Green Leaf Volatiles: Airborne Signals that Protect against Biotic and Abiotic Stresses

Green leaf volatiles (GLVs) are rapidly released by plant leaves upon damage. This makes them ideal signals to convey the presence of a damaging threat to other parts of the same plant, but also to plants nearby. There, GLVs were first found to activate defense responses against insect herbivores and necrotrophic pathogens. Aside from providing direct protection, GLVs also prime those responses resulting in an enhanced and/or accelerated response to these biotic stressors. Recently, it was shown that GLVs also provide protection against cold stress in plants, resulting in stress-specific transcript accumulation and subsequent reduced damage. Interestingly, this response was further associated with a stimulation of growth after the stress subsided. However, this growth compensation was only observed in cold stressed plants while control plants continued to grow normally. Common to all those stresses is that they can also cause the release of these compounds and it is safe to assume that this correlation lies at the evolutionary origin of their biological activity. However, the quantities and qualities of the emitted GLVs can vary significantly even in closely related species, suggesting that eco-physiological factors related to biotic and abiotic stresses may have been the driving force for the highly variable emission of these compounds. However, too little is known about the regulation of GLV emissions, signaling, and responses to support this hypothesis. In this presentation we will provide an overview of current knowledge regarding biosynthesis and signaling of GLVs in plants and will give an outlook into future areas of research that may provide essential information about the complex biological activities of these compounds.