5.3.3 Phytohormones
Phytohormones are molecules synthesized by defined organs that regulate plant
growth and have a prominent impact on plant metabolism. Additionally, they play a
vital role in the stimulation of response mechanisms of plant defense against stress.
Auxins, gibberellins, cytokinins (CK), abscisic acid (ABA), jasmonates (jasmonic
acid (JA), methyl jasmonate (MeJA)), salicylic acid (SA), brassinosteroids,
strigolactones, cinnamic acid (CA), among others, are examples of phytohormones.
Auxins and the auxin índole-3-acetic acid (IAA) act as promoters of growth and
developmental events in plants (cell división, elongation, and differentiation). CKs
are involved in the maintaining of cellular proliferation, differentiation, and prevention of senescence. ABA has an important role in the plant response to stress
and adaptation. Gibberellic acid (GA) is a plant growth regulator and has a vital role
in seed dormancy, formation of floral organs, and lateral shoot growth
(Egamberdieva et al. 2017). SA has an important role in plant stress tolerance
through modulation of antioxidative enzyme activities. JA is a lipid-derived compound synthesized via the octadecanoid pathway and is important in the development, structure, and flowering of plants (Złotek et al. 2020). CA is a bioprecursor of
podophyllotoxin and a huge number of plant substances, including tannins, flavonoids, etc. (Kašparová et al. 2018).
Currently, the use of phytohormones in agriculture and research has been
implemented as a strategy to induce the production of secondary metabolites
(Egamberdieva et al. 2017). The exogenous application of phytohormones by
spraying has resulted in increased production of various significant bioactive compounds in plants (Akram et al. 2020, Wang et al. 2018a). For example, Garcia-Ibañez
et al. (2019), applied MeJA, SA, and SA + MeJA to Bimi® plants resulting in a
differentiated response to each elicitor, all treatments showed an increased content of
GLs in leaves and inflorescences. Table 5.8 shows the result of plant elicitation with
phytohormones in the production of bioactive compounds of recent studies.
5.3.4 miRNA
MicroRNAs (miRNAs - length of 18 to 28 nucleotides) are noncoding RNAs. The
main function of these molecules is to participate in gene expression and regulation at
the post-transcriptional level by degrading mRNA or at the translational level by
blocking protein biosynthesis at different stages (Fig. 5.1), resulting in regulation of
plant development, metabolism, and response to biotic or abiotic stress (Tripathi et al.
2019). In plants miRNAs genes are transcribed by RNA polymerase II producing
primary miRNA (Pri-miRNA) which are important for the regulation of genome
integrity, primary and secondary metabolism, development, signal transduction,
signaling pathways, homeostasis, innate immunity, and environmental stress
responses (Vargas-Hernández et al. 2019; Wang et al. 2018b; Samad et al. 2019).
5 Role of Stress and Defense in Plant Secondary Metabolites …
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Phytohormones are molecules synthesized by defined organs that regulate plant
growth and have a prominent impact on plant metabolism. Additionally, they play a
vital role in the stimulation of response mechanisms of plant defense against stress.
Auxins, gibberellins, cytokinins (CK), abscisic acid (ABA), jasmonates (jasmonic
acid (JA), methyl jasmonate (MeJA)), salicylic acid (SA), brassinosteroids,
strigolactones, cinnamic acid (CA), among others, are examples of phytohormones.
Auxins and the auxin índole-3-acetic acid (IAA) act as promoters of growth and
developmental events in plants (cell división, elongation, and differentiation). CKs
are involved in the maintaining of cellular proliferation, differentiation, and prevention of senescence. ABA has an important role in the plant response to stress
and adaptation. Gibberellic acid (GA) is a plant growth regulator and has a vital role
in seed dormancy, formation of floral organs, and lateral shoot growth
(Egamberdieva et al. 2017). SA has an important role in plant stress tolerance
through modulation of antioxidative enzyme activities. JA is a lipid-derived compound synthesized via the octadecanoid pathway and is important in the development, structure, and flowering of plants (Złotek et al. 2020). CA is a bioprecursor of
podophyllotoxin and a huge number of plant substances, including tannins, flavonoids, etc. (Kašparová et al. 2018).
Currently, the use of phytohormones in agriculture and research has been
implemented as a strategy to induce the production of secondary metabolites
(Egamberdieva et al. 2017). The exogenous application of phytohormones by
spraying has resulted in increased production of various significant bioactive compounds in plants (Akram et al. 2020, Wang et al. 2018a). For example, Garcia-Ibañez
et al. (2019), applied MeJA, SA, and SA + MeJA to Bimi® plants resulting in a
differentiated response to each elicitor, all treatments showed an increased content of
GLs in leaves and inflorescences. Table 5.8 shows the result of plant elicitation with
phytohormones in the production of bioactive compounds of recent studies.
5.3.4 miRNA
MicroRNAs (miRNAs - length of 18 to 28 nucleotides) are noncoding RNAs. The
main function of these molecules is to participate in gene expression and regulation at
the post-transcriptional level by degrading mRNA or at the translational level by
blocking protein biosynthesis at different stages (Fig. 5.1), resulting in regulation of
plant development, metabolism, and response to biotic or abiotic stress (Tripathi et al.
2019). In plants miRNAs genes are transcribed by RNA polymerase II producing
primary miRNA (Pri-miRNA) which are important for the regulation of genome
integrity, primary and secondary metabolism, development, signal transduction,
signaling pathways, homeostasis, innate immunity, and environmental stress
responses (Vargas-Hernández et al. 2019; Wang et al. 2018b; Samad et al. 2019).
5 Role of Stress and Defense in Plant Secondary Metabolites …
179