Chlorophyll Fluorescence Imaging-Based Duckweed Phenotyping to Assess Acute Phytotoxic Effects

Abstract

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 Spirodela polyrhiza (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 in vivo 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.

Species-specific responses of Antarctic terrestrial microalgae to salinity stress. Comparative study in Klebsormidium sp. and Stigeoclonium sp.

“…The observed decrease in F M and F M ´ found at 3 M NaCl in Klebsormidium and Stigeoclonium is a well-known phenomenon found in previous salinity studies in cyanobacteria (Lu and Vonshak 2002), microalgae (Liang et al 2014) and vascular plants (e.g., Hniličková et al 2017, Oláh et al 2021. Rfd, which is considered an indicator of plant vitality under stressful con-ditions, decreased at the highest salinity level (3M NaCl) as well, in accordance with Shin et al (2020Shin et al ( , 2021, who also found a significant decrease in Rfd levels in plants exposed to the extreme salinity stress.…”

A Hormetic Spatiotemporal Photosystem II Response Mechanism of Salvia to Excess Zinc Exposure

“…Pulse-amplitude-modulated (PAM) fluorescence imaging enables analyses on spatial heterogeneities in photosynthetic parameters and is considered to be a developing tool to evaluate the changes that occur under unfavorable environmental conditions (biotic–abiotic) in the amount of the light energy use at the whole leaf’s surface [ 50 , 51 , 52 , 53 , 54 , 55 ]. The response of whole-leaf PSII photochemistry of heavy-metal-tolerant plant species has been shown to be heterogenous [ 14 , 33 , 39 ] and to be related to the whole-leaf spatial accumulation pattern of the heavy metal [ 56 ].…”

Photosynthesis and chlorophyll fluorescence of Iranian licorice (Glycyrrhiza glabra l.) accessions under salinity stress

“…Salt stress also alters the size and density of stomata, so that stomatal conductance decreases (Zhang et al, 2021). Parallel to a saltinduced increase in the minimal fluorescence (F0) and the noticeable drop in the maximal fluorescence (Fm), salt stress may also limit maximum quantum yield (Fv/Fm) (Olah et al, 2021). In a light-adapted state, it could potentially result in a decrease in photochemical quenching (qP), associated with a significant increase in the coefficient of nonphotochemical quenching (Navarro-Leoń et al, 2021;Zhang et al, 2021).…”