5.2.5 Volatile Organic Compounds
Volatile organic compounds (VOCs) are low-molecular weight compounds that are
emitted in the atmosphere in vapors or gaseous form. VOCs are produced as
secondary metabolites by micro- (bacteria and fungi) and macro-organisms (animals and plants) and play vital roles, such as regulation of physiological processes
and inter-organismal communication (Fincheira and Quiroz 2018; Rakshit et al.
2020). Plants can emit VOCs constitutively to attract pollinators and seed dispersers, or in response to a stimulus as a defense against insects or predators,
plant-to-plant communication, thermo-tolerance, and environmental stress adaptation (Vivaldo et al. 2017). Plant VOCs can be classified into terpenoids, fatty acid
derivatives, phenylpropanoids/benzenoids, and amino acid derivatives (Dudareva
et al. 2013). Under-ground VOC’s are emitted by plants through their roots (Rakshit
et al. 2020), where they also interact with bacteria and fungi in the rhizosphere zone
giving rise to a deep symbiotic plant-microorganisms relation (Dessaux et al. 2016).
Microorganisms benefit from root’s exudates while they produce nonvolatile
metabolites that affect the plant’s nutrient assimilation and benefits plant growth
(Dotaniya and Meena 2015).
A new plant–microbe interaction involving microbial volatile organic compounds (mVOCs) was discovered by (Ryu et al. 2003). In their study, they identified that volatile compounds from Bacillus subtilis act as strong promoters of
growth in Arabidopsis thaliana. Since then, studies focusing on mVOCs as potential
compounds with practical applications on regulating characteristics of agronomic
importance have emerged. Bacterial and fungal volatile compounds may activate
defense responses against biotic and abiotic stress, induce systemic resistance,
promote growth, and enhance health processes in plants (Kanchiswamy et al. 2015;
Piechulla and Degenhardt 2014). There are approximately 1000 mVOCs produced
by bacteria and fungi reported in the literature, a few examples include 3-hydroxy2-butanone (acetoin), 2,3-butanediol, 2-pentylfuran, or dimethylhexadecylmine
(Fincheira and Quiroz 2018; Piechulla and Degenhardt 2014).
The idea of using VOCs to elicit secondary metabolites in plants is novel and
still very little studied. There are cases of success in the literature to this purpose,
which are summarized in Table 5.5, most of them have shown that different volatile
compounds from bacterial can increase commercially valued components of
essential oils, such as monoterpenes, pulegone, menthone, menthol, limonene,
menthyl acetate, terpineol, and eugenol (Banchio et al. 2009; Santoro et al. 2011,
2016; Zhou et al. 2016). These studies are often performed in sterile plastic boxes or
petri dishes with divided into two compartments by a physical barrier so that
microbial and plant cultures interact without physical contact.
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173
Volatile organic compounds (VOCs) are low-molecular weight compounds that are
emitted in the atmosphere in vapors or gaseous form. VOCs are produced as
secondary metabolites by micro- (bacteria and fungi) and macro-organisms (animals and plants) and play vital roles, such as regulation of physiological processes
and inter-organismal communication (Fincheira and Quiroz 2018; Rakshit et al.
2020). Plants can emit VOCs constitutively to attract pollinators and seed dispersers, or in response to a stimulus as a defense against insects or predators,
plant-to-plant communication, thermo-tolerance, and environmental stress adaptation (Vivaldo et al. 2017). Plant VOCs can be classified into terpenoids, fatty acid
derivatives, phenylpropanoids/benzenoids, and amino acid derivatives (Dudareva
et al. 2013). Under-ground VOC’s are emitted by plants through their roots (Rakshit
et al. 2020), where they also interact with bacteria and fungi in the rhizosphere zone
giving rise to a deep symbiotic plant-microorganisms relation (Dessaux et al. 2016).
Microorganisms benefit from root’s exudates while they produce nonvolatile
metabolites that affect the plant’s nutrient assimilation and benefits plant growth
(Dotaniya and Meena 2015).
A new plant–microbe interaction involving microbial volatile organic compounds (mVOCs) was discovered by (Ryu et al. 2003). In their study, they identified that volatile compounds from Bacillus subtilis act as strong promoters of
growth in Arabidopsis thaliana. Since then, studies focusing on mVOCs as potential
compounds with practical applications on regulating characteristics of agronomic
importance have emerged. Bacterial and fungal volatile compounds may activate
defense responses against biotic and abiotic stress, induce systemic resistance,
promote growth, and enhance health processes in plants (Kanchiswamy et al. 2015;
Piechulla and Degenhardt 2014). There are approximately 1000 mVOCs produced
by bacteria and fungi reported in the literature, a few examples include 3-hydroxy2-butanone (acetoin), 2,3-butanediol, 2-pentylfuran, or dimethylhexadecylmine
(Fincheira and Quiroz 2018; Piechulla and Degenhardt 2014).
The idea of using VOCs to elicit secondary metabolites in plants is novel and
still very little studied. There are cases of success in the literature to this purpose,
which are summarized in Table 5.5, most of them have shown that different volatile
compounds from bacterial can increase commercially valued components of
essential oils, such as monoterpenes, pulegone, menthone, menthol, limonene,
menthyl acetate, terpineol, and eugenol (Banchio et al. 2009; Santoro et al. 2011,
2016; Zhou et al. 2016). These studies are often performed in sterile plastic boxes or
petri dishes with divided into two compartments by a physical barrier so that
microbial and plant cultures interact without physical contact.
5 Role of Stress and Defense in Plant Secondary Metabolites …
173