Drought stress is one of the most important environmental constraints that negatively affect crop growth and production worldwide. Recently, nanotechnology has increasingly been applied to improve tolerance in plants exposed to abiotic stresses such as drought. A pot experiment was conducted to examine the influence of nitric oxide donor sodium nitroprusside (SNP: 100 μM) in presence of TiO 2 nanoparticles (TiO 2 NPs: 500, 1000, and 2000 mg kg −1) on wheat seedlings under drought stress conditions. Water deficit negatively affected growth and photosynthetic parameters with simultaneous increase in activity of antioxidant enzymes. Under severe drought stress, soil-applied 2000 mg kg −1 TiO 2 NPs enhanced seedling dry weight (DW), relative water content (RWC), catalase (CAT) activity, ascorbate peroxidase (APX) activity, and proline content. Moreover, 2000 mg kg −1 TiO 2 NPs enhanced total chlorophyll (total Chl), carotenoids (Car), stomatal conductance (gs), and transpiration (E) under severe drought stress. However, addition of 100 μM SNP in presence of 2000 mg kg −1 TiO 2 NPs significantly increased seedling length (SL), superoxide dismutase (SOD) activity, total soluble proteins, net photosynthetic rate (Pn), and intercellular CO 2 concentration (Ci). The aforementioned treatment also significantly reduced hydrogen peroxide (H 2 O 2) and malondialdehyde (MDA) contents under severe drought stress. Our results suggest that foliar application of SNP in the presence of TiO 2 NPs can protect wheat seedlings against drought-induced oxidative damage.
<p>Effect of titanium dioxide nanoparticles (TiO2 NPs) (0, 500, 1 000 and<br />2 000 mg/L) and sodium nitroprusside (SNP) (0 and 100 M) as nitric<br />oxide (NO) donor, on wheat seed germination and seedling growth<br />were investigated under cadmium (Cd) stress (0, 50 and 100 mM CdCl2).<br />Concentration-dependent declining trends were observed in wheat<br />germination indices upon seed exposure to CdCl2 suspensions which<br />were more obvious under higher Cd stress. Exogenous sodium nitroprusside (SNP) and TiO2 nanoparticles (NPs) positively affected most germination indices under normal and stress conditions. In most cases, combined application of TiO2 NPs and SNP suspensions boosted stimulatory function of both compounds and moderated adverse effects of Cd treatments on wheat seed germination and seedling growth. 2 000 mg/L TiO2 + SNP (100 M) treatment recorded the best results regarding most germination indices under lower and higher (50 and 100 mM CdCl2) Cd stress. Overall, it could be concluded that application of TiO2 NPs in combination with SNP might be a promising approach in counteracting the adverse effects of Cd stress on wheat seed germination and early growth.</p>
A hybrid interactive/optimization technique is used to derive in approximate closed-form equations relating contact load to mean plane separation. Equations governing Hertz contact for the interaction of surface asperities are considered in which asperity shoulder-to-shoulder contact results in normal and tangential components of force. The normal component of asperity force is summed statistically to find total normal force between the two surfaces. The tangential force over a half-plane corresponding to a select direction is found accounting for the directionality of the tangential component of asperity forces. Two sets of approximate equations are found for each of the normal and half-plane tangential force components. The simplest forms of the approximate equations achieve accuracy to within 5% error, while other forms yield approximation error within 0.2%.
Seed germination and early seedling growth are sensitive to drought stress in wheat. A factorial experiment was arranged based on a completely randomized design with three replicates to study the impacts of TiO2 nanoparticles (TiO2 NPs: 0, 500, 1000 and 2000 mg.L) and sodium nitroprusside (SNP: 0 and 100 μM), as NO donor, on seed germination and seedling growth of wheat under polyethylene glycol (PEG)-induced drought stress (0, -0.4 and -0.8 MPa). Our results revealed that PEG-stimulated drought stress significantly decreased germination percentage (GP), germination energy (GE), germination rate (GR), root length (RL), shoot length (SL), root fresh weight (RFW), shoot fresh weight (SFW) and vigor index (VI) but increased mean germination time (MGT) in wheat seeds. However, application of TiO2 NPs and SNP alone or in combination significantly enhanced GP, GE, GR, RL, SL, RFW, SFW and VI up to 23.72%, 50%, 33.74%, 85.38%, 93.28%, 73%, 91.91% and 91.04% respectively, but significantly reduced MGT up to 28.36% under severe drought stress. Our results showed that application of TiO2 NPs and SNP alone or in combination can significantly alleviate the adverse effects of PEG-stimulated drought stress on seed germination and early seedling growth of wheat.
MWCNTs (Multi-walled carbon nanotubes), as an important nanomaterial, enters the soil through various anthropogenic sources. Our understanding of MWCNTs effects on plant growth is still not complete and needs to be more studied. In this study, the possible effects of MWCNTs (500, 1000 and 2000 mg kg-1) and 100 μM exogenous sodium nitroprusside (SNP, as NO donor) on growth, physiological and photosynthetic performance of barley plants under 100 and 200 mM NaCl stress were investigated in greenhouse conditions. The most of physiological and photosynthesis characteristics of barley seedling negatively impressed when the plants were grown in different concentrations of NaCl. In the presence of SNP, 500 mg kg-1 dosage of MWCNTs significantly enhanced relative water content (RWC), chlorophyll content, photosynthesis parameters and growth indices. Also, MWCNTs-treated plants combined with 100 μM SNP showed higher antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and lower malonyldialdehyde (MDA) and hydrogen peroxide (H 2 O 2) content under salinity stress. It is suggested that, MWCNTs in presence of SNP can greatly improve growth, as well as salt tolerance of barley plant by promoting water uptake, activities of antioxidant enzymes and photosynthesis performance.
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