Microspore embryogenesis in barley: anther pre-treatment stimulates plant defence gene expression

Microspore embryogenesis (ME) is a process in which the gametophytic pollen programme of the microspore is reorientated towards a new embryo sporophytic programme. This process requires a stress treatment, usually performed in the anther or isolated microspores for several days. Despite the universal use of stress to induce ME, very few studies have addressed the physiological processes that occur in the anther during this step. To further understand the processes triggered by stress treatment, we followed the response of anthers by measuring the expression of stress-related genes in two barley (Hordeum vulgare L.) cultivars differing in their ME response. Genes encoding enzymes involved in oxidative stress (glutathione-S-transferase, GST; oxalate oxidase, OxO), in the synthesis of jasmonic acid (13-lipoxygenase, Lox; allene oxide cyclase, AOC; allene oxide synthase, AOS) and in the phenylpropanoid pathway (phenylalanine ammonia lyase, PAL), as well as those encoding PR proteins (Barwin, chitinase 2b, Chit 2b; glucanase, Gluc; basic pathogenesis-related protein 1, PR1; pathogenesis-related protein 10, PR10) were up-regulated in whole anthers upon stress treatment, indicating that anther perceives stress and reacts by triggering general plant defence mechanisms. In particular, both OxO and Chit 2b genes are good markers of anther reactivity owing to their high level of induction during the stress treatment. The effect of copper sulphate appeared to limit the expression of defence-related genes, which may be correlated with its positive effect on the yield of microspore embryos.     

To complete their life cycle, pathogenic nematode-bacteria complexes deter scavengers from feeding on their host cadaver

The life cycle of commercially used molluscicidal rhabditid nematodes Phasmarhabditis hermaphrodita and entomopathogenic steinernematid nematodes is similar: infective stages carry symbiotic bacteria, which kill their host. Nematodes complete their life cycle feeding on the proliferating symbiont and the host tissue. After 1-2 weeks, new infective stages carrying the bacteria leave the host cadaver in search of new hosts. The removal of invertebrate cadavers by scavengers is extremely fast and represents a severe threat to the developing nematodes.Two-choice trials were used to assess prey choice of the generalist predator/scavenger Pterostichus melanarius (Coleoptera: Carabidae) between Deroceras reticulatum (Mollusca: Agriolimacidae) slugs or wax moth Galleria mellonella (Lepidoptera: Pyralidae) larvae killed by infection of P. hermaphrodita/Steinernema affine and control killed by freezing. We demonstrate that the presence of either of the two nematodes tested deters the beetles from consuming infected cadavers. As P. hermaprodita cannot infect an insect host, we hypothesise the deterrent effect being an evolutionary adaptation of the nematode/bacteria complex rather than the ability of the beetles to avoid potentially infective cadavers.     

Expression profiling in HcrVf2-transformed apple plants in response to Venturia inaequalis

Apple scab resistance is one of the most well-characterized plant–pathogen interactions in a woody plant species. While the HcrVf2 gene from the wild apple Malus floribunda 821 has proved capable of conferring scab resistance to the susceptible cv. Gala after genetic transformation, its identification represents only the first step in understanding the molecular mechanisms and, hence, the network of genes underlying the defence response. We used a PCR-based suppression subtractive hybridization to identify apple genes that are differentially expressed after Venturia inaequalis inoculation. Subtractive hybridization was performed between cDNA from challenged leaves of HcrVf2-resistant transgenic Gala and susceptible cv. Gala plants. A library of 523 unigenes was constructed and characterized by assigning a putative function via comparison with public databases. This set of pathogen-modulated apple genes includes many defence-related genes and is therefore an important source of information for understanding the molecular basis of the Malus–V. inaequalis interaction. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Induced resistance in intertidal macroalgae modifies feeding behaviour of herbivorous snails

Herbivory in terrestrial and marine systems can induce changes in plant chemistry affecting the foraging behaviour of herbivores. A model based on terrestrial plant-herbivore interactions predicts herbivory-induced changes in leaf chemistry to be manifested in (1) increased herbivore mobility, (2) increased feeding dispersal and (3) reduced tissue consumption by herbivores. This study is the first to demonstrate that herbivory-induced changes in the tissue chemistry of the brown seaweed Ascophyllum nodosum elicit the same response in the feeding behaviour of the gastropod Littorina obtusata as predicted for herbivorous insects, providing good evidence for the models validity across different ecosystems. The potential benefit of increased feeding dispersal to terrestrial plants as suggested by the model is the prevention of concentrated damage to apical tissues thereby preserving the plants ability to compete for light; A. nodosum does not conform to these predictions. Increased dispersal of feeding damage on A. nodosum away from primary frond tissues would reduce the likelihood of frond breakage implying a fitness benefit of induced resistance.     

Xylem sap protein composition is conserved among different plant species

Xylem sap from broccoli (Brassica oleracea L. cv. Calabrais), rape (Brassica napus L. cv. Drakkar), pumpkin (Cucurbita maxima Duch. cv. gelber Zentner) and cucumber (Cucumis sativus L. cv. Hoffmanns Giganta) was collected by root pressure exudation from the surface of cut stems of healthy, adult plants. Total protein concentrations were in the range of 100 g ml^–1. One-dimensional gel electrophoresis (SDS–PAGE) resulted in 10–20 visible protein bands in a molecular mass range from 10 to 100 kDa. The main bands were cut out, digested with trypsin, and analysed using tandem mass spectrometry. Fifty bands resulted in amino acid sequence information that was used to perform database similarity searches. Sequences from 30 bands showed high homology to proteins present in databases. Among them, we found mostly peroxidases, but could also identify the lectin-like xylem protein XSP30, a glycine-rich protein, serine proteases, an aspartyl protease family protein, chitinases, and a lipid transfer protein-like polypeptide. Sequence analysis predicted apoplastic secretion signals for all database entries similar to the partial xylem protein sequences. This and the lack of cross-reactivity with phloem protein-specific antibodies suggest that the proteins really originate from the xylem and do not result from phloem contamination. Most of the highly similar proteins probably function in repair and defence reactions. Some of the most abundant proteins (peroxidases, chitinases, serine proteases) were present in xylem exudate of all species analysed, often in more than one band. This indicates an important basic role of these proteins in maintaining xylem function.Abbreviations CHT Chitinase - 1D One-dimensional - GRP Glycine-rich protein - SP Serine protease - SSP Subtilisin-like serine protease - POX Peroxidase     

The interaction of thorns and symbiotic ants as an effective defence mechanism of swollen-thorn acacias

Evidence is provided for the interaction of ants (Crematogaster spp.) and thorns as a means of defence against browsing mammals for one species of African myrmecophyte, Acacia drepanolobium. Two experiments were conducted using goats as representative mammalian browsers. In the first experiment, the defences of individual branches were manipulated in order to assess the effectiveness of ants and thorns both on their own and together as anti-herbivore defences. It was shown that ants on their own are more effective defences for a single branch than having neither ants nor thorns, but ants from a single branch do not add significantly to the effectiveness of thorns as an anti-herbivore defence. The second experiment looked at the effect of a whole tree of ants and how they interacted with thorns in the defence of the tree. It was shown that ants from a whole tree do significantly add to the effectiveness of thorns as an anti-herbivore defence. In all cases, the goat refused to go back to and feed from a tree whose ants had just attacked it. Thorns on their own, however, do not act as total browsing deterrents. They slow down the rate of feeding but animals may compensate for this by feeding for longer periods of time. The interaction of a whole tree of ants and thorns is a very effective browsing deterrent which causes the animal to stop feeding almost immediately, therefore keeping the amount of foliage lost to a minimum. These results provide support for the hypothesis that the ant-acacia relationship (in the case of A. drepanolobium) evolved at least partly because of pressure from browsing mammals. Received: 20 October 1997 / Accepted: 28 February 1998     

A gene encoding a novel isoform of the PR-1 protein family from tomato is induced upon viroid infection

A Lycopersicon esculentum cDNA clone encoding an acidic-type pathogenesis-related protein (PR-lal) was isolated, sequenced and characterized. It contains an open reading frame of 175 amino acids and the mature protein, after cleavage of the 21 amino acid signals peptide, has a pl of 5.24. The protein shows highest homology (75% identity) with the basic pathogenesis-related prb-lb protein from tobacco. The PR-lal gene shows constitutive expression in roots from tomato plants. It is expressed in leaves and stems upon viroid infection, and appears to be induced by ethylene. Comparative studies of this gene and a related basic isoform of PR-1 indicate that the expression of these two members of the PR-1 gene family in tomato may be differentially regulated upon viroid infection.The nucleotide sequence data reported in this paper will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number X71592.     

麋鹿幼仔一周龄内的活动观察

本文对麋鹿幼仔(4雄、6雌)在初生一周龄内的活动进行了观察。结果表明,仔鹿白天大部分时间皆藏卧于隐蔽处,与鹿群呈隔离状态,其活动行为主要表现为求乳、运动、跟随或躲避等。初生仔鹿具有接近和跟随亲生母鹿的本能,在5日龄内其大部分活动都处在亲生母鹿的监护下,属伴随型;至6—7日龄后,仔鹿可随母鹿进入鹿群活动。