Volatile organic compounds in the strongly fragrant fern genus Melpomene (Polypodiaceae)

Volatile organic compounds (VOCs) are common among plants, both as attractants for pollinators and as defence against herbivores. While much studied among flowering plants, the prevalence and function of VOCs among ferns is little known. Using headspace sorption and gas chromatography, we analysed the VOCs of dried specimens of six species of grammitid fern (Polypodiaceae), including two species of the genus Melpomene, which is characterised by a distinctive sweet smell. We identified 38 VOCs, including 22 not previously recorded among ferns. The two species of Melpomene had distinct VOC cocktails, including 12 substances not found in the other four studied genera, mainly involving fatty acid derivatives (FADs) and aromatics. We propose that these VOCs have, at least in part, a function in herbivore defence, but note that the VOC bouquet of Melpomene is distinct from that typically found in angiosperms.     

Aggressive and Docile Colony Defence Patterns in Apis mellifera. A Retreater–Releaser Concept

Colony defence in Apis mellifera involves a variety of traits ranging from ‘aggressive’ (e.g. entrance guarding, recruitment of flying guards) to ‘docile’ (e.g. retreating into the nest) expression. We tested 11 colonies of three subspecies (capensis, scutellata, carnica) regarding their defensiveness. Each colony was selected as reportedly ‘aggressive’, ‘intermediate’ or ‘docile’ and consisted of about 10,000 bees. We applied three stimulation regimes (mechanical disturbance, exposure to alarm pheromones, and the combination of both) and measured their behaviours by tracking the rates of outflying bees at the entrance sites of the test hives. We provided evidence that for mechanical disturbances the test colonies resolved into two response types, if the ‘immediate’ defence response, assessed in the first minute of stimulation, was taken as a function of foraging: ‘releaser’ colonies allocated flying guards, ‘retreater’ colonies reduced the outside-hive activities. This division was observed irrespective of the subspecies membership and maintained in even roughly changing environmental conditions. However, if pheromone and mechanical stimulation were combined, the variety of colony defensiveness restricted to two further types irrespective of the subspecies membership: six of nine colonies degraded their rate of flying defenders with increasing foraging level, three of the colonies extended their ‘aggressiveness’ by increasing the defender rate with the foraging level. Such ‘super-aggressive’ colonies obviously are able to allocate two separate recruitment pools for foragers and flying defenders.     

Nep1-like proteins from plant pathogens: recruitment and diversification of the NPP1 domain across taxa

An emerging group of proteins found in many plant pathogens are related to their ability to cause plant cell death. These proteins may be identified by the presence of a common NPP1 (necrosis-inducing Phytophthora protein) domain, and have collectively been named NLPs (Nep1-like proteins). The NLPs are distinguished by their wide distribution across taxa and their broad spectrum of activity against dicotyledonous plants. The function of NLPs is not known but there is strong evidence that they may act as positive virulence factors, accelerating disease and pathogen growth in plant hosts. Interest in NLPs is gaining momentum as more members of this protein family are discovered in more species of plant pathogens.     

The cantharidin-induced oxidative burst in tobacco BY-2 cell suspension cultures

Summary The in vivo induction of H₂O₂ production was tested on tobacco cell suspension cultures (Nicotiana tabacum cv. Bright Yellow-2). The measurement of H₂O₂ was based on the oxidation of 3,5-dichloro-2-hydroxybenzensulfonic acid by endogenous peroxidases and spectrophotometric detection after reaction with 4-aminoanti-pyrine. The phosphatase inhibitor cantharidin induced a transient increase in H₂O₂ synthesis. The timing of the H₂O₂ production, the level of induction by cantharidin and the background H₂O₂ production were dependent on the tobacco cell concentration used. A concentration curve of cantharidin revealed saturating kinetics for the H₂O₂ detection (E₅₀=46 to 70 M, E_max=101 to 128 mol/h·g fresh weight). An inhibitor study with the tobacco BY-2 cells showed high inhibitions of the H₂O₂ induction with the flavin analogues diphenylene iodonium (I₅₀=1.26M) and acridine orange and with membrane-permeative thiol reagents (N-ethyl maleimide, N-pyrene maleimide, iodoacetate); whereas the nonpermeative thiol reagentp-chloromercuribenzoic acid was ineffective. Therefore, the induction of H₂O₂ production with phosphatase inhibitors (cantharidin) showed comparable properties to the elicitor-induced oxidative-burst response in other plant cells.Abbreviations AcOr acridine orange - AOS active-oxygen species - BY-2 Bright Yellow-2 - pCMBS p-chloromercuribenzoic acid - DHBS 3,5-dichloro-2-hydroxybenzenesulfonic acid - DMSO dimethylsulfoxide - DPI diphenylene iodonium - EtOH ethanol - H₂O₂ hydrogen peroxide - HRP horseradish peroxidase - MS Murashige and Skoog - NEM N-ethyl maleimide - NPM N-pyrene maleimide - O ₂ ^– superoxide - SOD superoxide dismutase     

Harpin induces mitogen-activated protein kinase activity during defence responses in Arabidopsis thaliana suspension cultures

Elicitation of Arabidopsis thaliana (L.) Heynh. suspension cultures with the bacterial protein harpin (from Pseudomonas syringae pv. syringae) induced the activation of two kinases of 39 and 44 kDa, as demonstrated by in-gel kinase assays using myelin basic protein (MBP) as a substrate. Both these kinases appeared to be tyrosine-phosphorylated upon activation, as demonstrated by treatment with tyrosine phosphatase and immunoprecipitation using an anti-phosphotyrosine monoclonal antibody. An inhibitor of mammalian mitogen-activated protein kinase (MAPK) activation, PD98059, inhibited harpin-induced MBPK activation, but did not inhibit the activity of these kinases. PD98059 also inhibited harpin-induced programmed cell death and defence gene expression, suggesting the involvement of harpin-induced MAPKs in defence responses in Arabidopsis thaliana. Received: 23 February 1999 / Accepted: 22 July 1999     

Differential defoliation of Eucalyptus grandis arises from indiscriminant oviposition and differential larval survival

1 The influence of six open-pollinated families (OPFs) of Eucalyptus grandis on both the growth and development of larvae and the oviposition preference of a paropsine chrysomelid ( Paropsis atomaria ) was investigated. The OPFs had previously been identified as differing in their susceptibility to defoliation by P. atomaria in forestry progeny trials.
2 Oviposition preference for resistant and susceptible foliage was tested using binary choice tests. These tests did not demonstrate any significant preference for either resistant or susceptible open-pollinated material indicating that adult host preference for susceptible trees was not a likely cause of differential defoliation.
3 Quantification and analysis of growth and development parameters for all larval stages of P. atomaria showed that feeding on genetic material identified as resistant resulted in a significant reduction of relative growth rate of first instar larvae and an alteration to normal feeding behaviour. There was also a trend towards increased larval mortality on resistant E. grandis .
4 We argue that although the magnitude of these effects was minor, interactions with additional biotic and abiotic sources of mortality in the field have the potential, when magnified over successive generations, to result in significant variation in defoliation of host genotypes in the field.     

Thaxtomin A induces programmed cell death in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> suspension-cultured cells

Thaxtomin A is the main phytotoxin produced by Streptomyces scabiei, the causative agent of common scab disease of potato. Pathogenicity of S. scabiei is dependent on the production of thaxtomin A which is required for the development of disease symptoms, such as growth inhibition and cell death. We investigated whether thaxtomin A-induced cell death was similar to the hypersensitive cell death that often occurs in response to specific pathogens or phytotoxins during the so-called hypersensitive response (HR). We demonstrated that thaxtomin A induced in Arabidopsis thaliana suspension-cultured cells a genetically controlled cell death that required active gene expression and de novo protein synthesis, and which involved fragmentation of nuclear DNA, a characteristic hallmark of apoptosis. The thaxtomin A-induced form of programmed cell death (PCD) was not a typical HR, since defence responses generally preceding or associated with the HR, such as rapid medium alkalization, oxidative burst and expression of defence-related genes PR1 and PDF1.2, were not observed in plant cells following addition of thaxtomin A. Thaxtomin A has been shown to inhibit cellulose biosynthesis (Scheible et al. in Plant Cell 15:1781, 2003). We showed that isoxaben, a specific inhibitor of cellulose biosynthesis, also induced in Arabidopsis cell suspensions a PCD similar to that induced by thaxtomin A. These data suggested that rapid changes in the plant cell wall composition and organization can induce PCD in plant cells. We discuss how rapid inhibition of cellulose biosynthesis may trigger this process.     

Root-to-shoot signalling: apoplastic alkalinization,a general stress response and defence factor in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis>)

Summary. We used a noninvasive microprobe technique to record in substomatal cavities of barley leaves the apoplastic pH response to different stress situations. When K⁺ (or Na⁺) activity at the roots of intact plants was increased from 1 to 50 mM, the leaf apoplastic pH increased by 0.4 to 0.6 units within 8 to 12 min when stomata were open, and within 15 to 20 min when stomata were closed. This reaction was accompanied by a correlative increase in K⁺ activity. Addition of 1 μM abscisic acid caused an apoplastic alkalinization of 0.5 to 0.8 units, and low temperatures (4 °C) increased pH by 0.2 to 0.3 units. Addition of 100 mM sorbitol or pH changes in the range 4.0 to 7.9 had no effect, ruling out that osmotic potential and/or pH is the carried signal. On detached leaves, the same treatments yielded qualitatively similar results, suggesting that the xylem is the most likely signal path. Following the attack of powdery mildew, the apoplastic pH of barley leaves substantially increases. We demonstrate that in susceptible barley, pretreatment (soil drench) with the resistance-inducing chemical benzo- (1,2,3)thiadiazole-7-carbothioic acid S-methyl ester markedly enhances this pH response. This is consistent with previous finding that apoplastic alkalinization is related to the degree of resistance towards this fungus. Correspondence and reprints: Botanisches Institut I, Justus-Liebig-Universit?t, Senckenbergstra?e 17, 35390 Gie?en, Federal Republic of Germany.