School of Biosciences, University of Exeter, Geoffrey Pope Building, Stocker Road, Exeter, EX4 4QG, Devon, UK.
Physiol Plant. 2011 Feb;141(2):130-40. doi: 10.1111/j.1399-3054.2010.01424.x. Epub 2010 Nov 19.
CO(2) fixation in mosses saturates at moderate irradiances. Relative electron transport rate (RETR) inferred from chlorophyll fluorescence saturates at similar irradiance in shade species (e.g. Plagiomnium undulatum, Trichocolea tomentella), but many species of unshaded habitats (e.g. Andreaea rothii, Schistidium apocarpum, Sphagnum spp. and Frullania dilatata) show non-saturating RETR at high irradiance, with high non-photochemical quenching (NPQ). In P. undulatum and S. apocarpum, experiments in different gas mixtures showed O(2) and CO(2) as interchangeable electron sinks. Nitrogen + saturating CO(2) gave high RETR and depressed NPQ. In S. apocarpum, glycolaldehyde (inhibiting photosynthesis and photorespiration) depressed RETR in air more at low than at high irradiance; in CO(2) -free air RETR was maintained at all irradiances. Non-saturating electron flow was not suppressed in ambient CO(2) with 1% O(2) . The results indicate high capacity for oxygen photoreduction when CO(2) assimilation is limited. Non-saturating light-dependent H(2) O(2) production, insensitive to glycolaldehyde, suggests that electron transport is supported by oxygen photoreduction, perhaps via the Mehler-peroxidase reaction. Consistent with this, mosses were highly tolerant to paraquat, which generates superoxide at photosystem I (PSI). Protection against excess excitation energy in mosses involves high capacity for photosynthetic electron transport to oxygen and high NPQ, activated at high irradiance, alongside high reactive oxygen species (ROS) tolerance.
在中等辐照度下，苔藓中的 CO2 固定达到饱和。在遮荫物种（如 Plagiomnium undulatum、Trichocolea tomentella）中，根据叶绿素荧光推断出的相对电子传递速率（RETR）在相似的辐照度下达到饱和，但许多无遮荫生境的物种（如 Andreaea rothii、Schistidium apocarpum、Sphagnum spp. 和 Frullania dilatata）在高光强下表现出非饱和的 RETR，同时具有高的非光化学猝灭（NPQ）。在 P. undulatum 和 S. apocarpum 中，不同气体混合物的实验表明 O2 和 CO2 可以相互作为电子汇。氮+饱和 CO2 可产生高的 RETR 和抑制 NPQ。在 S. apocarpum 中，甘油醛（抑制光合作用和光呼吸）在低光照强度下比在高光强下更能抑制空气呼吸中的 RETR；在无 CO2 的空气中，RETR 在所有辐照度下都得以维持。在环境 CO2 中添加 1%的 O2 并没有抑制非饱和电子流。这些结果表明，当 CO2 同化受到限制时，苔藓具有高的氧气光还原能力。非饱和的光依赖 H2O2 产生，对甘油醛不敏感，表明电子传递由氧气光还原支持，可能通过 Mehler-过氧化物酶反应。与此一致的是，苔藓对百草枯具有高度的耐受性，百草枯在光系统 I（PSI）中产生超氧化物。苔藓对过量激发能的保护涉及到高的光合电子传递到氧气的能力和高的 NPQ，在高光强下激活，同时具有高的活性氧物种（ROS）耐受性。
