Oláh Viktor, Hepp Anna, Irfan Muhammad, Mészáros Ilona
Department of Botany, Faculty of Science and Technology, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary.
Plants (Basel). 2021 Dec 14;10(12):2763. doi: 10.3390/plants10122763.
Duckweeds (Lemnaceae species) are extensively used models in ecotoxicology, and chlorophyll fluorescence imaging offers a sensitive and high throughput platform for phytotoxicity assays with these tiny plants. However, the vast number of potentially applicable chlorophyll fluorescence-based test endpoints makes comparison and generalization of results hard among different studies. The present study aimed to jointly measure and compare the sensitivity of various chlorophyll fluorescence parameters in (giant duckweed) plants exposed to nickel, chromate (hexavalent chromium) and sodium chloride for 72 h, respectively. The photochemistry of Photosystem II in both dark- and light-adapted states of plants was assessed via chlorophyll fluorescence imaging method. Our results indicated that the studied parameters responded with very divergent sensitivity, highlighting the importance of parallelly assessing several chlorophyll fluorescence parameters. Generally, the light-adapted parameters were more sensitive than the dark-adapted ones. Thus, the former ones might be the preferred endpoints in phytotoxicity assays. Fv/Fm, i.e., the most extensively reported parameter literature-wise, proved to be the least sensitive endpoint; therefore, future studies might also consider reporting Fv/Fo, as its more responsive analogue. The tested toxicants induced different trends in the basic chlorophyll fluorescence parameters and, at least partly, in relative proportions of different quenching processes, suggesting that a basic distinction of water pollutants with different modes of action might be achievable by this method. We found definite hormetic patterns in responses to several endpoints. Hormesis occurred in the concentration ranges where the applied toxicants resulted in strong growth inhibition in longer-term exposures of the same duckweed clone in previous studies. These findings indicate that changes in the photochemical efficiency of plants do not necessarily go hand in hand with growth responses, and care should be taken when one exclusively interprets chlorophyll fluorescence-based endpoints as general proxies for phytotoxic effects.
浮萍（浮萍科物种）是生态毒理学中广泛使用的模型，叶绿素荧光成像为这些微小植物的植物毒性测定提供了一个灵敏且高通量的平台。然而，大量潜在适用的基于叶绿素荧光的测试终点使得不同研究之间的结果比较和归纳变得困难。本研究旨在联合测量和比较在分别暴露于镍、铬酸盐（六价铬）和氯化钠72小时的浮萍（大薸）植物中各种叶绿素荧光参数的敏感性。通过叶绿素荧光成像方法评估植物在暗适应和光适应状态下光系统II的光化学过程。我们的结果表明，所研究的参数表现出非常不同的敏感性，突出了平行评估多个叶绿素荧光参数的重要性。一般来说，光适应参数比暗适应参数更敏感。因此，前者可能是植物毒性测定中更优选的终点。Fv/Fm，即文献中报道最广泛的参数，被证明是最不敏感的终点；因此，未来的研究也可能考虑报告Fv/Fo，因为它是更敏感的类似物。测试的毒物在基本叶绿素荧光参数以及至少部分在不同猝灭过程的相对比例上诱导了不同的趋势，这表明通过这种方法可能实现对具有不同作用模式的水污染物的基本区分。我们在对几个终点的反应中发现了明确的剂量效应关系模式。剂量效应关系出现在先前研究中相同浮萍克隆长期暴露于所施加毒物导致强烈生长抑制的浓度范围内。这些发现表明，植物光化学效率的变化不一定与生长反应同步，并且在仅将基于叶绿素荧光的终点解释为植物毒性效应的一般代理时应谨慎。
