Volatiles in the aquatic marine ecosystem: Ethylene and related plant hormones and sporulation in red seaweeds

Abstract

Reports on the production of volatile compounds in algae have been focused on what they produce rather than on their functions. In this scenario, a myriad of fatty acid derivatives, nitrogen-containing compounds, organic halogen compounds, sulphur compounds and compounds derived from transferase activity have been described. Recently, a broad range of these volatile compounds has also been identified under a physiological complex pattern in algae, inferring that seaweeds must somehow integrate signals not only to reply to environmental status but also as a response to their growth and development capacity. Evidence comes from algal mats, which suffer sudden increments in the number of reproductive structures and correspondingly abrupt decreases in biomass. Specifically, the emission of airborne substances, such as ethylene and dimethylsulphide (DMS), has provided valuable information on their participation in algal physiology. DMS is affected by environmental factors such as light and salinity. In addition, the time course of DMS and ethylene release has revealed that the synthesis of ethylene, via the alternative route of DMSP lyase, is not a priority in the red seaweeds. Furthermore, ethylene has a significant effect on the formation of reproductive structures and the sporulation of the red seaweeds Grateloupia imbricata and Pterocladiella capillacea. Our data suggest that the presence of putative receptors and the response of ethylene could be influenced by the length of exposure to this volatile. Unfortunately, despite the importance of all these facts in the formation of reproductive structures and spore germination, there is to date scant information at a molecular level, and little is known about the role of genes on these processes. In this chapter, we aim to compile the current knowledge of volatile compounds in algae. We will discuss the relation between the emission of volatiles and algal physiology and mainly focus on the involvement of volatiles in the reproduction of red seaweeds. As far as possible, we will try to unveil the molecular mechanisms of the perception of volatiles.