Mona Soliman

Abstract Increasing ultraviolet (UV) radiation is causing oxidative stress that accounts for growth and yield losses in the present era of climate change. Plant hormones are useful tools for minimizing UV-induced oxidative stress in plants, but their putative roles in protecting tomato development under UVC remain unknown. Therefore, we investigated the underlying mechanism of pre-and post-kinetin (Kn) treatments on tomato plants under UVC stress. The best dose of Kn was screened in the preliminary experiments, and this dose was tested in further experiments. UVC significantly decreases growth traits, photosynthetic pigments, protein content, and primary metabolites (proteins, carbohydrates, amino acids) but increases oxidative stress biomarkers (lipid peroxidation, lipoxygenase activity, superoxide anion, hydroxyl radical, and hydrogen peroxide) and proline content. Treatment of pre-and post-kinetin spraying to tomato plants decreases UVC-induced oxidative stress by restoring the primary and secondary metabolites’ (phenolic compounds, flavonoids, and anthocyanins) status and upregulating the antioxidant defense systems (non-enzymatic antioxidants as ascorbate, reduced glutathione, α-tocopherol as well as enzymatic antioxidants as superoxide dismutase, catalase, ascorbate peroxidase, glutathione peroxidase, glutathione-S-transferase, and phenylalanine ammonia-lyase). Thus, the application of Kn in optimum doses and through different modes can be used to alleviate UVC-induced negative impacts in tomato plants.

Graphical abstract

Abstract
In a controlled environment experiment, we studied how physiological changes in leaves during the vegetative phase regulate final grain yield of wheat crops in salt-affected soils. We also hypothesized that amendments such as biochar (SB) and selenium-chitosan nanoparticles (Se-NPs) can protect wheat plants from salt injury. 20-day-old wheat plants were submitted to 4-week salt stress (3000 ppm NaCl). Soybean straw biochar was mixed with soil media at planting and Se-NPs (30 ppm) was sprayed 5 days after the first salt stress treatment. At the end of 4-week Se-NPs treatment, one set of plants was harvested for studying leaf level physiological changes. The salt-stressed plants accumulated significantly high leaf Na
+
(~ 13-fold increase), which trigged oxidative and osmotic damage. This salt-induced cellular injury was evident from significantly high levels of lipid membrane peroxidation and inhibited photosynthesis. Our study suggested that leaf physiological impairment in wheat plants was translated into poor biomass production and grain yield loss at crop maturity. Compared with control, salt-stressed plants produced 43% lesser biomass during vegetative phase, and 62% lesser grain yield at maturity. Amendments such as SB and Se-NPs protected the plants from salt-induced cellular injury by restricting Na
+
transport toward leaf tissues. Plants treated with NaCl + SB + Se-NPs accumulated 50% less Na
+
concentrations in leaves compared with NaCl-treated plants. Our study also suggested that SB and Se-NPs can restore ionic homeostasis and carbon assimilation in salt-stressed wheat by upregulating key transporter genes in leaves.

The contamination of heavy metals is a cause of environmental concern across the globe, as their increasing levels can pose a significant risk to our natural ecosystems and public health. The present study was aimed to evaluate the ability of a copper (Cu)-resistant bacterium, characterized as Bacillus altitudinis
MT422188, to remove Cu from contaminated industrial wastewater. Optimum growth was observed at 37°C, pH 7, and 1 mm phosphate, respectively. Effective concentration 50 (EC
50
), minimum inhibitory concentration (MIC), and cross-heavy metal resistance pattern were observed at 5.56 mm, 20 mm, and Ni > Zn > Cr > Pb > Ag > Hg, respectively. Biosorption of Cu by live and dead bacterial cells in its presence and inhibitors 1 and 2 (DNP and DCCD) was suggestive of an ATP-independent efflux system.
B. altitudinis
MT422188 was also able to remove 73 mg/l and 82 mg/l of Cu at 4th and 8th day intervals from wastewater, respectively. The presence of Cu resulted in increased GR (0.004 ± 0.002 Ug
−1
FW), SOD (0.160 ± 0.005 Ug
−1
FW), and POX (0.061 ± 0.004 Ug
−1
FW) activity. Positive motility (swimming, swarming, twitching) and chemotactic behavior demonstrated Cu as a chemoattractant for the cells. Metallothionein (MT) expression in the presence of Cu was also observed by SDS-PAGE. Adsorption isotherm and pseudo-kinetic-order studies suggested Cu biosorption to follow Freundlich isotherm as well as second-order kinetic model, respectively. Thermodynamic parameters such as Gibbs free energy (∆G°), change in enthalpy (∆H° = 10.431 kJ/mol), and entropy (∆S° = 0.0006 kJ/mol/K) depicted the biosorption process to a feasible, endothermic reaction. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy-Dispersive X-Ray Spectroscopy (EDX) analyses revealed the physiochemical and morphological changes in the bacterial cell after biosorption, indicating interaction of Cu ions with its functional groups. Therefore, these features suggest the potentially effective role of
B. altitudinis
MT422188 in Cu bioremediation.

Pathogenic infestations are significant threats to vegetable yield, and have become an urgent problem to be solved. Rhizoctonia solani is one of the worst fungi affecting tomato crops, reducing yield in some regions. It is a known fact that plants have their own defense against such infestations; however, it is unclear whether any exogenous material can help plants against infestation. Therefore, we performed greenhouse experiments to evaluate the impacts of R. solani on 15- and 30-day old tomato plants after fungal infestation, and estimated the antifungal activity of nanoparticles (NPs) against the pathogen. We observed severe pathogenic impacts on the above-ground tissues of tomato plants which would affect plant physiology and crop production. Pathogenic infection reduced total chlorophyll and anthocyanin contents, which subsequently disturbed plant physiology. Further, total phenolic contents (TPC), total flavonoid contents (TFC), and malondialdehyde (MDA) contents were significantly increased in pathogen treatments. Constitutively, enhanced activities were estimated for catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) in response to reactive oxygen species (ROS)in pathogen-treated plants. Moreover, pathogenesis-related genes, namely, chitinase, plant glutathione S-transferase (GST), phenylalanine ammonia-lyase (PAL1), pathogenesis-related protein (PR12), and pathogenesis-related protein (PR1) were evaluated, with significant differences between treated and control plants. In vitro and greenhouse antifungal activity of silver nanoparticles (Ag NPs), chitosan nanoparticles, and Ag NPs/CHI NPs composites and plant health was studied using transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectrophotometry. We found astonishing results, namely, that Ag and CHI have antifungal activities against R. solani. Overall, plant health was much improved following treatment with Ag NPs/CHI NPs composites. In order to manage R. solani pathogenicity and improve tomato health, Ag/CHI NPs composites could be used infield as well as on commercial levels based on recommendations. However, there is an urgent need to first evaluate whether these NP composites have any secondary impacts on human health or the environment.

Copper (Cu)-induced stress caused adverse effects to plant growth and productivity thus considered as a severe threat for sustainable crop production. This article presents an overview of copper stress in plants. Copper participates in many physiological processes as a co-factor for catalysis of many metalloproteins; however, problem occurs when excess amount of copper is present in cells. The high concentration of copper suppresses biomass accumulation and linear plant growth. Copper affected root growth stronger than shoot growth. The reduced mobility of Cu in soil is due to its strong binding to organic and inorganic colloids, where it acts as a barrier to Cu toxicity in terrestrial plants. Excess of Cu inhibits a large number of enzymes and interferes with several aspects of plant biochemistry, including photosynthesis, pigment synthesis, and membrane integrity. So, the most important effect of copper toxicity is associated with the blocking of photosynthetic electron transport, leading to the production of radicals which start peroxidative chain reactions. Copper induces oxidative stress that involves induction of lipid peroxidation in the plant which further cause a severe damage to the cell membrane. High copper concentration can disturb the chloroplast ultrastructure by disturbing the photosynthetic process. Like chromium and iron, copper is also a redox metal that can have direct involvement in inducing oxidative stress in plants. In addition, Cu stress induced -production of reactive oxygen species is well recognized and controlled at both the production and consumption levels, through increased antioxidative systems.

Ethylene is a simple gaseous phytohormone, a hydrocarbon C2H4, with various roles in the regulation of plant development, growth and stress responses, and whole biological processes. Ethylene modifies efficiency and all functions by sharing information with other signalling pathways in regular and stressful ecosystems. It can achieve a variety of different metabolic mechanisms with significant results based on the accumulation rate and plant sensitivity. The results indicate that ethylene generates dual properties in acceptable tolerances through the cellular and molecular regulation of plant mechanisms. This book helps to better understand the potential mechanisms in natural and stressful situations as a signal molecule in plant production and development. In addition, a study explores how ethylene signalling has been used as signals for some alternating pathways in agriculture. This chapter studies the adaptation and responses of plants under various stress factors as well as the response of various kinds of ethylene.

Myo-inositol has gained a central position in plants due to its vital role in physiology and biochemistry. This experimental work assessed the effects of salinity stress and foliar application of myo-inositol (MYO) on growth, chlorophyll content, photosynthesis, antioxidant system, osmolyte accumulation, and gene expression in quinoa (Chenopodium quinoa L. var. Giza1). Our results show that salinity stress significantly decreased growth parameters such as plant height, fresh and dry weights of shoot and root, leaf area, number of leaves, chlorophyll content, net photosynthesis, stomatal conductance, transpiration, and Fv/Fm, with a more pronounced effect at higher NaCl concentrations. However, the exogenous application of MYO increased the growth and photosynthesis traits and alleviated the stress to a considerable extent. Salinity also significantly reduced the water potential and water use efficiency in plants under saline regime; however, exogenous application of myo-inositol coped with this issue. MYO significantly reduced the accumulation of hydrogen peroxide, superoxide, reduced lipid peroxidation, and electrolyte leakage concomitant with an increase in the membrane stability index. Exogenous application of MYO up-regulated the antioxidant enzymes’ activities and the contents of ascorbate and glutathione, contributing to membrane stability and reduced oxidative damage. The damaging effects of salinity stress on quinoa were further mitigated by increased accumulation of osmolytes such as proline, glycine betaine, free amino acids, and soluble sugars in MYO-treated seedlings. The expression pattern of OSM34, NHX1, SOS1A, SOS1B, BADH, TIP2, NSY, and SDR genes increased significantly due to the application of MYO under both stressed and non-stressed conditions. Our results support the conclusion that exogenous MYO alleviates salt stress by involving antioxidants, enhancing plant growth attributes and membrane stability, and reducing oxidative damage to plants.

Salinity stress is one of the major environmental constraints responsible for a reduction in agricultural productivity. This study investigated the effect of exogenously applied nitric oxide (NO) (50 μM and 100 μM) in protecting wheat plants from NaCl-induced oxidative damage by modulating protective mechanisms, including osmolyte accumulation and the antioxidant system. Exogenously sourced NO proved effective in ameliorating the deleterious effects of salinity on the growth parameters studied. NO was beneficial in improving the photosynthetic efficiency, stomatal conductance, and chlorophyll content in normal and NaCl-treated wheat plants. Moreover, NO-treated plants maintained a greater accumulation of proline and soluble sugars, leading to higher relative water content maintenance. Exogenous-sourced NO at both concentrations up-regulated the antioxidant system for averting the NaCl-mediated oxidative damage on membranes. The activity of antioxidant enzymes increased the protection of membrane structural and functional integrity and photosynthetic efficiency. NO application imparted a marked effect on uptake of key mineral elements such as nitrogen (N), potassium (K), and calcium (Ca) with a concomitant reduction in the deleterious ions such as Na+. Greater K and reduced Na uptake in NO-treated plants lead to a considerable decline in the Na/K ratio. Enhancing of salt tolerance by NO was concomitant with an obvious down-regulation in the relative expression of SOS1, NHX1, AQP, and OSM-34, while D2-protein was up-regulated.

Medicinal plants (MPs) account for 70–80% of use in primary care around the world, and this percentage indicates that the number of MP users is high; thus, it is necessary to focus studies on medicinal herbs to ensure their proper use. In addition, MPs have strong genotoxic effects, as some types of MPs can cause DNA damage. Any substance that raises the risk of cancer or a tumor in an organism is called a carcinogen. There are many genotoxic and carcinogenic substances in the environment that can directly or indirectly affect genetic material. There are also nanoparticles (NPs) derived from MPs. Carbon-based NPs contain many nanoscale materials, such as fullerenes and carbon nanotubes, as well as metals such as gold (Au), silver (Ag), and aluminum (Al). Unfortunately, few studies are concerned with the carcinogenicity of NPs from MPs, whereas many researchers are interested in genotoxic assessment. For this reason, there is an urgent need for more studies into the safety of MPs and NPs. Therefore, this study reviewed the genotoxicity and carcinogenicity of MPs and their derived NPs. We also emphasized the need for strict regulation and monitoring of MP usage.

Endophytic bacteria are useful for their safe services in plant growth improvement and for ameliorating abiotic and biotic stresses. Salt-tolerant plant-growth-promoting Kocuria rhizophila 14asp (accession number KF 875448) was investigated for its role in pea plants under a saline environment. Salt stress (75 mM and 150 mM NaCl) was subjected to two pea varieties, peas2009 and 9800-10, in a greenhouse under a complete randomized design. Different parameters such as plant growth promotion, relative water content, chlorophyll, antioxidants, and mineral contents were analyzed to elucidate the extent of tolerance persuaded by PGPB (plant-growth-promoting bacteria). Exhibition of adverse effects was noticed in uninoculated varieties. However, inoculation of K. rhizophila improved the morphological parameters, antioxidant enzymes, and minimized the uptake of Na+ in plants under various saline regimes. Pea variety 9800-10 exhibited more tolerance than peas2009 in all traits, such as root and shoot length, fresh and dry biomass, chlorophyll contents, and antioxidant enzymes. Our results showed that halotolerant K. rhizophila inoculation plays a vital role in enhancing plant growth by interacting ingeniously with plants through antioxidant systems, enduring saline conditions.

Any extrinsic agent that exerts a negative effect on plants’ physiology is usually defined as stress. Crop plants in a given habitat encounter myriads of non-biotic pressures such as high light intensity, salt, metal/metalloid, heat, drought, and/or ultraviolet or a combination of these stresses and biotic ones such as pathogens, weeds, and insect predation. In a natural environment, plants encounter these stresses simultaneously and respond and adapt to these environmental pressures by the regulatory circuitry networks involving various growth regulating signaling molecules. Stress induces too much production of reactive oxygen species (ROS). In order to acclimate/adapt to stress conditions, in current times, plants’ acclamatory and defense responses are being regulated by various exogenous phytoprotectants such as supplements of exogenous plant growth regulators (PGRs) that mediate the redox balance under dynamic environment. The use of exogenous PRGs to impart abiotic stress tolerance is an emerging and burgeoning topic. PGRs are signaling elicitors that regulate growth and development under optimal and stress conditions. However, the critical tolerance trade-off of methyl jasmonate (MeJ) and brassinosteroids (BRs) in inducing abiotic stress tolerance has received little attention. Therefore, in this present chapter, we present the role of these two selected PGRs and their crosstalk with other signaling molecules in improving abiotic stress in different crop plants.

The release of harmful wastes via different industrial activities is the main cause of heavy metal toxicity. The present study was conducted to assess the effects of heavy metal stress on the plant growth traits, antioxidant enzyme activities, chlorophyll content and proline content of Sesbania sesban with/without the inoculation of heavy-metal-tolerant Bacillus gibsonii and B. xiamenensis. Both PGP strains showed prominent ACC-deaminase, indole acetic acid, exopolysaccharides production and tolerance at different heavy metal concentrations (50–1000 mg/L). Further, in a pot experiment, S. sesban seeds were grown in contaminated and noncontaminated soils. After harvesting, plants were used for the further analysis of growth parameters. The experiment comprised of six different treatments. The effects of heavy metal stress and bacterial inoculation on the plant root length; shoot length; fresh and dry weight; photosynthetic pigments; proline content; antioxidant activity; and absorption of metals were observed at the end of the experiment. The results revealed that industrially contaminated soils distinctly reduced the growth of plants. However, both PGPR strains enhanced the root length up to 105% and 80%. The shoot length was increased by 133% and 75%, and the fresh weight was increased by 121% and 129%. The proline content and antioxidant enzymes posed dual effects on the plants growing in industrially contaminated soil, allowing them to cope with the metal stress, which enhanced the plant growth. The proline content was increased up to 190% and 179% by the inoculation of bacterial strains. Antioxidant enzymes, such as SOD, increased to about 216% and 245%, while POD increased up to 48% and 49%, respectively. The results clearly show that the utilized PGPR strains might be strong candidates to assist S. sesban growth under heavy metal stress conditions. We highly suggest these PGPR strains for further implementation in field experiments.

Excess selenium (Se) causes toxicity, and nitric oxide (NO)’s function in spermine (Spm)-induced tolerance to Se stress is unknown. Using wheat plants exposed to 1 mM sodium selenate—alone or in combination with either 1 mM Spm, 0.1 mM NO donor sodium nitroprusside (SNP) or 0.1 mM NO scavenger cPTIO—the potential beneficial effects of these compounds to palliate Se-induced stress were evaluated at physiological, biochemical and molecular levels. Se-treated plants accumulated Se in their roots (92%) and leaves (95%) more than control plants. Furthermore, Se diminished plant growth, photosynthetic traits and the relative water content and increased the levels of malondialdehyde, H2O2, osmolyte and endogenous NO. Exogenous Spm significantly decreased the levels of malondialdehyde by 28%, H2O2 by 37% and electrolyte leakage by 42%. Combined Spm/NO treatment reduced the Se content and triggered plant growth, photosynthetic traits, antioxidant enzymes and glyoxalase systems. Spm/NO also upregulated MTP1, MTPC3 and HSP70 and downregulated TaPCS1 and NRAMP1 (metal stress-related genes involved in selenium uptake, translocation and detoxification). However, the positive effects of Spm on Se-stressed plants were eliminated by the NO scavenger. Accordingly, data support the notion that Spm palliates selenium-induced oxidative stress since the induced NO elicits antioxidant defence upregulation but downregulates Se uptake and translocation. These findings pave the way for potential biotechnological approaches to supporting sustainable wheat crop production in selenium-contaminated areas.