Brodersen Kasper Elgetti, Nielsen Daniel Aagren, Ralph Peter J, Kühl Michael
Plant Functional Biology and Climate Change Cluster, University of Technology Sydney (UTS), 15 Broadway, Ultimo, Sydney, NSW, 2007, Australia.
Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, DK-3000, Helsingør, Denmark.
New Phytol. 2015 Feb;205(3):1264-1276. doi: 10.1111/nph.13124. Epub 2014 Nov 3.
Seagrass is constantly challenged with transporting sufficient O₂ from above- to belowground tissue via aerenchyma in order to maintain aerobic metabolism and provide protection against phytotoxins. Electrochemical microsensors were used in combination with a custom-made experimental chamber to analyse the belowground biogeochemical microenvironment of Zostera muelleri under changing environmental conditions. Measurements revealed high radial O₂ release of up to 500 nmol O2 cm(-2) h(-1) from the base of the leaf sheath, maintaining a c. 300-μm-wide plant-mediated oxic microzone and thus protecting the vital meristematic regions of the rhizome from reduced phytotoxic metabolites such as hydrogen sulphide (H₂S). H₂S intrusion was prevented through passive diffusion of O₂ to belowground tissue from leaf photosynthesis in light, as well as from the surrounding water column into the flow-exposed plant parts during darkness. Under water column hypoxia, high belowground H₂S concentrations at the tissue surface correlated with the inability to sustain the protecting oxic microshield around the meristematic regions of the rhizome. We also found increased pH levels in the immediate rhizosphere of Z. muelleri, which may contribute to further detoxification of H₂S through shifts in the chemical speciation of sulphide. Zostera muelleri can modify the geochemical conditions in its immediate rhizosphere, thereby reducing its exposure to H₂S.
海草一直面临着通过通气组织将足够的氧气从地上组织输送到地下组织的挑战，以维持有氧代谢并抵御植物毒素。电化学微传感器与定制的实验箱结合使用，以分析在不断变化的环境条件下，缪氏大叶藻的地下生物地球化学微环境。测量结果显示，叶鞘基部的径向氧气释放量高达500 nmol O2 cm(-2) h(-1)，维持了一个约300μm宽的植物介导的有氧微区，从而保护了根茎的重要分生组织区域免受诸如硫化氢（H₂S）等还原性植物毒性代谢物的侵害。在光照下，通过叶片光合作用产生的氧气向地下组织的被动扩散，以及在黑暗中从周围水柱向暴露于水流的植物部分扩散，可防止H₂S的侵入。在水柱缺氧的情况下，组织表面地下高浓度的H₂S与无法维持根茎分生组织区域周围的保护性有氧微屏蔽有关。我们还发现，缪氏大叶藻根际附近的pH值升高，这可能通过硫化物化学形态的变化有助于进一步解毒H₂S。缪氏大叶藻可以改变其根际附近的地球化学条件，从而减少其对H₂S的暴露。
