Redox biology response in germinating Phaseolus vulgaris seeds exposed to copper: Evidence for differential redox buffering in seedlings and cotyledon

The Identification of Broomcorn Millet bZIP Transcription Factors, Which Regulate Growth and Development to Enhance Stress Tolerance and Seed Germination

Broomcorn millet (Panicum miliaceum L.) is a water-efficient and highly salt-tolerant plant. In this study, the salt tolerance of 17 local species of broomcorn millet was evaluated through testing based on the analysis of the whitening time and the germination rate of their seeds. Transcriptome sequencing revealed that PmbZIP131, PmbZIP125, PmbZIP33, PmABI5, PmbZIP118, and PmbZIP97 are involved in seed germination under salt stress. Seedling stage expression analysis indicates that PmABI5 expression was induced by treatments of high salt (200 mM NaCl), drought (20% W/V PEG6000), and low temperature (4 °C) in seedlings of the salt-tolerant variety Y9. The overexpression of PmABI5 significantly increases the germination rate and root traits of Arabidopsis thaliana transgenic lines, with root growth and grain traits significantly enhanced compared to the wild type (Nipponbare). BiFC showed that PmABI5 undergoes homologous dimerization in addition to forming a heterodimer with either PmbZIP33 or PmbZIP131. Further yeast one-hybrid experiments showed that PmABI5 and PmbZIP131 regulate the expression of PmNAC1 by binding to the G-box in the promoter. These results indicate that PmABI5 can directly regulate seed germination and seedling growth and indirectly improve the salt tolerance of plants by regulating the expression of the PmNAC1 gene through the formation of heterodimers with PmbZIP131.

Cu and CuO Nanoparticles Affected the Germination and the Growth of Barley (Hordeum vulgare L.) Seedling

The application of Cu and CuO nanofertilizers in horticulture has been a promising strategy to promote plants' growth. In our study, increasing concentrations (10, 25, 50, 100, 250, 500, 1000, 2000 mg/L) were assessed for their inhibitory or stimulatory effects on barley (Hordeum vulgare L.) seedlings. Our results showed an enhancement of seed germination parameters (FGP, t50, cumulative germination rate, AUC), and seedling growth parameters (roots and shoots' lengths, fresh biomasses and dry biomasses) by the low concentrations of Cu NPs and CuO NPs, while concentrations above 500 mg/L displayed inhibiting effects. CuO NPs treatment showed a significant similitude with CuSO₄, which confirms that CuO NPs act mainly via released Cu ions. However, Cu NPs exhibited a different behavior since the nanosized particles contribute together with Cu ions in barley response to Cu NPs. This provides an overall picture of the way these nanoparticles may behave in plant systems.

Catalytic Biotransformations and Inhibition Study of Peroxidase from Luffa aegyptiaca

Background:

Present interest in catalytic bioconversions is concerned with 2 major environmental issues. (i) The replacement or substitution of oxidations which involves heavy metal salts and reagents by alternatives using H2O2 as the ecofriendly oxidant. (ii) The prominent issue is the increasing interest in the production of high chemoselectivity, regioselectivity and stereoselectivity of compounds in chemical reactions in order to achieve better byproducts. Keeping these points in view the work on peroxidases have been carried out which fullfills these two goals.

Objective:

To determine the enzyme activity in the available source to explore its catalytic efficiency in biotransformations of heavy metal compounds. Optimizing the effect of different oxidants for maximum activity of peroxidase and to study the nature of inhibition of peroxidase in presence of different metal ions.

Methods:

Enzyme extracted in large volume from Luffa aegyptiaca fruit. Peroxidase activity measured by spectrophotometric method. Peroxidase catalyzed rate of reaction was determined spectrophotometerically by making use of guaiacol as the substrate and in presence of H2O2, V2O5, VOSO4, VO(acac)2, (NH4)2(Ce(NO3)6), and (NH4)6Mo7.4H2O monitored at λmax = 470 nm. The haloperoxidase activity were assayed by monitoring the formation of halogen by UV/VIS spectra. The steady state velocity of the enzyme catalysed reaction was measured at different concentrations of metal ions like trivalent (Cr3+ and Al3+), divalent (Ca2+, Mg2+, Cd2+, Zn2+ and Ni2+) and monovalent (Na+ and K+) in the range of 0.0 mM to 100 mM at the fixed enzyme saturating concentration. Graph was plotted to determine the nature of enzyme activity inhibition.

Results:

Study of rate of reaction by steady state kinetics measurements confirmed peroxidase activity of order of 9.0 U in the fruit extract prepared. The oxidation potential required for the oxidation of guaiacol to tetraguaiacol is 0.575V and the reaction is irreversible. (NH4)2(Ce(NO3)6) and (NH4)6Mo7.4H2O oxidized guaiacol with the rate found to be 0.009 OD/sec in former substituent and the rate of formation of tetraguaiacol was much low in the later substituent found to be 0.003 OD/sec as compared to enzyme with rate 0.01 OD/sec. Enzyme peroxidase was able to oxidize Fe2+ and Mn2+ to Fe3+ and Mn3+ respectively in the reaction mixture. It is found that V2O5 is better oxidizing agent than H2O2 for catalytic oxidation of guaiacol as the substrate. Peroxidases in presence of H2O2 and KBr/KCl/KI act as a viable ecofriendly reagent for the halogenation reaction in organic synthesis. Nature of inhibition by Zn2+ and Ni2+ ions is competitive type. Enzyme activity is inhibited in presence of Cr3+ and Al3+ and the nature of inhibition is uncompetitive type.

Conclusion:

Luffa aegyptiaca is a better source of peroxidase having 9 U. UV-Visible spectrum analysis indicated that (NH4)2 (Ce(NO3)6 can substitute peroxidase enzyme under optimized conditions.( NH4)2(Ce(NO3)6 act as a cocatalyst by enhancing the activity twice. The enzyme with H2O2 and KBr/KCl/KI is a suitable environmentally suitable reagent for halogenation reaction in organic and inorganic synthesis. The rate of reaction is highest in presence of V2O5 as compared to other vanadium compounds. Thus V2O5 act as better oxidizing agent than H2O2. Chemical technology can be substituted by enzyme technology which should be developed to removal excess and toxic heavy metals. Salinity required for normal functioning of enzyme is 140mM NaCl and 90mM KCl. Enzyme activity enhanced in presence of Ca2+, Mg2+ and Cd2+ while inhibited in presence of Zn2+ and Ni2+. Nature of inhibition by Zn2+ and Ni2+ ions is competitive type. Enzyme activity is inhibited in presence of Cr3+ and Al3+ and the nature of inhibition is uncompetitive type. Extensive studies are needed to understand the mechanism of inhibition of manganese peroxidase activity by metal ions.

Nitric Oxide Pre-Treatment Advances Seed Germination and Alleviates Copper-Induced Photosynthetic Inhibition in Indian Mustard

This investigation tested the efficiency of nitric oxide (NO) in alleviation of Cu-induced adverse impacts on seed germination and photosynthesis in Indian mustard (Brassica juncea L.). Pre-treatment of B. juncea seeds with sodium nitroprusside (SNP; NO donor) significantly improved the seed germination rate and also alleviated Cu-accrued oxidative stress. However, in the absence of NO, Cu caused a higher reduction in seed germination rate. The presence of NO strengthened the antioxidant defense system (glutathione reductase, ascorbate peroxidase, and superoxide dismutase) and thereby sustained the lower lipid peroxidation, reduced H2O2 content, and thiobarbituric acid reactive substances in Cu-exposed seeds. NO pre-treated seeds also retained a higher amylase activity and exhibited an improved seed germination rate. This effect of NO under Cu stress was also seen in plants originated from the NO pre-treated seeds, where the role of NO pre-treatment was reflected in the improved photosynthetic potential of B. juncea. Overall, NO pre-treatment not only improved the germination rate in seeds but also carried its effects in the grown seedlings evidenced as improved photosynthesis and growth. Potential mechanisms involved in the action of NO pre-treatment included NO-mediated significant strengthening of the antioxidant defense system and decreases in Cu-caused oxidative stress parameters.

Plant abiotic stress response and nutrient use efficiency

Abiotic stresses and soil nutrient limitations are major environmental conditions that reduce plant growth, productivity and quality. Plants have evolved mechanisms to perceive these environmental challenges, transmit the stress signals within cells as well as between cells and tissues, and make appropriate adjustments in their growth and development in order to survive and reproduce. In recent years, significant progress has been made on many fronts of the stress signaling research, particularly in understanding the downstream signaling events that culminate at the activation of stress- and nutrient limitation-responsive genes, cellular ion homeostasis, and growth adjustment. However, the revelation of the early events of stress signaling, particularly the identification of primary stress sensors, still lags behind. In this review, we summarize recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling and discuss new directions for future studies.

Cadmium effects on embryo growth of pea seeds during germination: Investigation of the mechanisms of interference of the heavy metal with protein mobilization-related factors

This work aims to give more insight into mechanisms of action of cadmium (Cd) on germinating pea seeds (Pisum sativum L. var. douce province), specifically the different ways by which Cd cations may interfere with the principal factors involved during germination process, notably storage proteins mobilization, amino acids freeing and proteolytic activities. Obtained results revealed that the process of hydrolysis of main storage proteins showed a significant disruption, which resulted in the decrease of the release of free amino acids, thus imposing a lack in nitrogen supply of essential nutrients to growing embryo under Cd stress. This hypothesis was evidenced by Cd-induced changes occurring in main purified protein fractions; Albumins, Legumins and Vicilins, during their breakdown. Besides, at enzymatic level, the activities of main proteases responsible for this hydrolysis were altered. Indeed, assays using synthetic substrates and specific protease inhibitors followed by protease activity measurements demonstrated that Cd inhibited drastically the total azocaseinolytic activity (ACA) and activities of different proteolytic classes: cysteine-, aspartic-, serine- and metallo-endopeptidases (EP), leucine- and proline-aminopeptidases (LAP and PAP, respectively), and glycine-carboxypeptidases (Gly-CP). The data here presented may suggest that the vulnerability of the embryonic axes towards Cd toxicity could be explained as a result of eventual disruption of metabolic pathways that affect mobilization of reserves and availability of nutrients. In vitro studies suggest that Cd cations may act either directly on the catalytic sites of the proteolytic enzymes, which may cause their deactivation, or indirectly via the generation of oxidative stress and overproduction of free radicals that can interact with enzymes, by altering their activity and structure.