基于细胞膜表面电势探讨Ca与毒性离子在植物根膜表面的相互作用

Exploring the interactions between Ca and toxic ions at the cell membrane surface of plant roots in terms of electrical potential at cell membrane surface

有毒重金属离子的自由离子活度已被广泛认为是重金属最直接的活性形态,可以用来预测重金属的生物效应,而事实上生物体表的重金属离子浓度由于细胞表面膜电势的静电效应而与本体溶液中重金属的自由离子活度存在显著差异.细胞膜表面电势随溶液中离子组成变化而发生变化,本体介质中钙离子能通过电荷屏蔽和离子键结合来降低膜表面电势的电负性,从而减少阳离子如Al3+、Cu2+和Ni2+在膜表面的活度,增加阴离子如SeO42-和H2AsO4-在膜表面的活度,这种电负性降低的程度能通过Gouy-Chapman-Stern模型来量化.基于植物根表重金属离子活度可以更好地预测其生物效应.细胞膜表面电势为研究离子之间交互作用机制及其与植物效应之间的关系提供了一个全新的角度.

Free ion activity of toxic heavy metals has been widely recognized as the most active species for organism,and can be applied for predicting the biological effect of heavy metals.However,the concentration of heavy metal ions at the body surface of organism differs from their free ion activity in the bulk solution,because of cell membrane surface electrical potential （ψ0） which varies with solution compositions.An increase in common cation Ca in culture solutions reduces the negativity of ψ0 by charge screening and ion binding.The reduced negativity could result in reductions in membrane surface activities of cationic toxicants （e.g.Al3＋,Cu2＋ and Ni2＋） and increases in surface activities of anionic toxicants （e.g.SeO42- and H2AsO4-）.Therefore,Ca alleviates the toxicity of Al3＋,Cu2＋ and Ni2＋ but increases the toxicity of SeO42- and H2AsO4-.The values of ψ0 can be calculated with a Gouy-Chapman-Stern model in response to Ca concentrations in solutions.Based on the activity of heavy metal ions at the organism body surface,the biological effect of heavy metals can be well predicted.This study provides a novel avenue into understanding the mechanisms of plant-ion interactions and biological responses of plant.