Toxicity of sodium diethyl‐dithiocarbamate (NaDDC) on photoautotrophic growth of Anacystis nidulans IU 625

Abstract

AbstractThe effect of a graded concentration (0.05–0.6 mmol/1) of sodium diethyldithiocarbamate (NaDDC) on the growth rate of Anacystis nidulans was found to be concentration‐dependent. A 50% inhibition (I50) of the growth rate was observed at 0.28 mmol/1 of NaDDC. A sudden decrease in cellular absorbance at 435,625 and 675 nm on the third day, and followed by a gradual decrease up to the 6th day indicated an NaDDC‐induced bleaching of the chlorophyll α and phycocyanin pigments. Furthermore, an NaDDC‐induced increase in absorbency at 340 nm after 48 hrs of light incubation was indicative of the reduced state of the carriers. The result on the reduction of 1,6‐dichlorophenol indophenol (DCPIP), cytochrome c and NADP was an NaDDC‐induced stimulation of all the reductive processes, with saturating rates at approximately 0.4 mmol/1 of NaDDC. Furthermore, the rate of DCPIP reduction in the presence of NaDDC was inhibited by rotenone (100 μmol/l). SHAM (salicyl hydraxamic acid, 500 μmol/l) and DCMU (100 μmol/l). Similarly, the addition of 10 μmol/l of DCMU resulted in the inhibition of both cytochrome and NADP reductions. Therefore, the results suggested that NaDDC could bring about the over‐reduction of carriers by interacting with the electron transport chain on or before the DCMU sensitive site. An NaDDC‐dependent general increase in the fluorescence of chlorophyll a was further stimulated by the electron transport inhibitors. The result on oxygen evolution was a 50% inhibition (I50) of H2O2 and H2O2 supported O2 evolution at 0.12 and 0.19 mmol/1 of NaDDC, respectively. Taken together, these could suggest that the highly reduced state of carriers in the presence of NaDDC might be preventing the uphill electron flow from the light‐harvesting pigment complex, H2O and H2O2. Thus, the foregoing results inferred that the bleaching of pigments and over‐reduction of electron carriers ultimately accounted for the death of the organism.