J. Basic Microbiol. 32 (1992) 2. 119 - 121! r ) • (Department of Microbiology. 13arkatullah University, Bhopal 462026 (M .P.), India) Action of sodium diethyldithiocarbamate (NaDDC) on the HILL activity and chlorophyll fluorescence in Anacystis nidulans IU 625 D. P. SINGH, R. GOTIIALWAL and P. S. BISEN (Received 15 Novemher 1991 / Acceflle(/ 7 Jallt/ary 1992) Effect of sodium diethyldithiocarbamate (NaDDC) on chlorophyll f1uorescence and HILI . activity in AlIllCyslis ceIls exhibited stimulati o n o f both thc proccsses in a concentration-dependent manner (SINGH 1'1 al. 1989). Trcatment of cells with sodium dodccyl s ulphatc (I % w/ v) and tris (0.5 M) resulted into further stimulation of NaDDC s upported both f1uorescence emission and HILL activity. Additi on or energy consuming substrates like NaHCO J (3 mM) and 3-phosphoglyeeric acid (PGA 1 mM) could bring about quenching of NaDDC stimulated n uoreseence. However, iluoreseence quenching of carbon substratcs could be reversed in presence of DCMU (10 mM). Furthcr, the results on cytoehrome-c reduction. f1uorcsccnce emi ssio n and pigment absorption in the presence of NaDDC exhibited a 1'1-1 depcnd<;ncc (6 - 8) of Na DDC on these processes with maximum effect at pH 6. NaDDC-indueed general increase in the absorbance of pigments accompanied by hypsochromic shifts at 680 and 625 nm were indicative of conformational changes in the pigment protcin complcxcs. The results with energy transfer inhibitors showed that uncouplers like FCCP (10 Nigericin (10 and NH 4 CI (I mM) could significantly alter the effect of NaDDC on fluorescence emission and HILL activity, while antimycin (5 and N-ethylamalcimide (100 mM) had Ettie effect. These results, taken together, suggested that NaDDC-indlll:ed build up of proton gradient might be resulting into cessation of electron transport and stimulation of fluorescence by exerting a back pressure on the chargc separation property of membrane . Alkylderivative of thiocarbamates arc a class of organic fungicides. A number of studies ha ve been carried out on their toxicoiogica 'i properties in relation to the soil microorganisms (PAR- KER-RHODES 1943, MARTIN 1957, PARRY and WOOD 1959, SUPESTEUN el at. 1957). Sensitivity of the RhizohiulIl sp. towards these fungicides is greatly dependent on the surrounding pH conditions (SUI) and GUPTA 1972). It has been suggested that toxicity of these fungicides arc directly proportional to the content of dithiocarbamate radicals (AUDUS 1970). A little effort has been made to s tudy the effect of dithiocarbamatc s on the non-target, photosynthetic organi sms (AUDUS 1970, LAZAROFF 1967, VENKATRAMAN and RAJAYLAKSHMI 1972). We have reported that sodium diethyldithiocarbamate (NaDDC) in the range of millimolar concentrations (0.1- 1.0 mM) is toxic to the growt tl of cyanobacterium AI1(fcyslis nidu/alls (SINGH el at. 1989). Addition of NaDDC to the cell suspension of A. nidu/af/s has been found to cause bleaching of photosynthetic pigments and over-reduction of electron transport chain, which ultimately accounts for the death of organism. However, there is no satisfactory ex plana l ion about the mode and site ofNaDDC action on the photosynthetic energy transfer . In continuation to our earlier investigation , the present study is an attempt to ascertain the mechanism of NaDDC action on the photosynthetic electron transfer process in the cya no bactcri um AI/acysl is I/ii/u/alls. Materials and methods Organism and growth condition: The unicellular cyanobacterium Al/lJcyslis nidl/llJns IU 625 (ATCC 271.44) was obtaim:d through the courtscy of Dr. R. S. SAFFERMAN. U.S . Environmental Protcction