Influence of ozone on ribonuclease activity in wheat (Triticum aestivum) leaves

Nucleases are upregulated in potato tubers afflicted with zebra chip disease

The defense response of potato tubers afflicted with zebra chip disease involves oxidatively mediated upregulation of nucleases that likely modulate localized programmed cell death to restrict the phloem-mobile, CLso bacterial pathogen to the vasculature. Zebra chip (ZC) is a bacterial disease of potato (Solanum tuberosum L.) caused by Candidatus Liberibacter solanacearum (CLso). Tubers from infected plants develop characteristic brown discoloration of the vasculature, a result of localized programmed cell death (PCD). We examined the potential contribution of nucleases in the response of tubers to CLso infection. Specific activities of the major isozymes of dsDNase, ssDNase, and RNase were substantially upregulated in tubers from CLso-infected plants, despite their significantly lower soluble protein content. However, ZC disease had no effect on nuclease isozyme profiles. Activities of the predominant nuclease isoforms from healthy and CLso-infected tubers had similar pH optima, thermotolerance, and responses to metallic co-factors. Nuclease activities were heat stable to 60 °C and resistant to precipitation with 70% (v/v) isopropanol, which constitute effective techniques for partial purification. DNase and RNase isozyme activities were highest at pH 7.2-8.5 and 6.8-7.2, respectively, and profiles were similar for tubers from CLso-infected and non-infected plants. RNase activities were mostly insensitive to inhibition by EDTA, except at pH 8.5 and above. DNase activities were inhibited by EDTA but less sensitive to inhibition at high pH than the RNases. The EDTA-mediated inhibition of DNase (ds/ss) activities was restored with ZnSO₄, but not Ca⁺² or Mg⁺². By contrast, ZnSO₄ inhibited the activities of RNases. DTT and CuSO₄ inhibited the activities of all three nucleases. These results suggest that activation of tuber nucleases is dependent on the oxidation of sulfhydryl groups to disulfide and/or oxidation of Zn to Zn⁺². In light of previous published results that established extensive CLso-induced upregulation of oxidative stress metabolism in tubers, we propose a model to show how increased nuclease activity could result from a glutathione-mediated oxidation of nuclease sulfhydryl groups in diseased tubers. DNases and RNases are likely an integral part of the hypersensitive response and may modulate PCD to isolate the pathogen to the vascular tissues of tubers.

Evaluating impacts of biogenic silver nanoparticles and ethylenediurea on wheat (Triticum aestivum L.) against ozone-induced damages

Tropospheric ozone (O₃) is a phytotoxic pollutant that leads to a reduction in crop yield. Nanotechnology offers promising solutions to stem such yield losses against abiotic stresses. Silver nanoparticles are major nanomaterials used in consumer products however, their impact on crops under abiotic stress is limited. In this study, we evaluated the anti-ozonant efficacy of biogenic silver nanoparticles (B-AgNPs) and compared them with a model anti-ozonant ethylenediurea (EDU) against ozone phyto-toxicity. Growth, physiology, antioxidant defense, and yield parameters in two wheat cultivars (HD-2967 & DBW-17), treated with B-AgNPs (25 mg/L and 50 mg/L) and EDU (150 mg/L and 300 mg/L), were studied at both vegetative and reproductive stages. During the experimental period, the average ambient ozone concentration and accumulated dose of ozone over a threshold of 40 ppb (AOT40) (8 h day^-1) were found to be 60 ppb and 6 ppm h, respectively, which were sufficient to cause ozone-induced phyto-toxicity in wheat. Growth and yield for B-AgNPs as well as EDU-treated plants were significantly higher in both the tested cultivars over control ones. However, 25 mg/L B-AgNPs treatment showed a more pronounced effect in terms of yield attributes and its lower accumulation in grains for both cultivars. DBW-17 cultivar responded better with B-AgNPs and EDU treatments as compared to HD-2967. Meanwhile, foliar exposure of B-AgNPs (dose; 25 mg/L) significantly enhanced grain weight plant^-1, thousand-grain weight, and harvest index by 54.22 %, 29.46 %, and 14.21 %, respectively in DBW-17, when compared to control. B-AgNPs could enhance ozone tolerance in wheat by increasing biochemical and physiological responses. It is concluded that B-AgNPs at optimum concentrations were as effective as EDU, hence could be a promising ozone protectant for wheat.

The Promotive Effect of Cyanobacteria and Chlorella sp. Foliar Biofertilization on Growth and Metabolic Activities of Willow (Salix viminalis L.) Plants as Feedstock Production, Solid Biofuel and Biochar as C Carrier for Fertilizers via Torrefaction Process

The effect of foliar application of Cyanobacteria and Chlorella sp. monocultures on physiological activity, element composition, development and biomass weight of basket willow (Salix viminalis L.) and the possibility to prepare biofuel from it in the fortification process was studied. Triple foliar plant spraying with non-sonicated monocultures of Cyanobacteria (Anabaena sp. PCC 7120, Microcystis aeruginosa MKR 0105) and Chlorella sp. exhibited a considerably progressive impact on metabolic activity and development of plants. This biofertilization increased cytomembrane impermeability, the amount of chlorophyll in plants, photosynthesis productivity and transpiration, as well as degree of stomatal opening associated with a decreased concentration of intercellular CO2, in comparison to control (treatments with water, Bio-Algeen S90 or with environmental sample). The applied strains markedly increased the element content (N, P, K) in shoots and the productivity of crucial growth enzymes: alkaline or acid phosphorylase, total dehydrogenases, RNase and nitrate reductase. Treatments did not affect energy properties of the burnt plants. These physiological events were associated with the improved growth of willow plants, namely height, length and amount of all shoots and their freshly harvested dry mass, which were increased by over 25% compared to the controls. The effectiveness of these treatments depended on applied monoculture. The plant spraying with Microcystis aeruginosa MKR 0105 was a little more effective than treatment with Chlorella sp. and Anabaena sp. or the environmental sample. The research demonstrate that the studied Cyanobacteria and Chlorella sp. monocultures have prospective and useful potential in production of Salix viminalis L., which is the basic energy plant around the word. In this work, a special batch reactor was used to produce torrefaction material in an inert atmosphere: nitrogen, thermogravimetric analysis and DTA analysis, like Fourier-transform infrared spectroscopy. The combustion process of Salix viminalis L. with TG-MS analysis was conducted as well as study on a willow torrefaction process, obtaining 30% mass reduction with energy loss close to 10%. Comparing our research results to other types of biomasses, the isothermal temperature of 245 °C during thermo-chemical conversion of willow for the carbonized solid biofuel production from Salix viminalis L. biomass fertilized with Cyanobacteria and Chlorella sp. is relatively low. At the end, a SEM-EDS analysis of ash from torrefied Salix viminalis L. after carbonization process was conducted.

Differential effects of nickel dosages on in vitro and in vivo seed germination and expression of a high affinity nickel-transport family protein (AT2G16800) in trembling aspen (Populus tremuloides)

It has been demonstrated that a number of metals including mercury (Hg), zinc (Zn), cadmium (Cd), cobalt (Co), lead (Pb), copper (Cu), and nickel (Ni) decrease seed germination rates and plant growth. The threshold levels of metal toxicity on seed germination, plant development, and gene regulation have not been studied in detail. The main objective of this study was to assess in vitro and in vivo the effects of different doses of nickel on Trembling aspen (Populus tremuloides) seed germination and regulation of the high affinity nickel transporter family protein (AT2G16800) gene. The in vitro assays showed that Nickel completely inhibited seed germination even at the lowest concentration of 0.401 mg Ni per mL (in media) tested. However, when the same concentration of nickel (150 mg Ni per 1 kg of dry soil) was added to soil samples, during the vivo assays, almost all of the seeds germinated. Significant inhibition of seed germination was observed when soil samples were treated with at least 400 mg/kg of Ni. No damages were observed on growing seedlings treated with 150, 400, and 800 mg/kg of Ni. Only the highest dose of 1, 600 mg/kg resulted in visible leaf and stem damages and reduced growth on 75% of seedlings. A significant repression of the AT2G16800 gene was observed for the 400, 800, and 1600 mg/kg of nickel treatments compared to the water control with the lowest level of expression observed in samples treated with 800 mg/kg of Ni. Results of this study suggest that P. tremuloides populations will likely be sustainable for long term in sites that are highly contaminated with Ni including mining regions since the bioavailable amount of this metal is usually below 400 mg/kg in Canada.

High efficiency stratification of apple cultivar Ligol seed dormancy by phytohormones, heat shock and pulsed radio frequency

The aim of the study was to improve the effect of stratification of apple "Ligol" seeds by application of selected compounds, phytohormones, and physical methods For this purpose the seeds were stratified at 3°C in distilled water or in the presence of potassium nitrate (KNO₃), ethephon (ET), carbon monoxide (CO), hydrogen peroxide (H₂O₂), a mixture of KNO₃, ET, CO, H₂O₂, gibberellins (GA₃), 6-benzylaminopurine (BAP), jasmonic acid (JA), salicylic acid (SA) and a mixture of SA, GA₃, BAP, JA, nitric oxide (NO), hydrogen chloride (HCL). Arranged protocols included various durations and combinations of selected compounds and phytohormones as well as laser and red light, heat shock - 2h heat shock (45°C) and Pulsed Radio Frequency (PRF) were investigated by germination tests and the activity of selected enzymes, gas exchange and index of chlorophyll in leaves. The obtained results showed the possibility to shorten more effectively the time of the apple 'Ligol' dormancy removal by treatments of the stratified seeds at 3°C with different biological and physical methods Selected compounds and phytohormones acted collectively as a regulatory complex controlling the course of release from dormancy. Physical methods (PRF and heat shock) additionally contributed to dormancy breakage. Duration of phytohormones or compounds impacts during stratification should be prolonged to minimum 7days to assure more balanced conditions of the regulatory complex for the acceleration of dormancy a removal. The most beneficial results were obtained after seed stratification for 7days on filter paper moistened in KNO₃+Etephon+CO+H₂O₂ at 3°C, and then on filter paper moistened in phytohormones (GA₃+BAP+JA) till the end of seed germination (3°C). The application of this protocol could be a very useful tool in a shortening the apple breeding cycle since the period of removing dormancy was reduced by 38days in comparison to stratified in water. PRF has also the additive role in breaking dormancy of apple 'Ligol' seed. Positive effects of compounds and phytohormones applied during stratification remarkably accelerated the growth of developed from them seedlings. Further research is needed to optimize stratification methods with appropriate contents and concentrations of compounds and phytohormones combined with PRF exposure.

Essential roles and hazardous effects of nickel in plants

With the world's ever increasing human population, the issues related to environmental degradation of toxicant chemicals are becoming more serious. Humans have accelerated the emission to the environment of many organic and inorganic pollutants such as pesticides, salts, petroleum products, acids, heavy metals, etc. Among different environmental heavy-metal pollutants, Ni has gained considerable attention in recent years, because of its rapidly increasing concentrations in soil, air, and water in different parts of the world. The main mechanisms by which Ni is taken up by plants are passive diffusion and active transport. Soluble Ni compounds are preferably absorbed by plants passively, through a cation transport system; chelated Ni compounds are taken up through secondary, active-transport-mediated means, using transport proteins such as permeases. Insoluble Ni compounds primarily enter plant root cells through endocytosis. Once absorbed by roots, Ni is easily transported to shoots via the xylem through the transpiration stream and can accumulate in neonatal parts such as buds, fruits, and seeds. The Ni transport and retranslocation processes are strongly regulated by metal-ligand complexes (such as nicotianamine, histidine, and organic acids) and by some proteins that specifically bind and transport Ni. Nickel, in low concentrations, fulfills a variety of essential roles in plants, bacteria, and fungi. Therefore, Ni deficiency produces an array of effects on growth and metabolism of plants, including reduced growth, and induction of senescence, leaf and meristem chlorosis, alterations in N metabolism, and reduced Fe uptake. In addition, Ni is a constituent of several metallo-enzymes such as urease, superoxide dismutase, NiFe hydrogenases, methyl coenzyme M reductase, carbon monoxide dehydrogenase, acetyl coenzyme-A synthase, hydrogenases, and RNase-A. Therefore, Ni deficiencies in plants reduce urease activity, disturb N assimilation, and reduce scavenging of superoxide free radical. In bacteria, Ni participates in several important metabolic reactions such as hydrogen metabolism, methane biogenesis, and acetogenesis. Although Ni is metabolically important in plants, it is toxic to most plant species when present at excessive amounts in soil and in nutrient solution. High Ni concentrations in growth media severely retards seed germinability of many crops. This effect of Ni is a direct one on the activities of amylases, proteases, and ribonucleases, thereby affecting the digestion and mobilization of food reserves in germinating seeds. At vegetative stages, high Ni concentrations retard shoot and root growth, affect branching development, deform various plant parts, produce abnormal flower shape, decrease biomass production, induce leaf spotting, disturb mitotic root tips, and produce Fe deficiency that leads to chlorosis and foliar necrosis. Additionally, excess Ni also affects nutrient absorption by roots, impairs plant metabolism, inhibits photosynthesis and transpiration, and causes ultrastructural modifications. Ultimately, all of these altered processes produce reduced yields of agricultural crops when such crops encounter excessive Ni exposures.

Suppression of LX ribonuclease in tomato results in a delay of leaf senescence and abscission

Although present in different organisms and conserved in their protein sequence, the biological functions of T2 ribonucleases (RNase) are generally unknown. Tomato (Lycopersicon esculentum) LX is a T2/S-like RNase and its expression is known to be associated with phosphate starvation, ethylene responses, and senescence and programmed cell death. In this study, LX function was investigated using antisense tomato plants in which the LX protein level was reduced. LX protein levels normally become elevated when leaves senesce and antisense inhibition of LX retarded the progression of senescence. Moreover, we observed a marked delay of leaf abscission in LX-deficient plants. This correlated with specific induction of LX protein in the tomato mature abscission zone tissue. LX RNase gene regulation and the consequences of antisense inhibition indicate that LX has an important functional role in both abscission and senescence.

Inhibition of ribonuclease and protease activities in arsenic exposed rice seedlings: role of proline as enzyme protectant

When seedlings of two rice (Oryza sativa L.) cvs. Malviya-36 and Pant-12 were raised under 25 and 50 microM As2O3 in the medium an increase in the level of RNA, proteins and proline accompanied with a decline in the level of free amino acid pool was observed under arsenic supplementation compared to controls. In situ As3+ treatment caused a marked inhibition in activities of ribonuclease (RNase, EC 3.1.27.1), protease and leucine aminopeptidase (LAP, EC 3.4.11.1) whereas the activity level of carboxypeptidase (EC 3.4.16.5) was enhanced. In vitro supply of As2O3 in the enzyme assay medium beyond 400 microM resulted in gradual inhibition of RNase and beyond 5 microM inhibition of LAP activities. Addition of 1M proline in the assay medium significantly restored the loss in RNase activity due to in vitro arsenic treatment or due to osmotic stress created by incorporation of polyethylene glycol (PEG). Isoform pattern of RNase extracted from As3+ -exposed seedlings showed a significant alteration compared to its pattern in unexposed seedlings. Results suggest that arsenic exposure impairs hydrolysis of RNA and proteins in rice seedlings due to inhibition of RNase and proteases activities and that proline accumulating under As3+ toxicity appears to serve as enzyme protectant.

Effect of wheat leaf ribonuclease on tumor cells and tissues

The antiproliferative and antitumor effect of wheat leaf ribonuclease was tested in vitro on the human ML-2 cell line and in vivo on athymic nude mice bearing human melanoma tumors. The antiproliferative activity of this plant ribonuclease was negligible in comparison with bovine seminal ribonuclease. In the experiments in vivo, a significant decrease of the tumor size, however, was observed in the mice treated with wheat leaf ribonuclease (27 kDa) compared with the control RNase A and polyethylene glycol. In nude mice injected intratumoraly with wheat leaf ribonuclease, the tumor size decreased from 100% in the control mice to 39% in treated mice. In the mice treated with polyethylene glycol-conjugated wheat leaf ribonuclease, the tumor reduction was observed from 100 to 28%, whereas in counterparts treated with polyethylene glycol-conjugated bovine seminal ribonuclease the tumor inhibition was reduced from 100 to 33%. Certain aspermatogenic and embryotoxic activity of wheat leaf ribonuclease and bovine seminal ribonuclease also appeared, but was lower in comparison with the effect of onconase. Mutual immunological cross-reactivity between wheat leaf ribonuclease antigens on one side and animal RNases (bovine seminal ribonuclease, RNase A, human HP-RNase and onconase) on the other side proved a certain structural similarity between animal and plant ribonucleases. Immunogenicity of wheat leaf ribonuclease was weaker in comparison with bovine seminal ribonuclease (titer of antibodies 160-320 against 1280-2560 in bovine seminal ribonuclease). Interestingly, immunosuppressive effect of wheat leaf ribonuclease tested on mixed lymphocyte culture-stimulated human lymphocytes reached the same level as that of bovine seminal RNase. The antibodies against wheat leaf ribonuclease produced in the injected mice did not inactivate the biological effect of this plant RNase in vivo. This is probably the first paper in which plant ribonuclease was used as antiproliferative and antitumor drug against animal and human normal and tumor cells and tissues in comparison with animal ribonucleases.

Differential mRNA stability to endogenous ribonucleases of the coding region and 3' untranslated regions of wheat (Triticum aestivum L.) manganese superoxide dismutase genes

The sequences of the 3' untranslated region (UTR) of the manganese superoxide dismutase (MnSOD) genes in wheat (Triticum aestivum) were found to be quite variable with different predicted thermostabilities. The degradation rates of the 3' UTR variants and the coding region were measured following exposure to endogenous nucleases. The degradation rates of the 3' UTR variants for 15 min were not significantly different, meaning the degradation rates of the 3' UTR variants were not directly related to the thermostabilities. However, the degradation rate of the coding region was significantly faster than those of the 3' UTR variants. Further investigation revealed the coding region seemed to have specific sites for degradation, indicating a possibility of increasing MnSOD expression by the degradation site alteration.