# Chemical Diversity of Mediterranean Seagrasses Volatilome
## 4 Discussion
### Shared Compounds in Seagrass Species  
The four species shared FAD, terpenoids, and benzenoids, which are common plant volatile compounds alongside phenylpropanoids and amino acid derivatives [90]. It is not surprising to find these types of compounds in seagrass as well. Other marine organisms like macroalgae [91; 92] such as coral [93] also produce these compounds.  
Terpenoids are the largest class of plant-specialized metabolites [94] derived from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), synthesized via the mevalonic acid (MVA) in the cytosol and the methyl-eryththirol-phosphate (MEP) in plastids pathways [95; 96]. Shared terpenoids (e.g., \(\beta\)-cyclocitral and \(\beta\)-ionnone) are apocarotenoids formed by carotenoid cleavage dioxygenases or non-enzymatic processes [97]. Apocarotenoids, more soluble and volatile than carotenoids, act as hormones, controlling their development, and signals regulating cell response to oxidative stress, serving critical biological functions [98; 99]. Their role in the marine environment is unclear, but they likely offer protection against stressors, as seen in freshwater. \(\beta\)-cyclocitral acts as an inhibitor of competing microalgae during algal bloom in the eutrophic lakes [100; 101] and increases with plant density, possibly as an inhibitor of competing organisms [102]. \(\beta\)-ionone and geranyl acetone produced by cyanobacteria and algae exhibit strong toxic effects on algae cell growth [103]. Cyanobacterial \(\beta\)-ionone and \(\beta\)-cyclocitral also trigger cell death in freshwater plants [104]. Both compounds certainly provide a similar defense against biotic stresses in the marine environment and may also contribute to protection against abiotic stresses. In freshwater, the conditions of high light and temperature can promote the emission of \(\beta\)-ionone [105] and \(\beta\)-cyclocitral [106]. The four species' volatilomes also shared an oxygenated sesquiterpene: Farnesyl acetate commonly produced by brown algae [107], but its role in marine areas remains unknown. In terrestrial plants such as _Abelmoschus musculus_, farnesol acetate is produced in seeds where it shows an antibacterial activity [108]. It is also an important sex pheromone for the Click beetle, attracting females [109]. In the marine environment, it could potentially have an antibacterial role as well as being an important signaling agent.  
Benzenoids derived from L-phenylalanine constitute a large class of structurally diverse volatile compounds involved in plant reproduction and defense [94]. Benzaldehyde and benzenacetaldehyde have already been found in _P. oceanica_ and seaweeds [68; 72; 87; 110]. The role of benzenoids in marine environments is unknown. In the terrestrial environment, benzaldehyde derivatives show growth inhibition and antioxidant activities on _Brassica__campestris_[111], and most floral volatiles include benzenoid compounds own to their high smell potential required to attract pollinators [112; 113]. For example, once pollinated, _Petunia_ flowers produce ethylene, which rapidly induces the down-regulation of biosynthesis and emission of all benzenoids [113].  
FADs derive from linoleic and linolenic acid by deoxygenation catalyzed by lipoxygenases (LOX) [114]. Some of them are important herbivore-induced plant volatiles (HIPVs) immediately released after insect damage [94]. Although their exact roles in marine environments remain unknown, marine organisms produce these compounds in significant quantities (e.g., macroalgae [91; 115; 116] and seagrasses [43; 84]).