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Iron ion, an essential element for environmental as well as biological systems, has to be present in a controlled manner. Presence of excess iron and also the deficiency of iron ions in environmental (groundwater) and biological systems (blood serum and parts of the plant) is an enduring concern. Here we have developed a nano-sensor (FeNSOR) using a neutral micelle (TX-100) duly sensitized by porphyrin. We have also fabricated an instrument called “FeNSOR Device” (Iron sensor) based on the developed nano-sensor using a digital Pi-camera with associated hardware and software. The device works on the principle of fluorescence spectrophotometry. The efficacy of the nano-sensor and the device for the detection and estimation of iron ions in groundwater as well as in human blood serum is found to be in sub-molar range, having minimum interference with other ions. The limit of detection and the standard deviation of the mean were found to be $0.07~\mu \text{M}$ and $0.016~\mu \text{M}$ , respectively. The developed device is easy to handle, and has a higher sensitivity and repeatability than the commercially available ones. [ABSTRACT FROM AUTHOR]

Speciation study of microelements in soils is useful to assess their retention and release by the soil to the plant. Laboratory and greenhouse investigations were conducted for five soils of different agro-ecological zones (viz., Bhuna, Delhi, Cooch-Behar, Gurgaon, and Pabra) with diverse physicochemical properties to study the distribution of zinc (Zn) among the soil fractions with respect to the availability of Zn species for uptake by rice plant. A sequential extraction procedure was used that fractionated total soil Zn into water-soluble (WS), exchangeable (EX), specifically adsorbed (SA), acid-soluble (AS), manganese (Mn)-oxide-occluded (Mn-OX), organic-matter-occluded (OM), amorphous iron (Fe)-oxide-bound (AFe-OX), crystalline Fe-oxide-bound (CFe-OX), and residual (RES) forms. There was a wide variation in the magnitude of these fractions among the soils. The studies revealed that more than 90% of the total Zn content occurred in the relatively inactive clay lattice and other mineral-bound form (RES) and that only a small fraction occurred in the forms of WS, EX, OM, AFe-OX, and CFe-OX. Rice (Oryza sativa L.) cultivars differ widely in their sensitivity to Zn deficiency. Results suggested that Zn in water-soluble, organic complexes, exchange positions, and amorphous sesquioxides were the fractions (pools) that played a key role in the uptake of Zn by the rice varieties (viz., Pusa-933-87-1-11-88-1-2-1, Pusa-44, Pusa-834, Jaya, and Pusa-677). Isotopic ally exchangeable Zn (labile Zn) was recorded higher in Typic Ustrochrept of Pabra soil, and uptake of Zn by rice cultivars was also higher in this soil. The kinetic parameters such as maximum influx at high concentrations (Imax) and nutrient concentration in solution where influx is one half of Imax (Km) behaved differentially with respect to varieties. The highest Imax value recorded was 9.2×10-7 µmol cm-2 s-1 at the 5 mg kg-1 Zn rate for Pusa-933-87-1-11-88-1-2-1, and the same was lowest for Pusa-44, being 4.6×10-7 µmol cm-2 s-1 at the 5 mg kg-1 Zn rate. The Km value was highest for Pusa-44 (2.1×10-4µmol cm-2 s-1) and lowest for Pusa-933-87-1-11-88-1-2-1 (1.20×10-4µmol cm-2 s-1). The availability of Zn to rice cultivars in Typic Ustrochrepts of Bhuna and Delhi soils, which are characterized by higher activation energy and entropy factor, was accompanied by breakage of bonds or by significant structural changes. [ABSTRACT FROM AUTHOR]

To better understand the mechanisms responsible for differences in uptake and distribution of cadmium (Cd), nutrient-solution experiments were conducted with different varieties of rice ( Oryza sativa ), ‘Khitish’ and ‘CNRH3’. The plants were grown in a complete nutrient solution with different levels of pCd (-log free Cd +2 activity) and pFe [-log free iron (Fe +2 ) activity]. The required concentrations of chelating agent and metals were determined using a computerized chemical equilibrium model such as Geochem-PC. Experimental treatments included a combination of four pCd activity levels (0, 7.9, 8.2, and 8.5) applied as Cd (NO 3 ) 2 4H 2 O, and two pFe activity levels (17.0 and 17.8) applied as FeCl 3 . The application of both Cd and Fe in solution culture significantly affected plant growth, yield, and Cd accumulation in plant tissue. In general, yield of rice was decreased by an increase in amount of solution Cd; however, yield response varied among the cultivars. At the 7.9 pCd level, yields of rice cultivars ‘Khitish’ and ‘CNRH3’ were reduced to 69% and 65%, respectively, compared with control plants. Root Cd concentrations ranged from 2.6 mg kg -1 (control plants) to 505.7 mg kg -1 and were directly related to solution Cd concentrations. In rice plants, Cd toxicity symptoms resembled Fe chlorosis. Differential tolerance of varieties to phytotoxicity was not readily visible, but a significant interaction of substrate Cd and variety was obtained from dry-matter yields. Significant interactions indicated that response of tissue Cd concentration, plant Cd uptake, and translocation of Cd to the aerial parts were dependent on variety as well as substrate Cd. Uptake of Cd by roots was significantly higher than by shoots. Higher Cd uptake by rice plants decreased the uptake of other beneficial metals. The effect of Cd and Fe on the rate of phytometallophore release was also studied in the nutrient solution. Among the rice genotypes, ‘Khitish’ was the most sensitive to Cd toxicity. In both genotypes, with the onset of visual Cd-toxicity symptoms, the release of phytometallophore (PM) was enhanced. Among the rice varieties, ‘Khitish’ had the highest rate of PM release. Treatments with the metal ions studied produced a decrease in chlorophyll and enzyme activity. A decrease in concentrations of chlorophyll pigments in the third leaf was observed due to the highest activity level of Cd (pCd 7.9). Activities of enzymes such as peroxidase (POD) and superoxide dismutase (SOD) are altered by toxic amounts of Cd. Changes in enzyme activities occurred at the lowest activity of Cd (pCd 8.5) in solution. Peroxidase activity increased in the third leaf. Results showed that in contrast with growth parameters, the measurements of enzyme activities may be included as early biomarkers in a plant bioassay to assess the phytotoxicity of Cd-contaminated solution on rice plants. Evidence that Cd uptake and translocation are genetically controlled warrants the selection of varieties that assimilate the least Cd and that translocate the least metal to the plant part to be used for human and animal consumption. [ABSTRACT FROM AUTHOR]