The effects of diquat on gas exchange in illuminated C. vUlgaris have been
studied by manometric procedures. Estimates of dark oxygen uptake were made by
transfer of treated cells to darkness. Analysis of the results indicates that on adding
diquat to C. vUlgariB there is a rapid fall in the rate of apparent photosynthesis.
This is due to an immediate and large increase in dark metabolism (C02 and O2
exchange) accompanied by irreversible inhibition of real photosynthesis firstly,
then of respiration. At some unspecified stage a light-dependent oxygen uptake begins,
rises to a maximum rate, and declines to a low value, continuing after the inhibition
of respiration. These results are discussed in relation to the known effects of diquat
on plastid reactions and to the hypothesis that in illuminated green tissue diquat
produces a toxic substance which damages both the photosynthetic and respiratory
apparatus.
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