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Methylglyoxal functions as Hill oxidant and stimulates the photoreduction of O 2 at photosystem I: a symptom of plant diabetes
Author(s) -
SAITO RYOTA,
YAMAMOTO HIROSHI,
MAKINO AMANE,
SUGIMOTO TOSHIO,
MIYAKE CHIKAHIRO
Publication year - 2011
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2011.02344.x
Subject(s) - dcmu , methylglyoxal , photosystem ii , chloroplast , chemistry , photochemistry , photosynthesis , photosystem i , biochemistry , enzyme , gene
We elucidated the metabolism of methylglyoxal (MG) in chloroplasts of higher plants. Spinach chloroplasts showed MG‐dependent NADPH oxidation because of aldo‐keto reductase (AKR) activity. K m for MG and V max of AKR activity were 6.5 m m and 3.3 µ mol NADPH (mg Chl) −1 h −1 , respectively. Addition of MG to illuminated chloroplasts induced photochemical quenching (Qp) of Chl fluorescence, indicating that MG stimulated photosynthetic electron transport (PET). Furthermore, MG enhanced the light‐dependent uptake of O 2 into chloroplasts. After illumination of chloroplasts, accumulation of H 2 O 2 was observed. K m for MG and V max of O 2 uptake were about 100 µ m and 200 µ mol O 2 (mg Chl) −1 h −1 , respectively. MG‐dependent O 2 uptake was inhibited by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) and 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐ p ‐benzoquinone (DBMIB). Under anaerobic conditions, the Qp of Chl fluorescence was suppressed. These results indicate that MG was reduced as a Hill oxidant by the photosystem I (PSI), and that O 2 was reduced to O 2 – by the reduced MG. In other words, MG produced in chloroplasts is preferentially reduced by PSI rather than through AKR. This triggers a type of oxidative stress that may be referred to as ‘plant diabetes’, because it ultimately originates from a common metabolite of the primary pathways of sugar anabolism and catabolism.