Growth rates of S. polyrhiza were reduced by chromate concentrations higher than 50 μM. Analysis of plant cells by transmission electron microscopy revealed the accumulation of starch grains in the chloroplasts following the application of chromate at low concentrations or for short periods (100 μM for 2 days or 500 μM for 1 day). Increasing the chromate concentration (1000 μM for 1 day) or extending the period (100 μM for 4 days) resulted in the disappearance of most of the starch grains and the extensive formation of plastoglobuli. These results were confirmed by chemical analysis of the starch content. It has been suggested that this transient accumulation of starch was caused, first, by inhibition of the export of carbohydrates out of the plastids, and then by inhibition of photosynthesis. Chromate decreased the chlorophyll content and the chlorophyll a/b ratio. The quantitative analysis of the chlorophyll protein complexes showed that the photosystem II (core complex as well as connecting antenna) was more sensitive to chromate treatment than photosystem I and the peripheral light‐harvesting complex of photosystem II. This explains the previous results on time‐resolved chlorophyll a fluorescence (Appenroth et al. Environ. Pollut. [2001] 115, 49 ‐ 64). Photosynthesis is clearly an important target of chromate toxicity. Electron microscopic analysis showed damage to several membrane systems, such as that of thylakoids, chloroplast envelope, plasmalemma and, at higher concentrations, that of tonoplast and mitochondria. Thus, the membrane system is another target of chromate toxicity.
A comparative study has been made on the sensitivity of the yeast Pichia guilliermondii to Cr (III) and Cr (VI) as well as on the Cr uptake potential at growth-inhibitory concentrations of chromium. The strains used in the study were either isolated from natural sources or obtained from a laboratory strain collection. The results show that most of the natural strains were more tolerant to chromium and were able to grow in the presence of 5 mM Cr (III) or 0.5 mM Cr (VI), that is at concentrations which substantially inhibited the growth of laboratory strains. The cellular Cr content after treatment was similar for both strain types and ranged from 1.2-4.0 mg/g d.w. and 0.4-0.9 mg/g d.w., for Cr (III) and Cr (VI) forms, respectively, however, in one case of a natural strain it reached the value of 10 mg Cr (III)/g dry mass. Natural-source strains were grouped into four groups based on the yeasts' differential response to Cr (III) and Cr (VI). Hexavalent Cr-resistant mutants of a P. giuilliermondii laboratory strain, which revealed markedly changed capabilities of chromium accumulation, were obtained by means of UV-induced mutagenesis. Cr (VI) treatment triggered oversynthesis of riboflavin and the addition of exogenous riboflavin increased P. guilliermondii resistance to both Cr (III) and Cr (VI). Electrophoretic protein profiles revealed the induction and/or suppression of several proteins in response to toxic Cr (VI) levels.
The accumulation of chromium in) confirming the competition of chromate and sulphate for the same transporters. Simultaneously, the rate constant of Cr(V) AE AE AE AE Cr(III) reduction is increased in the apoplast (by the factor of 3) and decreased in the symplast (by the factor of 5). Treatment with higher sulphate concentrations (100 m M ) increases the accumulation of chromium by enhancing the rate constant of Cr(VI) transport into cells leaving other processes essentially unchanged. We suggest that 100 m M sulphate opens a new pathway for chromate transport into cells.
Due to the importance of S. agalactiae as a pathogen, many PCR primers have been published for this bacterium, designed largely for its detection in dairy and human samples, but many cross-reacting with S. iniae. The ability to differentiate between S. agalactiae and S. iniae in aquaculture derived samples is important as both infect fish, causing similar disease symptoms and are phenotypically similar, yet control strategies and zoonotic risk are species specific.
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