| Inhabitants of ecosystems have to be able to respond to changes in population and ecosystem composition. Plants should register the presence of herbivores and attract pollinators. Herbivores should be able to select a profitable source of nutrients, while predators have to be able to find their prey. Plant odours play a central role in these multitrophic interactions. Insects and mites are highly sensitive to volatile cues and plants utilise the emission of these signals as an efficient tool, not only to assure pollination but also to combat pests. However, plants do not communicate only with mites and insects through volatile compounds. Evidence is accumulating that these volatile signals can be detected by other plants, which react by activating defence mechanisms. This proposal aims to develop an analytical tool that will enable the study of the production, perception and processing of plant volatile signalling substances. Three closely connected research areas will be covered: a) volatile signalling between plants and mites, b) the role of plant volatiles in host specialisation and sexual communication of insects and c) plant-plant communication. - Volatile signalling between plants and mites. When plants are infested by herbivores they become attractive to natural enemies of these herbivores. The basis for this attraction are specific volatiles produced by the infested plants thus betraying the herbivores to predators. However, some spider mites strains adapt in such a way that their infestation, on for instance tomato plants, does not result in the emission of predator-attracting volatiles. This differential effect of the herbivore strain provides us with a tool for studying elicitation of volatile predator-attractants by tomato plants. This will also make it feasible to identify key-predator attractants and to assess behavioural responses of predators when confronted with a variable odour environment. - The role of plant volatiles in host specialisation and sexual communication of moths. Plant volatiles play a key role in host plant acceptance and subsequent host plant specialisation of lepidopterans. This host plant specialisation is thought to ultimately result in speciation. Essential for host plant specialisation is not only acceptance of a host plant, but also acceptance of mating partners feeding on this plant. This mating preference is highly determined by sex pheromones, which are often synthesised from precursors derived from the host plant. Thus host plant specialisation (and ultimately speciation) is the result of a phytochemically mediated interaction between not only the host plant and the herbivore, but also between the herbivore male and the herbivore female. We study the role of these phytochemicals in host plant specialisation and speciation of the moth Yponomeuta on four plant genera (Euonymus, Crategus, Prunus and Malus). - Plant-plant communication. Herbivore-infested plants start emitting volatiles that for instance attract predators, however this volatile blend also contains information that induces defence responses in uninfested neighbouring plants. A functional genomics / metabolomics approach is proposed to identify plant genes involved in the generation of these volatile signals and the subsequent defence responses. The expression level of candidate genes selected by micro-array analysis and from volatile biosynthesis pathways will be altered transiently. The biological responses of mites and neighbouring plants to this modified bouquet of volatiles will be recorded. The effects of these volatile signals on the physiology of the plants can be studied with pure volatile compounds or with genetically transformed plants overproducing certain volatiles. Using phenotypic parameters and molecular reporters from these analyses, a mutant screen will be initiated to select for mutants that can no longer "smell" the plants' volatile signal. - The instrument, a time-of-flight GC/MS. The metabolomics approach to the described biological questions requires the identification and quantification of ALL volatile substances, both major and minor. Because metabolic profiles have to be linked to biological observations, experiments will as a rule contain several replicates and several time-points or independent genetic populations. This will amount to a large number of samples per experiment. To make the best possible progress an instrument with the highest throughput capacity, sensitivity and accuracy is therefore essential. All these demands are united in a time-of-flight GC-MS instrument. |
