Spatial Heterogeneity of Cadmium Effects on <i>Salvia sclarea</i> Leaves Revealed by Chlorophyll Fluorescence Imaging Analysis and Laser Ablation Inductively Coupled Plasma Mass Spectrometry

• Main Authors: Michael Moustakas, Anetta Hanć, Anelia Dobrikova, Ilektra Sperdouli, Ioannis-Dimosthenis S. Adamakis, Emilia Apostolova
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Materials
• Subjects: bioimaging; clary sage; effective quantum yield (Φ<i>_PSΙΙ</i>); non-photochemical quenching (NPQ); photochemical quenching (<i>q</i>_{<span style="font-variant: small-caps">p</span>}<span style="font-variant: small-caps">)</span>; photoprotective mechanism; photosynthetic heterogeneity; phytoremediation; reactive oxygen species (ROS); singlet oxygen (¹O₂)
• Online Access: https://www.mdpi.com/1996-1944/12/18/2953

In this study, for a first time (according to our knowledge), we couple the methodologies of chlorophyll fluorescence imaging analysis (CF-IA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), in order to investigate the effects of cadmium (Cd) accumulation on photosystem II (PSII) photochemistry. We used as plant material <i>Salvia sclarea</i> that grew hydroponically with or without (control) 100 &#956;M Cd for five days. The spatial heterogeneity of a decreased effective quantum yield of electron transport (&#934;<i>_{PS&#921;&#921;}</i>) that was observed after exposure to Cd was linked to the spatial pattern of high Cd accumulation. However, the high increase of non-photochemical quenching (NPQ), at the leaf part with the high Cd accumulation, resulted in the decrease of the quantum yield of non-regulated energy loss (&#934;<i>_NO</i>) even more than that of control leaves. Thus, <i>S. sclarea</i> leaves exposed to 100 &#956;M Cd exhibited lower reactive oxygen species (ROS) production as singlet oxygen (¹O₂). In addition, the increased photoprotective heat dissipation (NPQ) in the whole leaf under Cd exposure was sufficient enough to retain the same fraction of open reaction centers (<i>q</i>_{<span style="font-variant: small-caps;">p</span>}<span style="font-variant: small-caps;">) </span>with control leaves. Our results demonstrated that CF-IA and LA-ICP-MS could be successfully combined to monitor heavy metal effects and plant tolerance mechanisms.