The adverse effects of cadmium on plants are accompanied by a limitation of photosynthesis, due to the production of reactive oxygen species, leading to oxidative damage to PSII and the disruption of key protein complexes involved in photosynthetic pathways. We investigated the effects of cadmium stress combined with high light in Arabidopsis thaliana, as dependent on the cadmium dose applied. The aim was to investigate the combined effect of the two stressors on photochemical processes with the hypothesis that Cd stress enhances the negative effect of the high light. The plants were treated with 0, 1, 10, and 50 mM Cd added as CdCl2 solution to soil (potted plants), and a high light stress. The highest dose (50 mM) induced a significant oxidative stress, reduced chlorophyll fluorescence parameters related to PSII functioning and increased energy dissipation mechanisms. Elevated Cd contents impaired the electron transport and limited PSII efficiency. OJIP analysis revealed a Cd-induced K- and L-band appearance documenting LHC-PSII limitation. The combination of Cd and high light stress resulted in the photoinhibition effects in PSII, i.e., a decrease in potential and effective yields of PSII.

• Keywords
• OJIP, cadmium, chlorophyll fluorescence, heavy metal, nonphotochemical quenching, photoinhibition, protective mechanisms,
• MeSH
• Arabidopsis * drug effects   radiation effects   physiology   metabolism   MeSH
• Chlorophyll metabolism   MeSH
• Photochemical Processes * drug effects   radiation effects   MeSH
• Photosynthesis * drug effects   radiation effects   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Stress, Physiological * drug effects   MeSH
• Cadmium * toxicity   pharmacology   MeSH
• Oxidative Stress drug effects   radiation effects   MeSH
• Reactive Oxygen Species metabolism   MeSH
• Light * MeSH
• Electron Transport drug effects   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll MeSH
• Photosystem II Protein Complex MeSH
• Cadmium * MeSH
• Reactive Oxygen Species MeSH

This study aimed to determine the photosynthetic performance and differences in chlorophyll fluorescence (ChlF) parameters between Eulophia dentata and its companion species Bletilla formosana and Saccharum spontaneum when subjected to different photosynthetic photon flux density (PPFDs). Leaf surfaces were then illuminated with 50, 100 (low PPFDs), 300, 500, 800 (moderate PPFDs); 1,000; 1,500; and 2,000 (high PPFDs) μmol m-2·s-1, and the ChlF parameters were measured during the whole process. Increasing nonphotochemical quenching of ChlF and decreasing potential quantum efficiency of PSII, actual quantum efficiency of PSII, and quantum efficiency ratio of PSII in dark recovery from 0-60 min were observed in all leaves. A significant and negative relationship was detected between energy-dependent quenching (qE) and photoinhibition percent in three species under specific PPFD conditions, whereas a significant and positive relationship was detected between photoinhibitory quenching (qI) and photoinhibition percent. The qE and qI can be easily measured in the field and provide useful ecological indexes for E. dentata species restoration, habitat creation, and monitoring.

• Keywords
• Bletilla, Eulophia, Saccharum, chlorophyll fluorescence, light intensity, photoinhibition,
• Publication type
• Journal Article MeSH