外生菌根真菌Paxillus involutus吸收Cd^(2+)及H_2O_2对Cd^(2+)内流的调控作用

Uptake of Cd^(2+) by ectomycorrhizal fungus Paxillus involutus and the modulation of H_2O_2 in Cd^(2+) influx

【目的】本文研究了外生菌根真菌Paxillus involutus对Cd^(2+)的吸收作用以及H_2O_2对Cd^(2+)内流的调控作用。【方法】以Paxillus involutus的2种菌株MAJ和NAU为研究材料,利用50μmol/L Cd Cl2对材料进行24 h处理,应用非损伤微测技术测定菌丝的Cd^(2+)和Ca^(2+)离子流。【结果】结果显示,Cd^(2+)处理后,MAJ和NAU菌丝的Cd^(2+)内流增强,同时也显著促进了Ca^(2+)的内流。Ca^(2+)通道抑制剂(Verapamil、Gd Cl3、TEA)处理后,Cd^(2+)和Ca^(2+)内流强度均明显减弱,表明Cd^(2+)是通过钙通透性离子通道(Ca PCs)进入菌丝细胞的。Cd^(2+)处理促进了Cd^(2+)和Ca^(2+)的内流,很可能是Cd^(2+)激活了菌丝质膜的Ca PCs。Ca^(2+)和Cd^(2+)的竞争性实验结果显示,高浓度的Ca^(2+)抑制菌株MAJ和NAU的Cd^(2+)内流;反过来,测试液中Cd^(2+)浓度的提高也明显降低了Ca^(2+)的内流强度,这证明Ca^(2+)和Cd^(2+)是竞争性地通过Ca PCs进入菌丝细胞的。此外还发现,H_2O_2(1.0 mmol/L)能增强菌丝的Cd^(2+)和Ca^(2+)内流,而ROS清除剂DMTU却显著抑制了菌株对Ca^(2+)和Cd^(2+)的吸收,表明H_2O_2在调控菌丝细胞Ca PCs介导Cd^(2+)内流的过程中具有重要作用。【结论】综上,外生菌根真菌Paxillus involutus对Cd^(2+)具有富集作用并且可以通过H_2O_2激活Ca PCs促进Cd^(2+)内流。

[Objective] The uptake of Cd2＋by ectomycorrhizal fungus Paxillus involutus and the modulation of H2O2 in Cd2＋influx were investigated in this study. [Method] Two Paxillus involutus strains,MAJ and NAU,were subjected to 50 μmol/L Cd Cl2 for 24 hours,and then fluxes of Ca2＋and Cd2＋were examined by non-invasive micro-test technique. [Result] The results showed that Cd2＋treatment caused the Cd2＋influx,and the Ca2＋influx was also significantly enhanced by Cd2＋in MAJ and NAU hyphae. However,the Cd2＋-elicited influxes of Cd2＋and Ca2＋were both restricted by Ca2＋channel inhibitors including Verapamil,Gd Cl3,TEA（ Tetraethylammonium）,indicating that Cd2＋and Ca2＋simultaneously entered the hyphal cell through plasma membrane（ PM） Ca2＋-permeable channels（ Ca PCs）. The promotion of Ca2＋by Cd2＋implied that Cd2＋activated Ca PCs,thus leading to an increased entry of Ca2＋,in addition to Cd2＋. Moreover competitive inhibition experiments were also conducted to verify whether Cd2＋and Ca2＋entered into the mycelium through Ca PCs in the PM. The influx of Cd2＋in MAJ and NAU was lowered by increased concentration of Ca2＋,and vice versa.Therefore, Cd2＋and Ca2＋competitively permeated the plasma membrane through Ca2＋-permeable channels. Additionally,the influxes of Ca2＋and Cd2＋in mycelium were enhanced by 1 mmol/L H2O2 while suppressed by the ROS scavenger,DMTU（ N,N＇-Dimethylthiourea）. This indicated that H2O2 could mediate the entry of Cd2＋through PM Ca2＋-permeable channels in fungal hyphae. [Conclusion]In conclusion,the ectomycorrhizal fungus Paxillus involutus has the ability of Cd2＋enrichment and the influx of Cd2＋can be facilitated through Ca PCs activated by H2O2.