PLANT PHYSIOLOGY , Vol 108, Issue 1 313-318, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Photosynthetic Nitrite Reduction as Influenced by the Internal Inorganic Carbon Pool in Air-Grown Cells of Synechococcus UTEX 625
N. A. Mir, C. Salon and D. T. Canvin
Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
Photosynthetic reduction of NO2- was studied in air-grown cells of a
cyanobacterium, Synechococcus UTEX 625. Addition of NO2- resulted in
significant amounts of chlorophyll a fluorescence quenching both in the
absence and presence of CO2, fixation inhibitors, glycolaldehyde or
iodoacetamide. The degree of NO2- quenching was insensitive to the O2
concentration in the medium. Addition of 100 [mu]M inorganic carbon in the
presence of glycolaldehyde and O2, leading to formation of the carbon pool
within the cells, resulted in pronounced fluorescence quenching. Removal of
O2 from the medium restored the fluorescence yield completely, and the
subsequent addition of NO2- quenched 36% of the variable fluorescence. From
the response to added 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the
quenching by NO2- appeared to be photochemical quenching, and
nonphotochemical quenching did not seem to be present. The reduction of
NO2- observed on its addition to inorganic carbon-depleted cells remained
uninfluenced by O2 or glycolaldehyde. The internal inorganic carbon pool in
the cells stimulated NO2- reduction, both in the presence and absence of
O2, by 4.8-fold. An increase in NO2- reduction by 0.5-fold was also
observed in the presence of O2 during simultaneous assimilation of carbon
and nitrogen in inorganic carbon-depleted cells. Contrary to this, under
anaerobiosis, NO2- reduction was suppressed when carbon and nitrogen
assimilation occurred together.
