Division of Plant Industry, CSIRO, GPO Box 1600, 2601, Canberra, ACT, Australia.
Planta. 1992 Feb;186(3):450-60. doi: 10.1007/BF00195327.
The obligate shade plant, Tradescantia albiflora Kunth grown at 50 μmol photons · m(-2) s(-1) and Pisum sativum L. acclimated to two photon fluence rates, 50 and 300 μmol · m(-2) · s(-1), were exposed to photoinhibitory light conditions of 1700 μmol · m(-2) · s(-1) for 4 h at 22° C. Photosynthesis was assayed by measurement of CO2-saturated O2 evolution, and photosystem II (PSII) was assayed using modulated chlorophyll fluorescence and flash-yield determinations of functional reaction centres. Tradescantia was most sensitive to photoinhibition, while pea grown at 300 μmol · m(-2) · s(-1) was most resistant, with pea grown at 50 μmol · m(-2) · s(-1) showing an intermediate sensitivity. A very good correlation was found between the decrease of functional PSII reaction centres and both the inhibition of photosynthesis and PSII photochemistry. Photoinhibition caused a decline in the maximum quantum yield for PSII electron transport as determined by the product of photochemical quenching (qp) and the yield of open PSII reaction centres as given by the steady-state fluorescence ratio, F'vF'm, according to Genty et al. (1989, Biochim. Biophys. Acta 990, 81-92). The decrease in the quantum yield for PSII electron transport was fully accounted for by a decrease in F'vF'm, since qp at a given photon fluence rate was similar for photoinhibited and noninhibited plants. Under lightsaturating conditions, the quantum yield of PSII electron transport was similar in photoinhibited and noninhibited plants. The data give support for the view that photoinhibition of the reaction centres of PSII represents a stable, long-term, down-regulation of photochemistry, which occurs in plants under sustained high-light conditions, and replaces part of the regulation usually exerted by the transthylakoid ΔpH gradient. Furthermore, by investigating the susceptibility of differently lightacclimated sun and shade species to photoinhibition in relation to qp, i.e. the fraction of open-to-closed PSII reaction centres, we also show that irrespective of light acclimation, plants become susceptible to photoinhibition when the majority of their PSII reaction centres are still open (i.e. primary quinone acceptor oxidized). Photoinhibition appears to be an unavoidable consequence of PSII function when light causes sustained closure of more than 40% of PSII reaction centres.
在 50 μmol 光子·m(-2)·s(-1)的条件下生长的专性荫生植物白花紫露草（Tradescantia albiflora Kunth）和适应两种光量子通量率（50 和 300 μmol·m(-2)·s(-1)）的豌豆（Pisum sativum L.）在 22°C 下，分别用 1700 μmol·m(-2)·s(-1)的光抑制条件下进行了 4 小时的处理。通过测量 CO2 饱和的 O2 释放来测定光合作用，并用调制叶绿素荧光和功能反应中心的闪光产量测定来测定光系统 II（PSII）。白花紫露草对光抑制最敏感，而在 300 μmol·m(-2)·s(-1)下生长的豌豆最具抗性，而在 50 μmol·m(-2)·s(-1)下生长的豌豆则表现出中等敏感性。研究发现，功能 PSII 反应中心的减少与光合作用和 PSII 光化学抑制之间存在很好的相关性。光抑制导致 PSII 电子传递的最大量子产率下降，如 Genty 等人（1989，Biochim. Biophys. Acta 990，81-92）所确定的那样，通过光化学猝灭（qp）和稳态荧光比 F'vF'm 产物确定的开放 PSII 反应中心的产量来确定。根据给定的光量子通量率，光抑制和非抑制植物的 qp 相似，因此 PSII 电子传递的量子产率的下降完全归因于 F'vF'm 的下降。在光饱和条件下，光抑制和非抑制植物的 PSII 电子传递量子产率相似。这些数据支持这样一种观点，即 PSII 反应中心的光抑制代表了在持续高光条件下植物中光化学的稳定、长期下调，它取代了通常由跨类囊体 pH 梯度施加的部分调节。此外，通过研究不同光适应的阳生和荫生物种对光抑制的敏感性与 qp 的关系，即开放到闭合 PSII 反应中心的分数，我们还表明，无论光适应如何，当植物的大部分 PSII 反应中心仍然开放（即，初级醌受体氧化）时，它们就容易受到光抑制。当光引起 PSII 反应中心的持续关闭超过 40%时，光抑制似乎是 PSII 功能不可避免的结果。
