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Excess copper predisposes photosystem II to photoinhibition in vivo by outcompeting iron and causing decrease in leaf
Eija Pätsikkä1, Marja Kairavuo, Frantisek Sersen
1Plant Physiology and Molecular Biology, Biocity A, University of Turku, FIN-20014 Turku, Finland.
Plant Physiology
|July 13, 2002
Summary
Copper (Cu) exposure enhances photoinhibition in bean plants by reducing chlorophyll and causing iron deficiency, making photosystem II more sensitive to light. This effect is linked to lower leaf optical density.
Area of Science:
- Plant Physiology
- Photosynthesis Research
- Environmental Stress Biology
Background:
- Photoinhibition, the light-induced damage to photosystem II, is a critical factor affecting plant productivity.
- Copper (Cu) is an essential micronutrient, but excess levels can induce toxicity and affect plant physiology.
- Understanding the mechanisms of Cu-induced stress is vital for agriculture and environmental science.
Purpose of the Study:
- To investigate the in vivo effects of excess copper (Cu2+) on photoinhibition in bean plants (Phaseolus vulgaris).
- To determine the role of chlorophyll content, thylakoid structure, and iron (Fe) deficiency in Cu-enhanced photoinhibition.
- To elucidate the relationship between leaf optical density and susceptibility to photoinhibition under Cu stress.
Main Methods:
- Bean plants were grown with varying Cu(2+) concentrations (0.3, 4, 15 microM).
- Photoinhibition was measured in vivo using lincomycin to inhibit recovery.
- Chlorophyll concentration, chloroplast Cu levels, and thylakoid membrane structure were analyzed.
- The impact of combined excess Fe and Cu treatments was assessed.
Main Results:
- Cu(2+)-treated plants exhibited faster photoinhibition in intact leaves compared to controls.
- Isolated thylakoids from Cu-treated plants were not more sensitive to photoinhibition.
- Cu treatment reduced leaf chlorophyll concentration and thylakoid membrane network.
- Supplementation with excess Fe alleviated Cu toxicity symptoms and reduced leaf Cu levels.
- Cu treatment led to iron deficiency, which was identified as the cause of enhanced photoinhibition.
Conclusions:
- Excess copper enhances photoinhibition in bean plants primarily by inducing iron deficiency, leading to reduced chlorophyll and increased photosystem II sensitivity.
- Direct effects of Cu on chloroplasts or oxidative stress are unlikely causes for the observed photoinhibition.
- Leaf optical density is causally linked to photoinhibition susceptibility, with implications for plant adaptation to light environments.