The Effeots of the Dipyridyl Diquat on the Metabolism of Chlorella Vulgaris I. Gas Exchange in the Light

Abstract

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.

Lipid Peroxidation and Chlorophyll Destruction Caused by Diquat during Photosynthesis in Scenedesmus

“…Effects of diquat alone. The time course of the inhibition of photosynthetic oxygen evolution by diquat (Figure la shows the same type of curve as was found by Turner et al (1970) for Chlorella and elegantly analyzed. Malondialdehyde is a breakdown product of tri-unsaturated fatty acid hydroperoxides, which can be formed under the influence of diquat in the light (Figure lb).…”