AI 3 +-Ca 2 + interactions in aluminum rhizotoxicity II . Evaluating the Ca 2 +-displacement hypothesis
AI 3 +-Ca 2 + interactions in aluminum rhizotoxicity II . Evaluating the Ca 2 +-displacement hypothesis
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通讯作者：
T. Kinraide;P. Ryan;L. Kochian
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作者：
T. Kinraide;P. Ryan;L. Kochian
提高Ca 2+浓度可缓解A13+、H +、Na +等引起的根毒性。这导致了一种假设，即有毒阳离子从运输通道或表面配体中置换出Ca 2+，而这些通道或表面配体必须被Ca 2+占据才能发生根伸长。本研究以小麦（Tr i t i cum a e t i v um L.）在AP+的情况下，我们已经确定，（i）Ca 2+，Mg 2+和Sr 2+是同样的改善，（ii）根伸长不增加作为Ca 2+取代生根培养基中的Mg 2+或Sr 2+，和（iii）根毒性是一个功能的AP +活性在根细胞膜表面的Gouy-Chapman-Stern模型计算。根毒性与计算的膜表面Ca 2+活性无关。与A13+相比，高浓度的三乙二胺钴离子（TEC 3+）引起的根毒性可被膜表面的Ca 2+特异性地缓解。H +诱导的根毒对膜表面Ca 2+的特异性反应较弱。我们的结论是，Ca 2+置换假说失败的情况下，AP +根毒性和改善阳离子（包括一价阳离子）发生，因为降低膜表面的负性和随之而来的降低膜表面活性的A13 +。然而，TEC 3 +可能是毒性的，而AP +则不是，因为它抑制了Ca 2+的摄取.具体的H + C a2+相互作用的性质是不确定的。
Several mineral rhizotoxicities, including those induced by A13+, H +, and Na +, can be relieved by elevated Ca 2+ in the rooting medium. This leads to the hypothesis that the toxic cations displace Ca 2+ from transport channels or surface ligands that must be occupied by Ca 2+ in order for root elongation to occur. In this study with wheat (Tr i t i cum a e s t i v u m L.) seedlings, we have determined, in the case of AP+, that (i) Ca 2+, Mg z+, and Sr 2+ are equally ameliorative, (ii) that root elongation does not increase as Ca 2+ replaces Mg 2+ or Sr 2+ in the rooting media, and (iii) that rhizotoxicity is a function solely of AP + activity at the root-cell membrane surface as computed by a Gouy-Chapman-Stern model. The rhizotoxicity was indifferent to the computed membranesurface Ca 2+ activity. The rhizotoxicity induced by high levels of tris(ethylenediamine)cobaltic ion (TEC3+), in contrast to A13+, was specifically relieved by Ca 2+ at the membrane surface. The rhizotoxicity induced by H + exhibited a weak specific response to Ca 2+ at the membrane surface. We conclude that the Ca2+-displacement hypothesis fails in the case of AP + rhizotoxicity and that amelioration by cations (including monovalent cations) occurs because of decreased membrane-surface negativity and the consequent decrease in the membrane-surface activity of A13 +. However, TEC 3 +, but not AP +, may be toxic because it inhibits Ca 2+ uptake. The nature of the specific H + C a 2+ interaction is uncertain.