Dr. Ahmed Mahmoud Saleh

An infographic diagram that summarizes the influence of SiNP-seed priming upon tomato plants under Orobanche infection conditions. GRW: growth, PHO: photosynthesis, NEAO: non-enzymatic antioxidants, ASE: antioxidant-scavenging enzymes. Infestation by parasitic weeds is one of the most important environmental challenges threatening cropping systems worldwide. Among these, branched broomrape ( Orobanche ramosa ), a root holoparasitic weed, detrimentally affects many crops especially tomato ( Lycopersicon esculentum ) and causes severe crop losses. The positive role of silicon nanoparticles (SiNPs) in the growth and yield of plants grown under stressful conditions has been reported. However, no study has investigated the impact of SiNPs on plant–weed interaction. In this study, we conducted a green-house experiment to assess the physiological implications of SiNPs on tomato under the Orobanche challenge. Orobanche infection alone markedly inhibited tomato growth and photosynthesis ( P < 0.0001) and induced oxidative damage via increased photorespiration ( P < 0.0001) and NADPH oxidase activities ( P < 0.01). Interestingly, SiNPs significantly reduced the infection severity by reducing both the number and biomass of Orobanche tubercles (13 and 31% decrease, respectively). Moreover, SiNPs dramatically ameliorated the physiological and biochemical disorders imposed by Orobanche in tomato. Consistently, SiNPs strengthened the cell wall of host roots by upregulating lignin biosynthesis that acts as a physical barrier against tubercle haustorial penetration. On the other hand, SiNPs caused a noticeable decrease in ROS production and improved both enzymatic and non-enzymatic detoxification systems, the thing that was more pronounced in roots than in shoots of infected tomato plants. Such organ-specific responses were confirmed by cluster analysis. Overall, this study suggests that tomato plants treated with SiNPs will be more tolerant to Orobanche infection through enhanced structural and metabolic responses.

Drought represents a major constraint for agricultural productivity and food security worldwide. Plant growth promoting actinobacteria have attracted the attention as a promising approach to enhance plant growth and yield under stressful conditions. In this regard, bioprospecting in arid and semi-arid environments could reveal uncommon bacteria with improved biological activities. In the present study, the ability of actinobacteria isolated from a semi-arid environment (Saudi Arabia) to mitigate the negative impact of drought on growth and physiology of maize, a drought-sensitive crop, has been investigated. Among the different actinobacterial isolates screened for secondary metabolites production and biological activities, isolate Ac5 showed high ability of flavonoid, phytohormones and siderophores production. Moreover, Ac5 improved the growth and photosynthesis and induced a global metabolic change in the bacterized plants under water-deficit conditions. Interestingly, Ac5 treatment significantly mitigated the detrimental effects of drought stress on maize. Reduced H2O2 accumulation and lipid peroxidation accompanied with higher levels of molecular antioxidants (total ascorbate, glutathione, tocopherols, phenolic acids and flavonoids) were observed in the bacterized plants. From the osmoregulation point of view, drought-stressed bacterized maize accumulated higher levels of compatible solutes, such as sucrose, total soluble sugars, proline, arginine and glycine betaine, as compared with the non-bacterized plants. Therefore, this study highlights the comprehensive impact of actinobacteria on the global plant metabolism and suggests the potential utilization of actinobacteria isolated from semi-arid environments to mitigate the negative impact of drought on crop plants.

Due to industrialization and expansion of nanotechnology, ecosystem contamination by nanoparticles is likely. Overall, nanoparticles accumulate in environmental matrices and induce phytotoxicity, however future climate (elevated CO2 (eCO2)) may affect the distribution of nanoparticles in ecosystems and alter their impact on plants. In the current study, nickel oxide nanoparticles (NiO-NPs) with an average diameter of 54 nm were synthesized using Triton X-100 and characterized by scanning electron microscopy (SEM), UV-VIS spectroscopy and Fourier transform infrared spectroscopy (FTIR). We have investigated the impact of NiO-NPs at a concentration of 120 mg kg−1 soil, selected based on the results of a preliminary experiment, on accumulation of Ni ions in wheat (Triticum aestivum L.) and how that could influence plant growth, photosynthesis and redox hemostats under two CO2 scenarios, ambient (aCO2, 400 ppm) and eCO2 (620 ppm). NiO-NPs alone reduced whole plant growth, inhibited photosynthesis and increased the levels of antioxidants. However, improved defense system was not enough to lessen photorespiration induced H2O2 accumulation and oxidative damage (lipid and protein oxidation). Interestingly, eCO2 significantly mitigated the phytotoxicity of NiO-NPs. Although, eCO2 did not affect Ni accumulation and translocation in wheat, it promoted photosynthesis and inhibited photorespiration, resulting in reduced ROS production. Moreover, it further improved the antioxidant defense system and maintained ASC/DHA and GSH/GSSG redox balances. Organ specific responses to NiO-NPs and/or eCO2 were indicated and confirmed by cluster analysis. Overall, we suggest that wheat plants will be more tolerant to NiO-NPs stress under future climate CO2.

Aluminum (Al) toxicity is a major constraint for crop production in acid soils. Therefore, looking for sustainable solutions to increase plant tolerance to Al toxicity is needed. Although several studies addressed the potential utilization of silica or silicon dioxide nanoparticles (SNPs) to ameliorate heavy metal phytotoxicity, the exact mechanisms underlying SNPs-induced stress tolerance are still unknown. The current study investigated how SNPs could mitigate Al toxicity in maize plants grown on acidic soil. The impact of Al alone or in combination with SNPs on Al accumulation and detoxification, plant growth, photosynthetic C assimilation and redox homeostasis has been investigated. Al accumulation in stressed-maize organs reduced their growth, decreased photosynthesis related parameters and increased production of reactive oxygen species, through induced NADPH oxidase and photorespiration activities, and cell damage. These effects were more pronounced in roots than in leaves. SNPs ameliorated Al toxicity at growth, physiological and oxidative damage levels. Co-application of SNPs significantly reduced the activities of the photorespiratory enzymes and NADPH oxidase. It stimulated the antioxidant defense systems at enzymatic (superoxide dismutase, catalase, ascorbate and glutathione peroxidases) and non-enzymatic (ascorbate, glutathione, polyphenols, flavonoids, tocopherols, and FRAP) levels. Moreover, SNPs increased organic acids accumulation and metal detoxification (i.e. glutathione-S-transferase activity) in roots, as a protective mechanism against Al toxicity. The SNPs induced-protective mechanisms was dependent on the applied Al concentration and acted in organ-specific manner. Overall, the current study suggests the promising application of SNPs as an innovative approach to mitigate Al phytotoxicity in acidic soils and provides a comprehensive view of the cellular and biochemical mechanisms underlying this mitigation capacity.

© 2017 The Botanical Society of Japan and Springer Japan KK Many plant families produce coumarin (COU) and its derivatives as secondary metabolites via the phenylpropanoid biosynthetic pathway. This ubiquitous group of phytochemicals was shown to have diverse physiological effects on cellular, tissue, and organ levels. So far, research dealing with the hormonal like behavior of COU and its interaction with the activity and/or transport of phytohormones is very limited. In the current study, the impact of COU on redox homeostasis in aleurone layers of wheat grains was investigated. Aleurone layers were incubated in either 1000 $μ$M COU or 5 $μ$M gibberellic acid (GA 3 ) alone or in combination with 5 $μ$M abscisic acid (ABA). Results revealed that both COU and GA 3 treatments induced the production of $\alpha$-amylase but inhibited the activities of superoxide dismutase, catalase and ascorbate peroxidase. The downregulation of antioxidant enzymes that is provoked by COU and GA 3 was accompanied by significant accumulation of both H 2 O 2 and malondialdehyde. In contrast with the effect of ABA, both COU and GA 3 treatments resulted in a significant reduction in cell viability as revealed by trypan blue staining. These results suggest that COU could disrupt the redox balance in aleurone layers through downregulation of the enzymatic antioxidant system. Therefore, the current study provides evidence for the gibberellin like activity of COU.

Many studies have discussed the influence of elevated carbon dioxide (eCO2) on modeling and crop plants. However, much less effort has been dedicated to herbal plants. In this study, a robust system for monitoring the levels of 94 primary and secondary metabolites and mineral profiles in two medicinal herbs, basil (Ocimum basilicum L.) and peppermint (Mentha piperita L.), under both ambient (aCO2, 360 ppm) and eCO2 (620 ppm) was employed. We also assessed how the changes in herbal tissue chemistry affected their biological activity. Elevated CO2 significantly increased herbal biomass, improved the rates of photosynthesis and dark respiration, and altered the tissue chemistry. Principal Component Analysis of the full data set revealed that eCO2 induced a global change in the metabolomes of the two plants. Moreover, Hierarchical Clustering Analyses showed quantitative differences in the metabolic profiles of the two plants and in their responsiveness to eCO2. Out of 94 metabolites, 38 and 31 significantly increased in basil and peppermint, respectively. Regardless of the plant species, the levels of non-structural carbohydrates, fumarate, glutamine, glutathione, ascorbate, phylloquinone (vitamin K1), anthocyanins and a majority of flavonoids and minerals were significantly improved by eCO2. However, some metabolites tended to show species specificity. Interestingly, eCO2 caused enhancement in antioxidant, antiprotozoal, anti-bacterial and anticancer (against urinary bladder carcinoma; T24P) activities in both plants, which was consequent with improvement in the levels of antioxidants metabolites such as glutathione, ascorbate and flavonoids. Therefore, this study suggests that the metabolic changes triggered by eCO2 in the target herbal plants improved their biological activities.

Genetically engineered plants could provide feasible and environmentally safe approach for phytoremediation of CN compounds. However, the survival capacity of transgenic plants under high doses of CN is disappointing. One of the possible causes of such phytotoxicity is the CN-induced inhibition of antioxidant systems that lead to accumulation of reactive oxygen species (ROS). Therefore, simultaneous overexpression of a CN degrading enzyme along with an oxidative stress-relieving protein could maintain the internal redox homeostasis and enhance CN-phytoremediation capacity under high doses of CN. In the present study, transgenic tobacco plants overexpressing the bacterial cyanidase (CYND) and the cyanobacterial glutathione-S-transferase (GST) separately and in combination have been generated. Significant growth recovery was observed for all transgenic plants under 10 mM CN compared to wild type plants. However, GST + CYND overexpressors showed the highest biomass accumulation under CN stress. Similarly, reduction in photosynthetic pigments and total carbohydrate levels were significantly recovered in transgenic plants especially at higher doses of CN (7.5 and 10.0 mM). Moreover, both GST and GST + CYND transgenic plants showed elevated activities of SOD and CAT compared to the wild type upon exposure to CN. MDA content, as an indicator of lipid peroxidation, was significantly decreased in all transgenic plants. However, the lowest level of MDA was observed in GST + CYND transgenic lines. These results suggest that synchronous overexpression of GST with CYND genes improves CN remediation capacity of tobacco by improvement of the antioxidant scavenging systems and keeping ROS under control.

The current study evaluated the allelopathic potential of Alhagi graecorum on germination and seedling growth of two common crop plants; bean (Vicia faba) and corn (Zea mays). Water soluble allelochemicals were extracted from the air dried-powdered shoots of A. graecorum at three different concentrations (2.0, 4.0 and 6.0%, w/v). The germination experiment revealed that seeds of both bean and corn have tolerance to the aqueous extract of A. graecorum, where concentrations up to 6.0% had no significant effect on percent of germination as compared with the untreated seeds. The results showed that the lowest concentration (2.0%) of the aqueous extract stimulated elongation of radicle and plumule as well as seedling biomass of both bean and corn, while the highest concentration (6.0%) was inhibitory. In addition, the growth of corn seedlings was retarded at the modest dose (4%) of the aqueous extract, while that for bean seedlings was promoted at the same concentration. Similarly, water soluble allelochemicals extracted from A. gaecorum shoots influenced accumulation of soluble sugars and proteins in a concentration and species dependent manner.