边缘细胞对荞麦根尖铝毒的防护效应和对细胞壁多糖的影响

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Root border cells(RBCs) are special cells that surround the root apices and are physically separate from the root cap epidermis.The mRNAs and proteins produced by RBCs differ from those produced by the root cap cells.RBCs and the mucilage they secrete are thought to have roles in protecting root tips from biotic and abiotic stresses,such as aluminum toxicity.In this research,we aimed to elucidate the role of RBCs in protecting root apices of buckwheat(Fygopyrum esculentum Moench) from Al toxicity,and to determine their effect on polysaccharide contents in the cell wall of root tips.We used two cultivars of buckwheat: the Al-tolerant genotype 'Jiangxi' and the Al-sensitive genotype 'Neimeng'.Seedlings were aeroponically cultured in 0.5 mmol/L CaCl2 solution,pH 4.5,containing 0,25,50 or 200 μmol/L AlCl3.All of the primary roots were sprayed with AlCl3 solutions,and one half of the roots was washed with a stream of distilled water every 4 h to remove the RBCs that continuously formed during the experimental period.We evaluated root growth,Al accumulation in root tips,phosphatase(APA) and pectin methylesterase(PME) activities,and polysaccharide contents in the roots.In roots subjected to Al treatment,elongation was inhibited and there was increased Al accumulation in the tips.Physical removal of RBCs from root tips resulted in more severe Al-induced inhibition of root elongation and greater Al accumulation in the root tips.For both buckwheat genotypes,removal of RBCs from the roots resulted in higher APA activity in the root tips compared with that in root tips with RBCs.This effect was more pronounced in the Al-tolerant genotype(Jiangxi) than in the Al-sensitive genotype(Neimeng).Physical removal of RBCs from root tips also significantly increased PME activity and the contents of pectin,hemicellulose 1,and hemicellulose 2 in the cell walls of the root tips.These results suggested that RBCs adhered to the root tips tend to exclude Al from the rice root apex,decrease the cell-wall polysaccharide content,and promote synthesis of APA,thereby promoting Al tolerance in buckwheat.