Differences In Response Of Tartary Buckwheat With Different Flavonoids Contents To Lead And Cadmium Stress

Tartary buckwheat(Fagopyrum tataricum)is an important multigrain crop originating in China.The crop is rich in flavonoids which have antioxidant,anti-inflammatory and hypolipidemic effects but is generally low in content in Poaceae species.However,the soil of many Tartary buckwheat producing areas has heavy metal pollution,raising concern of people about the food safety of Tartary buckwheat.Although the mechanism of heavy metal tolerance and accumulation is reported in some studies,the difference of the mechanism in buckwheat varieties with different flavonoid accumulating abilities is unclear.In this study,two Tartary buckwheat varieties with significant differences in flavonoid content,Xikuqiao(XQ,high flavonoid content variety,whose average total flavonoid content is 3.72%)and KQII.-3(KQ,low flavonoid content variety,whose average total flavonoid content is 2.60%),were studied,and the tolerant ability,physiological and biochemical response,uptake and accumulation characteristics and transcriptome response of buckwheat with high/low flavonoid content were analyzed in the pot control experiments,aiming to provide a theoretical basis for safe production of the crop on the Pb,Cd-contaminated soils,and provide technical support for the sustainable development of Tartary buckwheat.The major results are as follows:(1)There was no obvious difference in the absorption of Pb and Cd by XQ and KQ,but compared with XQ,the retention effect of roots on Pb by KQ under high concentration Pb concentrations was stronger and the transport coefficient was lower,while the difference in Cd content and transport factors between the roots and aboveground parts of the two cultivars was not obvious under Cd concentrations.At all concentrations,the Pb and Cd of in XQ and KQ are mainly stored in the cell wall and soluble components.The total distribution proportions of Pb in XQ and KQ are respectively more than 81% and 89%.The total distribution proportions of Cd in XQ and KQ are respectively more than 83% and 88%.The distribution ratio in KQ is higher.At all concentrations,most of Pb and Cd in XQ and KQ exist in the less toxic Na Cl-extracted and acetic acid-extracted forms in the two materials.The sum of the distribution proportions of Pb in XQ and KQ is respectively more than 53%and 55%.The sum of the distribution proportions of Cd in XQ and KQ is respectively more than 64% and 67%.The distribution in KQ is higher than that in XQ.These indicates that the high tolerance of KQ to Pb and Cd depends on stronger compartmentalization and detoxification ability.(2)The tolerance of Tartary buckwheat KQ with low-flavonoid content to Pb and Cd was higher than that of buckwheat XQ with high-flavonoid content,mainly because Pb and Cd concentrations had a weaker inhibitory effect on KQ biomass.The effect of Pb and Cd concentrations on the chlorophyll-a/b ratio of XQ was not obvious,but it caused a significant increase in the chlorophyll-a/b value of KQ(Pb concentrations decreased from 3.83 to 1.75;Cd concentrations decreased from 3.83 to 2.41),which improved the utilization ability of KQ to weak light.In addition,the content of glutathione,total flavonoids and quercetin increased by KQ under high concentrations of Pb and Cd compared with XQ(Pb concentrations,the flavonoids content of XQ is 3.72%-5.77%;the flavonoids content of KQ is 2.60%-4.28%),which was more effective in resisting oxidative damage caused by Pb and Cd concentrations,which was an important physiological basis for KQ’s stronger tolerance to Pb and Cd.(3)Pb and Cd concentrations had a stronger disturbance on the expression of Tartary buckwheat XQ gene with high-flavonoid content than buckwheat KQ with low-flavonoid content.The differentially expressed genes of XQ under Pb and Cd concentrations were mainly enriched in amino acid metabolism,starch and sucrose metabolism,lipid metabolism and other processes related to plant growth,while KQ was more involved in heavy metal detoxification processes such as ion homeostasis(Ca transporter and Fe transporter),antioxidant(oxidoreductase activity,glutathione metabolism and flavonoid biosynthesis),and the compartmentalized distribution of Pb and Cd by vacuole(ABC transporter).This is the molecular mechanism by which KQ is more resistant to Pb and Cd than XQ.