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Silicon (Si) is known to alleviate the adverse impact of different abiotic and biotic stresses by different mechanisms including morphological, physiological, and genetic changes. Photosynthesis, one of the most important physiological processes in the plant is sensitive to different stress factors. Several studies have shown that Si ameliorates the stress effects on photosynthesis by protecting photosynthetic machinery and its function. In stressed plants, several photosynthesis-related processes including PSII maximum photochemical quantum yield (Fv/Fm), the yield of photosystem II (φPSII), electron transport rates (ETR), and photochemical quenching (qP) were observed to be regulated when supplemented with Si, which indicates that Si effectively protects the photosynthetic machinery. In addition, studies also suggested that Si is capable enough to maintain the uneven swelling, disintegrated, and missing thylakoid membranes caused during stress. Furthermore, several photosynthesis-related genes were also regulated by Si supplementation. Taking into account the key impact of Si on the evolutionarily conserved process of photosynthesis in plants, this review article is focused on the aspects of silicon and photosynthesis interrelationships during stress and signaling pathways. The assemblages of this discussion shall fulfill the lack of constructive literature related to the influence of Si on one of the most dynamic and important processes of plant life i.e. photosynthesis. Previous article in issue

The modulatory effect of opera was investigated on the physiological and morphological aspects in soybean thriving in water stress environment. The data procured from current investigation indicated that water stress significantly declined the plant growth, leaf area in addition to photosynthetic efficiency, nitrate reductase activity and crop yield at various stages of growth such as vegetative (VS), flowering (FS) and pod filling stage (PFS). However, foliar application of opera (0.15%) was effective to enhance the the leaf area (42%), rate of photosynthesis (194%), and nitrate reductase activity (68%) at FS stage while the maximum enhancement in biomass accumulation (92%) and yield (119%) was observed at PFS stage as compared to their control plants. The opera is applied as foliar spray in field experiments to augment the assimilation of nitrogen and carbon in soybean which contributes to increased crop development and productivity under water stress conditions.

Heavy metal (HM) toxicity is vital environmental constraint that limits crop productivity worldwide. Several physiological processes necessary for plant survival have been found to be affected by HM toxicity. In recent farming, advanced mechanisms are being developed to overcome from the stresses to enhance the yield. The seed priming is an affordable method for plants to survive under abiotic and biotic stresses. Priming is useful for commercial seed lots by seed technologists to increase the vigor of the seeds in terms of germination potential and enhance the tolerance against various stresses. It also removes the pollution threats by minimizing the uses of chemical fertilizers. The seeds having deprived of quality in terms of seed germination and seedling characters ultimately affect the growth, photosynthetic performance and yield of the plants under HM stress. On the other hand seed primed with various seed priming methods such as hydropriming, hormonal priming, chemical priming, biopriming, magnetopriming and nanopriming perform well under HM toxicity. Seed priming methods have been considered as a unique approach to get rid of HM stress by enhancing the seed germination, seedling vigor, rate of photosynthesis, biomass accumulation and thus increase the crop productivity. The present review provides an overview of different seed-priming methods and their role in alleviation of adverse effects of HM stress in plants.

The experiments were conducted for the estimation of the mitigating effect of the static magnetic field (SMF of 200 mT for 1 h) treatment on soybean under ambient UV-B stress. The SMF treated (MT) and untreated (UT) seeds were grown inside iron cages covered with polyester filters for the purpose to filter UV-A + B (

Microalgae and cyanobacteria include procaryotic and eucaryotic photosynthetic micro-organisms that produce biomass rich in biomolecules with a high value. Some examples of these biomolecules are proteins, lipids, carbohydrates, pigments, antioxidants, and vitamins. Currently, microalgae are also considered a good source of biofuel feedstock. The microalga-based biorefinery approach should be used to promote the sustainability of biomass generation since microalga biomass production can be performed and integrated into a circular bioeconomy structure. To include an environmentally sustainable approach with microalga cultures, it is necessary to develop alternative ways to produce biomass at a low cost, reducing pollution and improving biomass development. Different strategies are being used to achieve more productivity in cultivation, such as magnets in cultures. Magnetic forces can alter microalga metabolism, and this field of study is promising and innovative, yet remains an unexplored area. This review presents the current trends in the magnetic biostimulation of microalgae for the application of cultivated biomass in different areas of biotechnology, biofuel, and bioenergy production, as well as environmental protection. info:eu-repo/semantics/publishedVersion

The study was performed to analyze the impact of seed pretreatment by static magnetic field (SMF) of 200 mT for 1 h on photosynthetic performance of soybean (Glycine max) seedlings under ambient (aUV-B) and supplemental ultraviolet-B (a+sUV-B) stress. Ambient and supplemental UV-B were found to decrease the plant growth, chlorophyll concentration, PSII efficiency, selected JIP-test parameters such as Fv/Fm, φEo, ΔV(I–P), PIABS, PItotal, and rate of photosynthesis in the leaves of soybean seedlings emerged from untreated (UT) seeds. aUV-B and a+sUV-B were observed to increase the synthesis of UV-B-absorbing substances (UAS), reactive oxygen species (ROS) like superoxide radical (O2·−) and hydrogen peroxide (H2O2), antioxidants like ascorbic acid and α-tocopherol and decrease the nitrate reductase (NR) activity; subsequently, it results in a decreased rate of photosynthesis, biomass accumulation, and yield. However, our results provided evidence that SMF pretreatment increased the tolerance of soybean seedlings to UV-B radiation by increased NO content and NR activity; higher efficiency of PSII, higher values of φEo, ΔV(I–P), PIABS, and PItotal, decreased intercellular CO2 concentration, lower amount of UAS, ROS, and antioxidants that consequently improve the yield of soybean plants under aUV-B as well as a+sUV-B stress. Thus, our results suggested that SMF pretreatment mitigates the adverse effects of UV-B stress by the enhancement in photosynthetic performance along with higher NO content which may be able to protect the plants from the deleterious effects of oxidative stress caused by UV-B irradiation.

Magnetopriming has emerged as a promising seed-priming method, improving seed vigor, plant performance and productivity under both normal and stressed conditions. Various recent reports have demonstrated that improved photosynthesis can lead to higher biomass accumulation and overall crop yield. The major focus of the present review is magnetopriming-based, improved growth parameters, which ultimately favor increased photosynthetic performance. The plants originating from magnetoprimed seeds showed increased plant height, leaf area, fresh weight, thick midrib and minor veins. Similarly, chlorophyll and carotenoid contents, efficiency of PSII, quantum yield of electron transport, stomatal conductance, and activities of carbonic anhydrase (CA), Rubisco and PEP-carboxylase enzymes are enhanced with magnetopriming of the seeds. In addition, a higher fluorescence yield at the J-I-P phase in polyphasic chlorophyll a fluorescence (OJIP) transient curves was observed in plants originating from magnetoprimed seeds. Here, we have presented an overview of available studies supporting the magnetopriming-based improvement of various parameters determining the photosynthetic performance of crop plants, which consequently increases crop yield. Additionally, we suggest the need for more in-depth molecular analysis in the future to shed light upon hidden regulatory mechanisms involved in magnetopriming-based, improved photosynthetic performance.

We have evaluated the contribution of nitric oxide (NO) in static magnetic field (SMF-200 mT for 1h) induced tolerance towards UV-B stress in soybean seedlings using various NO modulators like sodium nitroprusside (SNP), inhibitor of nitrate reductase (NR) sodium tungstate (ST), NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) and diphenylene iodonium (DPI) a NADPH oxidase inhibitor. The UV-B exposure significantly reduced germination, seedling growth together with activities of total amylase, NOS and NR in seedlings from un-primed seeds whereas SMF-primed seedlings showed significant enhancement in all these parameters along with higher level of NO/ROS. The supply of NO donor, SNP further improved all the seedlings parameters in un-primed and SMF-primed seeds after UV-B exposure. While ST, L-NAME and DPI significantly reduced the SMF-induced seedling performance after UV-B exposure. The gene expression study also showed significant up-regulation of α-amylase (GmAMY1, GmAMY2), nitric oxide synthase (GmNOS2) and nitrate reductase (GmNR2) encoding genes in UV-B exposed SMF-primed seedlings over un-primed seedlings. In particular, SNP+UV-B treatment enhanced the GmNOS2 expression in both unprimed (31.9-fold) and SMF-primed (93.2-fold) seedlings in comparison to their respective controls of CK+UV-B. In contrast, L-NAME+UV-B treatment reduced the SMF-induced GmNOS2 expression (4.8-fold) and NOS activity (76%). It confirmed that NO may be the key signaling molecule in SMF stimulated tolerance towards UV-B stress during early seedling growth and NOS may possibly be accountable for SMF-triggered NO production in soybean seedlings exposed to UV-B irradiations.

Crop yield can be raised by establishment of adequate plant stand using seeds with high germination ratio and vigor. Various pre-sowing treatments are adopted to achieve this objective. One of these approaches is the exposure of seeds to a low-to-medium level magnetic field (MF), in pulsed and continuous modes, as they have shown positive results in a number of crop seeds. On the basis of the sensitivity of plants to MF, different types of MF have been used for magnetopriming studies, such as weak static homogeneous magnetic fields (0–100 μT, including GMF), strong homogeneous magnetic fields (milliTesla to Tesla), and extremely low frequency (ELF) magnetic fields of low-to-moderate (several hundred μT) magnetic flux densities. The agronomic application of MFs in plants has shown potential in altering conventional plant production systems; increasing mean germination rates, and root and shoot growth; having high productivity; increasing photosynthetic pigment content; and intensifying cell division, as well as water and nutrient uptake. Furthermore, different studies suggest that MFs prevent the large injuries produced/inflicted by diseases and pests on agricultural crops and other economically important plants and assist in reducing the oxidative damage in plants caused by stress situations. An improved understanding of the interactions between the MF and the plant responses could revolutionize crop production through increased resistance to disease and stress conditions, as well as the superiority of nutrient and water utilization, resulting in the improvement of crop yield. In this review, we summarize the potential applications of MF and the key processes involved in agronomic applications. Furthermore, in order to ensure both the safe usage and acceptance of this new opportunity, the adverse effects are also discussed.

This study investigates the effect of static magnetic field (SMF) pre-treatment in ameliorating arsenic (As) toxicity in soybean plants in relation to growth, photosynthesis and water transport through leaf venation. Soybean (Glycine max variety JS-9560) seeds pre-treated with SMF (200 mT for 1 h) were grown in four levels of arsenate-polluted soil (As(V); 0, 5, 10 and 50 mg kg-1 ) in order to find out the impact of magnetopriming on plant tolerance against As toxicity. Quantitative image analysis of soybean leaf venation showed a narrowing in the width of midrib with increasing As(V) contamination in non-primed seeds. The morphological variations are also supported by the physiological parameters such as reduction in efficiency of photosystem II, plant performance index, stomatal conductance and photosynthetic rate in the presence of As(V) for non-primed seeds. However, remarkable increase was observed in all the measured parameters by SMF pre-treatment at all the concentrations of As(V) used. Even for the highest concentration of As(V) (50 mg kg-1 soil), SMF pre-treatment caused significant enhancement in plant height (40%), area of third trifoliate leaves (40%), along with increase in width of the midrib (17%) and minor vein (13%), contributing to increase in the water uptake, that resulted in higher primary photochemistry of PSII (12%), performance index (50%), stomatal conductance (57%) and photosynthetic rate (33%) as compared to non-primed ones. Consequently, magnetopriming of dry seeds can be effectively used as pretreatment for reduction of As toxicity in soybean plants.

In the tropics, solar UV-B background level is often high and can affect growth and development of vegetables. Fenugreek (Trigonella foenum-graecum L.), which is not native to India, may be detrime...

Maize and Soybean seeds were pre-treated with static magnetic field (SMF) of 200 mT for 1 h to evaluate the effect of magnetopriming on germination and early growth characteristics of seeds under saline conditions. The adverse effect of NaCl induced salt stress was found on percentage germination and germination related parameters. Enhanced percentage germination and early seedling growth parameters (root and shoot length, and vigour indices) under different salinity levels (0–100 mM NaCl) indicated that magnetopriming was more effective in alleviating salinity stress at early seedling stage of both maize and soybean as compared to untreated seeds. α- amylase and protease activities were also higher in SMF treated seeds under both non-saline and saline conditions. This could have resulted in faster hydration of enzymes in SMF treated seeds leading to higher rate of germination. Increased levels of superoxide radical and hydrogen peroxide was found in germinating magnetoprimed seeds of maize and soybean, under both the growing conditions. Enhancement in seed germination and seedling vigour under both the growing conditions by SMF treatment may be due to the combined effect of enhanced α- amylase and protease activities and enhanced levels of free radicals in the seeds.

Anthropogenic activities are creating various ecological problems, thus emerging diversity of abiotic stresses like water, salinity, temperature, cold, heavy metal, ozone, and UV radiation. Significant loss in plant growth rate and yield due to these stresses has imparted a major challenge to the food security globally. Response to such abiotic stresses has been studied well from the physiological level to the molecular level. Photosynthesis and carbon fixation is pivotal for all the plants that are affected by mostly all abiotic stresses. The downregulation of Calvin–Benson–Bassham cycle is also augmented by stomatal closure, CO2 diffusion through stomata, decreased activity of ribulose bisphosphate carboxylase/oxygenase activity, which in turn decreases the CO2 assimilation, consequently resulted in reduced biomass accumulation and crop yield. Other response includes the synthesis of stress hormones such as abscisic acid, regulating factor for stomatal opening, and generation of reactive oxygen species causing oxidative stress. There is a complex network of interaction and regulation that acts during stress situation and helps plant to adapt accordingly. This chapter focuses on the damaging effect of various abiotic stresses on Calvin–Benson–Bassham cycle and provides updated information on the cycle and the factors associated with its regulation.

The concurrent occurrence of more than one abiotic stress in plants is a regular consequence in natural field environment. The heavy metals and deficiency of water are two different abiotic stress factors that affect plant system by their single or simultaneous existence. In recent times, due to the industrial revolution, the contamination of agricultural soil by different heavy metals has increased drastically. For plants, some of the heavy metals are considered as essential nutrients in microquantities, which help in plant growth and development, whereas some are considered nonessential and show a visible toxic effect even at low concentration. Water deficit is a condition of inadequate supply of water in plants due to limited water availability that results in damaging effects in plants. Both of these stresses, that is, metal and water deficit, when combined to a certain level, result in some consequences in plants that might have responses similar to that of individual stress, or these responses might completely differ from that of single stress. Previous relevant literature suggested that plants have unique and sometimes complex responses against different abiotic stress combinations that cannot be directly compared with those of individual stress effects. At present, very few reports are available on mutual and interactive effects of metal and water-deficit stress in plants. Hence, it is essentially required to analyze numerous stress responses in different plants to understand the underlying mechanism of interaction and develop resistant varieties against various stresses but maintaining high yields. This chapter reviewed the articles related to different abiotic stresses’ interaction with plants, specifically heavy metal and deficiency of water; with an attempt to elucidate the morphological, physiological, and biochemical effects on the plants. We have discussed the combined metal and water-deficit stress to understand the responses of plants against these two stresses individually and in combination.

In the present study, experiments were performed to investigate the role of nitric oxide (NO) in magnetopriming-induced seed germination and early growth characteristics of soybean (Glycine max) seedlings under salt stress. The NO donor (sodium nitroprusside, SNP), NO scavenger (2-[4-carboxyphenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, CPTIO), inhibitors of nitrate reductase (sodium tungstate, ST) or NO synthase (N-nitro-L-Arg-methyl ester, LNAME) and NADPH oxidase inhibitor (diphenylene iodonium, DPI) have been used to measure the role of NO in the alleviation of salinity stress by static magnetic field (SMF of 200 mT, 1 h). Salt stress (50 mM NaCl) significantly reduced germination and early growth of seedlings emerged from non-primed seeds. Pre-treatment of seeds with SMF positively stimulated the germination and consequently promoted the seedling growth. ST, LNAME, CPTIO and DPI significantly decreased the growth of seedling, activities of α-amylase, protease and nitrate reductase (NR), hydrogen peroxide (H2 O2 ), superoxide (O2 •- ) and NO content in roots of seedlings emerged from non-primed and SMF-primed seeds. However, the extent of reduction was higher with ST in seedlings of SMF-primed seeds under both conditions, whereas SNP promoted all the studied parameters. Moreover, the generation of NO was also confirmed microscopically using a membrane permanent fluorochrome (4-5-diaminofluorescein diacetate [DAF-2 DA]). Further, analysis showed that SMF enhanced the NR activity and triggered the NO production and NR was maximally decreased by ST as compared to LNAME, CPTIO and DPI. Thus, in addition to ROS, NO might be one of the important signaling molecules in magnetopriming-induced salt tolerance in soybean and NR may be responsible for SMF-triggered NO generation in roots of soybean.

The effect of seed pre-treatment with a static magnetic field (SMF) of 200 mT for 1 h on the impact of ambient UV (280–400 nm) stress was tested using soybean var. JS-335 seeds. The SMF-pre-treated and untreated seeds were sown in plastic nursery bags placed in iron mesh cages covered with polyester filters that cutoff UV-B (

Experiments were conducted to study the effects of static magnetic fields (SMFs) on the venation network of soybean leaves using the synchrotron-based X-ray micro-imaging technique. The seeds of soybean (Glycine max, variety JS-335) were pretreated with different SMFs from 50 to 300 mT in steps of 50 mT for 1 h. The phase-contrast images obtained showed that, as the strength of the SMF increased, the area, width of the midrib, area of the midrib and minor vein of the middle leaflets of third trifoliate leaves also increased up to the SMF strength of 200 mT (1 h) and decreased thereafter. Quantification of the major conducting vein also showed the differences in the major and minor vein structures of the soybean leaves as compared with control leaves. Further, the phase-retrieval technique has been applied to make the segmentation process easy and to quantify the major and minor veins in the venation network. The width and area of midrib enhancement by pre-treatment with SMF implies an enhancement in the uptake of water, which in turn causes an increased rate of photosynthesis and stomatal conductance.

The effectiveness of magnetopriming was assessed for alleviation of salt-induced adverse effects on soybean growth. Soybean seeds were pre-treated with static magnetic field (SMF) of 200 mT for 1 h to evaluate the effect of magnetopriming on growth, carbon and nitrogen metabolism, and yield of soybean plants under different salinity levels (0, 25, and 50 mM NaCl). The adverse effect of NaCl-induced salt stress was found on growth, yield, and various physiological attributes of soybeans. Results indicate that SMF pre-treatment significantly increased plant growth attributes, number of root nodules, nodules, fresh weight, biomass accumulation, and photosynthetic performance under both non-saline and saline conditions as compared to untreated seeds. Polyphasic chlorophyll a fluorescence (OJIP) transients from magnetically treated plants gave a higher fluorescence yield at J-I-P phase. Nitrate reductase activity, PIABS , photosynthetic pigments, and net rate of photosynthesis were also higher in plants that emerged from SMF pre-treated seeds as compared to untreated seeds. Leghemoglobin content and hemechrome content in root nodules were also increased by SMF pre-treatment. Thus pre-sowing exposure of seeds to SMF enhanced carbon and nitrogen metabolism and improved the yield of soybeans in terms of number of pods, number of seeds, and seed weight under saline as well as non-saline conditions. Consequently, SMF pre-treatment effectively mitigated adverse effects of NaCl on soybeans. It indicates that magnetopriming of dry soybean seeds can be effectively used as a pre-sowing treatment for alleviating salinity stress. Bioelectromagnetics. 37:455-470, 2016. © 2016 Wiley Periodicals, Inc.

The hydraulic efficiency of a leaf depends on its vascular structure as this is responsible for transport activities. To investigate the effect of exclusion of UVAB and UVB radiation from the solar spectrum on the micro-structure of leaves of soybean (Glycine max, variety JS-335), a field experiment was conducted using synchrotron-based phase contrast imaging (PCI). Plants were grown in specially designed UV exclusion chambers, and wrapped with filters that excluded UVB (280–315 nm) or UVAB (280–400 nm), or transmitted all the ambient solar UV (280–400 nm) radiation (filter control). Qualitative observation of high-resolution X-ray PCI images obtained at 10 keV has shown the differences in major and minor vein structures of the leaves. The mid-rib width of the middle leaflet of third trifoliate leaves, for all treatments, were obtained using quantitative image analysis. The width of the mid-rib of the middle leaflet of third trifoliate leaves of UVB excluded plants was found to be more compared to leaves of filter control plants, which are exposed to ambient UV. The mid-rib or the main conducting vein transports water and sugars to the whole plant; therefore, mid-rib enhancement by the exclusion of solar UV radiation possibly implies enhancement in the leaf area which in turn causes an increased rate of photosynthesis.

Ultraviolet-B (UV-B) is a significant abiotic stress factor exerting multiple effects on plant growth. This study was undertaken to unravel if selenium (Se), an element known to increase the stress tolerance, is able to defend soybean plants against detrimental effects of ambient UV. Soybean plants were grown in soil supplemented with Se at 0, 0.1 and 1.0 mg kg− 1 soil under ambient and filtered solar UV. The influence of ambient and filtered solar UV and of Se was determined on growth of above/below-ground parts, biomass accumulation, rate of photosynthesis, protein, nitrate reductase activity, leghemoglobin content and yield in soybean var. JS 335. Both the low and high Se dosage significantly enhanced the growth of above-ground parts (plant height, leaf area and total biomass accumulation) as well as the growth of below-ground parts (root length, root biomass, number of nodules and fresh weight of nodules) as compared to their control (0 mg kg− 1 soil) plants under ambient and filter control treatments (+ UV-B and UV-A). Leghemoglobin content was higher in the root nodules and the total chlorophyll, total soluble protein and NR activity in leaves were also significantly increased by Se as compared to their controls under ambient and filter control treatments. Similarly, exclusion of solar UV radiations also significantly enhanced these parameters except NR activity as compared to the controls. Selenium increased the grain yield of soybean under ambient conditions. The results suggest that the increased yield of soybean by Se and UV exclusion was related to increased carbon and nitrogen fixation which was evident by the increased rate of photosynthesis, higher activity of nitrate reductase and high amount of leghemoglobin in root nodules of soybean. An increase in physiological indices with Se supply confirmed that Se plays a positive role in improving UV (280–400 nm) tolerance of soybean seedlings. A comparison of results of growing plants in supplementation of Se in soil under ambient UV and without Se supplementation in soil under solar UV exclusion indicates a parallelism between the two effects. Both enhanced the growth of the plants and accumulation of biomass, hence enhanced fixation of carbon and nitrogen, ultimately enhanced the crop yield. Thus Se supply significantly increased the growth and yield of soybean under ambient UV stress.

Plants resort to many adaptive strategies in response to abiotic environmental stresses such as salinity, dehydration, cold, heat, osmotic and UV-B stress which affect seed germination, plant growth, development, photosynthesis, and yield. Magnetopriming is a non-invasive physical stimulation of dry seeds with a static magnetic field (SMF), used to improve vigor and field emergence in seeds. This chapter discusses the protection of plants from the adverse effects of abiotic stresses, such as salinity, by SMF pre-treatment. The adverse effect of NaCl-induced salt stress has been observed on germination, growth, yield and various physiological attributes of many crop plants. The perusal of relevant literature reveals that SMF pre-treatment to the seeds significantly increased the percentage germination, early seedling characteristics, plant-growth attributes, biomass accumulation, photosynthetic performance, nitrogen fixation and yield under both non-saline and saline conditions. Chlorophyll, a fluorescence transient from SMF-treated plants, gave a higher fluorescence yield at J–I–P phase in leaves of plants that emerged from SMF-pre-treated seeds even under saline conditions. Photosynthetic pigments, the efficiency of PSII, performance index based on absorption of light energy, photosynthesis, nitrogenase and nitrate reductase activities were also higher in plants emerged from SMF pre-treated seeds, which resulted in an improved yield of the plants even in the presence of salt stress. As a result, SMF pre-treatment ameliorates salt stress so that the plants do not have to divert their metabolic energy in detoxification of ROS produced under stress conditions. Thus SMF pre-treatment to the seeds eliminates the need for defense against abiotic salt stress. Hence magnetopriming of dry seeds can be effectively used as a pre-sowing treatment in order to mitigate abiotic-stressinduced adverse effects on different crop plants under field conditions. In conclusion, SMF may be a good tool for improving agricultural production in the future because of its moderating effect towards high temperature, drought, salinity and UV-B stress.

Scarcity of water is a severe environmental restriction to plant productivity. Crop growth and yields are negatively affected by sub-optimal water supply due to physical damages, physiological disruptions, and biochemical changes. Here, we have reviewed the effects of water deficit stress on the germination and growth, water and nutrient relations, photosynthesis, and respiration in plants, particularly in maize. Oxidative stress is often associated as a secondary stress with primary drought stress. Therefore, injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. This chapter also describes the mechanism of drought resistance in plants on a morphological, physiological, and molecular basis. Plants display a range of mechanisms to withstand drought stress, such as deep root systems for enhanced water uptake, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes such as glycine betaine and proline have optimistic effects on membrane integrity and enzyme along with adaptive roles in mediating osmotic adjustment under drought. Plant growth regulators such as cytokinin, abscisic acid, and jasmonic acid induce several cellular mechanisms associated with drought resistance. At molecular levels, up- and downregulation of many drought-responsive genes and transcription factors have been characterized, such as the genes encoding for late embryogenesis abundant (LEA) proteins, dehydration responsive element binding proteins, and aquaporins. The development of crop varieties with increased tolerance to drought, both by conventional breeding methods and by genetic engineering, is an important approach to meet up global food demands with less water.

Free radicals are defined as any molecular species which are proficient of independent existence and consist of an unpaired electron in their atomic orbital. These free radicals are derived from reactive oxygen or reactive nitrogen species which are generally produced in cellular metabolism and tend to increase under stress conditions. The most vulnerable biological targets of these reactive species include biomolecules such as proteins, lipids, and nucleic acids. To neutralize the adverse effect of free radicals, a strong antioxidant mechanism is required in plant cells. Wheat is one of the major cereals in the world, which is used in food and nonfood products. Wheat is cultivated in tropical and subtropical regions both under rain-fed and irrigated conditions, as it has a high level of adaptation. Wheat has a well-known antioxidant defense mechanism, i.e., enzymatic and nonenzymatic. However, crop production is adversely affected by environmental stresses alone or in combination. These stresses are commonly due to salinity, drought, waterlogging, cold, heavy metals, etc. Recent studies suggest the use of algal consortium in the soil, treatment with external agents like organic acids, signaling molecules, essential elements, seed priming, etc. can lead to a constructive approach toward a high yield of wheat under adverse conditions.

The elevated ultraviolet-B (UV-B, 290–315 nm) has sensitive alarm because it causes drastic effects on growth, photosynthesis, and crop yield. Globally, increased UV-B has a great challenge for production of wheat. Therefore, in this chapter, a brief attempt has been made to summarize the wheat responses and tolerance to UV-B radiation. Over the last two decades, most of the studies were on the mechanisms of UV-B tolerance along with the physiological, biochemical, and morphological responses of wheat plants to UV-B stress. The experimental results showed that ambient UV-B (aUV-B) and supplemental UV-B (sUV-B) radiations have adverse effects on growth of wheat crops such as shortening plant height, reducing leaf area, slowing physiological activity, and decreasing biomass and photosynthetic performance and yield. The perusal of literature recommended the enhanced UV-B irradiation lessens the production of crop yield via disturbing the number and weight of grains. The levels of superoxide radical (O2.-) and hydrogen peroxide (H2O2) were enhanced by UV-B (ambient and supplemental) along with enhanced peroxidation of lipids (LPO) and electrolyte leakage. Wheat plants possess many protective and tolerance mechanisms to reduce the effect of oxidative stress caused by UV-B stress. In response to aUV-B and sUV-B, defense mechanisms get activated in the form of the increased superoxide dismutase, catalase, ascorbic acid, and guaiacol peroxidase activities, and all nonenzymatic antioxidants are found to increase in wheat. Enhanced and ambient UV-B radiation had harmful effects on photosynthetic parameters like photosystem II (Hill reaction, chlorophyll, chlorophyll a fluorescence, electron transport rate (ETR), and yield), thylakoid, and enzymes of the dark reaction like carbonic anhydrase (CA), ribulose bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC), malic dehydrogenase (MDH), and chlorophyllase in wheat. Inter- and intraspecific variations were observed in the susceptibility of wheat to UV-B which imply the potential efforts in breeding programs for improved tolerance to UV-B radiation. On the other hand, exclusion of solar UV-B from solar spectrum enhanced the growth, biomass, photosynthetic performance, and yield of wheat plants as compared to the ambient and enhanced UV-B.

The negative effect on plant responses are expected due to increased amounts of ultraviolet B UV B radiation reaching on the Earth rsquo s surface by stratospheric ozone depletion Cytokinins CKs are essential phytohormones in plant growth and development Perusal of relevant literature reveals that CKs mitigate the oxidative damage caused by abiotic stresses like salt drought high temperature and heavy metal due to their antioxidant effects However very few reports are available on the interaction of CKs with UV B stress on the expansion growth of the cucumber cotyledons CKs induced the expansion growth of the excised cucumber cotyledons in the darkness CKs induced expansion growth of cucumber cotyledons in darkness was inhibited by supplemental UV B UV B radiation enhanced the level of oxyradicals like superoxide and hydroxide radicals in the excised cucumber cotyledons which was evident by EPR spectroscopy CKs like Zeatin TDZ BAP and FAP reduced the level of oxyradicals produced in the dark grown cucumber cotyledons while promoting the expansion growth of the cotyledons Production of oxyradical in UV B exposed cotyledons showed that these oxyradicals might partially account for inhibition of expansion growth Since considerable amount of oxyradicals were quenched by CKs at higher concentrations and micro g ml it partially restores the inhibition of expansion growth caused by UV B stress It indicates that overproduction of oxyradicals by UV B could not be entirely responsible for the inhibition of CKs induced expansion growth of cotyledons which might be caused by some other physiological changes caused by UV B irradiation in addition to the production of oxyradicals UV B is also known to inactivate protein inhibitor of peroxidase in cucumber cotyledons This may reduce the antioxidants defence and enhance the damaging effects of oxyradicals for the growth of cotyledons

In many areas of the world, salinity is a major abiotic stress-limiting growth and productivity of plants due to increasing use of poor quality of water for irrigation and soil salinisation. Various physiological traits, metabolic pathways and molecular or gene networks are involved in plant adaptation or tolerance to salinity stress. This chapter deals with the adaptive mechanisms that plants can employ to cope with the challenge of salt stress and provide updated overview of salt-tolerant mechanisms in major glycophytic crops with a particular interest in rice (Oryza sativa), soybean (Glycine max), wheat (Triticum aestivum) and Arabidopsis plants. Salt stress usually inhibits seed germination, seedling growth and vigour, biomass accumulation, flowering and fruit set in major glycophytic crops. In addition, elevated Na + levels in agricultural lands are increasingly becoming a serious threat to the world agriculture. Plants suffer osmotic and ionic stress under high salinity due to the salts accumulated at the outside of roots and those accumulated at the inside of the plant cells, respectively. Salinity stress significantly reduces growth and productivity of glycophytes, which are the majority of agricultural products. Plants tolerant to NaCl implement a series of adaptations to acclimate to salinity, including morphological, physiological, biochemical and molecular changes regulating plant adaptation and tolerance to salinity stress. These changes affect plant growth and development at different levels of plant organisation, e.g. they may reduce photosynthetic carbon gain and leaf growth rate and increase in the root/canopy ratio and in the chlorophyll content in addition to changes in the leaf anatomy that ultimately lead to preventing leaf ion toxicity, thus maintaining the water status in order to limit water loss and protect the photosynthesis process. Finally, we also provide an updated discussion on salt-induced oxidative stress at the subcellular level and its effect on the antioxidant machinery in major glycophyte crops plants. In response to salinity stress, the productions of ROS, such as singlet oxygen, superoxide, hydroxyl radical and hydrogen peroxide, are enhanced, and overexpression of genes leading to increased amounts and activities of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST)/glutathione peroxidase (GPX) increases the performance of plants under stress. The molecular mechanism of stress tolerance is complex and requires information at the miRNA/omics level to understand it effectively. During abiotic stress conditions, the advancement of “omics” is providing a detailed fingerprint of proteins, transcripts or all metabolites upregulated or downregulated in plant cells. However, the regulatory mechanisms of these protein-coding genes are largely unknown; in this regard, the microRNAs (miRNAs) may prove extremely important in deciphering these gene regulatory mechanisms and the stress responses. Some miRNAs are functionally conserved across plant species and are regulated by salt stress. In major crops through transgenic technologies, miRNAs represent themselves as potent targets to engineer abiotic stress tolerance, due to the critical roles in post-transcriptional regulation of gene expression in response to salinity and resultant growth attenuation.