Imprimatins A and B: Novel plant activators targeting salicylic acid metabolism in Arabidopsis thaliana

Plant activators are agrochemicals that protect plants from a broad range of pathogens by activating the plant immune system. Unlike pesticides, they do not target pathogens; therefore, plant activators provide durable effects that are not overcome by pathogenic microbes. Although certain plant activators have been applied to paddy fields for more than 30 years, the molecular basis of the underlying immune induction are unclear. From the screening of 10,000 diverse chemicals by a high-throughput screening procedure to identify compounds that specifically enhance pathogen-induced cell death in Arabidopsis cultured cells, we identified 7 compounds, which we designated as immune priming chemicals (Imprimatins). These compounds increased disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants. Pretreatments increased the accumulation of endogenous salicylic acid (SA) but reduced its metabolite, SA-O-β-D-glucoside (SAG). Imprimatins inhibited the enzymatic activities of 2 SA glucosyltransferases (SAGTs) in vitro at concentrations effective for immune priming. Single and double knockout Arabidopsis plants for both SAGTs consistently exhibited enhanced disease resistance and SA accumulation. Our results demonstrate that the control of the free SA pool through SA-inactivating enzymes can be a useful methodology to confer disease resistance in plants. SAGTs can pave the way for target-based discovery of novel crop protectants.     

Integrated control of rice kernel smut disease using plant extracts and salicylic acid

The effects of salicylic acid (SA) at three concentrations i.e. 2.5, 5 and 7 mM and plant extracts from pick tooth (Ammi visnaga), liquorice (Glycyrrhiza glabra), artemisia (Artemisia judaica), mint (Mentha viridis), clove (Syzygium aromaticum) and blue gum (Eucalyptus globulus) on the infection of rice kernel smut disease caused by Tilletia barclayana were studied. Spraying of rice plants with different concentrations of SA at seven days before infection was the most effective treatment against pathogen infection. Among all plant extract treatments, M. viridis and S. aromaticum were the most effective treatments. Additionally, our results showed increased levels of peroxidase, polyphenol oxidase, phenylalanine ammonia lyase and chitinase as well as total protein contents in the treated plants compared with the control. In conclusion, accumulations of these oxidative enzymes in plants treated with SA and plant extracts provide their role in the activation of induced resistance against T. barclayana.     

穆棱林区野生东北马鹿种群冬季食物组成模式与植物代谢产物的关系

高纬度地带,在冬季食物资源有限的环境中,野生大型有蹄类动物满足营养需求的同时,需要对植物中次生代谢产物进行平衡,回避有害物质并选择对机体有益的成分,从而形成特定的食物组成模式。以东北马鹿（Cervus elaphus xanthopygus）为研究对象,于2020年11月,在黑龙江穆棱东北红豆杉国家级自然保护区境内,采集东北马鹿粪便和植物样本。通过粪便显微分析法确定保护区内马鹿冬季食物组成,采用k-means聚类分析揭示马鹿冬季食物组成模式。应用广泛靶向代谢组技术对部分植物中次生代谢产物的含量进行全覆盖定性和相对定量检测,将食物组成与次生代谢产物数据整合,进行曼特尔检验（Mantel test）分析,以探究植物次生代谢产物对马鹿种群内食物组成模式的影响。结果表明,林区内马鹿种群冬季共采食30种植物,其中木本植物占92.48%;且种群内分别呈现出以东北红豆杉（Taxus cuspidata）,簇毛槭（Acer barbinerve）,毛榛子（Corylus mandshurica）为主要食物的不同食物组成模式。广泛靶向代谢组技术共检测出638种次生代谢产物,有25种代谢物与马鹿采食频率显著相关,其中多数萜类物质抑制马鹿采食,而鞣质类物质对马鹿的采食选择有一定的正向作用;Mantel test结果显示,上述25种物质中黄酮、鞣质、萜类化合物相对含量与不同马鹿个体食物组成显著相关,说明这些代谢物相对含量和性质的差异会造成种群内不同个体食物组成的差异,是种群内形成不同食物组成模式的原因之一。从植物次生代谢产物角度揭示了该地区东北马鹿种群冬季食物组成模式呈现差异的可能因素,为进一步研究大型有蹄类营养策略和植物化学防御关系提供基础依据。     

Growth, metabolic profiling and enzymes activities of Catharanthus roseus seedlings treated with plant growth regulators

The effect of different growth regulators on growth and the production of terpenoid indole alkaloids as well as some enzymes involved in the biosynthesis were studied in Catharanthus roseus seedlings. The seedlings were grown on MS solid medium containing different concentrations of each growth regulator for a period of one month. Extracted alkaloids were analyzed by HPLC for determination of terpenoid indole alkaloid quantities. Continuous availability of growth regulators induced different alkaloids with variable effects among the regulators. Gibberellic acid at concentration of either 5.8 M or 11.6 M resulted in elongation of shoots with lowering the number of leaves. Abscisic acid has a retardant effect on growth. Ethylene did not effect the growth pattern at concentration of 100 M but seedlings were not tolerant to higher concentrations. Methyljasmonate reduced the growth of the root system. Methyljasmonate was a general inducer for all alkaloids and increased the activity of strictosidine glucosidase. Ethylene applications promoted the pathways towards ajmalicine, serpentine, tabersonine and vindoline. Similar effect as for ethylene was observed for abscisic acid. Salicylic acid treatment increased the production of serpentine, tabersonine and higher concentration of salicylic acid induced vindoline accumulation. Peroxidase activity was also induced by salicylic acid. Gibberellic acid has little effect on alkaloid levels.     

Simultaneous effect of calcium,magnesium, copper and cobalt ions on sapogenin steroids content in callus cultures of Agave amaniensis

The simultaneous effect of calcium, cobalt, copper and magnesium ions and their interactions on growth and sapogenin steroids accumulation in callus cultures of Agave amaniensis was studied by using a central composite second-order rotatable design. The absence of calcium ions in media increased the sapogenin steroid content, while relatively high concentration of magnesium, cobalt and copper ions simultaneously inhibited the sapogenin steroid formation. This revised version was published online in June 2006 with corrections to the Cover Date.     

外源SA和NO对NaCl胁迫下番茄幼苗生长、光合及离子分布的影响

以番茄(Lycopersicon esculentum Mill.)品种‘秦丰保冠’为试材,采用营养液培养法,研究单独和复配施用外源水杨酸(SA)、一氧化氮(NO)供体硝普钠(SNP)对100mmol/L NaCl胁迫下番茄幼苗生长、光合及离子分布的影响。结果表明:(1)单独和复配外施SA、SNP均能有效抑制NaCl胁迫下番茄幼苗叶片光合色素(Chla、Chlb、Chla+b和Car)含量、Chla/b值、净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、瞬时水分利用效率(WUEt)、表观光能利用效率(LUEapp)和表观CO2利用效率(CUEapp)的下降及Car/Chla+b值和胞间CO2浓度(Ci)的升高,并以SA和SNP复配处理效果最明显。(2)NaCl胁迫下,外源SA、SNP单独和复配处理的番茄幼苗各器官(叶、茎和根)中Cl-、Na+含量和Na+/K+、Na+/Ca2+、Na+/Mg2+值显著降低,而K+、Ca2+和Mg2+的含量却不同程度提高,其中以SA和SNP复配处理效果最好。(3)单独和复配外施SA、SNP均能有效减轻NaCl胁迫对番茄幼苗生长的抑制作用,并促进各器官生物量的积累和壮苗的形成,且以SA和SNP复配处理效果更佳。研究表明,复配外施SA和SNP在诱导番茄幼苗提高抗(耐)盐能力方面具有协同增效作用。     

Isolation and characterization of the plant immune-priming compounds Imprimatin B3 and -B4, potentiators of disease resistance in Arabidopsis thaliana

Plant activators are chemical crop protectants that fortify the immune system in plants. Unlike pesticides that target pathogens, plant activators provide durable effects against a broad spectrum of diseases, which have not been overcome by pathogenic microbes. Plant activators are not only useful agrochemicals, but can also help to elucidate the details of the plant immune system. Using an established high-throughput screening procedure, we previously identified 5 compounds, designated as Imprimatins, which prime plant immune response. These compounds increased disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants by inhibiting 2 salicylic acid (SA) glucosyltransferases (SAGTs), resulting in accumulation of the phytohormone SA. Here, we report the isolation of 2 additional Imprimatins, B3 and B4, which are structurally similar to Imprimatin B1 and B2. Because these compounds did not have strong inhibitory effects on SAGTs in vitro, they may exert their function after metabolic conversion in vivo.     

The effect of calcium concentration on the toxicity of copper, lead and zinc to yolk-sac fry of brown trout, Salmo trutta L., in soft, acid water

Yolk-sac fry of brown trout were exposed to three levels of single trace metals (Cu, 20,40,80 nmol 1^-1; Pb, 12·5,25,50 nmol 1^-1; Zn, 75,150,300 nmol 1^-1) typical of concentrations reported for acid soft waters, in flowing, artificial, soft water media maintained at pH 4·5 and [Ca] of 20 or 200 μmol 1^-1for 30 days.
Mortalities were high in fry subjected to all levels of the three trace metals at [Ca] 20 μmol 1^-1, with 80% of the total deaths occurring between days 11 and 15 of the experiment. 25% mortality occurred at low [Ca] and pH 4·5 in the absence of trace metals, with only one death recorded at [Ca] 200 μmol1^-1'(Cu, 80 nmol 1^-1). At high [Ca] all three levels of Cu and Pb impaired net Na and K uptake; Cu was the only metal to reduce the uptake of Ca. The Zn treatments had no significant effect on mineral uptake. Calcification of centra was reduced by all three Cu treatments at [Ca] 200 μmol 1^-1. The lowest Zn concentration (75 nmol 1^-1) was the only other treatment to impair skeletal development. In the absence of trace metals, low [Ca] significantly reduced Ca, Na and K uptake, skeletal calcification and dry mass at pH 4·5.
The deleterious effects of low Cu, Pb and Zn concentrations at low pH and low [Ca], and the ameliorative effect of higher ambient [Ca], are discussed in relation to fishery status in soft, acid waters.     

Alleviation of copper toxicity in germinating pea seeds by IAA,GA3, Ca and citric acid

The ameliorating effects of four exogenous effectors were investigated in germinating pea seeds exposed to copper excess. The results showed that the application of IAA, GA₃, Ca or citric acid alleviated Cu-induced inhibition of growth and simultaneously reduced the oxidative stress injury, particularly contents of hydrogen peroxide, malondialdehyde and carbonyl groups. The improving effects can probably be mediated by the decreases in lipoperoxidation and protein oxidation as evidenced by changes in antioxidant enzyme activities. In addition, the efficiency of this recovery was compared within two types of treatments. Obtained results demonstrated that the stress abruption by the addition of effectors after three days of Cu application (treatment of type II) seems to be more effective than the simultaneous application of ‘Cu?+?effectors’ at the beginning of germination (treatment of type I). Data could provide some clues to physiological and biochemical mechanisms of the response of germinating seeds to the addition of chemicals under heavy metal stress.     

The effect of calcium on the production of ethylene and abscisic acid by fungus Fusarium culmorum and by wheat seedlings infected with that pathogen

Wheat seedlings infected and non-infected with Fusarium culmorum were grown on mediums with different content of calcium (0, 2, 4, 8 mM). It was found that the higher the content of calcium in the medium, the greater the amounts of ethylene produced in both non-infected and infected wheat seedlings, whereas the level of ABA in their tissues was decreased. Taking into consideration the fact that ethylene inhibits, whereas ABA stimulates the growth and development of Fusarium culmorum, it may be assumed that the production of ethylene increased under the influence of calcium and the decreased level of ABA in wheat seedlings causes the reduction growth and development of pathogen and as a result it lowers the degree of infection of wheat seedlings by this fungus. Thus, on the base of the obtained results it may be concluded that the inhibiting influence of calcium on injurying the wheat seedlings by Fusarium culmorum may be caused by the influence of this cation on the hormone balance in the plant.     

Identification of <Emphasis Type="Italic">Ganoderma</Emphasis>, the causal agent of basal stem rot disease in oil palm using a molecular method

From comparison of the alignments of the internally transcribed spacers (ITS) of ribosomal DNA from Ganoderma associated with oil palm basal stem rot (BSR) and other Ganoderma species, two specific primer pairs were selected to provide a specific DNA amplification of pathogenic Ganoderma in oil palm. Each primer pair produced a single PCR product of about 450 bp (for primer pair IT1–IT2) and 334 bp (for primer pair IT1–IT3) when oil palm Ganoderma DNA was used. No PCR amplification product was observed when other Ganoderma species DNA was used in PCR amplification with these primer pairs. Three specific restriction enzyme sites were identified in the ITS and intergenic spacer (IGS1) regions. The restriction enzymes MluI, SacI and HinfI were used to digest the ITS-PCR product and restriction enzymes TfiI, ScaI and HincII were used to digest the IGS1-PCR product. Of the three restriction enzymes used in each rDNA region, MluI specifically digested the ITS regions, and TfiI specifically digested the IGS1 region of oil palm Ganoderma. Analysis of the published ITS nucleotide sequences of 31 Ganoderma species showed that the MluI restriction site was not present in other Ganoderma species. The use of both specific primers and restriction enzyme analysis can be applied as a standard protocol to identify pathogenic Ganoderma in oil palm. In this study, the use of specific primers and PCR-RFLP analyses of the rDNA gave consistent results for the characterisation of pathogenic Ganoderma, and indicated that Ganoderma strains associated with BSR disease in oil palms belong to a single species.     

Involvement and interaction of various signaling compounds on the plant metabolic events during defense response,resistance to stress factors,formation of secondary metabolites and their molecular aspects

Plants are a nearly unlimited source of phytochemicals. The plants produce various secondary metabolites, which are useful in its interaction with the environment, various stress factors and development of resistance against pathogen attack. A wide array of external stimuli are capable of triggering changes in the plant cell which leads to a cascade of reactions, ultimately resulting in the formation and accumulation of secondary metabolites which helps the plant to overcome the stress factors. The biotic and abiotic elicitors can result in an enhancement of the secondary metabolite production. The stimuli are perceived by receptors, which then result in the activation of the secondary messengers. These then transmit the signals into the cell through the signal transduction pathways leading to gene expression and biochemical changes. There is interplay of the signaling molecules also which regulates the entire pathway. This review is oriented towards the factors, which influence signal transduction pathway(s) with special reference to polyamines, calcium, jasmonates, salicylates, nitric oxide and ethylene. The interplay of these components to elicit a defense response is discussed. Molecular aspects of disease resistance and regulation of plant secondary metabolism has also been presented.     

Phytohormonal changes in intact shoots of wheat and oilseed rape treated with the acylcyclohexanedione growth retardant prohexadione calcium

The effects of the acylcyclohexanedione-type growth retardant prohexadione calcium on seedling growth and endogenous levels of immunoreactive phytohormone-like substances in shoots of wheat ( Triticum aestivum L. cv. Kanzler) and oilseed rape ( Brassica napus L. ssp. napus cv. Lirajet) were studied. After treatment of seedlings with increasing retardant concentrations in hydroponics, plant height and fresh weight of shoots were reduced by up to 40%. Concomitantly, the amount of immunoreactive gibberellins decreased, on a fresh weight basis, when compared with levels in the shoots of control plants. In contrast, the levels of abscisic acid and dihydrozeatin riboside and isopentenyladenosine-type cytokinins were considerably elevated by the growth retardant. The content of 3-indoleacetic acid decreased slightly. These results suggest that, in addition to its effect on gibberellin content, prohexadione calcium also influences the levels of endogenous abscisic acid and cytokinins.     

Physiological evaluation of drought stress tolerance and recovery in Verbascum sinuatum plants treated with methyl jasmonate,salicylic acid and titanium dioxide nanoparticles

Abstract

The genus Verbascum L. (Scrophulariaceae) includes medicinal plants, which have several bioactive compounds especially saponins. The possible recovery ability of Verbascum sinuatum from drought stress conditions was assessed by using salicylic acid (SA), methyl jasmonate (MJA) and titanium dioxide nanoparticles (TiO₂NPs) as plant growth regulators (PGRs) in liquid culture media. Thirty days-old plants were exposed to different concentrations of polyethylene glycol (PEG-6000) for creating artificial drought conditions (0, ?0.3, and ?0.6?MPa osmotic potential) and also treated with 200?µM methyl jasmonate (MJA), 100?µM salicylic acid (SA) and 20?ppm TiO₂ nanoparticles (TiO₂NPs). Results showed that the growth parameters and the content of photosynthetic pigments decreased at higher drought level (?0.6?MPa). However, SA and TiO₂NPs alleviated the adverse effects of drought stress by increasing water stress tolerance through promotion of enzymatic and nonenzymatic antioxidant defense systems. MJA negatively affected the growth parameters and increased the content of malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and total saponin and also the activity of peroxidase (POD) and polyphenol oxidase (PPO). Based on the results obtained from this study, the recovery treatments mainly affected the defense-related metabolism in Verbasum sinuatum plants.     

Short Communication: Induction of systemic resistance and salicylic acid accumulation in Oryza sativa,L. in the biological suppression of rice blast caused by treatments with Pseudomonas spp.

Two strains of rice-associated pseudomonads Pseudomonas fluorescens 7-14 and P. putida V14i caused an induced systemic resistance (ISR) in three cultivars of rice. ISR response coincided with increased levels of salicylic acid and biological suppression (25%) of rice blast disease. When the strains of the bacteria with lacZY molecular marker tracking system were applied to rice seeds as a seed-coat, they persisted on rice roots for entire duration of the crop (110 days) but migrated to the rice shoot only up to 14 to 16 days. Bacteria applied as a root-dip did not migrate to aerial parts of the rice plant. Bacteria infiltrated into the rice stem survived for 20 days after the treatment and were not detected on the surface of the stem. It is suggested that the ISR triggered by these bacteria which were spatially separated from the rice blast pathogen, is an important mechanism for the biological suppression of rice blast.     

The effects of abscisic acid and methyl jasmonate on 1-aminocyclopropane 1-carboxylic acid conversion to ethylene in hypocotyl segments of sunflower seedlings,and their control by calcium and calmodulin

The conversion of 1-aminocyclopropane 1-carboxylic acid (ACC) to ethylene by hypocotyl segments of sunflower (Helianthus annuus L.) seedlings was inhibited by abscisic acid (ABA) and methyl jasmonate (Me-Ja), and this inhibitory effect increased with increasing concentration of both growth regulators. On the contrary, CaCl, enhanced ACC conversion to ethylene at the concentrations of 10^-4 M and 5 x 10^-4 M, however lower and higher concentrations had no significant action. CaCl, (5 x 10^-4M) seemed to magnify the inhibition of the reaction induced by ABA, whereas it reduced (5 x 10^-4M) and even abolished (10^-3M) the inhibitory action of Me-Ja. The results obtained with a Ca²⁺ chelator (EGTA), a Ca²⁺ channel blocker (nifedipine) and calmodulin antagonists (W7 and TFP), given in association with ABA or Me-Ja, suggested that calcium was involved in the inhibition of ACC conversion to ethylene by ABA and Me-Ja through an interaction with calmodulin. However, the mechanism of action of the two growth regulators seemed to be different, since all treatments which resulted in a decrease in cytosolic Ca²⁺ concentration or in calmodulin action induced a decrease in the effect of ABA and an increase in the effect of Me-Ja.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane 1-carboxylic acid - EFE ethylene for enzyme - EGTA ethylene glycol-bis-2-aminoethyl tetraacetic acid - Me-Ja methyl jasmonate - NIF nifedipine - TFP trifluoperazine dihydrochloride - W7 N-(6-aminohexyl)5-chloro-l-naphthalenesulfonamide hydrochloride     

Biofortification of crops with seven mineral elements often lacking in human diets – iron, zinc, copper, calcium, magnesium, selenium and iodine

The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of 'promoter' substances, such as ascorbate, β-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of 'antinutrients', such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.     

Growth of Arabidopsis seedlings on high fungal doses of Piriformospora indica has little effect on plant performance,stress, and defense gene expression in spite of elevated jasmonic acid and jasmonic acid-isoleucine levels in the roots

The endophytic fungus Piriformospora indica colonizes the roots of many plant species including Arabidopsis and promotes their performance, biomass, and seed production as well as resistance against biotic and abiotic stress. Imbalances in the symbiotic interaction such as uncontrolled fungal growth result in the loss of benefits for the plants and activation of defense responses against the microbe. We exposed Arabidopsis seedlings to a dense hyphal lawn of P. indica. The seedlings continue to grow, accumulate normal amounts of chlorophyll, and the photosynthetic parameters demonstrate that they perform well. In spite of high fungal doses around the roots, the fungal material inside the roots was not significantly higher when compared with roots that live in a beneficial symbiosis with P. indica. Fifteen defense- and stress-related genes including PR2, PR3, PAL2, and ERF1 are only moderately upregulated in the roots on the fungal lawn, and the seedlings did not accumulate H₂O₂/radical oxygen species. However, accumulation of anthocyanin in P. indica-exposed seedlings indicates stress symptoms. Furthermore, the jasmonic acid (JA) and jasmonic acid-isoleucine (JA-Ile) levels were increased in the roots, and consequently PDF1.2 and a newly characterized gene for a 2-oxoglurate and Fe²⁺-dependent oxygenase were upregulated more than 7-fold on the dense fungal lawn, in a JAR1- and EIN3-dependent manner. We conclude that growth of A. thaliana seedlings on high fungal doses of P. indica has little effect on the overall performance of the plants although elevated JA and JA-Ile levels in the roots induce a mild stress or defense response.