A marine phytoplankton (Prymnesium parvum) up-regulates ABC transporters and several other proteins to acclimatize with Fe-limitation.

Iron (Fe) is one of the vital limiting factors for phytoplankton in vast regions of the contemporary oceans, notably the high nutrient low chlorophyll regions. Therefore, it is apparent to be acquainted with the Fe uptake strategy of marine phytoplankton under Fe-limited condition. In the present study, marine phytoplankton Prymnesium parvum was grown under Fe-deplete (0.0025 µM) and Fe-rich (0.05 µM) conditions, and proteomic responses of the organism to Fe conditions were compared. In sodium dodecyl sulfate (SDS) gel electrophoresis, 7 proteins (16, 18, 32, 34, 75, 82, and 116 kDa) were highly expressed under Fe-deplete condition, while one protein (23 kDa) was highly expressed under Fe-rich condition. These proteins were subjected to 2-dimensional gel electrophoresis (2-D DIGE) to differentiate individual proteins, and were identified by matrix-assisted laser desorption-ionization-time of flight-mass spectrometer (MALDI-TOF-MS) analysis. The results showed that under Fe-deplete condition P. parvum increases the biosynthesis of ATP binding cassette (ABC) transporters, flagellar associated protein (FAP), and Phosphoribosylaminoimidazole-succinocarboxamide synthase. These proteins are assumed to be involved in a number of cellular biochemical processes that facilitate Fe acquisition in phytoplankton. Under Fe-deplete condition, P. parvum increases the synthesis of ribulose biphosphate carboxylase (RuBisCo), malate dehydrogenase, and two Fe-independent oxidative stress response proteins, manganese superoxide dismutase (MnSOD) and Serine threonine kinase (STK). Thus, marine phytoplankton may change their Fe acquisition strategy by altering the biosynthesis of several proteins in order to cope with Fe-limitation.

Arsenic accumulation in rice (Oryza sativa L.): human exposure through food chain.

Although human exposure to arsenic is thought to be caused mainly through arsenic-contaminated underground drinking water, the use of this water for irrigation enhances the possibility of arsenic uptake into crop plants. Rice is the staple food grain in Bangladesh. Arsenic content in straw, grain and husk of rice is especially important since paddy fields are extensively irrigated with underground water having high level of arsenic concentration. However, straw and husk are widely used as cattle feed. Arsenic concentration in rice grain was 0.5+/-0.02 mg kg(-1) with the highest concentrations being in grains grown on soil treated with 40 mg As kg(-1) soil. With the average rice consumption between 400 and 650 g/day by typical adults in the arsenic-affected areas of Bangladesh, the intake of arsenic through rice stood at 0.20-0.35 mg/day. With a daily consumption of 4 L drinking water, arsenic intake through drinking water stands at 0.2mg/day. Moreover, when the rice plant was grown in 60 mg of As kg(-1) soil, arsenic concentrations in rice straw were 20.6+/-0.52 at panicle initiation stage and 23.7+/-0.44 at maturity stage, whereas it was 1.6+/-0.20 mg kg(-1) in husk. Cattle drink a considerable amount of water. So alike human beings, arsenic gets deposited into cattle body through rice straw and husk as well as from drinking water which in turn finds a route into the human body. Arsenic intake in human body from rice and cattle could be potentially important and it exists in addition to that from drinking water. Therefore, a hypothesis has been put forward elucidating the possible food chain pathways through which arsenic may enter into human body.

Effect of arsenic on photosynthesis, growth and yield of five widely cultivated rice (Oryza sativa L.) varieties in Bangladesh.

A glass house experiment was conducted to investigate the effect of soil arsenic on photosynthetic pigments, chlorophyll-a and -b, and their correlations with rice yield and growth. The experiment was designed with three replications of six arsenic treatments viz. control, 10, 20, 30, 60, 90 mg of As kg(-1) soil. Arsenic concentration in initial soil, to which the above mentioned concentrations of arsenic were added, was 6.44+/-0.24 mg kg(-1). Both chlorophyll-a and -b contents in rice leaf decreased significantly (p<0.05) with the increase of soil arsenic concentrations. No rice plant survived up to maturity stage in soil treated with 60 and 90 mg of As kg(-1). The highest chlorophyll-a and -b contents were observed in control treatment (2.62+/-0.24 and 2.07+/-0.14 mg g(-1) were the average values of chlorophyll-a and -b, respectively of the five rice varieties) while 1.50+/-0.20 and 1.04+/-0.08 mg g(-1) (average of five rice varieties) of chlorophyll-a and -b, respectively were the lowest. The content of photosynthetic pigments in these five rice varieties did not differ significantly (p>0.05) from each other in control treatment though they differed significantly (p<0.05) from each other in 30 mg of As kg(-1) soil treatment. Among the five rice varieties, chlorophyll content in BRRI dhan 35 was found to be mostly affected with the increase of soil arsenic concentration while BRRI hybrid dhan 1 was least affected. Well correlations were observed between chlorophyll content and rice growth and yield suggesting that arsenic toxicity affects the photosynthesis which ultimately results in the reduction of rice growth and yield.

Isolation and characterisation of tilapia beta-actin promoter and comparison of its activity with carp beta-actin promoter.

The regulatory sequence including proximal promoter, untranslated exon 1 and intron 1 of the beta-actin gene from tilapia (Oreochromis niloticus) has been isolated and spliced to a beta-galactosidase reporter gene to test its activity. Comparisons of promoter activity have been carried out with three different constructs: (1) 1.6 kb tilapia beta-actin regulatory sequence, (2) 1.5 kb carp beta-actin regulatory sequence, and (3) 4.7 kb carp beta-actin regulatory sequence. Although the 1.6 kb tilapia beta-actin regulatory sequence gave slightly different expression patterns in tilapia embryos assayed by in situ X-gal staining, no difference was observed in expression level when the tilapia sequence was compared with the 4.7 kb carp beta-actin regulatory sequence by quantitative assay. In comparison with the 1.5 kb carp beta-actin regulatory sequence, the 1.6 kb tilapia beta-actin regulatory sequence gave higher expression levels in tilapia embryos, while a reverse result was observed in zebrafish embryos. In cell transfection experiments, the 1.6 kb tilapia beta-actin regulatory sequence showed three to four times better activity in blue gill cells than either the 4.7 kb carp beta-actin or the 1.5 kb carp beta-actin regulatory sequences. The 1.6 kb tilapia beta-actin regulatory sequence also drove higher reporter gene activity in somatic cells of tilapia than did the 4.7 kb carp beta-actin regulatory sequence following direct injection of constructs into muscle. Therefore, taken together, the data demonstrate that the tilapia beta-actin promoter can be used as an efficient regulatory sequence to produce autotransgenic tilapia.