|Field, Taylor - PLANT BIOLOGY UOFI URBANA|
|Nedbal, Lada - PLANT BIOLOGY UOFI URBANA|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 1997
Publication Date: N/A
Interpretive Summary: Light energy driven electron transfer reactions within chloroplast of higher plants is well known and has been under intense investigation for more than three decades. This study demonstrates that electron transfer also occurs in the dark in the chloroplast of sunflower and other higher plants. This dark respiratory activity involves the same plastoquinone pool present in the photosynthetic membrane that functions in light-driven electron transfer. The significance of this finding is that it demonstrates a mechanism by which normally light-dependent reactions can remain active in the dark for important metabolic process such as starch degradation.
Technical Abstract: Although it is generally assumed that the plastoquinone pool of thylakoid membrane in leaves of higher plants is rapidly oxidized upon darkening, this is often not the case. Monitoring the redox state of the plastoquinone pool in leaves, it was found that in many species of plants, the pool actually became more reduced following a light to dark transition. Far red light, which preferentially drives photosystem I turnover, could effectively oxidize the plastoquinone pool. Plastoquinone was rereduced in the dark within a few seconds when far red illumination was removed. The rate and extent of rereduction are inhibited by rotenone and enhanced by carbon monoxide fumigation consistent with the involvement of a type I NADPH dehydrogenase and a terminal oxidase. It appears that this chlororespiratory activity results in proton accumulation and ATP synthase reduction.