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THE SUSCEPTIBILITY OF MUNG BEAN CHLOROPLASTS TO PHOTOINHIBITION IS INCREASED BY AN EXCESS SUPPLY OF IRON TO PLANTS: A PHOTOBIOLOGICAL ASPECT OF IRON TOXICITY IN PLANT LEAVES
Author(s) -
Kim Chang Sook,
Jung Jin
Publication year - 1993
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1993.tb04912.x
Subject(s) - photoinhibition , photosynthesis , chloroplast , thylakoid , toxicity , electron transport chain , chemistry , sunlight , botany , horticulture , iron deficiency , photosystem ii , biology , biochemistry , medicine , physics , organic chemistry , astronomy , anemia , gene
In an attempt to elucidate the underlying mechanisms for iron toxicity in plants, the combined effects of iron overload and light intensities on the photosynthetic capacity of leaves were particularly focussed upon in this study, using mung bean seedlings grown under varied conditions regarding the supply of light and iron. The seedlings, when supplied with excess iron (up to 1.0 m M ) and low light (40 W/m 2 ), did not suffer any loss of photosynthesis; further, the typical symptoms of iron toxicity, as shown in the leaves grown in sunlight at ca 450 W/m 2 on an average, were not seen in those. Nonetheless, excess iron supply resulted in a marked increase in photosensitivity of the low light‐adapted seedlings. A large portion of iron accumulated in chloroplasts by the supply of excess iron was found to be incorporated into thylakoids as nonheme iron (NHI), which acts as a potent sensitizer, photogenerating singlet oxygen ( 1 O 2 ). The generation rate of 1 O 2 from thylakoids linearly increased with increasing content of NHI; this was in parallel with the NHI content dependence of photoinactivation rates of photosynthetic electron transport and key enzymes of the Calvin cycle in chloroplasts. The results suggest that Fe‐dependent photosensitization reactions, occurring via the 1 O 2 mechanism, may be deeply involved in cellular processes leading to developing iron toxicity symptoms in plants.