Role Of Nonselective Cation Channels In Cadmium Transport And Accumulation In Willows

Soil cadmium(Cd)pollution in China is serious,and the exceedance rate of Cd pollution sites is as high as 17.39%.Phytoremediation is the most cost-effective measure to solve heavy metal pollution in large area soils.Willow(Salix spp.)has a strong uptake and transport capacity for Cd and is widely used in the international phytoremediation field.Nonselective cation channels(NSCCs)are one of the important pathways for Cd uptake and transport by plants;however,the role of NSCCs in Cd uptake and accumulation in willow is still unclear.In this study,we used the tree type willow Salix jiangsuensis ’1 72’ and S.jiangsuensis ’799’ as well as shrub type willows S.integra ’Dahongtou’ and S.integra‘Yizhibi’were used to study the effects of the NSCCs inhibitor lanthanum(La)on the growth and physiological and biochemical responses of willow under Cd stress and on Cd uptake and The main results of the study were as follows:(1)NSCCs were involved in the uptake,translocation and accumulation of Cd in willow,and LaCl3 significantly(P<0.001)reduced the Cd content and enrichment coefficients in different species and tissues of willow.There were species differences in the contribution of NSCCs to the accumulation of Cd in willow,and their contribution rates were,from largest to smallest:’Yizhibi’>‘Dahongtou’>‘172’>‘799’,with the highest contribution to ’Yizhibi’ with 76.62%of whole plant contribution.(2)La significantly(P<0.05)reduced the Cd content in the subcellular fractions of willow leaves and roots,but did not change the compartmentalization mechanism of Cd in willow,and the proportion of Cd in the subcellular fractions of different tissues was from large to small:cell wall fraction>soluble fraction>membrane and organelle fraction.The addition of La significantly(P<0.05)reduced the Cd content in the NaClextracted state of the root system,but increased the proportion of the Ethanol-extracted state of the leaves and roots.(3)La negatively affected the growth and physiology of willow:both single Cd and La treatments and combined Cd-La treatments significantly(P<0.05)inhibited the height and biomass of willow,decreased the photosynthetic pigment content and net photosynthetic rate of leaves,and La also inhibited the uptake of mineral nutrients in willow,especially Mg and Mn in leaves.(4)The uptake of Cd by willow root systems involves not only NSCCs(including Ca2+ channels)but also transport proteins such as H+-ATPase and sulfur-containing proteins on the plasma membrane,and different species differ in their sensitivity to inhibitors of these channels and transport proteins.Except for ’Dahongtou’,which is not sensitive to Verapamil,LaCl3(NSCCs blocker),Vanadate(H+-ATPase on the plasma membrane)and Verapamil(Ca2+ channel blocker)significantly(P<0.05)inhibited the net flux of Cd2+ in willow root systems of the four species.(5)Transcriptome analysis of the root systems of‘Yizhibi’and ’799’revealed a total of 391 genes associated with NSCCs,of which ’Yizhibi’ accounted for 118 and 273 in ’799’,and most of these genes were related to glutamate receptors,accounting for 40.68%and 30.77%in the 2 varieties,respectively;followed by cyclic nucleotide channels,accounting for 26.27%and 20.51%,respectively.Under Cd stress,the relative expression levels of GLR28 and CNG20 in the root system of‘Yizhibi’were significant(P<0.05),while La was significantly increased(P<0.05)inhibited the relative expression of these genes,but in the root system of ’799’,the relative expression of CNG20 was significantly treated by single Cd or La treatment(P<0.05),the relative expression level of CNGC2 in roots of ’799’ was significantly decreased by single Cd and La treatment and Cd-La combined treatment(P<0.05),but CNGC2 was significantly increased in the root system of ’’Yizhibi’ under single Cd or La treatment(P<0.05),indicating that there were differences in the types of NSCCs involved in Cd transport in different willow roots.In summary,this study clarified the contribution of NSCCs in Cd uptake and accumulation in shrub willow and tree willow and the differences in expression of NSCCs-related genes in the root systems of the two willow type,providing a basis for elucidating the Cd uptake pathways in willow roots.It was also found that La had some inhibitory effect on the growth and physiological and biochemical processes of willow,and there was a synergistic effect with Cd complex treatment.Therefore,further studies on the regulatory effects of La on the growth,physiology and biochemistry of willow and NSCCs are needed,and the results of this paper also provide new insights into the mechanisms of Cd uptake and accumulation in woody plants regulated by rare earth elements.