TABLE 3.

Enhancement of secondary metabolites under stress to cope with stressed conditions in plants.

Stress	Production of secondary metabolites	Response of plants	References
Drought	Phenolics	Activates antioxidant property of plants, PAL enzyme activity Provide defense against microbial pathogens, insect pests and large herbivores	García-Calderón et al., 2015; Rezayian et al., 2018;
	Anthocyanins/Flavonoids/Amino acids/Alkaloids	Increase antioxidant activity and anti-inflammatory response, affects transamination, glycolysis, citric acid cycle and glutamate- mediated proline biosynthesis and promotes ripening of leaves	Cakir and Cebi, 2010; Bowne et al., 2012; Guo et al., 2018;
	Terpenes	Increase in photosynthesis and leaf water status, alleviate oxidative damage on cellular membrane, Increase defense against phytophagous insects, fungi and microbes	Turtola et al., 2003
Heat Stress	Polyamines phenyl amides	Increases defense	Edreva et al., 2008
Cold stress	Phenolics	Increases defense	Griffith and Yaish, 2004
Antifungal	Phenolics	Increases defense	Mishra et al., 2006; Jain et al., 2015
Antiviral	Phenolics	Increases defense	Özçelik et al., 2011
Salt stress	Polyphenolic alkaloids	Increases defense	Martínez-Ballesta et al., 2014; Rivero et al., 2018
Light stress	Triterpenes	Increases defense	Fournier et al., 2003
Anti-insect	Monoterpenes	Increases defense	Ahmed et al., 2017
Anti-herbivores	Amino acids, Glucoside	Increases defense	Moulin et al., 2006; Mazid et al., 2011