Rijavec Tomaž, Lapanje Aleš
Institute of Metagenomics and Microbial TechnologiesLjubljana, Slovenia; Department of Environmental Sciences, Jožef Stefan InstituteLjubljana, Slovenia.
Institute of Metagenomics and Microbial TechnologiesLjubljana, Slovenia; Department of Environmental Sciences, Jožef Stefan InstituteLjubljana, Slovenia; Remote Controlled Theranostic Systems Lab, Saratov State UniversitySaratov, Russia.
Front Microbiol. 2016 Nov 18;7:1785. doi: 10.3389/fmicb.2016.01785. eCollection 2016.
Plant growth promoting rhizobacteria produce chemical compounds with different benefits for the plant. Among them, HCN is recognized as a biocontrol agent, based on its ascribed toxicity against plant pathogens. Based on several past studies questioning the validity of this hypothesis, we have re-addressed the issue by designing a new set of experiments, to test if HCN-producing rhizobacteria could inhibit the growth of phytopathogens. The level of HCN produced by the rhizobacteria does not correlate with the observed biocontrol effects, thus disproving the biocontrol hypothesis. We developed a new concept, in which HCN does not act as a biocontrol agent, but rather is involved in geochemical processes in the substrate (e.g., chelation of metals), indirectly increasing the availability of phosphate. Since this scenario can be important for the pioneer plants living in oligotrophic alpine environments, we inoculated HCN producing bacteria into sterile mineral sand together with germinating plants and showed that the growth of the pioneer plant French sorrel was increased on granite-based substrate. No such effect could be observed for maize, where plantlets depend on the nutrients stored in the endosperm. To support our concept, we used KCN and mineral sand and showed that mineral mobilization and phosphate release could be caused by cyanide . We propose that in oligotrophic alpine environments, and possibly elsewhere, the main contribution of HCN is in the sequestration of metals and the consequential indirect increase of nutrient availability, which is beneficial for the rhizobacteria and their plant hosts.
促进植物生长的根际细菌会产生对植物有不同益处的化合物。其中，HCN被认为是一种生物防治剂，基于其对植物病原体的毒性。基于过去几项对该假设有效性提出质疑的研究，我们通过设计一组新实验重新探讨了这个问题，以测试产生HCN的根际细菌是否能抑制植物病原体的生长。根际细菌产生的HCN水平与观察到的生物防治效果不相关，从而推翻了生物防治假设。我们提出了一个新概念，即HCN并非作为生物防治剂起作用，而是参与基质中的地球化学过程（例如金属螯合），间接提高磷酸盐的有效性。由于这种情况对于生活在贫营养高山环境中的先锋植物可能很重要，我们将产生HCN的细菌与发芽的植物一起接种到无菌矿砂中，结果表明在基于花岗岩的基质上先锋植物法国酸模的生长有所增加。对于玉米则未观察到这种效果，因为玉米幼苗依赖胚乳中储存的养分。为了支持我们的概念，我们使用了KCN和矿砂，结果表明氰化物可导致矿物质的活化和磷酸盐的释放。我们提出，在贫营养的高山环境以及可能在其他地方，HCN的主要作用在于螯合金属以及随之而来的间接提高养分有效性，这对根际细菌及其植物宿主是有益的。
