Karrikinolide residues in grassland soils following fire: Implications on germination activity

Smoke plays a positive role in promoting seed germination and enhancing post-germination processes. The compound in smoke is 3-methyl-2H-furo[2,3-c]pyran-2-one (KAR₁). Recently a structurally related butenolide [3,4,5-trimethylfuran-2(5H)-one, (trimethylbutenolide, TMB)], which inhibits germination and reduces the effect of KAR₁, was isolated. The mechanisms of action and interaction of these karrikins are unknown. In addition, the ecological significance of fires in altering soil-smoke-chemistry and the spatial dimensions of the influence on burnt sites and neighbouring areas are undetermined. This study quantified KAR₁ and TMB residues in soils following fire and assessed the germination activity of burnt soil extracts. Soil samples from 0 to 2, 2 to 4, 4 to 6 and 6 to 8 cm depths were extracted using dichloromethane and bioassayed using Lactuca sativa L. achenes (seeds). At all soil depths, L. sativa seeds exhibited significantly greater percentage germination when treated with burnt soil extracts compared to the no-burn soil (control). The L. sativa seeds also showed significantly greater percentage germination when treated with soil extracts from the adjacent plots. Compared to the no-burn soil, higher concentrations of KAR₁ and TMB were detected in the surface layers of the burnt soils. Considerable concentrations of KAR₁ and TMB were also detected in no-burn soil indicating that sources other than fire may also generate karrikins. Findings of this study imply that post-fire increases in KAR₁ residues in the soil may influence soil seed bank stimulation of certain smoke-responsive plant communities in both burnt and adjacent non-burnt areas.     

Plant-derived smoke: Old technology with possibilities for economic applications in agriculture and horticulture

Fire and smoke have been used in traditional agricultural systems for centuries. In recent years, biologically active compounds have been isolated from smoke with potential uses in agriculture and horticulture. This article highlights the possibilities of using smoke-water or smoke-derived butenolide (3-methyl-2H-furo[2,3-c]pyran-2-one, termed karrikinolide, KAR₁) for the cultivation of agricultural and horticultural crops. Treatments with smoke-water show promising results for improving seed germination, seedling growth and crop productivity. In certain cases, even under adverse conditions, such as low or high temperatures and low osmotic potentials, smoke-water or a KAR₁ solution can promote seed germination and seedling growth. This phenomenon is of great significance when seeds are sown under drought conditions. Smoke-technology, therefore, has potential for use in arid and semi-arid regions. Possibilities may also exist for controlling some plant diseases and managing weeds with the use of smoke or KAR₁ solutions. In addition, smoke-technology can possibly economize the use of commercial chemical fertilizers, pesticides and herbicides, making it a feasible technology for organic farming and for resource-poor farmers in developing nations. The positive role of smoke-water in flowering and fruiting of crops cannot be overlooked as the karrikins found in smoke are now recognized as potential new plant growth regulators. Very low concentrations of smoke-water or a KAR₁ solution are effective in promoting germination and post-germination growth. Thus, early harvesting and increasing the productivity of crops using smoke-technology may be possible. Here we review some of the effects of smoke and KAR₁ on various crop species and discuss the potential uses of smoke technology in agriculture and horticulture.     

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).     

Is broad-scale smoke–water application always a useful tool for improving seedling emergence in post-mining restoration? Evidence from jarrah forest restoration in Western Australia

It has been widely advocated that smoke–water application to topsoil can substantially improve restoration success by enhancing seed germination. This is despite few studies having tested the effects of smoke–water on seedling emergence in field-scale restoration trials. Here we report the effects of applying a commercially available smoke solution (Regen 2000®), at rates between 0 and 100 mL m^− 2, on jarrah forest sites being restored after bauxite mining in the southwest of Western Australia. Smoke solutions stimulated the seed germination of a range of species in laboratory experiments. In addition, smoke–water stimulated germination of Stylidium affine seeds sown directly into the first field experiment. However, apart from the effect on sown S. affine seeds, smoke–water application had no effect on subsequent seedling numbers, species richness or the relative proportion of seedlings in different growth-form categories in either of the two field experiments. These findings suggest that smoke–water application does not always ensure enhanced restoration outcomes.     

Transcriptome analysis of germinating maize kernels exposed to smoke-water and the active compound KAR<Subscript>1</Subscript>

Background  

Smoke released from burning vegetation functions as an important environmental signal promoting the germination of many plant species following a fire. It not only promotes the germination of species from fire-prone habitats, but several species from non-fire-prone areas also respond, including some crops. The germination stimulatory activity can largely be attributed to the presence of a highly active butenolide compound, 3-methyl-2H-furo[2,3-c]pyran-2-one (referred to as karrikin 1 or KAR₁), that has previously been isolated from plant-derived smoke. Several hypotheses have arisen regarding the molecular background of smoke and KAR₁ action.     

Germination responses of Croton macrostachyus (Euphorbiaceae) to various physico-chemical pretreatment conditions

Croton macrostachyus Hochst. ex Del. (Euphorbiaceae) is a multipurpose, deciduous, and medium sized tree of pantropic occurrence. Because the species has numerous useful qualities (e.g., establishment and growth in disturbed sites, drought tolerance, fast growth rate, copious litter/necromass production, suitability for agroforestry, and ability to attract avian frugivores), its speedy restoration has become increasingly critical. Germination studies were therefore conducted on seeds pooled from five widely located provenances with a view to supporting efforts geared toward the speedy propagation and restoration of this valuable tree species. Seed pretreatments were achieved using various dilution levels of plant-derived smoke–water (1:1, 1:10, 1:100 and 1:1000), as well as gibberellic acid (GA₃) or potassium nitrate (KNO₃) ranging in concentration from 0.1 to 100 μmol. The control was to use distilled water for seed pretreatment. Seeds were germinated under either illuminated (ca 60 μmol m^− 2 s^− 1; cool-white fluorescent lamp) or non-illuminated conditions. Experiments on the impact of seed storage durations, as well as storage temperatures were also conducted. The study found that germination percentage (GP: ca 90%), and mean germination time (MGT: 14 days) were significantly (P < 0.001) better when seeds were pretreated with smoke–water and germinated under non-illuminated conditions, than when these were pretreated with various concentrations of GA₃ or KNO₃ (GP and MGT of ca 65% and 20 days, respectively). Germination percentage (GP) and germination vigor (GV) declined with increasing storage-time for all storage temperatures, but GV's decline was faster for seeds stored at 22 °C than for those stored at 5 and 15 °C. On the other hand, mean germination time (MGT) increased significantly (P < 0.01) with seed storage-time of up to 8 months at 5, 15, and 22 °C, but the increase was more marked for seeds stored at 22 °C than for those stored at 5 and 15 °C. From these investigations, it is concluded that germination of C. macrostachyus seeds through use of smoke–water is faster, cheaper, and technically less demanding, compared to that of either GA₃ or KNO₃. The study also concludes that C. macrostachyus is intermediate between orthodox and recalcitrant seeds, and that it is non-photoblastic.     

The effects of smoke derivatives on in vitro seed germination and development of the leopard orchid Ansellia africana

Plant‐derived smoke and smoke‐isolated compounds stimulate germination in seeds from over 80 genera. It has also been reported that smoke affects overall plant vigour and has a stimulatory effect on pollen growth. The effect of smoke on orchid seeds, however, has not been assessed. In South Africa, orchid seeds from several genera may be exposed to smoke when they are released from their seedpods. It is therefore possible that smoke may affect their germination and growth. Therefore, the effects of smoke [applied as smoke‐water (SW)] and two smoke‐derived compounds, karrikinolide (KAR₁) and trimethylbutenolide (TMB), were investigated on the germination and growth of orchid seeds in vitro. The effect of SW, KAR₁ and TMB were investigated on the endangered epiphytic orchid, Ansellia africana, which is indigenous to tropical areas of Africa. Smoke‐water, KAR₁ and TMB were infused in half‐strength MS medium. The number of germinated seeds and number of seeds and protocorm bodies to reach predetermined developmental stages were recorded on a weekly basis using a dissecting microscope for a 13‐week period. Infusing SW 1:250 (v:v) into half‐strength MS medium significantly increased the germination rate index (GRI) and the development rate index (DRI) of the A. africana seeds. All the SW treatments significantly increased the number of large protocorm bodies at the final stage of development. Infusing KAR₁ into the growing medium had no significant effect on germination or development of the seeds. The TMB treatment, however, significantly reduced the GRI and DRI of A. africana seeds.     

Tools for conservation of Balsamorhiza deltoidea and Balsamorhiza sagittata: Karrikin and thidiazuron-induced growth

Wildfires are having both devastating and regenerative impacts on the ecosystems in the Pacific Northwest of North America. Balsamorhiza sagittata and B. deltoidea (balsamroot) are ecologically important species in this region, and B. sagittata populations are increasing, while B. deltoidea is critically imperiled. The aim of this research was to establish in vitro protocols for germination and regeneration of Balsamorhiza spp. to enable conservation efforts. It was hypothesized that karrikins, which are plant growth regulators released from burning plants during wildfires, would induce seed germination in Balsamorhiza spp. Three karrikins (KAR₁, KAR₂, and KAR₁₁) were tested for the ability to enhance germination in these species at two levels (5 or 10 μM). KAR₂ had the strongest positive effect on germination and induced 47% and 60% germination, respectively, in B. sagittata seeds compared to 14% germination obtained in the control (water agar media). In B. deltoidea, KAR₂ treatment resulted in a germination rate of 73.1% and 100%, compared to 69% in the control. A germplasm collection of seedlings of both species was established for conservation and regeneration experiments. Thidiazuron treatment (10 μM) induced formation of embryo-like structures in seedlings of both B. sagittata and B. deltoidea, with regenerants originating from the crown of seedlings. The present study provides in vitro methods for conservation and mass propagation of Balsamorhiza species.

     

Induction of agricultural weed seed germination by smoke and smoke-derived karrikin (KAR<Subscript>1</Subscript>), with a particular reference to <Emphasis Type="Italic">Avena fatua</Emphasis> L.

Plant-derived smoke, its water extract—the smoke water (SW), and karrikin (KAR₁) present in the smoke stimulate seed germination in plants from fire-prone and fire-free areas, including weeds and cultivated plants. There are also plants, the seeds of which can respond only to smoke, but not to KAR₁, and vice versa. Smoke and/or KAR₁ can be applied in horticulture, agriculture, and revegetation. This review describes effects of smoke and KAR₁ on weed seed germination and focuses mainly on the recent knowledge about the physiological role of these factors in dormancy release and germination of Avena fatua caryopses. The involvement of gibberellins, ethylene, and abscisic acid (ABA) in the response to smoke or KAR₁ is discussed. Effects of smoke or KAR₁ on the contents of reactive oxygen species (ROS), non-enzymatic antioxidants, and activity of the enzymes participating in ROS removal are presented. Cell cycle activity in the response to SW and KAR₁ is also considered. Effects of KAR₁ on thermodormancy release in A. fatua caryopses are highlighted, as well.     

Effects of salt,alkali and salt–alkali mixed stresses on seed germination of the halophyte Salsola ferganica (Chenopodiaceae)

Salsola ferganica L. (Chenopodianceae) is an annual halophytic species. Experiments were carried out in laboratory to determine the effects of temperature, perianths and various types of salinity on seed germination and germination recovery. Seeds were germinated at 6 levels of temperature with perianths, plus perianths and removed perianths in complete darkness for 9 days. The germination responses of the seeds without perianths at 25 °C were determined over a wide range of NaCl, NaHCO₃ or NaCl–NaHCO₃ mixed stress for 13 days. Perianths seriously affected germination as a barrier for seed germination and the optimal temperature was at 25 °C. Highest germination percentage was obtained under control and seed germination was progressively inhibited with the increase of salinity concentration. The negative effect of NaHCO₃ at the same concentration on germination was stronger than that of NaCl and NaCl–NaHCO₃ mixed. When substrate salinity was removed, seeds exposed to a high NaCl concentration (400–800 mM), NaHCO₃ (50–200 mM) and NaCl–NaHCO₃ mixed (100–400 mM) germinated well. Final germination of Salsola ferganica seeds was significantly affected by types of salt at the low salinity (?200 mM) and with increased salinity it was influenced mainly by salinity concentration for various proportion of salt–alkali mixed stress.     

Karrikins: A new family of plant growth regulators in smoke

Karrikins are a chemically defined family of plant growth regulators discovered in smoke from burning plant material. Karrikins are potent in breaking dormancy of seeds of many species adapted to environments that regularly experience fire and smoke. The recent discovery that karrikins trigger seed germination and control seedling growth in taxa that would rarely experience fire indicates that their significance could extend far beyond fire ecology. This is exemplified by new studies showing that seeds of Arabidopsis thaliana respond sensitively and specifically to karrikins in smoke. These exciting discoveries might be explained if karrikins are produced in the environment by processes other than fire, such as by chemical or microbial degradation of vegetation in response to disturbance of the soil or removal of the plant canopy. Another hypothesis is that plants contain endogenous karrikins that function naturally in the control of seed germination and that species from fire-prone habitats have evolved to respond also to exogenous karrikins. A variant on this hypothesis is that karrikins mimic endogenous plant hormones such as terpenoids that control seed germination. The evidence for these hypotheses is discussed, but whatever the explanation karrikins are now firmly established as an important family of naturally occurring plant growth regulators.     

3D-QSAR (CoMFA,CoMSIA), molecular docking and molecular dynamics simulations study of 6-aryl-5-cyano-pyrimidine derivatives to explore the structure requirements of LSD1 inhibitors

Recently, Histone Lysine Specific Demethylase 1 (LSD1) was regarded as a promising anticancer target for the novel drug discovery. And several small molecules as LSD1 inhibitors in different structures have been reported. In this work, we carried out a molecular modeling study on the 6-aryl-5-cyano-pyrimidine fragment LSD1 inhibitors using three-dimensional quantitative structure–activity relationship (3D-QSAR), molecular docking and molecular dynamics simulations. Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were used to generate 3D-QSAR models. The results show that the best CoMFA model has q² = 0.802, r²_ncv = 0.979, and the best CoMSIA model has q² = 0.799, r²_ncv = 0.982. The electrostatic, hydrophobic and H-bond donor fields play important roles in the models. Molecular docking studies predict the binding mode and the interactions between the ligand and the receptor protein. Molecular dynamics simulations results reveal that the complex of the ligand and the receptor protein are stable at 300 K. All the results can provide us more useful information for our further drug design.     

Effect of yak rumen content treatments on seed germination of 11 alpine meadow species on the Qinghai-Tibetan Plateau

The Qinghai-Tibetan Plateau is located in the ‘Third Pole’ of the world, characterized by a harsh environment. Despite this, the alpine meadow ecosystem have developed over a wide area but serious grassland degradation is threatening the ecological environment on the Plateau. Recruitment of new plants to the population, via germination and establishment, is vital to plant community survival. Previous work on the seeds in this area has mainly focused on community-wide germination strategies, seed germination characteristics and their correlations with seed size and seed mass. However, there have been no studies on the effects of soaking in rumen contents on the plant seed germination characteristics of alpine meadow species. The present study had two main objectives: (i) to determine the effect of fresh rumen content from yaks on seed germination characteristics and seedling growth of species common to the eastern Tibetan Plateau alpine meadow, and (ii) to develop an effective method to enhance seed germination. Seeds of 11 common species were collected together with fresh rumen content from three yaks that grazed there. Seed germination tests were conducted after they had been soaked in rumen content for one of six soaking periods (12, 24, 36, 48, 60 or 72 h). The seeds were incubated under natural light conditions of 8 h light at 25 °C and 16 h darkness at 15 °C, for the germination period of 34 days. The results showed that seed germination and seedling growth were affected by soaking time, seed coat completeness and seed type. After soaking in rumen content, the germination percentages of scarified (peeled or with the seed coat cut through) seeds of some species (true seeds Oxytropis ochrocephala and Medicago ruthenia var inschanica, nutlet Carex enervis, achenes Anemone rivularis and Polygonum sibiricum) and complete seeds of C. enervis, and A. rivularis were improved but the duration of soaking was also important. Seed germination of caryopsis Achnatherum inebrians (a toxic grass) was significantly inhibited by any exposure to rumen fluids. Scarified seeds generally had higher germination percentages than complete ones after treatment, but with the increase in soaking time, germination percentages declined and scarified seeds were more sensitive to the treatment than the complete seeds. After soaking in yak rumen content, the germination indices of scarified M. ruthenia at 12 h treatment, O. ochrocephala and achene Rumex acetosa at 12–24 h treatment, nutlet Kobresia humilis at 24 h treatment, P. sibiricum at 24–48 h treatment, C. enervis at 12–48 h treatment and A. rivularis at 12–60 h treatment were significantly higher than the control (P < 0.05), while the germination indices of complete C. enervis seeds at 12 h and 36 h treatment, and A. rivularis at 12–60 h treatment were significantly higher compared with the control. The germination indices of other species gradually decreased with the increase in soaking time. We concluded that yak rumen digestion could enhance, inhibit or not affect seed germination and seedling growth of the alpine meadow species, which might influence seedling recruitment, interspecific competition, and the plant community structure of the eastern Tibetan Plateau alpine meadow. Overall, yak digestion has a positive effect on alpine meadow seed germination and seed dispersal.     

Smoke-water effect on the germination of Amazonian tree species

Smoke stimulates seed germination of a range of species from ecosystems that may or may not be fire prone. We evaluated the effects of smoke-water on germination of ten tree species of economic value in the Amazon region. Two materials were burnt to produce smoke-water: germination paper and the wood of Cecropia palmata Willd. Seven dilutions of the solutions were tested. Seeds of nine forest trees were germinated under controlled laboratory conditions (25 °C ± 2 °C) in the laboratory. Bertholletia excelsa Humb. & Bonpl., was tested in the nursery (approximately 25–36 °C) because of its large seeds. Irrespective of the material burned, smoke-water significantly increased seed germination of three species: Cordia goeldiana Hub., Ochroma pyramidale (Cav. ex Lam.) Urb. and Jacaranda copaia (Aubl.) D. Don. and there was a significant inhibitory effect on Swietenia macrophylla King. Germination was accelerated by smoke in J. copaia, B. excelsa and Bellucia grossularioides (L.) Triana. The most pronounced effect was observed in B. excelsa, as the mean germination time of 108 d (control) was reduced to 76 d with smoke-water made from germination paper (dilution of 1:25) and to 61 d with the one from Cecropia wood (dilution of 1:250). For five of the ten species studied, smoke-water either increased or accelerated seed germination, irrespective of the materials used for its production. Seeds with low vigour and prolonged germination time seemed to be more receptive to smoke.     

Novel Ru(II) oximato complexes with silent oxygen atom: Synthesis,chemistry and biological activities

A series of octahedral complexes, [Ru(CO)(EPh₃)₂(bhmh)] (E = P or As; H₂bhmh = benzoic acid (2-hydroxyimino-1-methyl-propylidene)-hydrazide), [Ru(CO)(EPh₃)₂(ihmh)] (H₂ihmh = isonicotinic acid (2-hydroxyimino-1-methyl-propylidene)-hydrazide), [Ru(CO)(EPh₃)₂(hhmh)] (H₂hhmh = 2-hydroxy-benzoic acid (2-hydroxyimino-1-methyl-propylidene)-hydrazide) have been prepared by a facile procedure. X-ray structure determination of three of the complexes revealed that the hydrazone ligand coordinates through the imine and the oxime nitrogen and the amide oxygen atoms. In all the complexes, the N–OH moiety of the oxime is deprotonated to give an N–O^? species and this oxygen atom did not coordinate to the central metal atom. The oxidation–reduction processes for each of these complexes have been determined in CH₃CN by cyclic voltammetry. The complexes displayed two oxidation couples and one irreversible reduction response between +1.6 and ?1.6 V. The trend in the half wave potentials reflects the electronic nature of the hydrazone ligand. Antibacterial activity of the ligands and the complexes has been evaluated against five pathogenic bacteria. The binding of the complexes with herring sperm DNA has also been investigated by UV–Vis spectroscopy and cyclic voltammetry.     

Synthesis of bis-Schiff bases of isatins and their antiglycation activity

Bis-Schiff bases 1–27 have been synthesized and their in vitro antiglycation potential has been evaluated. Compounds 21 (IC₅₀ = 243.95 ± 4.59 μM), 20 (IC₅₀ = 257.61 ± 5.63 μM), and 7 (IC₅₀ = 291.14 ± 2.53 μM) showed an excellent antiglycation activity better than the standard (rutin, IC₅₀ = 294.46 ± 1.50 μM). This study has identified a series of potential molecules as antiglycation agents. A structure–activity relationship has been studied, and all the compounds were characterized by spectroscopic techniques.     

Aroylguanidine-based factor Xa inhibitors: The discovery of BMS-344577

We report the design and synthesis of a novel class of N,N′-disubstituted aroylguanidine-based lactam derivatives as potent and orally active FXa inhibitors. The structure–activity relationships (SAR) investigation led to the discovery of the nicotinoyl guanidine 22 as a potent FXa inhibitor (FXa IC₅₀ = 4 nM, EC_2×PT = 7 μM). However, the potent CYP3A4 inhibition activity (IC₅₀ = 0.3 μM) of 22 precluded its further development. Detailed analysis of the X-ray crystal structure of compound 22 bound to FXa indicated that the substituent at the 6-position of the nicotinoyl group of 22 would be solvent-exposed, suggesting that efforts to attenuate the unwanted CYP activity could focus at this position without affecting FXa potency significantly. Further SAR studies on the 6-substituted nicotinoyl guanidines resulted in the discovery of 6-(dimethylcarbamoyl) nicotinoyl guanidine 36 (BMS-344577, IC₅₀ = 9 nM, EC_2×PT = 2.5 μM), which was found to be a selective, orally efficacious FXa inhibitor with an excellent in vitro liability profile, favorable pharmacokinetics and pharmacodynamics in animal models.     

Syntheses of coumarin–tacrine hybrids as dual-site acetylcholinesterase inhibitors and their activity against butylcholinesterase,Aβ aggregation,and β-secretase

Exploring small-molecule acetylcholinesterase (AChE) inhibitors to slow the breakdown of acetylcholine (Ach) represents the mainstream direction for Alzheimer’s disease (AD) therapy. As the first acetylcholinesterase inhibitor approved for the clinical treatment of AD, tacrine has been widely used as a pharmacophore to design hybrid compounds in order to combine its potent AChE inhibition with other multi-target profiles. In present study, a series of novel tacrine–coumarin hybrids were designed, synthesized and evaluated as potent dual-site AChE inhibitors. Moreover, compound 1g was identified as the most potent candidate with about 2-fold higher potency (K_i = 16.7 nM) against human AChE and about 2-fold lower potency (K_i = 16.1 nM) against BChE than tacrine (K_i = 35.7 nM for AChE, K_i = 8.7 nM for BChE), respectively. In addition, some of the tacrine–coumarin hybrids showed simultaneous inhibitory effects against both Aβ aggregation and β-secretase. We therefore conclude that tacrine–coumarin hybrid is an interesting multifunctional lead for the AD drug discovery.     

Enhancing seedling growth of Jatropha curcas—A potential oil seed crop for biodiesel

The effects of aerosol smoke (AS), smoke-water (SW), potassium nitrate (KNO₃), naphthalene acetic acid (NAA) and indole-3-butyric acid (IBA) on germination and seedling growth of Jatropha curcas were investigated. Seed coat removal accelerated water imbibition and germination occurred within 48 h. Seeds subjected to AS failed to germinate over a 90 day period. There were no significant differences in germination percentage between the treatments and untreated control (intact- and shelled-seed). However, shelled-seeds had the shortest mean germination time (MGT). Seedlings developed from treated seeds were planted in trays under shade house conditions and growth traits measured after 3 months. Soaking intact-seeds in SW, KNO₃ and NAA (24 h) produced significantly heavier and longer seedlings, which resulted in higher vigour indices (VI) compared to the control treatments. These results provide empirical evidence of the stimulatory effect of SW, KNO₃ and NAA on J. curcas seedling growth and vigour and the continuation of the effect over time. The approach of treating intact-seeds of J. curcas with plant growth substances prior to planting will help in producing healthy seedlings and possibly improve crop productivity.