Anatomical and ultrastructural alterations in Ceratopteris pteridoides under cadmium stress: A mechanism of cadmium tolerance.

The present research is an appraisal of anatomical and ultrastructural alterations in aquatic fern, Ceratopteris pteridoides under cadmium (Cd) exposure. Plants were cultured hydroponically for 12 consecutive days in different Cd treatments: 10 µM L-1 (CDT1), 20 µM L-1 (CDT2), 40 µM L-1 (CDT3) and 60 µM L-1 (CDT4). Anatomical and ultrastructural changes of different vegetative tissues of C. pteridoides were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cd stress significantly (P < 0.05) decreased water content percentage (WC%), relative growth rate (RGR) and root activity in C. pteridoides, especially at highest Cd concentration (treatment CDT4). Significant (P < 0.05) drop of stress tolerance indices (STI) was noticed in C. pteridoides under treatment CDT4. Anatomical study of the Cd-treated C. pteridoides showed stomatal closure of leaves, reduction of diameter in xylem tracheids of stem and root, and decrease of intercellular spaces. Furthermore, ultrastructural alterations of leaf, stem, and root cells were evident with a damaged membrane system of chloroplast and mitochondria, disorganization of chloroplastic components, accumulation of large starch grains and plastoglobules, and formation of multivesicular bodies. The deposition of electron-dense material in the cell wall of root cells can be regarded as an important tolerance mechanism of C. pteridoides under Cd stress. Fourier transform infrared (FTIR) spectroscopy analysis of Cd-treated C. pteridoides biomass illustrated Cd-binding interaction with O-H, N-H, C-H, C≡C, CË­O, PË­O, -C-OH and CS functional groups of different metabolites.

Antimony induced structural and ultrastructural changes in Trapa natans.

Antimony (Sb) is considered as a priority toxic metalloid in the earth crust having no known biological function. The current study was carried out in a hydroponic experiment to study the accumulation of ecotoxic Sb in subcellular level, and to find out the ultrastructural damage caused by Sb in different vegetative parts of Trapa natans. Sb-induced structural and ultrastructural changes of T. natans were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). Experimental plants were exposed to different Sb(III) treatments: SbT1 (1.5 µmol/L), SbT2 (40 µmol/L) and SbT3 (60 µmol/L). Calculated bioconcentration factor (BCF) and translocation factor (TF) showed that at higher concentration (SbT2, SbT3), T. natans is a potent phytoexcluder whereas it can translocate a substantial amount of Sb to the aerial parts at lower concentration (SbT1). SEM analysis revealed Sb-mediated structural changes in the size of stomatal aperture, intercellular spaces and vascular bundles of different vegetative tissues of T. natans. TEM results showed subcellular compartmentalization of Sb in vacuole and cell wall as electron dense deposition. This is considered as a part of strategy of T. natans to detoxify the deleterious effects under Sb stress conditions. Fourier transform infrared spectroscopy (FTIR) study of plant biomass revealed possible metabolites of T. natans which can bind Sb.

Soil PAHs against varied land use of a small city (Tezpur) of middle Brahmaputra Valley: seasonality, sources, and long-range transport.

This study reports soil PAHs from a small city (Tezpur) of the mid-Brahmaputra Valley. The soil PAHs has been assessed from representative land use using detailed protocol of extracting, cleaning, and quantitative analysis by HPLC technique. The concentrations of PAHs showed minimum spatial variability and yet showed strong seasonal variability, which could be typical of small cities having weak local source strengths. On examining the air mass reaching the region, it appeared that there has been explicit effect of long-range transport. The HYSPLIT back trajectories reaching the study area during different seasons showed variations in terms of their origins and transport pathways. This might have led to differential long-range transport of PAHs, which is reflected in the seasonal variabilities of the concentrations of PAHs. The seasonal variations were much profound with the highest ΣPAHs concentration during post-monsoon (7961 ng g-1) followed by pre-monsoon (2414 ng g-1) and monsoon (773 ng g-1) season. The toxicity of the PAHs was examined as BaP equivalent (BaPeq) concentrations, which were found to be on the lower side as compared to the studies conducted elsewhere. The percentage contribution of 3- and 4-ring compounds was found to be greater. An attempt also was made to apportion the sources of the PAHs by application of diagnostic ratios, principal component analysis-multiple linear regression (PCA-MLR) and hierarchal cluster analysis (HCA), which revealed that coal and biomass burning and vehicular emissions are the major contributors to the PAHs load in Tezpur city.

Tolerance mechanism of cadmium in Ceratopteris pteridoides: Translocation and subcellular distribution.

Hydroponic experiment was conducted to investigate the biochemical responses and accumulation behaviour of cadmium (Cd) in aquatic fern, Ceratopteris pteridoides, under four different levels of exposure. Plants were grown in 10 µM (CdT1), 20 µM (CdT2), 40 µM (CdT3) and 60 µM (CdT4) concentrations of Cd for 12 consecutive days and Cd accumulation in different plant parts, cell levels and growth medium was estimated. In C. pteridoides, Cd removal kinetics was best described by pseudo-second-order kinetic model. Increased accumulation of Cd in the plants was detected in a concentration dependent manner with maximum under 60 µM of Cd (CdT4) exposure (191.38 mg kg-1, 186.19 mg kg-1 and 1316.34 mg kg-1 in leaves, stems and roots, respectively). Cell wall of C. pteridoides is identified as crucial Cd storage site with the highest (28-69%) accumulation followed by organelles (14-44%) and soluble fraction (6-46%). Increased leaf proline, malondialdehyde (MDA) and protein content with significant reduction (P < 0.05) in chlorophyll concentration and upregulation of antioxidant enzymes catalase (CAT), guaiacol peroxidase (POD) and superoxide dismutase (SOD) reveals the presence of Cd resistance mechanism in C. pteridoides. Calculated higher (>1) bioconcentration factor (BCF) and lower (<1) translocation factor (TF) values evinced the suitability of C. pteridoides in Cd phytostabilization rather than phytoextraction.

Provenance, prevalence and health perspective of co-occurrences of arsenic, fluoride and uranium in the aquifers of the Brahmaputra River floodplain.

The present work focuses on understanding the provenance, prevalence and health perspective of As and F- along with possible co-occurrence of uranium (U) in the aquifers of the Brahmaputra floodplains (BFP), India. Groundwater (n = 164) and sediment samples (n = 5) were obtained from the upper, middle and lower BFP. Energy dispersive spectroscopy (EDX) revealed the presence of As, U and Fe in the sediment matrix. Regression analysis showed a weaker relationship between As and F- co-occurrence. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) suggested reductive dissolution of Fe (hydr)oxides responsible for As release in the BFP, especially in the upper and lower BFP. Bicarbonate appeared to compete with As oxyanions for adsorption on positively charged surfaces leading to As release. Arsenic desorption in presence of PO43-, F- and HCO3- at elevated pH appeared greatest in the upper BFP, suggesting the highest potential for co-occurrence. Co-occurrence, were mainly in isolated aquifers of the upper BFP owing to desorption of adsorbed As and F- from Fe (hydr)oxides at higher pH. Weathering and dissolution of clay minerals in the upper BFP, and competitive desorption in presence of HCO3- and PO43- in the middle and lower BFP, respectively, explain variabilities in F- release. Amorphous Fe (hydr)oxides like ferrihydrite act as sinks of U. Concentrations of As and F- will likely increase in the future as projected from the saturated levels of goethite and ferrihydrite. Hazard indices (HI) revealed that children (3-8 years) were at greater health risk than adults.

Coupling fractionation and batch desorption to understand arsenic and fluoride co-contamination in the aquifer system.

The present work is an attempt to study As and F+ coevality using laboratory based assays which couples fractionation and batch dissolution experiments. Sequential extraction procedure (SEP) resulting into five "operationally defined phases", was performed on sediment and soil samples collected from the Brahmaputra flood plains, Assam, India. High correlation between the Fe (hydr)oxide fraction and total As content of the soil/sediment sample indicates the involvement of Fe (hydr)oxides as the principal source of As. F- being an anion has high potential to be sorbed onto positively charged surfaces. Findings of the SEP were used to design the batch desorption experiments by controlling the Fe (hydr)oxide content of the soil/sediment. Desorption of As and F- was observed under acidic, neutral and alkaline pH from untreated and Fe (hydr)oxide removed samples. Highest amount of As and F- were found to be released from untreated samples under alkaline pH, while the amount leached from samples with no Fe (hydr)oxide was low. The study showed that the Fe (hydr)oxide fraction commonly found in the soils and sediments, had high affinity for negatively charged species like F- oxyanions of As, AsO43- (arsenate) and AsO33- (arsenite). Fe (hydr)oxide fraction was found to play the major role in co-evolution of As and F-. Two sorption coefficients were proposed based on easily leachable fraction and As present in the groundwater of sampling location for understanding of contamination vulnerability from the leaching.

Source contributions of Polycyclic Aromatic Hydrocarbons in soils around oilfield in the Brahmaputra Valley.

Surface soils from Borholla oilfield in the upper Brahmaputra Valley in India were studied for the USEPA's 16 priority Polycyclic Aromatic Hydrocarbons (PAHs). Analysis of PAHs was carried out by high performance liquid chromatography (HPLC) system equipped with an UV detector. Seasonality in PAHs concentrations was evident and the concentrations were found to be greater in post-monsoon season. There has been a dominance of low molecular weight PAHs (80-90% of total PAHs) indicating recent deposition from combustion sources. The concentration profiles appeared in the decreasing order of 3-ring >2-ring >4-ring >5-ring >6 ring PAHs. The sources of PAHs were identified using isomer pair ratios and Principal Component Analysis-Multiple Linear Regression (PCA-MLR) and Positive Matrix Factorisation (PMF). The ratios of diagnostic pairs indicated for both pyrogenic and petrogenic input of PAHs. The PCA-MLR modelling revealed that the <16% of contribution came from petrogenic origin and the rest 85% was found to be from pyrogenic sources. The PMF model also shown that <19% of PAHs source were petrogenic origin whereas rest from pyrogenic origin. The correlations of black carbon (BC) with PAHs also supported the pyrogenic contribution. The analysis of air mass back trajectories revealed that there has been contribution of both local and distant sources, through long range transport of pollutants, which were deposited to the site.