The effect of shikimate onNostoc linckia

Growth, heterocyst frequency and nitrogenase-catalysed hydrogen evolution, but not nitrogenase activity, hydrogen uptake and photosynthetic O₂ evolution activities of the cyanobacteriumNostoc linckia, were significantly affected by shikimic acid (up to 10 g/ml). Exposure ofN. linckia to shikimic acid at 50 g/ml for 24 h caused fragmentation of filaments into 10- to 15-celled trichomes.

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Résumé L'acide shikimique (jusqu'à 10 g/ml) anecte de manière significative la croissance, la fréquence des hétérocystes, l'emission d'hydrogène catalysée par la nitrogénase, et de manière non significative l'activité de la nitrogénase, le prélèvement d'hydrogène et la génération photosynthetique d'O₂ de la cyanobactérieNostoc linckia. L'exposition deN. linckia à l'acide sinkinique à 50 g/ml pendant 24h a causé la fragmentation des filaments en trichomes de 10 à 15 cellules.

     

Uptake of 2,4-Dichlorophenoxyacetic Acid by Pseudomonas fluorescens

Factors influencing the uptake of the sodium salt of 2,4-dichlorophenoxyacetic acid (2,4-D), under conditions in which no net metabolism occurred, were investigated in an effort to determine both the significance of "non-metabolic" uptake as a potential agent in reducing pesticide levels and the mechanisms involved. Uptake of 2,4-D was affected by pH, temperature, and the presence of other organic and inorganic compounds. Uptake was more pronounced at pH values less than 6, which implies that there may be some interaction between charged groups on the cell and the ionized carboxyl group of 2,4-D. Active transport, carrier-mediated diffusion, passive diffusion, and adsorption were considered as possible mechanisms. Though uptake was inhibited by glucose, sodium azide, and fluorodinitrobenzene (but not by uranyl ion), 2,4-D was not accumulated against a concentration gradient, a necessary consequence of an active transport system, nor was isotope counterflow found to occur. Thus, carrier-mediated diffusion was finally precluded, implying that uptake probably occurs by a two-step process: sorption onto the cell wall followed by passive diffusion into the cytoplasm.     

Growth Rates of a Pseudomonad on 2,4-Dichlorophenoxyacetic Acid and 2,4-Dichlorophenol

The growth of a pseudomonad on 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4-DCP (2,4-dichlorophenol) was studied in batch and continuous culture. The optimum growth rate using 2,4-D was 0.14/h at 25 C in a pH range from 6.2 to 6.9. Highest specific growth rate using 2,4-DCP was 0.12/h at 25 C in a pH range from 7.1 to 7.8. Growth was strongly inhibited by 2,4-DCP above a concentration of 25 mg/liter whereas no appreciable inhibition was observed with 2,4-D at concentrations up to 2,000 mg per liter. Growth on 2,4-DCP was described by Monod kinetics at subinhibitory concentrations but the inhibition by 2,4-DCP exhibited an unusual linear response to substrate concentration, and did not fit a model based on noncompetitive inhibition. The lag phase of batch cultures was found to depend on both 2,4-DCP concentration and prior adaptation of the inoculum. A study such as this on the kinetics of growth on related substrates may be useful as a method of finding the rate-limiting step in a metabolic sequence.     

2,4-二氯苯氧乙酸的研究进展

2,4-二氯苯氧乙酸经常作为除草剂和植物生长调节剂使用,在农林业中发挥了重大作用,尤其在水果(如柑橘)保鲜中应用广泛,但其毒性问题也受到广泛关注,因此了解2,4-D的生理作用、在生物及环境中的代谢降解、残留毒性和提取鉴定等的研究进展很有必要.     

Mineralization of 2,4-Dichlorophenoxyacetic Acid (2,4-D) and Mixtures of 2,4-D and 2,4,5-Trichlorophenoxyacetic Acid by Phanerochaete chrysosporium

Evidence is presented for mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) in nutrient-rich media (high-nitrogen and malt extract media) by wild-type Phanerochaete chrysosporium and by a peroxidase-negative mutant of this organism. Mass balance analysis of [U-ring-¹⁴C]2,4-D mineralization in malt extract cultures showed 82.7% recovery of radioactivity. Of this, 38.6% was released as ¹⁴CO₂ and 27.0, 11.2, and 5.9% were present in the aqueous, methylene chloride, and mycelial fractions, respectively. 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were simultaneously mineralized when presented as a mixture, and mutual inhibition of degradation was not observed. In contrast, a relatively higher rate of mineralization of 2,4-D and 2,4,5-T was observed when these compounds were tested as mixtures than when they were tested alone.     

Some Physiological Responses of Chlorella pyrenoidosa to 2,4-Dichlorophenoxyacetic Acid

An 18-h treatment of synchronously-grown Chlorella pyrenoidosawith 2,4-D did not significantly alter the size, dry weight,degree of synchrony, or pigment content of the cells, nor weredetectable quantities of ethylene produced. When Chlorella pyrenoidosawas treated with 5?10^–4 M 2,4-D, there was a statisticallysignificant stimulation of both net oxygen uptake and productionwhile 5?10 M 2,4-D inhibited both processes. When Chlorellapyrenoidosa was treated with 5?10^–4 M and 5?10^–3M 2,4-D, significantly greater amounts of glycollate were presentin the culture medium, even though an assay for glycollate dehydrogenaseshowed that the activity of this enzyme from 2,4-D-treated Chlorellapyrenoidosa was three times greater than in control cells. Looselybound 2,4-D was partitioned from a nonaqueously isolated chloroplastfraction, while other cell fractions failed to show detectablequantities of 2,4-D. It is postulated that in Chlorella pyrenoidosathe chloroplast is a target for 2,4-D action and that interferencein photorespiratory processes may underlie the observed responses.     

Control of Morphogenesis in Sorghum by 2,4-Dichlorophenoxyacetic Acid and Cytokinins

2, 4-Dichlorophenoxyacetic acid caused a shortening of rootsand shoots when mature seeds of Sorghum bicolor (L.) Moenchcv. BT3197 were germinated on Murashige and Skoog (MS) mediumthat contained 2,4-D. Shoot growth was restored with cytokinins.A callus formed at the nodal region, the further differentiationof which was determined by the ratio of 2,4-D and cytokininsin the initial culture medium. A high auxin to cytokinin ratiopromoted primarily root differentiation while a high cytokininto auxin ratio promoted multiple bud development. Isolated shootapical meristem with the subtending node produced embryogeniccallus at low cytokinin levels and green buds on high cytokininlevels when cultured in the presence of 2,4-D. It is concludedthat cells potentially capable of differentiation into roots,somatic embryos or axillary buds are present in the first nodalregion. Sorghum bicolor, organogenesis, embryogenesis, 2, 4-D: cytokinin ratios, tissue culture     

A Bioluminescent Whole-Cell Reporter for Detection of 2,4-Dichlorophenoxyacetic Acid and 2,4-Dichlorophenol in Soil

A bioreporter was made containing a tfdRP_DII-luxCDABE fusion in a modified mini-Tn5 construct. When it was introduced into the chromosome of Ralstonia eutropha JMP134, the resulting strain, JMP134-32, produced a sensitive bioluminescent response to 2,4-dichlorophenoxyacetic acid (2,4-D) at concentrations of 2.0 μM to 5.0 mM. This response was linear (R² = 0.9825) in the range of 2.0 μM to 1.1 × 10² μM. Saturation occurred at higher concentrations, with maximal bioluminescence occurring in the presence of approximately 1.2 mM 2,4-D. A sensitive response was also recorded in the presence of 2,4-dichlorophenol at concentrations below 1.1 × 10² μM; however, only a limited bioluminescent response was recorded in the presence of 3-chlorobenzoic acid at concentrations below 1.0 mM. A significant bioluminescent response was also recorded when strain JMP134-32 was incubated with soils containing aged 2,4-D residues.