P.K. Mohapatra

Growth pattern changes of Chlorella vulgaris and Anabaena doliolum due to toxicity of dimethoate and endosulfan

Effects of pesticides in the ecosystem do not remain restricted to target organisms but rather extend to nontarget organisms like microorganisms which play an important role in the food chain vis-a-vis biological processes such as biogeochemical cycling, production, decomposition, interaction with other organisms, etc. Agrochemicals contaminate surface waters of agricultural regions and effectively inhibit growth, pigment biomass and survival rate of freshwater phytoplankton (Lal 1984; Adhikary 1989; Mandal and Mohanty 1990: Netrawali and Gandhi 1990). However, other toxicity method such as effect on growth pattern is useful to achieve standardization. The present paper describes the effects of two pesticides, viz., dimethoate and endosulfan on the growth patterns of Chlorella vulgaris and Anabaena doliolum.

Photosynthetic and fluorescence responses of Solanum melangena L. to field application of dimethoate

The organophosphorus insecticide dimethoate, at field concentration (1.419+/-0.086mga.i.g(-1)fr.wt. of leaf tissue) did not cause any significant degradation of chlorophylls and carotenoids in Solanum melangena L. On the other hand, there was significant reduction of photosynthesis, transpiration and stomatal conductance during 6h after spray application of the insecticide. Distinct change of OJIP fluorescence transient with increase of J and I rise and corresponding decrease in P rise was observed during 6h after insecticide application. The fluorescence parameters, viz., relative variable fluorescence at J level (V(j)), net rate of PS II closure (M(0)), energy dissipation (DI(0)/RC) and maximum trapping rate of active PS II (TR(0)/RC), during the same treatment period, showed significant increase but variable fluorescence (F(v)), fluorescence yield (TR(0)/Abs), electron transport probability (ET(0)/TR(0)), and activity of RC (ET(0)/RC) showed significant decrease. All physiological and fluorescence parameters, and the OJIP fluorescence transient recovered steadily to the control level during 48h after insecticide application. There was continuous reduction in the insecticide content of the leaf tissue during the observation period.

Variation in effects of four OP insecticides on photosynthetic pigment fluorescence of Chlorella vulgaris Beij.

Effects of the insecticides quinalphos, chlorfenvinphos, dimethoate and phorate on photosystem activity of Chlorella vulgaris were investigated by different chlorophyll fluorescence measurements. Exposure to each of the insecticides increased the proportion of inactivated PS II reaction center. Quinalphos and chlorfenvinphos caused OJIP fluorescence reduction at all levels by decreasing the proportion of Q(A)-reducing PS II reaction centers (RCs). The other two insecticides affected OJIP fluorescence rise by hindering the electron transport beyond Q(A). Insecticide treatment resulted in decrease of the density of active RC and performance indices (PI) by enhanced dissipated energy flux per active RC. Antenna size was severely minimized by quinalphos and chlorfenvinphos treatment whereas other two insecticides had no such effect. Each insecticide treatment caused increase of photosystem antenna/core and PS II/PS I fluorescence ratios. Quinalphos and chlorfenvinphos affected the donor sides of photosystems whereas dimethoate and phorate inhibited electron transfer beyond Q(A) (acceptor side).

Salt induced changes in the growth of Chlorococcum humicolo and Scenedesmus bijugatus under nutrient limited cultures

Due to climatic changes in tropics, saline water bodies are often subject to natural fluctuations of salinity through precipitation, dessication, drought conditions or anthropogenic interference. Growth and persistence of algae under these conditions require physiological tolerance and/or resistant stages in the life cycle. Salinity, which ranges from 95.9-174.7 mg/L as NaCI, is considered as an important parameter for the Indradyumna pond (485 x 396 sq ft, maximum depth 5 m) of Puri, Orissa for it is located at a distance of 1 km from the Bay of Bengal. The fluctuation of salinity level of the pond has been observed during 1988-1991 mostly due to excessive use by innumerable number of pilgrims all over the year (Dash 1992). Increased salinity favors growth of cyanobacteria because this is the only group of photoautotrophic plankton taxa requiring Na + for growth (Allen and Arnon 1955). Green algal species like halotolerant planktonic algae (Hellebust and Le Gresley 1985), Chlorella, Ankistrodesmus and Scenedesmus (Kessler 1980) have also been found to be favored by increased salinity. However, the rationale of studying salinity tolerance of algae under nutrient limited conditions seems to be more appropriate in the bioassay method because it is established that the susceptibility / resistance characteristic of an algal species to external stress is nutritionally determined (Herbert and Bradley 1989; Mohapatra and Mohanty 1992). Accordingly, it was decided to see the effects of salinity stress on two indigenous phytoplankton species viz., Chlorococcum humicolo (Nag) Rabenh. and Scenedem~us bijugatus KUtz. in culture with differential nutrient enrichment using the sterile pond water as medium.

Comparative toxicity of two organophosphorus insecticides on membrane integrity of Chlorella vulgaris. I. effect on membrane permeability

Abstract The organophosphorus insecticides dimethoate and quinalphos caused reduction in accumulation of uranine by Chlorella vulgaris Beijerinck cells with increase in their concentrations (0-500 µM L- 1 ) in growth medium. On the other hand, there was increase in the loss of metabolites and non-metabolizable compounds like 2-deoxyglucose and 2-aminoisobutyric acid (AIBA) from the treated cells during 2 hr of treatment period. But significant loss of protein from cells was observed only at concentrations ≥ 350 µM L- 1 of the insecticides. The toxic effect of quinalphos on membrane permeability was more pronounced at each selected concentration compared to that of dimethoate. With dimethoate treatment the loss of 2-deoxyglucose, AIBA and other cellular metabolites was observed at ≥ 350 µM L- 1 concentration while with quinalphos treatment such effect was reported at ≥ 10 µM L- 1 concentration. Increased permeability of the plasma membrane of intact cells is expected to be caused by the reduction in integrity of membrane lipids. The results are discussed to arrive at the conclusion on mechanism of action of insecticides on actively growing autotrophic cells.