Scent Molecules as Mediators of Optimal Defence in Algae and Non-seed Plants

The theory of optimal defence states that plants implement defensive phytochemistry according to their physiological status and availability of resources. A major component of such defence is deployment of volatile organic compounds (VOCs) in response to external stress factors. Compositions and abundance of VOCs, however, are altered by complex feedback mechanisms to suit the environmental, nutritional and developmental conditions of the plant, as well as the type and intensity of incident stress. This phenomenon has been studied in detail in many flowering plants and conifers, but remains under-explored in other gymnosperms, non-seed plants and algae. Nonetheless, studies have shown that VOCs released by algae and bryophytes affect biological communities over short and long ranges. Further investigations are required not only for ecological considerations, but also due to overall impacts of stress-induced emission of VOCs on agro-forestry and aquaculture operations. Moreover, induction of physiological stress has been demonstrated in algae, ferns, conifers and flowering plants to enhance the production of substances of medicinal/industrial importance, including VOCs. This chapter looks into the roles of environmental and developmental parameters, and resulting feedback cycles, in the production and emission of VOCs in algae and non-seed terrestrial plants.