As species,antioxidant enzymes and cell ultrastructure?between the four cultivars.The result showed that the roots As concentration of four cultivars were higher than those in shoots.The concentration of free radical in high-As accumulation cultivars were higher than that in low-As accumulation cultivars.The chlorophyll concentration,root activity,antioxidant enzymes and GSH in the low-As accumulation cultivars were higher than that in the high-As accumulation cultivars.The result showed that the enzyme system?SOD,CAT,APX?and non-enzymatic system activity?GSH?was strengthened to resist the stress of As.As?V?was reduced to As?III?and accumulated in the root system,which is one of the reasons that aggravate the As toxicity to Chinese flowering cabbages.Transmission electron microscope observation revealed that there were no obvious differences in chloroplast structures between the four cultivars under low As treatment,but obvious changes in cell ultrastructures among four cultivars under high As treatment.Compared with low-As accumulator,high-As accumulator suffered greater damage in chloroplast structures.For example,more thylakoids in chloroplasts of high-As accumulator were grouped in irregular morphology,gradually disintegrated,more starch grains disappeared and more Osmium particles,plastoglobuli accumulated in the chloroplasts.As for the low-As accumulator,the chloroplasts and mitochondria swelled in the mesophyll cell,but it maintained their integrity and enhanced vacuolar compartmentalization.The result suggested that the low-As accumulator possessed higher As tolerance than that of high-As accumulator.