It is known that rice roots take up cadmium (Cd) via the symplastic route mediated by membrane-bound mineral transporters. Here we provide evidence that apoplastic bypass flow is another Cd uptake route in rice. High concentrations of Cd rendered apoplastic bypass flow rate increased in rice seedlings. These concentrations of Cd compromised membrane integrity in the root meristem and transition zone. Polyethleneglycol and proline inhibited the Cd-induced apoplastic bypass flow and Cd transfer to the shoots. Loss-of-function mutant of the Cd uptake transporter, nramp5, showed Cd transport to the shoot comparable to the wild type. At a low Cd concentration, increased apoplastic bypass flow rate by NaCl stress resulted in an elevation of Cd transport to shoots both in the wildtype and nramp5. These observations indicate that apoplastic bypass flow in roots carries Cd transport leading to xylem loading of Cd in addition to the symplastic pathway mediated by mineral transporters under stressed conditions.

已知的是，稻根占用镉（Cd）通过由膜结合的矿物转运蛋白介导的共质体的路线。在这里，我们提供证据表明质外体旁路流是水稻中另一种 Cd 吸收途径。高浓度的 Cd 使水稻幼苗的质外体旁路流速增加。这些 Cd 浓度损害了根分生组织和过渡区的膜完整性。聚乙二醇和脯氨酸抑制 Cd 诱导的质外体旁路流动和 Cd 向芽的转移。Cd 吸收转运蛋白的功能丧失突变体nramp5显示出与野生型相当的 Cd 转运到枝条。在低 Cd 浓度下，NaCl 胁迫增加的质外体旁路流速导致野生型和nramp5。这些观察表明，除了由矿物转运蛋白在压力条件下介导的共生途径外，根中的质外体旁路流还携带 Cd 转运，导致 Cd 的木质部负载。