Sudhakar Srivastava

Seasonal variations in the spatial distribution of root tips in teak (Tectonia grandis Linn. f.) plantations in the Varanasi Forest Division, India

SummarySeasonal variations in the spatial distribution of root tips were studied in 19 and 29 year old teak plantations, located on red and alluvial soils respectively. The pattern was essentially similar at both sites, but generally the alluvial soil site exhibited a greater number of root tips. Root tips decreased with increasing distance from the tree base. Through-out most of the year the relative distribution of root tips decreased with depth; the difference between 0–10 and 10–20 cm depths was marginal, but 20–40 cm depth contained distinctly fewer root tips. At all distances a similar seasonal trend was noticed, a mid rainy season peak being followed by a steady decline until the dry summer except for an abrupt rise to a smaller peak in February after the winter rains.The root tip density was positively correlated with the ≤2 mm root biomass and both showed a similar bimodal annual cycle. Of three environmental variables studied, soil moisture and rainfall were significantly positively correlated with root tip densityl the relationship between soil temperature and root tip density was negative and non-significant. The combined effect of soil moisture and temperature on root tip density, evaluated by a multiple regression model, accounted for 80–95% of the variation in root tip density.

A study on the effect of cadmium on the antioxidative defense system and alteration in different functional groups in castor bean and Indian mustard

Abstract The present study was planned to delineate the role of antioxidants and different functional groups of Ricinus communis and Brassica juncea in the tolerance mechanisms toward cadmium (Cd) for phytoremediation. Application of Cd caused a reduction in dry biomass of 53.84% and 26.58% in root and 45.33% and 33.84% in shoots of B. juncea and R. communis, respectively. Antioxidant enzymes, namely superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and glutathione-S-transferase, and metabolites (proline) increased in both the species due to Cd exposure. The metal caused substantial changes in the functional groups present in the roots and leaves of the plants. A number of new peaks appeared in the Cd-treated plants, which indicate the production of the compounds responsible for the metal tolerance of these plants. R. communis has been found to possess a good antioxidant defense system against Cd stress and may be used for the phytoremediation of metal-contaminated soils in place of edible crops, which enhance the risk of contaminating the food chain. It has been observed that R. communis accumulated 213.39 and 335.68 mg Cd in roots and shoots, respectively, whereas B. juncea accumulated 28.19 and 310.15 mg Cd in the roots and shoots, respectively.

The Journey of Arsenic from Soil to Grain in Rice

Arsenic (As) is a non-essential toxic metalloid whose elevated concentration in rice grains is a serious issue both for rice yield and quality, and for human health. The rice-As interactions, hence, have been studied extensively in past few decades. A deep understanding of factors influencing As uptake and transport from soil to grains can be helpful to tackle this issue so as to minimize grain As levels. As uptake at the root surface by rice plants depends on factors like iron plaque and radial oxygen loss. There is involvement of a number of transporters viz., phosphate transporters and aquaglyceroporins in the uptake and transport of different As species and in the movement to subcellular compartments. These processes are also affected by sulfur availability and consequently on the level of thiol (-SH)-containing As binding peptides viz., glutathione (GSH) and phytochelatins (PCs). Further, the role of phloem in As movement to the grains is also suggested. This review presents a detailed map of journey of As from soil to the grains. The implications for the utilization of available knowledge in minimizing As in rice grains are presented.

Selenate mitigates arsenite toxicity in rice (Oryza sativa L.) by reducing arsenic uptake and ameliorates amino acid content and thiol metabolism.

Arsenic (As) is a toxic element with the potential to cause health effects in humans. Besides rice is a source of both amino acids (AAs) and mineral nutrients, it is undesired source of As for billions of people consuming rice as the staple food. Selenium (Se) is an essential metalloid, which can regulate As toxicity by strengthening antioxidant potential. The present study was designed to investigate As(III) stress mitigating effect of Se(VI) in rice. The level of As, thiolic ligands and AAs was analyzed in rice seedlings after exposure to As(III)/Se(VI) alone and As(III)+Se(VI) treatments. Selenate supplementation (As(III) 25μM+Se(VI) 25μM) decreased total As accumulation in both root and shoot (179 & 144%) as compared to As(III) alone treatment. The As(III)+Se(VI) treatment also induced the levels of non-protein thiols (NPTs), glutathione (GSH) and phytochelatins (PCs) as compared to As(III) alone treatment and also modulated the activity of enzymes of thiol metabolism. The content of amino acids (AAs) was significantly altered with Se(VI) supplementation. Importantly, essential amino acids (EAAs) were enhanced in As(III)+Se(VI) treatment as compared to As(III) alone treatment. In contrast, stress related non-essential amino acids (NEAAs) like GABA, Glu, Gly, Pro and Cys showed enhanced levels in As(III) alone treatment. In conclusion, rice supplemented with Se(VI) tolerated As toxicity with reduced As accumulation and increased the nutrition quality by increasing EAAs.

Emerging Aspects of Bioremediation of Arsenic

Arsenic is a toxic element whose widespread contamination in highly populated regions of world has led to environmental and human health concerns. Millions of people residing in contaminated areas are forced to drink water and eat food containing arsenic beyond maximum permissible limits. As the extent of problem is huge, there is need to devise cost-effective measures to tackle the problem. Physicochemical methods available presently are costly and are not easily operable by the poor people. Bioremediation comprises application of biological organisms and/or components in the removal/stabilisation of the contaminant. This review will focus on arsenic removal aspects of bioremediation and will also discuss prospects of utilising biological components for restricting arsenic entry into crop plants specifically rice.

Zinc supplementation imparts tolerance to arsenite stress in Hydrilla verticillata (L.f.) Royle

ABSTRACT The present study was aimed to analyze the effects of external Zn supply on arsenic (As) toxicity in Hydrilla verticillata (L.f.) Royle. The plants were exposed to arsenite (AsIII; 10 μM) with or without 50 and 100 μM Zn. The level of As accumulation (μg g−1 dw) after 2 and 4 days was not significantly affected by Zn supply. The plants showed a significant stimulation of the thiol metabolism (nonprotein thiols, cysteine, glutathione-S-transferase activity) upon As(III) exposure in the presence of Zn as compared to As(III) alone treatment. Besides, they did not experience significant toxicity, measured in terms of hydrogen peroxide and malondialdehyde accumulation, which are the indicators of oxidative stress. The minus Zn plants suffered from oxidative stress probably due to insufficient increase in thiols to counteract the stress. Stress amelioration by Zn supply was also evident from antioxidant enzyme activities, which came close to control levels with increasing Zn supply as compared to the increase observed in As(III) alone treatment. Variable Zn supply also modulated the level of photosynthetic pigments and restored them to control levels. In conclusion, an improved supply of Zn to plants was found to augment their ability to withstand As toxicity through enhanced thiol metabolism.

Utilizing the Potential of Microorganisms for Managing Arsenic Contamination: A Feasible and Sustainable Approach

Arsenic (As) contamination is a serious issue throughout the world. The scale of problem is being realized to be even greater with the discovery of new As contaminated regions with time. Rice is a staple crop across the world with approximately half of the world population dependent on rice for their daily dietary intake especially in Southeast Asian countries. It is not only the consumption of rice grains but also food products based on rice, which contribute towards As exposure to humans. Plant growth promoting microorganisms (PGPMs) constitute a diverse group of microorganisms including bacteria, fungi and microalgae. These are associated with the rhizospheric zone of plants. They improve plant growth through different mechanisms like increase of nutrients level in plants, improved soil quality, siderophore and hormone production, changes in biochemical properties of plants etc. Another important assistance imparted by PGPMs is the altered speciation of As in the soil through methylation and subsequent change in the bioavailability of As to the plants. Further, a change in As speciation also affects As uptake and transport in plants. The purpose of this review is to discuss importance of PGPM association in As toxicity amelioration in plants along with favourably reducing As concentrations in crop plants or increasing As accumulation in phytoremediator plants. This review also presents mechanisms of action of PGPMs and describes both laboratory- and field-studies on the application of PGPMs for tackling As-contamination. The future prospects of successful utilization of PGPMs are also discussed.

Vermiremediation of metal(loid)s via Eichornia crassipes phytomass extraction: A sustainable technique for plant amelioration

Eichhornia crassipes (water hyacinth), imparts deficiency of soluble arsenic and other toxic metal (loid)s through rhizofiltration and phytoaccumulation. Without proper management strategy, this phytoremediation of metal (loid)s might fail and get reverted back to the environment, contaminating the nearby water bodies. This study, focused on bio-conversion of phytoremediating hyacinths, spiked with 100 times and greater arsenic, lead and cadmium concentrations than the average water contamination, ranging in 58.81 ± 0.394, 16.74 ± 0.367, 12.18 ± 0.153 mg Kg-1arsenic, 18.95 ± 0.212, 9.53 ± 0.054, 6.83 ± 0.306 mg kg-1 lead and 2.79 ± 0.033, 1.39 ± 0.025, 0.92 ± 0.045 mg kg-1 cadmium, respectively in root, shoot and leaves, proving its phytoaccumulation capacity. Next, these hyacinths has been used as a source of organic supplement for preparing vermicompost using Eisenia fetida following analysis of total metal content and sequential extraction. Control soil was having 134.69 ± 2.47 mg kg-1 arsenic in compare to 44.6 ± 0.91 mg kg-1 at premature stage of compost to 23.9 ± 1.55 mg kg-1 at mature compost indicating sustainable fate of phytoremediated vermicompost. This vermiremediation of arsenic and other toxic elements, restricted the bioavailability of soil pollutants. Furthermore, processed compost amended as organic fertilizer, growing chickpea, coriander, tomato and chilli plant, resulted in negligible metal(loid)s in treated samples, enhancing also plants growth and production.

Heavy Metal Tolerance in Crop Plants: Physiological and Biochemical Aspects

Plants are immobile and they have to adapt against adverse conditions of the environment for their survival. Heavy metal (HM) toxicity is posing a serious concern for the plant life and seriously hampering the food grain productivity. Heavy metals include the transition metals essential for plant nutrition as well as the nonessential elements. All these elements become toxic to crop plants when they are present at high tissue concentrations. Elevated concentration of HMs in soil may be due to natural as well as anthropogenic activities. Plants growing in HM-contaminated regions may accumulate a significant amount of these HMs. This paves a way for HMs to enter into food chain posing serious health concerns for animal and human life. A number of morphological, biochemical, and physiological alterations occur during HM toxicity including alteration in uptake mechanism and transportation of water, root and shoot growth, oxidative stress, and changes in HM complexing ligands for sequestration of these HMs into vacuole to reduce the HM concentration in cytoplasm. The present chapter deals with the physiological and biochemical responses of plants to HM toxicity along with shedding light on uptake and transport mechanisms of HMs in brief.

Statistical optimization of cyclodextrin glycosyltransferase (CGTase) production from Bacillus macerans in batch cultivation and its purification

Cyclodextrin glycosyltransferase (CGTase) catalyzes the formation of Cyclodextrins from starch by an intramolecular transglycosylation reaction. In the present study, the CGTase enzyme was produced from Bacillus macerans NCIM 2131, using shake flask fermentation. Soluble starch and yeast extract were screened as the best carbon and nitrogen source at an individual factor level for enhancing CGTase activity. Similarly, ferrous ion and arginine were found to activate CGTase production in comparison to various other trace metals and amino acids tested. The synergistic effect of individual parameters of CGTase activity and process optimization of cultural condition was performed by response surface methodology (RSM). The optimized media comprised 24 g/L soluble starch; 32.5 g/L ferrous ion, and 15.0 g/L arginine with CGTase activity of 24.23 IU/mL. The final CGTase activity was very close to the predicted value of 24.82 IU/mL with 97.0% validation. Shake flask optimized conditions were further scaled up to 7.5 L fermenter (working volume: 3.0 L) which gave 2.6 folds (64.3 IU/mL) increase in enzyme activity. The enzyme was partially purified by ammonium sulfate precipitation and scanning electronic microscopy (SEM) was used to study the qualitative properties of produced enzyme.