M. Mamunur Rahman

Effect of external iron and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake in rice (Oryza sativa L.).

This study was conducted to investigate the effect of external iron status and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake. Rice seedlings (Oryza sativa L.) were used as model plant, and were grown in artificially contaminated sandy soils irrigated with Murashige and Skoog (MS) culture solution. Arsenate uptake in roots and shoots of rice seedlings were affected significantly (p>0.05) while dimethylarsinic acid (DMAA) was not by the additional iron and chelating ligand treatments. Regardless of iron concentrations in the soil solution, HIDS increased arsenic uptake for roots more than EDTA and EDDS. Chelating ligands and arsenic species also influenced iron uptake in rice roots. Irrespective of arsenic species, HIDS was found to be more effective in the increase of iron bioavailability and uptake in rice roots compared to other chelants. There was a significant positive correlation (r=0.78, p<0.05) between arsenate and iron concentrations in the roots of rice seedlings grown with or without additional iron indicating that arsenate inhibit iron uptake. In contrast, there was no correlation between iron and DMAA uptake in roots. Poor correlation between iron and arsenic in shoots indicated that iron uptake in shoots was neither affected by additional iron nor by arsenic species. Compared to the control, chelating ligands increased iron uptake in shoots of rice seedlings significantly (p<0.05). Regardless of additional iron and arsenic species, iron uptake in rice shoots did not differed among EDTA, EDDS, and HIDS treatments.

The significance of biodegradable methylglycinediacetic acid (MGDA) for iron and arsenic bioavailability and uptake in rice plant

Methylglycinediacetic acid (MGDA) is a readily biodegradable complexing agent in compliance with Organization for Economic Cooperation and Development standards. In the present study, the use of MGDA for iron (Fe) and arsenic (As) bioavailability and uptake by rice plants (Oryza sativa L.) was investigated. The highest plant biomass was observed at pH 7, and the growth of rice seedlings decreased significantly (p < 0.05) with increasing pH of the nutrient solution. This might be due to Fe deficiency to the plant at alkaline pH. When rice seedlings were grown with different concentrations of MGDA (0.1, 0.25, 0.5, 1.0, 2.5, and 5 mM), the highest plant biomass was observed at 0.25 mM MGDA, while further increases of the ligand concentration decreased the plant growth. Fe concentrations on rice root surfaces decreased gradually with increasing MGDA concentrations in the growing medium, while Fe concentrations in rice roots and shoots increased with increasing MGDA concentrations up to 0.25 mM and then decreased gradually. This indicates that the concentration of the chelating ligand influences Fe uptake in the plant. Arsenic concentrations on rice root surfaces decreased, while As concentrations in roots and shoots increased with the addition of MGDA in the growing medium, indicating that the ligand enhanced As bioavailability and uptake in rice. The mechanism behind the MGDA effect on Fe and As uptake in plant is likely to be due to that Fe exists mostly in insoluble particulate forms [e.g., ferric oxide (Fe2O3), ferric hydroxide (Fe(OH)3) and ferric oxyhydroxide (FeOOH)] at neutral or alkaline pH, and the soluble [e.g., ferric ion (Fe3+), iron hydroxide ion (Fe(OH)2+) and iron dihydroxide ion ( )] and apparently soluble (colloidal) fractions of Fe are increased at moderate concentrations of the ligand that increases Fe bioavailability. Since arsenate [As(V)] binds to the insoluble Fe-oxides/hydroxides, the binding sites for As(V) decreases with the increase of the soluble fractions of Fe by the ligand, which slightly increased As uptake in rice plants.

Comparative Growth Performances of Tea Saplings Raised in the Poly and Gunny Bags

Polythene or poly bags (plastic bags) are widely used for raising young plants in the nursery which are cheap, light weight, extremely durable and widely available. Plastic bags are principally used to raise tea saplings/seedlings in the nursery. The drawback of the plastic bags made the planters think to find out alternate eco-friendly materials for raising tea saplings. Jute fiber, which comes from a plant called jute (Corchorus spp.) is mostly consisting of cellulose, is 100% bio-degradable and recyclable and thus environmentally friendly (FAO, 2015). Jute has gained an advantage as being an eco-friendly option instead of poly and paper bags. Poly bags are non-biodegradable and manufacturing paper bags requires large quantities of wood. Jute has none of these problems but higher cost is a setback for it. Some other disadvantages of jute may include a decreased strength when wet, and also becomes subject to microbial attack in humid climates. For tree nurseries in general, physiological quality criteria are prioritized for seedling establishment after planting (Villar-Salvador et al., 2004). Though the effect of different management practices (e.g., pot size, substrate, fertilizer supply, and planting density) are reported to greatly affect the physiological quality of tree nursery seedlings (Ahmad et al., 2012) effect of potting materials (materials to support the plant growth medium) specially the effect of jute bags on seedling growth is scarcely reported. Considering the above facts an attempt has been made in the nursery of Bangladesh Tea Research Institute to observe the growth performances of tea saplings raised in the poly and gunny (jute) bags as well as the durability of both types of bags to investigate the potential of the gunny bags to be used in the nursery for raising tea saplings.

A marine phytoplankton Prymnesium parvum upregulates the component proteins of photosystem II under iron stress

Iron is an essential limiting factor for primary production in many marine systems. The present study investigated differential regulation of protein expression in marine phytoplankton Prymnesium parvum under low Fe concentration. The phytoplankton was grown in f/2 culture medium in artificial seawater with low (0.0025 μM) and high (0.05 μM) Fe concentrations. Two-dimensional differential gel electrophoresis and matrix-assisted laser desorption-ionization-time of flight-mass spectrometer analysis were performed for protein identification and characterization. The growth of the alga declined substantially under the low Fe compared to the high Fe concentration. Under low Fe conditions, P. parvum upregulated 10 proteins including chloroplastic ATP synthase subunit b, D2 protein of PSII, D1 protein of PSII reaction centre, and light harvesting complex II protein, most of which are associated with photosynthetic activities in PSII. The results suggest that the marine alga P. parvum altered the biosynthesis of several photosynthetic proteins in order to cope with low Fe conditions.

A Fluorescent-Based HPLC Assay Using 4-Chloro-7-nitrobenzo-2-oxa-1, 3-diazole as Derivatization Agent for the Determination of Iron Bioavailability to Red Tide Phytoplankton

A new fluorescent-based high-performance liquid chromatography (HPLC) assay using 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-C1) was employed to determine iron (Fe) bioavailability to red tide phytoplankton in seawater. After growing four red tide species (Prymnesium parvum, Heterosigma akashiwo, Eutreptiella gymnastica, and Oltmannsiellopsis viridis) in f/2 artificial seawater under different Fe conditions, soluble extracts of the phytoplankton were derivatized using different fluorescent reagents (NBD-C1, 4-fluoro-7-nitrobenzo-2-oxa-1,3-diazole; NBD-F, fluorescamine, and ortho-phthalaldehyde; OPA) followed by HPLC assay. Among the four fluorescent reagents, NBD-C1 was most effective for derivatizing the phytoplankton extracts which would consist of proteins and peptides. HPLC chromatograms of the NBD-derivatized extracts showed gradual changes (decrease/increase) of six peaks for different Fe conditions. Four of the peaks decreased, while two peaks increased with the increase of Fe concentrations in the culture medium. Considering the consistency and sensitivity of chromatogram peaks E and A to different Fe, phosphate and nitrate conditions for all phytoplankton studied, the ratio of these two peaks (IE/A) has been proposed as the indicator of Fe bioavailability to red tide phytoplankton.