Evaluation Of Cadmium Accumulation In Leaves Of Different Tobacco Varieties And Study On The Difference Of Foliar Cadmium Distribution

Tobacco is a plant that is easy to accumulate cadmium.The cadmium in cigarette tobacco leaves can enter the human body with mainstream smoke during smoking,thereby endangering human health.Therefore,research on cadmium in tobacco has attracted much attention in recent years.It is particularly important to understand the characteristics of cadmium accumulation in different tobacco varieties,and to explore the mechanism of cadmium uptake,transport,accumulation and efflux in tobacco.In this study,87 tobacco varieties were selected as the research object.Under different concentrations of cadmium,the leaf cadmium high accumulation type(K326)and the leaf cadmium low accumulation type(N.rustica)were selected.Subsequently,the total leaf cadmium content and leaf surface cadmium content of K326 and N.rustica were determined and analyzed,and it was found that the leaf surface cadmium content/total leaf cadmium content of K326 was much higher than that of N.rustica.Because tobacco glandular trichome can accumulate and excrete cadmium,we speculate that K326 has a different ability to secrete cadmium from the glandular trichome of N.rustica,so that the leaf surface cadmium content/total cadmium content of K326 is higher,and the leaves can accumulate more cadmium.Further analysis of K326 and N.rustica glandular hair morphology,glandular trichome density,glandular trichome development-related gene expression,confirmed K326 total glandular trichome density,long-stalked secreted glandular trichome density,short-stalked glandular trichome density,glandular trichome development genes NtCTTC,CYP71D16,NtPhP and NtLTP1 were higher than those of N.rustica.The research results are expected to provide a reference for reducing cadmium in tobacco leaves during tobacco production.The main findings are as follows:(1)The cadmium content in leaves of 87 tobacco varieties was measured and clustered,and it was found that they could be clustered into three types:high leaf cadmium accumulation,medium leaf cadmium accumulation and low leaf cadmium accumulation.K326 and N.rustica showed the same performance under different cadmium concentrations.Both K326 showed a high-accumulation type of leaf cadmium,and N.rustica showed a low-accumulation type of leaf cadmium.At the same time,the comparison of tolerance index showed that K326 showed high tolerance and N.rustica showed low tolerance.(2)The total cadmium content and leaf surface cadmium content of K326 and N.rustica were determined and analyzed.It was found that the total cadmium content and leaf surface cadmium content of K326 were higher than those of N.rustica,which were 1.44 and 6.20 times higher than those of N.rustica,respectively.The total cadmium content and leaf surface cadmium content of K326 and N.rustica both increased with the prolonging of cadmium treatment time.The leaf surface cadmium content/total leaf cadmium content of K326 was 4.3 times higher than that of N.rustica,indicating that K326 distributed more cadmium accumulated in the leaf to the leaf surface.(3)The morphology and density of glandular trichome of K326 and N.rustica were measured and analyzed.It was found that K326 glandular trichome were mainly composed of long-stalked secretory glandular trichome and short-stalked glandular trichome,while N.rustica glandular trichome were mainly composed of long-stalked non-secretory glandular trichome,short-stalked glandular trichome.The total glandular trichome density,long-stalked secretory glandular trichome density,long-stalked nonsecretory glandular trichome density,and short-stalked glandular trichome density of K326 and N.rustica were significantly greater than those of the control under cadmium treatment.The total glandular trichome density,long-stalked secretory glandular trichome density,and short-stalked glandular trichome density of K326 were 1.75,1.6,and 2 times higher than those of the control,respectively.The density of short-stalked glandular trichome was 2,2 and 2 times higher than those of the control,respectively.From the comparison of the two varieties under cadmium treatment,the density of longstalked glandular trichome,short-stalked glandular trichome density,and total glandular trichome density of K326 were 2.31,2.07,and 2.21 times higher than those of N.rustica,respectively.The density of long-stalked secretory glandular trichome of K326 was much higher than that of N.rustica,which might be one of the reasons for the higher leaf surface cadmium content/total leaf cadmium content of K326.(4)The expression levels of genes related to the growth and development of glandular trichome in K326 and N.rustica were determined and analyzed.The relative expression levels of NtCTTC,CYP71D16,NtPhP and NtLTP1 genes in K326 were1.68 and 1.681.74,1.71,1.29 times higher than those in N.rustica,respectively.The relative expression levels of NtCTTC,CYP71D16,NtPhP and NtLTP1 genes were significantly increased under cadmium treatment in both varieties compared with the control.The relative expression levels of NtCTTC,CYP71D16 and NtLTP1 genes were higher in K326 than in N.rustica under both cadmium treatment and control conditions,indicating significant interspecific differences in glandular trichome growth and development between the two cultivars.