Membrane potentials (V m ) and intracellular calcium variations were studied in Lima bean (Phaseolus lunatus) leaves when the Mediterranean climbing cutworm (Spodoptera littoralis) was attacking the plants. In addition to the effect of the feeding insect the impact of several N-acyl Glns (volicitin, N-palmitoyl-Gln, N-linolenoyl-Gln) from the larval oral secretion was studied. The results showed that the early events upon herbivore attack were: a) a strong V m depolarization at the bite zone and an isotropic wave of V m depolarization spreading throughout the entire attacked leaf; b) a V m depolarization observed for the regurgitant but not with volicitin {N-(17-hydroxy-linolenoyl)-Gln} alone; c) an enhanced influx of Ca 21 at the very edge of the bite, which is halved, if the Ca 21 channel blocker Verapamil is used. Furthermore, the dose-dependence effects of N-acyl Gln conjugatestriggered influx of Ca 21 studied in transgenic aequorin-expressing soybean (Glycine max) cells, showed: a) a concentrationdependent influx of Ca 21 ; b) a configuration-independent effect concerning the stereochemistry of the amino acid moiety; c) a slightly reduced influx of Ca 21 after modification of the fatty acid backbone by functionalization with oxygen and; d) a comparable effect with the detergent SDS. Finally, the herbivore wounding causes a response in the plant cells that cannot be mimicked by mechanical wounding. The involvement of Ca 21 in signaling after herbivore wounding is discussed.

In response to herbivore (Spodoptera littoralis) attack, lima bean (Phaseolus lunatus) leaves produced hydrogen peroxide (H 2 O 2 ) in concentrations that were higher when compared to mechanically damaged (MD) leaves. Cellular and subcellular localization analyses revealed that H 2 O 2 was mainly localized in MD and herbivore-wounded (HW) zones and spread throughout the veins and tissues. Preferentially, H 2 O 2 was found in cell walls of spongy and mesophyll cells facing intercellular spaces, even though confocal laser scanning microscopy analyses also revealed the presence of H 2 O 2 in mitochondria/peroxisomes. Increased gene and enzyme activations of superoxide dismutase after HW were in agreement with confocal laser scanning microscopy data. After MD, additional application of H 2 O 2 prompted a transient transmembrane potential (V m ) depolarization, with a V m depolarization rate that was higher when compared to HW leaves. In transgenic soybean (Glycine max) suspension cells expressing the Ca 21 -sensing aequorin system, increasing amounts of added H 2 O 2 correlated with a higher cytosolic calcium ([Ca 21 ] cyt ) concentration. In MD and HW leaves, H 2 O 2 also triggered the increase of [Ca 21 ] cyt , but MD-elicited [Ca 21 ] cyt increase was more pronounced when compared to HW leaves after addition of exogenous H 2 O 2 . The results clearly indicate that V m depolarization caused by HW makes the membrane potential more positive and reduces the ability of lima bean leaves to react to signaling molecules.

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Summary• The function of fungal volatiles in fungal-plant interactions is poorly understood. The aim here was to address this lack of knowledge, focusing on truffles, ectomycorrhizal fungi that are highly appreciated for their aroma.• The effect of volatiles released by truffles was tested on Arabidopsis thaliana in a closed chamber bioassay. The volatiles produced by Tuber melanosporum , Tuber indicum and Tuber borchii fruiting bodies inhibited A. thaliana in terms of root length and cotyledon leaf size, and in some cases induced a bleaching of the seedlings, thus indicating toxicity. Ten synthetic volatiles were tested in a similar way. The strongest inhibitory effect was observed with C 8 molecules such as 1-octen-3-ol, an alcohol with a typical 'fungal smell'.• Two of these C 8 compounds were further tested to investigate their mechanism of action. 1-Octen-3-ol and trans -2-octenal induced an oxidative burst (hydrogen peroxide, H 2 O 2 ) in the A. thaliana leaves as well as a strong increase in the activities of three reactive oxygen species (ROS)-scavenging enzymes.• These results demonstrate that fungal volatiles inhibit the development of A. thaliana and modify its oxidative metabolism. Even though limited to laboratory observations, these results indicate the presence of a hitherto unknown function of fungal volatiles as molecules that mediate fungal-plant interactions.New Phytologist (2007) 175 : [417][418][419][420][421][422][423][424]