Enhancing Drought Tolerance in Wheat through Improving MorphoPhysiological and Antioxidants Activities of Plants by the Supplementation of Foliar Silicon

The main objective of the research is to assess the role of foliar application of silicon (Si) for enhancing the survival ability of wheat under drought stress through improving its morphology, physicochemical and antioxidants activities. Treatments were five doses of Si at the rate of 2, 4, 6 and 8 mM and a control. After completion of seeds germination, pots were divided into four distinct groups at various field capacity (FC) levels, such as 100% FC (well-irrigated condition), 75% FC (slight water deficit), 50% FC (modest water deficit) and 25% FC (severe water deficit stress condition). Foliar application of Si at the rate of 2, 4, 6 and 8 mM and a control were given after 30 days of sowing at the tillering stage of wheat. Findings of the present investigation indicated that increasing the level of water deficit stress reduced the morphological parameters (such as root and shoot fresh and dry-biomass weight) and physico-biochemical events ((such as chlorophyll contents by estimating SPAD value), total free amino acid (TFAA), total soluble sugar (TSS), total soluble protein (TSP), total proline (TP), CAT (catalase), POD (peroxidase), SOD (superoxide dismutase) and APX (ascorbate peroxidase)) of wheat; while foliar application of Si at 6 mM at tillering stage enhanced the drought tolerance in wheat by increasing morphology and physiochemical characters under all levels of drought stress. Similarly, antioxidants activities in wheat also enhanced by the application of Si at 6 mM under normal as well as all drought stress levels. Therefore, it may be concluded that foliar application of Si at 6 mM at the tillering stage of wheat is an important indication for increasing the drought tolerance by improving the morphology, physico-biochemical and antioxidants activities in plants under deficit water (drought) conditions.     

Karrikins Discovered in Smoke Trigger Arabidopsis Seed Germination by a Mechanism Requiring Gibberellic Acid Synthesis and Light

Discovery of the primary seed germination stimulant in smoke, 3-methyl-2H-furo[2,3-c]pyran-2-one (KAR₁), has resulted in identification of a family of structurally related plant growth regulators, karrikins. KAR₁ acts as a key germination trigger for many species from fire-prone, Mediterranean climates, but a molecular mechanism for this response remains unknown. We demonstrate that Arabidopsis (Arabidopsis thaliana), an ephemeral of the temperate northern hemisphere that has never, to our knowledge, been reported to be responsive to fire or smoke, rapidly and sensitively perceives karrikins. Thus, these signaling molecules may have greater significance among angiosperms than previously realized. Karrikins can trigger germination of primary dormant Arabidopsis seeds far more effectively than known phytohormones or the structurally related strigolactone GR-24. Natural variation and depth of seed dormancy affect the degree of KAR₁ stimulation. Analysis of phytohormone mutant germination reveals suppression of KAR₁ responses by abscisic acid and a requirement for gibberellin (GA) synthesis. The reduced germination of sleepy1 mutants is partially recovered by KAR₁, which suggests that germination enhancement by karrikin is only partly DELLA dependent. While KAR₁ has little effect on sensitivity to exogenous GA, it enhances expression of the GA biosynthetic genes GA3ox1 and GA3ox2 during seed imbibition. Neither abscisic acid nor GA levels in seed are appreciably affected by KAR₁ treatment prior to radicle emergence, despite marked differences in germination outcome. KAR₁ stimulation of Arabidopsis germination is light-dependent and reversible by far-red exposure, although limited induction of GA3ox1 still occurs in the dark. The observed requirements for light and GA biosynthesis provide the first insights into the karrikin mode of action.Germination is a critical event in the plant life cycle, as the timing of emergence from the protective seed coat is crucial for survival and reproductive success. A variety of abiotic stimuli, including light, temperature, and nitrates, provide information about the external environment that affects germination. Seed dormancy gates responses to these factors. Upon maturation, physiologically dormant seeds are in a primary dormant (PD) state, which is lost during afterripening. The transition between a PD and nondormant state is both gradual and reversible and results in relaxation of the set of environmental conditions under which a seed will germinate (Baskin and Baskin, 2004; Finch-Savage and Leubner-Metzger, 2006).Despite decades of research, seed dormancy remains a complex physiological state that is not well understood. The plant hormones abscisic acid (ABA) and GA are mutually antagonistic central players in the germination decision (Finch-Savage and Leubner-Metzger, 2006; Finkelstein et al., 2008). The role of dormancy establishment and maintenance has been attributed to ABA, while GA has been implicated in the initiation and completion of germination. The ratio of ABA to GA signaling, rather than absolute amounts of the hormones, appears to be critical to dormancy breaking (Finch-Savage and Leubner-Metzger, 2006). Environmental stimuli and phytohormones influence the ABA/GA balance, although the mechanisms of signal integration and hormone cross talk are still largely unknown.In many biodiverse regions, fire events provide an irregular but important opportunity for seedling establishment by freeing up key resources such as light, space, and nutrients (Van Staden et al., 2000; Dixon et al., 2009). A clear example of this is seen in the flush of new growth in the immediate postfire environment, indicating potent activation of the soil seed bank. Heat is not required for the germination response, as cold smoke application induced an up to 48-fold increase in the number of germinating seedlings and approximately 3-fold enrichment in species abundance in field trials (Roche et al., 1997; Rokich et al., 2002). It has now been well established that smoke is a broadly effective stimulant that enhances germination of approximately 1,200 species in more than 80 genera worldwide (Dixon et al., 2009). Attempts to study smoke effects on plant physiology have been confounded by the complex mixture of components within smoke, some of which confer toxicity at high concentrations. Bioassay-guided fractionation of smoke water culminated in the discovery and synthesis of the primary germination stimulant 3-methyl-2H-furo[2,3-c]pyran-2-one (KAR₁; Flematti et al., 2004). With the recent identification of three analogous active compounds in smoke water fractions (Fig. 1A; G. Flematti, unpublished data), this family of butenolide molecules have been designated karrikins, after “karrik,” the first recorded Aboriginal Nyungar word for smoke (Dixon et al., 2009).Open in a separate windowFigure 1.Partial structural similarity between the karrikin family of plant growth regulators and strigolactones. A, Molecular structures of KAR₁ (3-methyl-2H-furo[2,3-c]pyran-2-one), KAR₂ (2H-furo[2,3-c]pyran-2-one), KAR₃ (3,5-dimethyl-2H-furo[2,3-c]pyran-2-one), and KAR₄ (3,7-dimethyl-2H-furo[2,3-c]pyran-2-one). B, Molecular structures of a natural (strigol) and a synthetic (GR-24) strigolactone.The parent molecule, KAR_1, is a potent stimulant that enhances germination in some species at subnanomolar concentrations (Flematti et al., 2004; Stevens et al., 2007). In field trials, KAR₁ is effective at less than 5 g ha⁻¹ compared with 10 ton ha⁻¹ smoke water and thus may have practical value in agriculture, conservation, and restoration (Stevens et al., 2007). Smoke water fractions containing KAR₁ have been reported to enhance seedling vigor of several weed and crop species, indicating potential use for KAR₁ as a seed priming agent to improve germination and seedling establishment (Jain et al., 2006; Jain and Van Staden, 2006; Kulkarni et al., 2006; van Staden et al., 2006; Daws et al., 2007a). Since its discovery, a widespread capacity for KAR₁ germination response among angiosperms has been demonstrated (Flematti et al., 2004; van Staden et al., 2004, 2006; Merritt et al., 2006; Daws et al., 2007a; Stevens et al., 2007). Thus, karrikins may be considered a novel class of plant growth regulators with broad impact. To gain a better understanding of the mechanism by which karrikins trigger seed germination and explore their interaction with ABA and GA, we examined KAR₁ responses in Arabidopsis (Arabidopsis thaliana).     

Physiological Responses of Spring Durum Wheat Cultivars to Early-season Drought in a Mediterranean Environment

The Mediterranean climate of North Africa is characterized byuncertain rainfall immediately after seedling emergence, leadingto drought early in the growing season which depresses durumwheat production. However, there is limited understanding ofthe physiological basis of resistance of spring durum wheatto drought in rainfed Mediterranean regions. The objectivesof this study were to examine differences in some physiologicalcharacters among spring durum wheat cultivars in response toduration of early-season drought, and to determine the relationshipof these characters to drought resistance. In two field experiments(1995 and 1996 growing seasons) and a glasshouse experiment(1996), six spring sown durum wheat cultivars were evaluatedunder four water regimes: well irrigated and three differentwater deficits from emergence until the onset of tillering,mid-tillering or at the end of tillering. Cultivars differedin their response. Decreases in photosynthesis soon after droughtstress was imposed resulted mainly from reduced stomatal conductance.Continued water deficits also reduced mesophyll photosyntheticactivity. Possible factors determining the drought-resistanceof a cultivar are lower sensitivity of CO₂exchange rate, netCO₂uptake to water loss ratio, stomatal resistance, relativewater content and greater osmotic adjustment under stress. Furthermore,there is sufficient intraspecific variation in these physiologicalattributes to suggest their use as selection tools.Copyright1998 Annals of Botany Company Wheat;Triticum durumDesf.; early-season drought; physiological responses.     

Field tests with insecticides and insect growth regulators to control insect pests of cowpea and its effects on certain beneficial insects

A small‐plot tests were conducted on cowpea, Vigna ungiculata (L.) Walp, to determine the effectiveness of 14 selected insecticides representing four insecticide classes (organophosphates, carbamates, pyrethroids, and insect growth regulators, IGRs), and four insecticide/IGR mixtures on cowpea insect pests and its effects on certain beneficial insects. By day 3 after treatement, the insecticides phenthoate, isoxathion, cyanophos, carbaryl, and cypermethrin used at sub‐recommended rates reduced the leafhopper, Empoasca spp., populations by >83% than those in the control. On that day, all insecticide treatments significantly reduced the cowpea aphid, Aphis craccivora, numbers below that of the control. The prothiofos, isoxathion, pirimicarb, and fenpropathrin treatments provided continuing control to both leafhoppers and aphids through day 21 after spraying. It seems that most insecticide treatments were not effective in whitefly, Bemisia tabaci, control. The best control of the whitefly immatures was obtained by day 3 after spraying in plots received thiodicarb (76%) and fenpropathrin (60%). All selected insecticides and rates used had very low residual effect against B. tabaci immatures. By day 3 posttreatment, the carbaryl (2.02 kg/ha) caused completely protection for cowpea pods frMw blue pea butterfly, Lampides boeticus, larvae. The IGRs, flufenoxuron and Dowco‐439, applied alone and those applied in mixtures with insecticides, carbaryl/teflubenzuron, chlorpyrifos/XRD‐473, and methomyl/ flufenoxuron, exhibited satisfactory control (>81%) to butterfly larvae on day 7 posttreatment. All treatments did not exhibit a considerable residual activity against L. boeticus larvae through 2–3 weeks followed spray. Most insecticides applied at the higher rates used significantly reduced the numbers of limabean pod borer, Etiella zinckenella, larvae found in cowpea pods collected on day 7 after application. The IGRs, flufenoxuron and Dowco‐439, applied alone, at 0.119 kg/ha, or in mixtures, methomyl/flufenoxuron (0.167 kg/ha) and chlorpyrifos/Dowco‐439 (0.911 kg/ha) caused >73% control of E. zinckenella larvae through day 21 posttreatment. The best control of cowpea weevil, Callosobru‐chus spp., adults (>83%), on day 3 after spraying, was obtained in treatments of cyanophos (1.19 kg/ha), prothiofos (1.43 kg/ha), flufenoxuron (0.119 kg/ha), and chlorpyrifos/Dowco‐439 (0.911 kg/ha). The IGR flufenoxuron applied alone or in mixture, methomyl/flufenoxuron (0.164 kg/ ha) exhibited satisfactory residual activity against Callosobruchus adults through day 21 posttreatment. Percentage seed damage by the larvae of cowpea weevils was significantly lower in most treatments than that of control. Populations of insect predators found in all treated plots were extremely reduced than those found in untreated plots. By day 21 after spraying, the IGRs flufenoxuron, XRD‐473, and Dowco‐439, applied at the low rate of 0.071 kg/ha, seemed to be less effect against insect predators than other insecticides used.     

A method to test compounds for feeding deterrence towards redlegged earth mite (Acarina: Penthaleidae)

A bioassay, based on a membrane sachet technique, has been developed to identify antifeeding compounds affecting the redlegged earth mite, Halotydeus destructor (Acari: Penthaleidae). The method consists of counting H. destructor numbers on membrane sachets in choice experiments, which was quicker and more efficient than weighing the mites. Five per cent aqueous glucose solution was used as a feeding stimulant, with Tween 80® at 5% concentration as a solubilising agent for water-insoluble compounds. (+)-Catechin, rutin, biochanin A, formononetin, chlorogenic acid, and gramine acted as feeding deterrents at 1% concentration. Quercetin (1 %) and azadirachtin (100 ppm) had no significant effect. At lower concentrations (0.01%), compounds showed antifeeding (gramine), phagostimulating (quercetin and chlorogenic acid), or no effects on mite numbers. Dose-dependent deterrent effects of plant extracts were demonstrated with the bioassay, which could be used for other mites.     

The Influence of Plant-Growth Factors on the Initiation and Growth of Crown-Gall Tumours on Primary Pinto Bean Leaves

The number of tumours developing on primary pinto bean leaves(Phaseolus vulgaris L. variety Pinto) inoculated with Agrobacteriumtumefaciens (Smith and Town.) Conn, strain B6, was increasedby as much as 100 per cent through the addition of several plant-growthfactors and antagonists of some of these factors to the freshlyinoculated leaves. Naphthylacetic acid, gibberellic acid, (2-chloroethyl)trimethylammonium chloride, and adenine gave a biphasic responsewith optimal promotions of tumour initiation at 10^-5 to 10^-4mg/ml. Tri-iodobenzoic acid and 4-chlorophenoxyisobutyric acidwere most active at 10^-1 mg/ml. Mean tumour diameter showeda direct correlation with tumour number in these experiments.The results show tumour initiation to be sensitive to growthfactor changes, possibly through a heightened traumatic responseof the wounded leaves. The growth of the tumours was unaffectedby these additions except as they altered tumour number andthis secondarily affected tumour growth.     

A SIMPLE ALTERNATIVE TO GENERALIZED PROCRUSTES ANALYSIS: APPLICATION TO SENSORY PROFILING DATA

A statistical method for analyzing sensory profiling data obtained by means of fixed vocabulary or free choice profiling is discussed. The most interesting feature of this method is that it involves only simple statistical treatment and can therefore be performed using standard software packages. The outcomes of this method are compared to those of Generalized Procrustes Analysis on the basis of two data sets obtained, respectively, by means of fixed vocabulary and free choice profiling. A significance test is also discussed in order to assess whether the overall configuration of the products is meaningful. This significance test is based upon a simulation study involving the permutation procedure.     

10-Undecanhydroxamic acid, a hydroxamate derivative of the undecanoic acid, has strong antimicrobial activity through a mechanism that limits iron availability

Undecanoic acid (UDA) is a fatty acid with significant antimycotic activity. In this work we have synthesized 10-undecanhydroxamic acid, a hydroxamate derivative of the UDA, and tested its antimicrobial activity on different microorganisms. Our results demonstrate that this compound has higher efficacy than UDA against a variety of fungi and bacteria. Analysis of the intracellular concentration of protein involved in iron transport in Salmonella enterica serovar Typhimurium suggests that its antimicrobial effect actually relies on the ability to chelate iron ions, providing an efficient mechanism to interfere with microbial growth.