Screening and evaluation of chilli (<i>Capsicum annuum</i> L.) genotypes for waterlogging tolerance at seedling stage

Waterlogging is an illustrious abiotic stress and the constrictions it enforces on plant roots have negative effects on growth and development. This study was undertaken to investigate waterlogging stress tolerant potential in chilli (Capsicum annum L.) genotypes through evaluating morphological, physiological, biochemical and anatomical parameters. Thirty-five days old seedlings of 10 chilli genotypes were exposed to waterlogging stress maintaining water height 3–5 cm over the soil surface artificially for three days. This duration (36–38 DAE) was termed as waterlogging period, and subsequent withdrawal of waterlogging condition (39–45 DAE) was regarded as a recovery phase. Based on their survival performance, two tolerant genotypes viz., SRC-517 and BARI morich-2 and two susceptible genotypes viz., AHM-206 and RI-1(6) were selected for studying stress tolerance mechanism. Under waterlogging, however, both genotypes (tolerant and susceptible) exhibited reduced root shoot length, dry weight ratio, petiole weight and leaf area, and noticeable reduction regarding these parameters was observed in susceptible genotypes. Moreover, tolerant genotypes displayed a higher recovery than susceptible genotypes after removal of waterlogging stress. Lower reduction of leaf area and photosynthetic pigments as well as higher reduction of relative water content (RWC) were noticed in susceptible genotypes. Higher accumulation of proline and total antioxidant capacity (TAC) during waterlogging condition in tolerant genotypes suggested lower oxidative damage. Although both genotypes lost total soluble sugar (TSS) relative to control at waterlogging stress, better performance was recorded in tolerant genotypes. During the period after the removal of extra water, a similar genotypic response in terms of TSS gain was seen. Undoubtedly, under flooding conditions, the development of aerenchyma cells in tolerant genotypes is a means of tolerance mechanism for long-term survival. Thus, the morpho-physiological and biochemical changes help to understand the tolerance mechanism in chilli under waterlogging stress.     

Mycorrhiza improves plant growth and photosynthetic characteristics of tea plants in response to drought stress

Tea plants are sensitive to soil moisture deficit, with the level of soil water being a critical factor affecting their growth and quality. Arbuscular mycorrhizal fungi (AMF) can improve water and nutrient absorption, but it is not clear whether AMF can improve the photosynthetic characteristics of tea plants. A potted study was conducted to determine the effects of Claroideoglomus etunicatum on plant growth, leaf water status, pigment content, gas exchange, and chlorophyll fluorescence parameters in Camellia sinensis cv. Fuding Dabaicha under well-watered (WW) and drought stress (DS) conditions. Root mycorrhizal colonization and soil hyphal length were significantly reduced by the eight-week DS treatment. AMF inoculation displayed a significant increase in shoot and root biomass production. The relative water content, leaf water potential, nitrogen balance index, pigment content, maximum photometric effect (Fv/Fm, QY_max), and steady-state photometric effect Y (II) (QY_Lss) decreased dramatically, while the leaf water saturation deficit and steady-state non-photochemical fluorescence quenching (NPQ_Lss) generally increased under DS conditions. Mycorrhizal treatment induced significantly higher relative water content, leaf water potential, nitrogen balance index, pigment (chlorophyll, flavonoid, and anthocyanin) content, net photosynthesis rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, QY_max, and QY_Lss; however, it resulted in a lower leaf water saturation deficit and NPQ_Lss under both WW and DS conditions, as compared with non-mycorrhizal plants. These results imply that AMF promoted tea plant growth and alleviated negative effects of DS by promoting gas exchange, regulating the water status of leaves, and regulating photosynthetic parameters.     

Effects of <i>Tsukamurella tyrosinosolvens</i> P9 on growth,physiology and antioxdant enzyme of peanut under drought stress and after re-watering

Background: The plant-growth-promoting rhizobacterium Tsukamurella tyrosinosolvens is a rare strain of actinomycete, in order to recognize and expand the ecological functions of rare actinomycetes. Methods: In this experiment, we studied the effect of Tsukamurella tyrosinosolvens P9 on the drought resistance of peanut by inoculating peanut seedlings in pots and measuring the growth and physiological indicators of peanut under drought stress and re-watering conditions. Results: The results showed that during drought stress, the relative water content of the soil and leaves, chlorophyll content, and stomatal length, width, and aperture were significantly decreased while the levels of malondialdehyde (MDA), H₂O₂ and stomatal density were significantly increased. Peanut growth was also inhibited. However, inoculation with the P9 strain significantly promoted the growth of peanut under drought stress as plant height, fresh weight, root length and root weight were significantly higher compared with the uninoculated drought stress group. In addition, in P9-inoculated plants, the water and chlorophyll contents were significantly higher and the activities of the antioxidant enzymes CAT and SOD were significantly increased (except during the six days of drought treatment). While the stomatal length, width, and aperture were improved, the levels of MDA and H₂O₂ were significantly decreased. NBT staining showed that inoculation with P9 reduced O²⁻ accumulation under stress. After re-watering, the physiological indexes of inoculated plants recovered more quickly and grew better. Conclusions: The results showed that T. tyrosinosolvens P9 enhanced drought resistance and improves peanut growth by increasing leaf water content, increasing photosynthesis, regulating stomatal closure, and improving antioxidant enzyme activity.     

Overexpression of a sugarcane<i> ScCaM</i> gene negatively regulates salinity and drought stress responses in transgenic <i>Arabidopsis thaliana</i>

Calmodulin (CaM) proteins play a key role in signal transduction under various stresses. In the present study, the effects of a sugarcane ScCaM gene (NCBI accession number: GQ246454) on drought and salt stress tolerance in transgenic Arabidopsis thaliana and Escherichia coli cells were evaluated. The results demonstrated a significant negative role of ScCaM in the drought and salt stress tolerance of transgenic lines of A. thaliana, as indicated by the phenotypes. In addition, the expression of AtP5CS and AtRD29A, two genes tightly related to stress resistance, was significantly lower in the overexpression lines than in the wild type. The growth of E. coli BL21 cells expressing ScCaM showed weaker tolerance under mannitol and NaCl stress. Taken together, this study revealed that the ScCaM gene plays a negative regulatory role in both mannitol and NaCl stresses, and it possibly exerts protective mechanisms common in both prokaryotes and eukaryotes under stress conditions.     

Physiological and biochemical responses of Brassica napus L. to drought-induced stress by the application of biochar and Plant Growth Promoting Rhizobacteria

Climate change induces biotic and abiotic stress conditions, which badly affect the yield of crops with leading to the biochemical and physiological damages to plants. Biochar and plant growth promoting rhizobacteria (PGPR) alleviate the effect of drought condition therefore a field study was conducted to examine the single and combine application of drought tolerant Pseudomonas sp. and Staphylococcus sp. with biochar of Morus alba L. wood to mitigate the adverse effects of drought stress in two genotypes of Brassica napus L. including Punjab sarson and westar. Physioco-chemical analysis of biochar showed 5.4 cmol/kg cation exchange capacity, 6.9 ds/m electrical conductivity, pH of 9.6, 0.50 g/cm³ bulk density, and organic carbon 3.64%. Synergistic application of PGPR and biochar developed the plant antioxidant enzyme including catalase (CAT) and ascorbate peroxidase (APX) and also enhanced the content of photosynthetic pigments like chlorophyll pigments, carotenoids content, and anthocyanin content. Scanning electron microscope (SEM) study revealed that biochar and PGPR improved epidermal vigor and stomatal physiology. Malondialdehyde (MDA), hydrogen peroxide (H₂O₂), APX, and osmolyte content including proline increased in drought stress, which were then decreased by these growth promoters. These results are very important as they illustrate the potential of PGPR and biochar to alleviate the adverse consequences of drought stress and offer a way of increasing the tolerance of B. napus L. plant grown under induced drought stress.     

Sliding wear behaviour of ion implanted ultra high molecular weight polyethylene against a surface modified titanium alloy Ti-6Al-4V

A study has been made of the sliding wear behaviour of untreated and ion implanted ultra high molecular weight polyethylene (UHMWPE) against a surface modified titanium alloy (Ti-6Al-4V) using a pin on disc apparatus. It was found that the presence of water lubrication and a very smooth counterface was necessary to maintain low wear rates of the UHMWPE. A ‘zero wear’ effect was observed when nitrogen implanted UHMWPE was tested against very smooth counterfaces (R_a ≈ 0.03 μm) of either surface oxidized or nitrogen implanted Ti-6Al-4V under water lubrication. The enhanced mechanical and physical properties of the surface treated materials are believed to be responsible for the improved wear performance.     

The biomechanical,chemical and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs

Megapodes are galliform birds endemic to Australasia and unusual among modern birds in that they bury their eggs for incubation in diverse substrates and using various strategies. Alectura lathami and Leipoa ocellata are Australian megapodes that build and nest in mounds of soil and organic matter. Such unusual nesting behaviours have resulted in particular evolutionary adaptations of their eggs and eggshells. We used a combination of scanning electron microscopy, including electron backscatter diffraction and energy‐dispersive X‐ray spectroscopy, to determine the fine structure of the eggshells and micro‐CT scanning to map the structure of pores. We discovered that the surface of the eggshell of A. lathami displays nodes similar to those of extinct titanosaur dinosaurs from Transylvania and Auca Mahuevo egg layer #4. We propose that this pronounced nodular ornamentation is an adaptation to an environment rich in organic acids from their nest mound, protecting the egg surface from chemical etching and leaving the eggshell thickness intact. By contrast, L. ocellata nests in mounds of sand with less organic matter in semiarid environments and has eggshells with weakly defined nodes, like those of extinct titanosaurs from AM L#3 that also lived in a semiarid environment. We suggest the internode spaces in both megapode and titanosaur species act as funnels, which concentrate the condensed water vapour between the nodes. This water funnelling in megapodes through the layer of calcium phosphate reduces the likelihood of bacterial infection by creating a barrier to microbial invasion. In addition, the accessory layer of both species possesses sulphur, which reinforces the calcium phosphate barrier to bacterial and fungal contamination. Like titanosaurs, pores through the eggshell are Y‐shaped in both species, but A. lathami displays unique mid‐shell connections tangential to the eggshell surface and that connect some adjacent pores, like the eggshells of titanosaur of AM L#4 and Transylvania. The function of these interconnections is not known, but likely helps the diffusion of gases in eggs buried in environments where occlusion of pores is possible.     

<i>Claroideoglomus etunicatum</i> improved the growth and saline– alkaline tolerance of <i>Potentilla anserina</i> by altering physiological and biochemical properties

To investigate the effects of arbuscular mycorrhizal (AM) fungi on the growth and saline–alkaline tolerance of Potentilla anserina L., the seedlings were inoculated with Claroideoglomus etunicatum (W.N. Becker & Gerd.) C. Walker & A. Schüßler in pot cultivation. After 90 days of culture, saline–alkaline stress was induced with NaCl and NaHCO₃ solution according to the main salt components in saline–alkaline soils. Based on the physiological response of P. anserina to the stress in the preliminary experiment, the solution concentrations of 0 mmol/L, 75 mmol/L, 150 mmol/L, 225 mmol/L and 300 mmol/L were treated with stress for 10 days, respectively. The mycorrhizal colonization rate, mycorrhizal dependence, chlorophyll content, malondialdehyde content, antioxidant enzyme activities, osmoregulation substances content and water status were measured. The results showed that with the increase of NaCl and NaHCO₃ stress concentration, mycorrhizal colonization rate, colonization intensity, arbuscular abundance and vesicle abundance decreased, and reached the lowest value at 300 mmol/L. Strong mycorrhizal dependence was observed after the symbiosis with AM fungus, and the dependence was higher under NaHCO₃ treatment. Under NaCl and NaHCO₃ stress, inoculation with AM fungus could increase chlorophyll content, decrease malondialdehyde content, increase activities of superoxide dismutase, peroxidase and catalase, increase contents of proline, soluble sugar and soluble protein, increase tissue relative water content and decrease water saturation deficit. It was concluded that salt–alkali stress inhibited the colonization of AM fungus, but the mycorrhiza still played a positive role in maintaining the normal growth of plants under salt–alkali stress.     

Locating water-soluble vital stains in plant tissues by freeze-substitution and resin-embedding

Vital stains, moving in the transpiration stream in leaf apoplast, may be kept in place through freezing, freeze-substitution, embedding and sectioning, to reveal their position in the living plant. This technique has been used to study the details of movement of water out of the veins of leaves, and has wide application in histochemistry with water-labile dyes, and for following dye movements in protoplasm. Patterns of water movement in the leaf of Zea mays L. are presented as an example.     

Polyphosphate at the Streptomyces lividans cytoplasmic membrane is enhanced in the presence of the potassium channel KcsA

The distribution of polyphosphate (polyP) within the cytoplasmic membrane of Streptomyces lividans hyphae or protoplasts has been determined at high spatial resolution by elemental mapping using energy‐filtered electron microscopy (EFTEM). The results revealed that polyP was best traceable after its interaction with lead ions followed by their precipitation as lead sulphide. Concomitant studies of the S.lividans wildtype (WT) strain and its co‐embedded mutant ΔK (lacking a functional kcsA gene) were conducted by labelling as the surface matrix of either one was labelled by cationic colloidal thorium dioxide. Within the WT strain, additional polyP was found to accumulate distinctly at the inner face of the cytoplasmic membrane. After removal of the cell wall (within protoplasts), the polyP‐derived lead‐sulphide (PbS) precipitate formed clusters of fibrillar material extending up to 50 nm into the cytoplasm. This feature was absent in the ΔK mutant strain. Together the results revealed that the presence of the KcsA channel and the structured polyP coincide.     

Asymptotic approach to the constant velocity of hydrogen delamination growth

We consider delamination crack growth controlled by gas diffusion into the crack. If the gas is accumulated inside the delamination, after some incubation period, the crack starts growing under the pressure of the accumulated gas. An important example is given by hydrogen-induced delamination. Hydrogen absorbed by a metal is typically dissolved in the proton form within the lattice. Some of the protons reach the surface of pre-existing or freshly created cracks or delaminations where they recombine with electrons and form molecular hydrogen in the crack cavity. Since the molecular form of hydrogen is thermodynamically more stable, this process leads to accumulation of hydrogen gas inside the delamination crack. Under the excessive hydrogen pressure fracture often takes place even in the absence of any additional external loading. It is especially dangerous if the metal is covered with coating, where because of the dissimilarity of materials, microscopic voids appear more frequently. This leads first to hydrogen precipitation within these coating–metal interface voids and then to their development. This results in the delaminating of the coating. As it is well known, in the absence of aggressive media the cracking resistance of a material is characterized by a unique constant: so that if the stress intensity factor is smaller than this constant, the crack is fixed, and if it is larger, the crack moves in a dynamic regime. But in the presence of aggressive media, particularly hydrogen, the crack development is characterized by a smooth kinetic function v(K_I), which is dependence of the crack velocity on the stress intensity factor, with the lower threshold value of resistance K_scc smaller than the static critical stress intensity factor K_Ic. As numerically shown in the author's earlier work for the internal crack growth, the crack velocity first increases in accordance with the kinetic function, until reaching some value of v_s, and remains at the same level afterwards. Since, as has been obtained by the author in the previous paper, kinetic equations for internal and delamination cracks are essentially identical, the same conclusion can be derived for the latter. In this paper the stability and asymptotic approach to the constant velocity of delamination growth is proved analytically. If v_s is known, the corresponding value of the stress intensity factor, K_s, is obtained by substituting v_s into the kinetic function v(K_I).     

Tribological Properties of Self-Assembled Monolayers and Their Substrates Under Various Humid Environments

Using friction force microscopy (FFM) under controlled environments, we have systematically investigated the humidity effect on the frictional properties of two important classes of self-assembled monolayers (SAMs), i.e., N-octadecyltrimethoxysilane (OTE, CH₃(CH₂)₁₇Si(OCH₃)₃) on SiO₂(OTE/SiO₂), and N-alkanethiols on Au(111), together with their respective substrates. Experimental results show that both OTE and alkylthiol SAMs can decrease the friction force between a Si₃N₄ atomic force microscope (AFM) tip and substrates. The nearly humidity-independent friction of the two kinds of SAMs indicates that these SAMs are ideal lubricants in applications of micro-electro-mechanical systems (MEMS) under different environments. The humidity dependence—as the humidity increases, the friction first increases and then decreases—of the two substrates, SiO₂ and Au(111), can be explained by the adsorption of water. The decrease in the friction at high humidity is attributed to the low viscosity in the multilayers of water, while the increase in the friction at low humidity can be explained by the high viscosity between the water monolayer and the surfaces (AFM tip and sample), possibly due to the confinement effects. The effect of modification of the AFM tip with alkanethiol molecules on the humidity dependence of Au(111) friction has also been investigated.     

Role of foliar spray of plant growth regulators in improving photosynthetic pigments and metabolites in <i>Plantago ovata</i> (Psyllium) under salt stress–A field appraisal

Salinity is one of the major abiotic factors that limit the growth and productivity of plants. Foliar application of plant growth regulators (PGRs) may help plants ameliorate the negative impacts of salinity. Thus, a field experiment was conducted at the Botanical Garden University of Balochistan, Quetta, to explore the potential role of PGRs, i.e., moringa leaf extract (MLE; 10%), proline (PRO; 1 µM), salicylic acid (SA; 250 µM), and thiourea (TU; 10 mM) in ameliorating the impacts of salinity (120 mM) on Plantago ovata, an important medicinal plant. Salinity hampered plant photosynthetic pigments and metabolites but elevated oxidative parameters. However, foliar application of PGRs enhanced photosynthetic pigments, including Chl b (21.11%), carotenoids (57.87%) except Chl a, activated the defense mechanisms by restoring and enhancing the metabolites, i.e., soluble sugars (49.68%), soluble phenolics (33.34%), and proline (31.47%), significantly under salinity stress. Furthermore, foliar supplementation of PGRs under salt stress led to a decrease of about 43.02% and 43.27% in hydrogen peroxide and malondialdehyde content, respectively. Thus, PGRs can be recommended for improved photosynthetic efficiency and metabolite content that can help to get better yield under salt stress, with the best and most effective treatments being those of PRO and MLE to predominately ameliorate the harsh impacts of salinity.     

Scanning electron microscopy applied to seed-borne fungi examination

The aim of this study was to test the standard scanning electron microscopy (SEM) as a potential alternative to study seed-borne fungi in seeds, by two different conditions of blotter test and water restriction treatment. In the blotter test, seeds were subjected to conditions that enabled pathogen growth and expression, whereas the water restriction method consisted in preventing seed germination during the incubation period, resulting in the artificial inoculation of fungi. In the first condition, seeds of common bean (Phaseolus vulgaris L.), maize (Zea mays L.), and cotton (Gossypium hirsutum L.) were submitted to the standard blotter test and then prepared and observed with SEM. In the second condition, seeds of cotton (G. hirsutum), soybean (Glycine max L.), and common bean (P. vulgaris L.) were, respectively, inoculated with Colletotrichum gossypii var. cephalosporioides, Colletotrichum truncatum, and Colletotrichum lindemuthianum by the water restriction technique, followed by preparation and observation with SEM. The standard SEM methodology was adopted to prepare the specimens. Considering the seeds submitted to the blotter test, it was possible to identify Fusarium sp. on maize, C. gossypii var. cephalosporioides, and Fusarium oxysporum on cotton, Aspergillus flavus, Penicillium sp., Rhizopus sp., and Mucor sp. on common bean. Structures of C. gossypii var. cephalosporioides, C. truncatum, and C. lindemuthianum were observed in the surface of inoculated seeds. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc.     

Hot deformation behaviour of bimodal sized Al2O3/Al nanocomposites fabricated by spark plasma sintering

The deformation behaviour of bimodal sized Al₂O₃/Al nanocomposites were investigated by hot compression tests conducted in the temperature range 350–500°C and strain rates of 0.001, 0.01 and 0.1 s^–1. The dynamic recrystallisation behaviour of the nanocomposites strongly depended on the forming parameters. The bimodal sized Al₂O₃ particles played a crucial role in the recrystallised microstructure. The addition of bimodal sized Al₂O₃ particles led to a significant increase of activation energy of plastic deformation, corroborating the enhanced resistance of the nanocomposite to hot deformation. This was also reflected by the increased compressive yield strength in the nanocomposite due to both dislocation strengthening caused by n‐Al₂O₃ and preventing the grain growth due to the presence of μ‐Al₂O₃ at grain boundaries. It was found that with the decrease of Z values, local strain induced by deformation was released and the grain size of aluminium matrix gradually increased, indicating that the main softening mechanism of the bimodal sized Al₂O₃/Al nanocomposites was dynamic recrystallisation (DRX). The lower the Z value was, the easier the DRX occurred. The highly beneficial role of the bimodal sized Al₂O₃ reinforcement in improving the high‐temperature performance of aluminium matrix nanocomposite was discussed.     

Evaluation of trace element contamination using Armadillo officinalis Duméril, 1816 (Crustacea,Isopoda) as a tool: An ultrastructural study

To estimate trace element bioaccumulation in Armadillo officinalis, specimens were collected from Ghar El Melh lagoon then exposed for 3 weeks in contaminated sediments with copper, zinc, and cadmium. From the first week until the end of the experiment, a decrease in A. officinalis growth related to the increase of Cd concentration in the sediment was recorded. However, a mass gain was highlighted under Cu and Zn exposures. At the end of experiment, body metal concentrations were measured using flame atomic emission spectrometry. Results of the bioaccumulation factor showed that the species could be considered as a macroconcentrator of copper (BAF > 2) and a deconcentrator of zinc (BAF < 2). Microscopy observations of hepatopancreas cells showed morphological and histological changes even at the lowest concentration. They consisted in the microvillus border destruction, lipid droplets modifications, trace element accumulation, and the condensation of the majority of cellular organelles. The degree of these alterations was found to be dose‐dependent. Through these results, the isopod A. officinalis could be used as relevant monitor organisms for soil metal contamination.     

The effect of bridging on fatigue crack growth behavior in Aramid Patched Aluminum Alloy(APAL)

A new hybrid composite (APAL: Aramid Patched Aluminum Alloy), consisting of a 2024-T3 aluminum alloy plate sandwiched between two aramid/epoxy laminate (HK 285/RS 1222), was developed. Fatigue crack growth behavior was examined at stress ratios of R=0.2, 0.5 using the aluminum alloy and two kinds of the APAL with different fiber orientation (0°/90° and 45° for crack direction). The APAL showed superior fatigue crack growth resistance, which may be attributed to the crack bridging effect imposed by the intact fibers in the crack wake. The magnitude of crack bridging was estimated quantitatively and determined by a new technique on basis of compliances of the 2024-T3 aluminum alloy and the APAL specimens. The crack growth rates of the APAL specimens were reduced significantly as comparison to the monolithic aluminum alloy and were not adequately correlated with the conventional stress intensity factor range(ΔK). It was found that the crack growth rate was successfully correlated with the effective stress intensity factor range (ΔK _eff =K _br -K _ct ) allowing for the crack closure and the crack bridging. The relation between da/dN and theΔK _eff was plotted within a narrow scatter band regardless of kind of stress ratio (R=0.2, 0.5) and material (2024-T3 aluminum alloy, APAL 0°/90° and APAL±45°). The result equation was as follow:da/dN=6.45×10⁻⁷(ΔK _eff )^2.4.     

<i>In vitro</i> propagation of <i>Opuntia ellisiana</i> Griff. and acclimatization to field conditions

The genus Opuntia is a valuable forage resource in arid and semiarid lands during periods of drought and shortage of herbaceous plants. However, absolute minimum temperatures in the plains of Mendoza represent a limiting factor to cultivate several species.
Opuntia ellisiana is a cold hardy species, so the goals of this study were to massively propagate it using in vitro culture techniques, and then to acclimatize plantlets obtained to field conditions.
Different sterilization protocols were tested. Areoles were isolated in laminar airflow cabinet, and cultured on Murashige-Skoog medium, supplemented with sucrose and different BAP and IBA combinations. Explants were grown at 27±2ºC, under a 16-h photoperiod. The shoots produced were used in the rooting assay using different auxin combinations. In the most efficient growth treatment, plantlets reached 100% shooting after 35 days of culture, and a mean length of 10.2 mm after 49 days of culture. A 100% rooted plantlets was obtained on a medium containing 5 mg L^-1 IBA, after 12 days of culture. Acclimatization was achieved under greenhouse conditions, showing 100% plantlet survival.
This study suggests that O. ellisiana can be successfully micropropagated by areoles, and easily acclimatizated to field conditions.