西花蓟马的鉴别及其与近缘种的区别

西花蓟马是我国2 0 0 3年在北京新发现的外来入侵害虫,因虫体很小鉴定困难。该文提供了西花蓟马详细的形态鉴别特征,同时给出了与西花蓟马相似的烟蓟马、花蓟马和佛罗里达花蓟马共4种花蓟马的鉴定检索表。     

Behavioural and chemical evidence of a male‐produced aggregation pheromone in the flower thrips Frankliniella intonsa

The response of adult flower thrips Frankliniella intonsa (Trybom) (Thysanoptera: Thripidae) to conspecifics is investigated in Y‐tube olfactometer bioassays. The results show that both males and females are attracted to the odours of adult males, which indicates a male‐produced aggregation pheromone in this species. Gas chromatography‐mass spectroscopy analyses of headspace volatiles collected on solid‐phase microextraction fibres show that two major components and six minor components are present in volatiles from males but not in females. Further gas chromatography‐mass spectroscopy analyses reveal that the two major components in head‐space volatiles produced by F. intonsa males are the same compounds that are reported in volatiles of Frankliniella occidentalis males: (R)‐lavandulyl acetate and neryl (S)‐2‐methylbutanoate. However, the quantity of these two compounds in the volatiles differs between the species.     

Dehydration yields distinct transcriptional shifts associated with glycogen metabolism and increases feeding in the western flower thrips,Frankliniella occidentalis

We examined water balance characteristics and the influence of desiccating conditions on the physiology and behavior of adult western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Western flower thrips are globally invasive and likely to contend with shifts in water availability across their expansive geographic range. Basic water balance characteristics, including water mass and dry mass, were established for adult males and females, revealing a distinct sexual dimorphism wherein females are larger, and males retain a larger percentage of their body mass as water. Males lose relative water mass more quickly and their survival times are shorter compared to females. RNA-seq analysis identified significant enrichment of a multitude of factors including carbohydrate transport and metabolism in dehydrated males and females. This was validated by altered glycogen levels, suggesting a rapid depletion in glycogen during dehydration. The probability of thrips feeding significantly increases when desiccation occurs, potentially to replenish water content and nutrient reserves. Our results establish the fundamental water balance characteristics of adult thrips and indicate that dehydration significantly influences the survivorship and feeding behavior of thrips; all of which being crucial factors that contribute to their capacity as vectors for plant pathogens.     

Functional characterization of a methionine gamma-lyase in Arabidopsis and its implication in an alternative to the reverse trans-sulfuration pathway

Methionine gamma-lyase (MGL) catalyzes the degradation of L-methionine to alpha-ketobutyrate, methanethiol and ammonia. The Arabidopsis (Arabidopsis thaliana) genome includes a single gene (At1g64660) encoding a protein (AtMGL) with approximately 35% identity to bacterial and protozoan MGLs. When overexpressed in Escherichia coli, AtMGL allowed growth on L-methionine as sole nitrogen source and conferred a high rate of methanethiol emission. The purified recombinant protein exhibited a spectrum typical of pyridoxal 5'-phosphate enzymes, and had high activity toward l-methionine, L-ethionine, L-homocysteine and seleno-L-methionine, but not L-cysteine. Quantitation of mRNA showed that the AtMGL gene is expressed in aerial organs and roots, and that its expression in leaves was increased 2.5-fold by growth on low sulfate medium. Emission of methanethiol from Arabidopsis plants supplied with 10 mM L-methionine was undetectable (<0.5 nmol min(-1) g(-1) FW), suggesting that AtMGL is not an important source of volatile methanethiol. Knocking out the AtMGL gene significantly increased leaf methionine content (9.2-fold) and leaf and root S-methylmethionine content (4.7- and 7-fold, respectively) under conditions of sulfate starvation, indicating that AtMGL carries a significant flux in vivo. In Arabidopsis plantlets fed L-[(35)S]methionine on a low sulfate medium, label was incorporated into protein-bound cysteine as well as methionine, but incorporation into cysteine was significantly (30%) less in the knockout mutant. These data indicate that plants possess an alternative to the reverse trans-sulfuration pathway (methionine-->homocysteine-->cystathionine-->cysteine) in which methanethiol is an intermediate.     

Potential role of annexin AnnAt1 from Arabidopsis thaliana in pH-mediated cellular response to environmental stimuli

Plant annexins, Ca(2+)- and membrane-binding proteins, are probably implicated in the cellular response to stress resulting from acidification of cytosol. To understand how annexins can contribute to cellular ion homeostasis, we investigated the pH-induced changes in the structure and function of recombinant annexin AnnAt1 from Arabidopsis thaliana. The decrease of pH from 7.0 to 5.8 reduced the time of the formation of ion channels by AnnAt1 in artificial lipid membranes from 3.5 h to 15-20 min and increased their unitary conductance from 32 to 63 pS. These changes were accompanied by an increase in AnnAt1 hydrophobicity as revealed by hydrophobicity predictions, by an increase in fluorescence of 2-(p-toluidino)naphthalene-6-sulfonic acid (TNS) bound to AnnAt1 and fluorescence resonance energy transfer from AnnAt1 tryptophan residues to TNS. Concomitant lipid partition of AnnAt1 at acidic pH resulted in its partial protection from proteolytic digestion. Secondary structures of AnnAt1 determined by circular dichroism and infrared spectroscopy were also affected by lowering the pH from 7.2 to 5.2. These changes were characterized by an increase in beta-sheet content at the expense of alpha-helical structures, and were accompanied by reversible formation of AnnAt1 oligomers as probed by ultracentrifugation in a sucrose gradient. A further decrease of pH from 5.2 to 4.5 or lower led to the formation of irreversible aggregates and loss of AnnAt1 ionic conductance. Our findings suggest that AnnAt1 can sense changes of the pH milieu over the pH range from 7 to 5 and respond by changes in ion channel conductance, hydrophobicity, secondary structure of the protein and formation of oligomers. Further acidification irreversibly inactivated AnnAt1. We suggest that the pH-sensitive ion channel activity of AnnAt1 may play a role in intracellular ion homeostasis.     

The level of jasmonic acid in Arabidopsis thaliana and Phaseolus coccineus plants under heavy metal stress

The effect of heavy metal stress as a potent abiotic elicitor for triggering an accumulation of jasmonic acid (JA) was investigated. Copper and cadmium in in vivo conditions induced accumulation of jasmonates in mature leaves of Arabidopsis thaliana and in young and oldest Phaseolus coccineus plants. The dynamics of jasmonate accumulation showed a biphasic character in both plants. In the first phase, after 7 (A. thaliana) or 14 h (P. coccineus) of exposure to Cu or Cd, a rapid increase of JA level occurred, followed by a rapid decrease observed during 7 successive hours. In the next phase, a repeated but slow increase of JA content occurred. The heavy metal stress induced in particular a more stable (3R,7R) form of jasmonates. These results indicate that JA is connected with the mechanism of toxic action of both heavy metals in plants, differentially reacting to exogenous JA and possessing variable dynamics depending on the plants studied as well as their growth stage.     

Increased Resistance to Extracellular Cation Block by Mutation of the Pore Domain of the Arabidopsis Inward-rectifying K+ Channel KAT1

Inward-rectifying potassium channels in plant cells provide important mechanisms for low-affinity K⁺ uptake and membrane potential control in specific cell types, including guard cells, pulvinus cells, aleurone cells and root hair cells. K⁺ channel blockers are potent tools for studying the physiological functions and structural properties of K⁺ channels. In the present study the structural and biophysical mechanisms of Cs⁺ and TEA⁺ block of a cloned Arabidopsis inward-rectifying K⁺ channel (KAT1) were analyzed. Effects of the channel blockers Cs⁺ and TEA⁺ were characterized both extracellularly and intracellularly. Both external Cs⁺ and TEA⁺ block KAT1 currents. A mutant of KAT1 (``m2KAT1'; H267T, E269V) was produced by site-directed mutagenesis of two amino acid residues in the C-terminal portion of the putative pore (P) domain. This mutant channel was blocked less by external Cs⁺ and TEA⁺ than the wild-type K⁺ channel. Internal TEA⁺ and Cs⁺ did not significantly block either m2KAT1 or KAT1 channels. Other properties, such as cation selectivity, voltage-dependence and proton activation did not show large changes between m2KAT1 and KAT1, demonstrating the specificity of the introduced mutations. These data suggest that the amino acid positions mutated in the inward-rectifying K⁺ channel, KAT1, are accessible to external blockers and may be located on the external side of the membrane, as has been suggested for outward-rectifying K⁺ channels. Received: 31 July 1995/Revised: 5 January 1996     

Salt tolerance requires cortical microtubule reorganization in Arabidopsis

Although the results of some studies indicate that salt stress affects the organization of microtubules, it remains an open question whether microtubules play an active role in the plant's ability to withstand salt stress. In the present study, we showed that salt stress-induced wild-type Arabidopsis seedling roots display right-handed skewed growth and depolymerization of the cortical microtubules. The results of a long-term observational study showed that cortical microtubules depolymerized then reorganized themselves under salt stress. Stabilization of microtubules with paclitaxel resulted in more seedling death under salt stress, while disruption of microtubules with oryzalin or propyzamide rescued seedlings from death. Seedlings in which the cortical microtubules were reorganized did not succumb to salt stress. These results suggest that both depolymerization and reorganization of the cortical microtubules are important for the plant's ability to withstand salt stress. Depolymerizing microtubules by drugs rescues seedlings from death under salt stress. This rescue effect was abolished by removing calcium from the medium or treatment with a calcium channel inhibitor. Depolymerization of the microtubules is followed by an increase in the free cytoplasmic calcium concentration. The addition of calcium to the growth medium increased the number of seedlings in which recovery of the cortical microtubules occurred, whereas the removal of calcium decreased the number of seedlings in which recovery occurred. Therefore, depolymerization of the cortical microtubules raises intracellular calcium concentrations, while reorganization of the cortical microtubules and seedling survival may be mediated by calcium influx in salt stress.     

Permeability of Boric Acid Across Lipid Bilayers and Factors Affecting It

Boron enters plant roots as undissociated boric acid (H₃BO₃). Significant differences in B uptake are frequently observed even when plants are grown under identical conditions. It has been theorized that these differences reflect species differences in permeability coefficient of H₃BO₃ across plasma membrane. The permeability coefficient of boric acid however, has not been experimentally determined across any artificial or plant membrane. In the experiments described here the permeability coefficient of boric acid in liposomes made of phosphatidylcholine was 4.9 × 10⁻⁶ cm sec⁻¹, which is in good agreement with the theoretical value. The permeability coefficient varied from 7 × 10⁻⁶ to 9.5 × 10⁻⁹ cm sec⁻¹ with changes in sterols (cholesterol), the type of phospholipid head group, the length of the fatty acyl chain, and the pH of the medium. In this study we also used Arabidopsis thaliana mutants which differ in lipid composition to study the effect of lipid composition on B uptake. The chs1-1 mutant which has lower proportion of sterols shows 30% higher B uptake compared with the wild type, while the act1-1 mutant which has an increased percentage of longer fatty acids, exhibited 35% lower uptake than the wild type. Lipid composition changes in each of the remaining mutants influenced B uptake to various extents. These data suggest that lipid composition of the plasma membrane can affect total B uptake. Received: 15 October 1999/Revised: 11 February 2000     

Biological control of the western flower thrips,Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in glasshouse sweet peppers with Orius spp. (Hemiptera: Anthocoridae). A comparative study between O. niger (Wolff) and O. insidiosus (Say)

In a comparative study for biocontrol of the western flower thrips (WFT) in commercial sweet peppers Orius spp. effectively controlled WFT. The introduced native Orius niger had replaced the introduced imported Orius insidiosus by the end of the growing season.     

AHK5 histidine kinase regulates root elongation through an ETR1-dependent abscisic acid and ethylene signaling pathway in Arabidopsis thaliana

The Arabidopsis thaliana genome encodes a small family of histidine (His) protein kinases, some of which have redundant functions as ethylene receptors, whereas others serve as cytokinin receptors. The most poorly characterized of these is authentic histidine kinase 5 (AHK5; also known as cytokinin-independent 2, CKI2). Here we characterize three independent ahk5 mutants, and show that they have a common phenotype. Our results suggest that AHK5 His-kinase acts as a negative regulator in the signaling pathway in which ethylene and ABA inhibit the root elongation through ETR1 (an ethylene receptor).     

Consequences of the overproduction of methyl jasmonate on seed production, tolerance to defoliation and competitive effect and response of Arabidopsis thaliana

* Accumulation of methyl jasmonate (MeJA) after herbivore attack in plants is associated with the induction of defenses that can benefit fitness, but are costly to express; effects often explored using exogenous application of jasmonates. * Here I explored the consequences of the overexpression of MeJA on seed production, tolerance to defoliation and competitive effect and response, using a genotype of Arabidopsis thaliana that overexpresses jasmonic acid carboxyl methyltransferase (JMT) and contains threefold higher levels of MeJA than wild-type plants. * Without competition, JMT plants produced 37-40% less total seed mass than vector controls or wild-type plants, and had reduced seed germination. Defoliation reduced height more strongly in wild-type than in JMT plants, but reduced total seed production equally. In a competition experiment, the presence of a neighbor reduced fitness more strongly in wild-type than in JMT plants, but JMT plants exhibited dampened opportunity costs and benefits of induction with jasmonic acid of itself or its neighbor. This may have related to the higher constitutive expression but reduced inducibility of jasmonate-mediated defenses, including trypsin inhibitors, exhibited by JMT plants. * In natural plant populations, overexpression of MeJA-mediated responses should be beneficial to resistance to herbivores, pathogens and competitors, but is directly costly to fitness and probably constrains plasticity in response to changing environmental conditions.     

西花蓟马取食与机械损伤对菜豆叶片抗氧化系统的影响

本文研究了西花蓟马Frankliniella occidentalis(Pergande)取食和机械损伤诱导对菜豆抗氧化系统的影响,比较了不同损伤形式诱导的抗氧化酶活力和抗氧化物质含量的变化差异。结果表明,西花蓟马取食和机械损伤均可诱导菜豆叶片内过氧化物酶(POD)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)3种抗氧化酶活性有不同程度的升高,但两种处理诱导的抗氧化酶活性变化规律不完全相同,各种酶活性达到最高点时间不同,西花蓟马取食对抗氧化酶活力的诱导作用大于机械损伤的。两种处理诱导下的类胡萝卜素的含量变化不大,但不论西花蓟马取食还是机械损伤均导致菜豆叶片内类黄酮和总酚含量整体呈下降趋势,西花蓟马的取食诱导的下降幅度大于机械损伤的。因此,西花蓟马取食诱导明显高于机械损伤对菜豆抗氧化系统的影响。     

Positive association between thrips and spider mites in seedling cotton

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Pre-conditioning the epigenetic response to high vapor pressure deficit increases the drought tolerance of Arabidopsis thaliana

Epigenetic modification of the genome via cytosine methylation is a dynamic process that responds to changes in the growing environment. This modification can also be heritable. The combination of both properties means that there is the potential for the life experiences of the parental generation to modify the methylation profiles of their offspring and so potentially to “pre-condition” them to better accommodate abiotic conditions encountered by their parents. We recently identified high vapor pressure deficit (vpd)-induced DNA methylation at 2 gene loci in the stomatal development pathway and an associated reduction in leaf stomatal frequency.¹ Here, we test whether this epigenetic modification pre-conditioned parents and their offspring to the more severe water stress of periodic drought. We found that 3 generations of high vpd-grown plants were better able to withstand periodic drought stress over 2 generations. This resistance was not directly associated with de novo methylation of the target stomata genes, but was associated with the cmt3 mutant’s inability to maintain asymmetric sequence context methylation. If our finding applies widely, it could have significant implications for evolutionary biology and breeding for stressful environments.     

A Kinetic Model with Ordered Cytoplasmic Dissociation for SUC1, an Arabidopsis H+/Sucrose Cotransporter Expressed in Xenopus Oocytes

To elucidate the kinetic properties of the Arabidopsis H⁺/sucrose cotransporter, SUC1, with respect to transmembrane voltage and ligand concentrations, the transport system was heterologously expressed in Xenopus laevis oocytes. Steady-state plasma membrane currents associated with transport of sucrose were measured with two-electrode voltage clamp over the voltage range −180 to +40 mV as a function of extracellular pH and sugar concentrations. At any given voltage, currents exhibited hyperbolic kinetics with respect to extracellular H⁺ and sugar concentrations, and this enabled determination of values for the maximum currents in the presence of each ligand (i ^H _max , i ^S _max for H⁺ and sucrose) and of the ligand concentrations eliciting half-maximal currents (K ^H _m , K ^S _m ). The i ^H _max and i ^S _max exhibited marked and statistically significant increases as a function of increasingly negative membrane potential. However, the K ^H _m and K ^S _m decreased with increasingly negative membrane potential. Furthermore, at any given voltage, i ^S _max increased and K ^S _m decreased as a function of the external H⁺ concentration. Eight six-state carrier models—which comprised the four possible permutations of intracellular and extracellular ligand binding order, each with charge translocation on the sugar-loaded or -unloaded forms of the carrier—were analyzed algebraically with respect to their competence to account for the ensemble of kinetic observations. Of these, two models (first-on, first-off and last-on, first-off with respect to sucrose binding as it passes from outside to inside the cell and with charge translocation on the loaded form of the carrier) exhibit sufficient kinetic flexibility to describe the observations. Combining these two, a single model emerges in which the binding on the external side can be random, but it can only be ordered on the inside, with the sugar dissociating before the proton. Received: 23 January 1996/Revised: 16 April 1997