Permeability and channel-mediated transport of boric acid across membrane vesicles isolated from squash roots
Permeability and channel-mediated transport of boric acid across membrane vesicles isolated from squash roots
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DOI：
10.1104/pp.124.3.1349
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发表时间：
2000-11-01
期刊：
影响因子：
7.4
通讯作者：
Brown, PH
中科院分区：
文献类型：
--
作者：
Dordas, C;Chrispeels, MJ;Brown, PH
硼是植物生长必需的微量元素，不同植物体内的硼含量差异很大，但其被细胞吸收的机制尚不清楚。硼以硼酸的形式存在于土壤溶液中，并以这种形式进入根部。我们测定了从南瓜（Cucurbita pepo）根中获得的纯化质膜囊泡的硼透性系数，发现其为3 × 10(-7) +/-1.4 × 10(-8) cm s(-1)，比微粒体囊泡的透性高6倍。氯化汞和根皮素（一种非特异性通道阻滞剂）部分抑制了硼酸I的质膜囊泡的渗透（30%-39%）。氯化汞的抑制作用很容易被2-巯基乙醇逆转。硼转运到质膜囊泡的激活能为10.2千卡摩尔（-1）。综上所述，这些数据表明硼进入植物细胞部分是通过质膜脂质双分子层的被动扩散，部分是通过蛋白质通道。主要内在蛋白（MIP） PIP1在非洲爪蟾卵母细胞中的表达导致卵母细胞的硼通透性增加30%。其他测试的mip （PIP3、MLM1和GlpF）没有这种效果。我们假设某些mip，比如最近被证明可以运输小的中性溶质的mip，也可能是硼进入植物细胞的通道。
Boron is an essential micronutrient for plant growth and the boron content of plants differs greatly, but the mechanism(s) of its uptake into cells is not known. Boron is present in the soil solution as boric acid and it is in this form that it enters the roots. We determined the boron permeability coefficient of purified plasma membrane vesicles obtained from squash (Cucurbita pepo) roots and found it to be 3 x 10(-7) +/-1.4 x 10(-8) cm s(-1), six times higher than the permeability of microsomal vesicles. Boric acid I, permeation of the plasma membrane vesicles was partially inhibited (30%-39%) by mercuric chloride and phloretin, a non-specific channel blocker. The inhibition by mercuric chloride was readily reversible by 2-mercaptoethanol. The energy of activation for boron transport into the plasma membrane vesicles was 10.2 kcal mol(-1). Together these data indicate that boron enters plant cells in part by passive diffusion through the lipid bilayer of the plasma membrane and in part through proteinaceous channels. Expression of the major intrinsic protein (MIP) PIP1 in Xenopus laevis oocytes resulted in a 30% increase in the boron permeability of the oocytes. Other MIPs tested (PIP3, MLM1, and GlpF) did not have this effect. WE postulate that certain MIPs, like those that have recently been shown to transport small neutral solutes, may also be the channels through which boron enters plant cells.