What shapes our knowledge of the relationship between water deficiency stress and plant volatiles?

In this review, we attempt to highlight the issues related to plant volatile and essential oil studies in connection with drought stress. Our literature search included all publications on drought stress related to either the biosynthetic context of volatiles, or the ecophysiology and environmental interactions of species via these compounds. In addition, we surveyed publications on practical questions, such as the optimization of cultivation techniques of essential oil bearing plants. Emphasis was placed on theories explaining regularities in the detected symptoms of test plants and discrepancies of other results. Carbon allocation from primarily metabolism to secondary one, competition of parallel terpenoid pathways and the surplus of reductive power are the main theories that are discussed around. During evaluation, the main question was: which principles have already been justified in the biosynthesis/accumulation/emission of plant volatiles due to drought stress? What are the strengths and limitations of the theories? In discussing results from different scientific fields, the intention is to reveal logical connections that are yet to be addressed in the future co-operative multidisciplinary research. The simple question—whether drought stress increases the biosynthesis/accumulation/emission of plant volatiles—is not adequate any more. According to current scientific knowledge, the fine-tuning of all related variables is the challenge of next generation studies, especially for MAP species.