The Effects of the Dipyridyl Diquat on the Metabolism of Chlorella Vulgaris III. Dark Metabolism: Effects on Respiration Rate and the Path of Carbon

Abstract

When O. vulgaris is treated in complete darkness with diquat at concentrations which are toxic in the light, there is a rapid and large stimulation of oxygen uptake with no significant alteration in the R,Q. If the O. vulgaris has been darkened for some hours before the addition of diquat there is a two- to threefold stimulation of the rate of respiration, which subsequently remains constant or falls only slowly for up to 500 min. With pre-illuminated or glucose-treated O. vulgaris, diquat causes a much greater stimulation of dark respiration, rapidly declining to near the control rate. Tracer studies with 14C02 and [14C]glucose show that diquat when added in darkness to O. vulgaris accelerates the breakdown of starch and the loss of 14C from most intermediate substances of carbohydrate metabolism. The exception to this is the rapid accumulation of 14C counts in citric acid. These results are discussed and a mechanism for the action of diquat in darkness is proposed.