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The current study explored the role of ionic copper (CuCl

Numerous advances have been made to mitigate the repercussion of toxic metals on photosynthetic prokaryotes, i.e. cyanobacteria. One strategy is exogenous supplementation of plant growth regulators (PGRs). This perhaps intensifies the resistance ability of cyanobacteria to encounter the environmental stresses by augmenting their physiological functioning and decontaminant efficiency. Thus, the aim of the present study was to determine if the PGRs auxin (indole-3 acetic acid, IAA; 300 nM) and cytokinin (kinetin, KN; 10 nM) are able to mitigate the toxic environmentally relevant doses of chromium (CrVI; 100 and 150 µM) in cyanobacteria (Nostoc muscorum ATCC 27,683 and Anabaena sp. PCC 7120). The response was assessed by estimating oxidative stress [in vitro and in vivo (superoxide radical; O2·−, hydrogen peroxide H2O2 and malondialdehyde equivalents contents; MDA)], feasible alteration in whole cell oxygen evolution, ascorbate–glutathione cycle and their metabolites. Intracellular Cr accumulation raised the production of ROS by down-regulating the photosynthetic rate due to decreased pigment contents (Chl a; chlorophyll a, Car; carotenoids and PC; phycocyanin) and reduced growth despite the accelerated activity of the ascorbate–glutathione (AsA-GSH) cycle enzymes (viz. APX; ascorbate peroxidase, GR; glutathione reductase and DHAR; dehydroascorbate reductase). Concurrently, exogenous PGRs (auxin and cytokinin) moderated the negative effects of Cr on the growth, by lowering the cellular Cr accumulation and ROS level and by modulating the pigment system, photosynthesis and a further rise in the efficiency of AsA-GSH cycle, thereby acting as positive regulators of the metal detoxification machinery. Thus, exogenous application of PGRs (auxin and cytokinin) could improve the growth in cyanobacteria in Cr-polluted environments, hence maintaining productivity in paddy cultivation as well as having potential to be used as bio-remediator in metal-contaminated aquatic systems.

This review explains the transport, mobility, resistance and detoxification of toxic metalloid arsenic (As) in plants. Arsenic is ubiquitously present in Earth’s crust; however, numerous human interventions such as rapid industrialization use of As-based pesticides, insecticides and discharge of industrial wastes in water bodies leads to cumulative increase in As in the environment and has become a global challenge. Arsenic exists in different organic and inorganic forms, but inorganic forms such as pentavalent arsenate (AsV) and trivalent arsenite (AsIII) are more toxic and actively taken up by plants. Its toxicity is marked by generation of reactive oxygen species (ROS) that are capable of degrading various biomolecules of the cellular systems. To keep the ROS under the limit, plants have an array of enzymatic antioxidants such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione-S-transferase (GST); and non-enzymatic antioxidant like ascorbate, proline, and cysteine. Contrary to this, As-hyper-accumulator plants survive under high concentration of As through the strenuous action of Asv reduction into AsIII followed by the vacuolar compartmentalization of complex or inorganic As. Hence, this review focuses on the potential sources of As in the environment, its speciation and toxicity, and tolerance strategies in plants.

Exposure time, metal bio-accumulation, and upregulation of ascorbate-glutathione (AsA-GSH) cycle are the key factor that provide tolerance against heavy metal stress. Thus, the current study is an endeavor to prove our hypothesis that regulation of arsenate (AsV: 50, 100, and 150 mM) and arsenite (AsIII: 50, 100, and 150 μM) toxicity is time dependent (48-96 h) due to modulation in bio-accumulation pattern, AsA-GSH cycle, and non-enzymatic antioxidants in two paddy field cyanobacteria Nostoc muscorum ATCC27893 and Anabaena sp. PCC7120. After 48 h, reduction in growth associated with increased sensitivity index, As bio-accumulation, and oxidative stress was observed which further intensified after 96 h but the degree of damage was lesser than 48 h. It denotes a significant recovery in growth after 96 h which is correlated with decreased As bio-accumulation and oxidative stress due to increased efficiency of AsA-GSH cycle and non-enzymatic antioxidants. Both the species of As caused significant rise in oxidative biomarkers as evident by in -vitro analysis of O2·-, H2O2, and MDA equivalent contents despite appreciable rise in the activity antioxidative enzymes APX, DHAR, and GR. The study concludes that among both forms of arsenic, AsIII induced more toxic effect on growth by over-accumulating the ROS as evident by weak induction of AsA-GSH cycle to overcome the stress as compared to AsV. Further, with increasing the time exposure, apparent recovery was noticed with the lower doses of AsV, i.e., 50 and 100 mM and AsIII, i.e., 50 and 100 μM; however, the toxicity further aggravated with higher dose of both AsV and AsIII. Study proposes the deleterious impact of AsV and AsIII on cyanobacteria N. muscorum and Anabaena sp. but the toxicity was overcome by time-dependent recovery.

The present study deals with impact of varied doses of arsenite (AsIII; 50, 100 and 150 µM) and arsenate (AsV; 50, 100 and 150 mM) on growth, photosynthetic pigments, photochemistry of photosystem II, oxidative biomarkers, (O2•¯, H2O2 and MDA equivalents contents) and activity of antioxidant enzymes in diazotrophic cyanobacterium Nostoc muscorum after 48 and 96 h of the treatments. The reduction in growth, pigment contents (Chl a, Phy and Car) and PS II photochemistry was found to increase with enhanced accumulation of test metal in cells, and the damaging effect on photosynthetic pigments showed the order (Phy > chl a> Car). The negative effect on PS II photochemistry was due to significant decrease in the value of JIP kinetics ϕP0, FV/F0, ϕE0,Ψ0 and PIABS except F0/FV and significant rise in values of energy flux parameters such as ABS/RC, TR0/RC, ET0/RC and DI0/RC. Both the species of arsenic caused significant rise in oxidative biomarkers as evident by in vitro and in vivo analysis of (O2•¯, H2O2 and MDA equivalents contents) despite of appreciable rise in the activity antioxidative enzymes such as SOD, POD, CAT and GST. The study concludes that in among both forms of arsenic, arsenite effect was more dominant on growth, photosynthetic pigments; oxidative stress biomarkers as evident by weak induction of anti-oxidative defense system to overcome the stress as compared to arsenate.

The current study was undertaken to elucidate the impact of the herbicide pretilachlor (3 µg ml−1 and 6 µg ml−1) on cyanobacteria, Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 under three levels of photoacclimatization (suboptimum, 25 µmol photon m−2 s−1; optimum, 75 µmol photon m−2 s−1; and supra-optimum, 225 µmol photon m−2 s−1) by analyzing certain physiological (biomass accumulation, photosynthesis, Chl a fluorescence and respiration) and biochemical parameters (photosynthetic pigments‒ chlorophyll a, carotenoids and phycocyanin; reactive oxygen species‒ O2•¯, H2O2, lipid peroxidation; antioxidant system‒ superoxide dismutase, peroxidise, catalase and glutathione-S-transferase). The light conditioning played the most prominent role in deciding the extent of herbicide toxicity on both the tested cyanobacteria as the maximum toxicity was observed in suboptimum light acclimatized cyanobacterial cells corroborated by the least growth in the same cells. The impact of pretilachlor treatment on photosystem II photochemistry viz. φP0, Ѱ0, φE0, PIABS, ABS/RC, TR0/RC, ET0/RC and DI0/RC was also altered by light acclimatization. The percent rise in oxidative stress markers (SOR and H2O2) and consequent lipid peroxidation (MDA equivalents) were also highest in suboptimum light acclimatized cells exposed to pretilachlor which could not be prospered with compatible antioxidant performance. Conversely, supra-optimum light acclimatized cells of both the cyanobacteria was found to accelerate the activities of all the studied enzymes and thus able to counterbalance the pretilachlor toxicity and supported the healthier growth.

Arsenic poisoning in aquatic ecosystem is a global concern that obstructs the productivity of agricultural lands (paddy fields) by targeting the growth of cyanobacteria. The cyanobacteria also tolerate and accumulate elevated concentration of arsenic (As) inside the cell and excrete out from cells in less toxic forms after the successive time interval. Thus to validate this, the study was carried out at two different time intervals, i.e., 48 h and 96 h. Two redox forms of As arsenate (AsV) and arsenite (AsIII) at different concentrations (50, 100, and 150 mM AsV; 50, 100, and 150 μM AsIII) caused substantial reduction in growth, pigments (Chl a/Car and phycobiliproteins: phycocyanin, allophycocyanin, and phycoerythrin), inorganic nitrogen ( nitrate (NO3−) and nitrite (NO2−)) uptake, activity of enzymes (NR, NiR, GS, and GOGAT) of nitrogen metabolism, biochemical constituents (protein, carbohydrate, and exopolysaccharide (EPS) contents of Nostoc muscorum, and Anabaena sp. PCC7120. The tested doses of AsV and AsIII after 48 h of exposure exhibited adverse impact on these parameters, but after 96 h with lower doses of AsV (50 mM and 100 mM) and AsIII (50 μM and 100 μM), significant recovery was recorded. Contrary to this, at higher dose of AsV (150 mM) and AsIII (150 μM), the adverse impact was further aggravated with increasing time exposure. Contrary to the activity of NR, NiR, GS, and GOGAT, GDH activity (alternative NH3+ assimilating enzyme) was found to increase, and after 96 h, the activity showed declining trend but still higher than the control. The biochemical constituent EPS (first protective barrier) under scanning electron microscope showed more accumulation of dry adsorbent in the case of AsIII stress hence displayed more toxic nature of AsIII than AsV. The study concludes that with increasing time exposure, the recovery in growth and related parameters mainly at lower doses of AsV and AsIII points toward adaptability of cyanobacteria which was more pronounced in Nostoc muscorum.

Plant, during its entire life cycle, from seedling to reproductive stage, faces changing environment that is sometimes unfavorable for growth and developmental processes; plants develop specific mechanism to overcome these environmental stresses. Adverse environmental factors are categorized majorly in two categories: first biotic factors that include pathogen and herbivore attacks, and second, abiotic factors that include drought, heat, cold, nutrient deficiency, and heavy-metal accumulation in the soil. Among these, salt, drought, and temperature affect the geographical distribution of plant species as well as disrupt the plant metabolism. As a consequence, they limit the quality and quantity of food production in agriculture and reducing the food demand for growing population, and to overcome these adverse effects, tolerance mechanism in plants has been well studied. In general, various environmental factors (biotic and abiotic) induce the plant resistance by activation of stress tolerance genes. The average temperature was found to be increased by 0.2°C/year and it has to be increased by 1.8°C–4°C at the end of year 2100, hence temperature is pondered to be one of the utmost detrimental stress. Climate change due to temperature is a global concern that has altered the physiological and biochemical activities of plant, thereby reducing the productivity of crops. Increased temperature continuously caused heat stress in plants, which depends upon the quality, intensity, and duration of light. Generation of reactive oxygen species is a common phenomenon exhibited by all environmental factors (biotic and abiotic), including heat stress that damaged the macromolecules, such as DNA, proteins, and lipids, and plants are under oxidative stress. Furthermore, heat stress also altered the expression of genes that participate in the formation of and responsible for production of osmoprotectants, detoxifying enzymes, transporters, and regulatory proteins. On contrary to this, heat stress inhibits the protein folding, affects the membrane (lipid bilayer) fluidity and cytoskeleton arrangement, and also affects the vegetative and reproductive tissue. Rise in temperature up to a certain limit is beneficial for plant that regulates the circadian rhythms in plants, regulates plant movements (opening/closing of corolla), and also affects the geographical distribution of plants in nature. Plants susceptibility toward pathogen was also enhanced by high temperature. Infection capacity of tobacco mosaic and tomato-spotted wilt viruses were found to be increased when ambient temperature increased and caused viral diseases in tobacco (Nicotiana tabacum) and pepper (Capsicum annuum), respectively. In wheat genotypes, its sensitivity toward Cochliobolus sativus (caused spot blotch) was associated with increase in nighttime temperature.

Any external factors either biotic or abiotic that significantly reduced the plants’ ability to convert light energy into biomass are studied under a broad category termed stresses that negatively influence the metabolic activities of plants. Along with biotic and abiotic stresses, overgrowing population also caused a lot of pressure on agricultural fields to fulfill the food demand, but the crops productivity was not increased in such manner as population increased. In natural environment, primary producers, that is, plants face a number of adverse environmental conditions such as high salinity, drought, cold, and heat that limits the biomass production and yield of staple food crops; hence, it is a global concern to fulfill the food demand. Various anthropogenic activities contribute to the abiotic stress that changes the climate of environment that causes threat to food security. These adverse environmental changes hamper the various physiological and metabolic factors that results in death of plants. A physiological alteration under abiotic stresses includes growth inhibition associated with photosynthetic pigment loss, decreased whole-cell oxygen evolution (photosynthesis), and significant increase in oxygen consumption. Plants stimulate various adoptive changes in response to abiotic stresses at physiological, cellular, and molecular level or through genetic regulation or reprogramming the expression of gene. Physiological adaptation includes change in protein modification at transcriptional level as well as at posttranslational level that leads the change in particular phenotype that significantly avoids the stressful conditions. One such approach is through the modification in gene expression and also through the activity of sRNAs, which switches on protective mechanisms, that is, the genes that involve in defense systems are upregulated and gens that involve in toxicity are downregulated. Role of proteomics as stress-tolerance mechanism is well known, whereas the role of sRNA as stress regulators is an emerging molecular tool. Further, due to the development of modern molecular techniques, molecular mechanisms in plants give much more attention to identify the stress-responsive proteins and their regulatory gene networks under posttranslational level. In this line, small noncoding RNAs (sRNAs) are considered posttranscriptional regulatory factor in gene regulation under adverse environmental factors and involved in plant development. In molecular world, RNAs are basically categorized into two into transfer RNA and ribosomal RNA, and the only difference in sRNAs from other forms of RNAs is relatively small size of genome (20–30 nt) as well as having capacity to make complex with argonaute (AGO) family proteins considered key components of RISC (RNA-induced silencing complex). Among various types of sRNA, two are major, that is, microRNAs and small interfering RNAs that actively mediate the gene regulation, splicing, DNA methylation, chromatin, protein, and nucleotide modification and sRNA-mediated gene silencing termed RNA interference (RNAi). RNAi significantly inhibits the process of transcription or translation by sequence-specific gene regulation initiated by dsRNA and frequently presents in plants as well as in animals, fungi, and ciliates. The present time is totally dependent on crop improvement techniques under adverse environmental conditions by the use of various molecular approaches and among them RNAi is considered an important tool of genetic engineering and functional genomics. In this chapter, we briefly describe the biogenesis of sRNA and their pivotal role against abiotic stress tolerance.

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Plants, principally spices and herbs, have been given much more attention because they are considered important for flavoring and coloring foods and their use as condiments. Herbs and spices have been used for generations by humans as food and also to treat ailments since they are full of medicinal and antioxidant properties and contain bioactive compounds like tannins, alkaloids, phenolics, flavonoids, polyphenols, and vitamins, which help in healing diseases. Spices and herbs contain biomolecules that play a crucial role in healthcare and fitness levels. Spices and herbs have been considered as esoteric food adjuncts as they play numerous roles like being coloring agents, flavoring agents, preservatives, food additives, and having uses in the medicinal and pharmaceutical industries.

Plants are the eminent source of essential elements which are constructing blocks of living organism in the form of protein, carbohydrate, fats and fibres. Living organism, including plants, requires nutrients for their better growth and developmental processes. Based upon the necessity, nutrients are categorized as macro- and micronutrients. Carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulphur, calcium, iron and magnesium are the various plant macronutrients, while micronutrients include manganese, copper, boron, molybdenum and chlorine. Plants are able to draw these mineral nutrients in a balanced way either from soil organic matter or by the use of organic or inorganic fertilizers. Mineral nutrition is acquired by a complex network of root transporters that regulate import of minerals from the soil solution to plants. The requirement of these nutrients varies from plant to plant, and scarcity of these nutrient elements intervenes the metabolic processes. However excessive uptake induces toxicity and causes poor growth associated with reduction in crop production. Hence, balanced nutrient approach is important for proper crop yield. This chapter describes the essential nutrients, the chemical forms in which they are available to plants, their function in plants, their deficiency system, and recommended nutrient levels in plant tissues of selected crops and future prospective of nutrient management approach.

Heavy metal contamination is a prime environmental concern that threatens plants productivity, animal, and human health. Heavy metals occur in the earth’s crust, but due to their persistent and stable character, they cannot be degraded or destroyed. Various natural and anthropogenic processes release these heavy metals into the environment and contaminate the agricultural soils which is further associated with health hazard due to dietary intake of contaminated vegetables. The modern agricultural practices i.e. prolonged application of fertilizers, pesticides has resulted in the degradation of the ecosystem and accumulation of heavy metals especially in crop plants. Vegetable crops are vital for the human diet and in particular provide the nutrients to maintain normal health. The exposure of plants to heavy metals results in accumulation of metal content inside the plant cell via specific transport mechanisms. This alters the physiological and biochemical process that negatively affects the growth and development of plants. Heavy metals consequently alter the electron transport chain and generate ROS; singlet oxygen (1O2), hydroxyl radical (HO•), superoxide radical (O2•−), and hydrogen peroxide (H2O2). Albeit, ROS at low concentrations serves the role as important signalling molecules that are generally in equilibrium with antioxidant molecules but at higher concentrations impose adverse effect by interacting with macromolecules. Besides this, heavy metals also down-regulate the specific genes that are involved in the stress responses. Thus introduction of heavy metals in food chain and consumption of contaminated vegetables and its toxicity is a serious concern. Furthermore, strategy and policy are required to control the limits of accumulation in crop plants and vegetables.

In recent days, the rapid development of industries and uncontrolled anthropogenic activities increased the concentration of various heavy metals in all types of environments, that is, aquatic as well as terrestrial/soil. Therefore, organisms thriving in such environments regularly face high metal concentrations which in turn adversely affect their growth and development. Among these organisms, cyanobacteria are very precious due to their tremendous ability to perform oxygenic photosynthesis. Apart from this, a number of cyanobacteria are well known to fix atmospheric N2 and play important role in geochemical cycling of N2. In this chapter, we have provided information about the impact of heavy metals on the important physiological processes affecting biomass accumulation. We have also tried providing the strategies adapted at cellular (secretion of some chelates) as well as molecular (OMICS approach) levels by cyanobacteria to overcome the stress generated by heavy metals. However, there is still a dearth of knowledge related to mechanisms that help in establishing this tolerance/adaptation, most of the studies are being performed in plant system, while cyanobacterial system is still not much interrogated at the molecular level so that they can be used in several metal remediation programs. The future studies must utilize multidisciplinary approach including OMICS to establish the role of these cyanobacteria under heavy metal stress tolerance.

The field of nanotechnology has gained increased attention and has quickly intensified over the years due to its unique properties and diverse applications in different fields of science and technology. Different kinds of nanomaterials and their applications have been introduced; however, among them, carbon-based nanomaterials, including graphite, diamond, fullerene, graphene, and carbon nanotubes (CNTs), have been extensively studied. CNTs are of great importance due to their excellent optical, mechanical, electrical, and thermal properties. Production, use, reuse, destruction, and transportation are major sources of CNTs in the environment. CNTs are widely used in plant sciences (phytonanotechnology), which alter conventional plant production systems, detoxify chemicals (pesticides and fertilizers), increase disease resistance, and act as plant growth regulators. This chapter mainly describes the role of CNTs in plant sciences and soil communities with reference to other parameters.

In order to know the impact of elevated level of UV-B on arsenic stressed Helianthus annuus L. var. DRSF-113 plants, certain physiological (growth - root and shoot lengths, their fresh masses and leaf area; photosynthetic competence and respiration) and biochemical parameters (pigments - Chl a and b, Car, anthocyanin and flavonoids; reactive oxygen species - superoxide radicals, H2O2; reactive carbonyl group, electrolyte leakage; antioxidants - superoxide dismutase, peroxidise, catalase, glutathione-S-transferase, proline) of their seedlings were analysed under the simultaneous exposures of two arsenic doses (6mgkg-1 soil, As1; and 12mgkg-1 soil, As2) and two UV-B doses (1.2kJm-2d-1, UV-B1; and 3.6kJm-2d-1, UV-B2). As1 and As2 alone declined all the studied growth parameters - along with photosynthetic pigments which were further aggravated after the simultaneous exposures of predefined levels of UV-B. Each As exposure was accompanied by significant accumulation of As in root, shoot and leaves and was substantiated by simultaneous exposures of UV-B doses which manifested into suppressed growth, decreased chlorophyll contents and photosynthesis. In similar conditions, other photo-shielding pigments, viz. carotenoids, anthocyanin and flavonoids along with respiration and oxidative stress markers such as O2•¯, H2O2; and indicators of cell membrane damage like MDA (malondialdehyde), RCG (reactive carbonyl group), electrolyte leakage were enhanced by As, and became more pronounced after the simultaneous exposures of UV-B doses. As doses stimulated the activities of SOD, POD, CAT, GST and Pro which got further accelerated after the simultaneous exposures of UV-B doses.