Photoinhibition of photosystem I is accelerated by dimethyldithiocarbamate, an inhibitor of superoxide dismutase, during light-chilling of spinach leaves.

In vivo photoinhibition of photosystem I (PS I) was investigated at chilling temperature using the leaves of the chilling-resistant spinach plant treated with an inhibitor of superoxide dismutase, diethyldithiocarbamate (DDC). When spinach leaves were treated with DDC during chilling at 4 degrees C for 12 h with a light intensity of 120 micromol m(-2) s(-1), the activity of PS I and the content of iron-sulfur centers declined to about 50% and 25% of the non-DDC-treated controls, respectively. A native green gel analysis of thylakoid membranes isolated from the DDC-treated leaves resolved a novel chlorophyll-protein complex, which was identified as the light-harvesting complex I (LHC I)-deficient PS I complex when examined by 77 K fluorescence spectroscopy and two-dimensional sodium dodecyl sulfate gel electrophoresis. The possible dissociation of LHC I as an early structural change in the PS I complex after DDC-induced photoinhibition of PS I is discussed.