190
H. B. Slama et al.
Ethylene and ACC Deaminase: Ethylene is a gaseous hormone that is responsible for plant growth. The biosynthesis of ethylene starts by converting Sadenosylmethionine (SAM) to 1-aminocyclopropane-1-carboxylate (ACC) by 1aminocyclopropane-1-carboxylate synthase (ACS) enzyme. Ethylene level gets
elevated when exposed to stress conditions, resulting in reducing plant growth
(Hardoim et al. 2008). In this case, bacteria could interfere by sequestering plant
ACC and breaking it down into ammonia and α-ketobutyrate, thus reducing ethylene
negative effect, enhancing plant stress resistance, and plant development (Naveed
et al. 2014; Noumavo et al. 2016).
b. Indirect plant growth promotion
Bacterial indirect plant growth promotion is achieved by limiting abiotic stresses
or preventing the deleterious effects of pathogenic organisms, via (i) biological
control of pathogens (producing inhibitory allelochemicals, antibiotics, and cell walldegrading enzymes), (ii) parasitism, (iii) competition for niches and bioavailable
nutrients, (iv) signal interference (quorum sensing), (v) volatile compounds synthesis
(VOCs), and (vi) inducing systemic resistance (ISR) (Glick 2012; Alvin et al. 2014;
Sheoran et al. 2015).
8.6.5 Production of Cell Wall-Degrading Enzymes
Microbial cell wall-degrading enzymes play a major role in host plant protection from
biotic stresses (Goswami et al. 2016). Extracellular enzymes produced by endophytic strains include chitinases, dehydrogenases, β-glucanases, amylases, cellulases, lipases, etc. (Gupta et al. 2015). Both chitinase and β-glucanase are effective
in inhibiting the proliferation of hyphal by lysis and detangling of mycelia and other
morphologies of fungal pathogens (Vejan et al. 2016).
8.6.6 Hydrogen Cyanide Production (HCN)
Volatile compounds production include hydrogen cyanide (HCN), aldehydes, alcohols, ketones, etc. (Ulloa-Ogaz et al. 2015). Particularly, HCN is a key factor of
disease proliferation (Ramette et al. 2003), since cyanide is a metabolic inhibitor
that acts by protecting plants from colonization or competition (Passari et al. 2016).
8.6.7 Volatile Organic Compounds (VOCs)
The low molecular weight volatile organic compounds (VOCs) involve phenylpropanoids, terpenoids, and fatty acid derivatives, they are endowed with
H. B. Slama et al.
Ethylene and ACC Deaminase: Ethylene is a gaseous hormone that is responsible for plant growth. The biosynthesis of ethylene starts by converting Sadenosylmethionine (SAM) to 1-aminocyclopropane-1-carboxylate (ACC) by 1aminocyclopropane-1-carboxylate synthase (ACS) enzyme. Ethylene level gets
elevated when exposed to stress conditions, resulting in reducing plant growth
(Hardoim et al. 2008). In this case, bacteria could interfere by sequestering plant
ACC and breaking it down into ammonia and α-ketobutyrate, thus reducing ethylene
negative effect, enhancing plant stress resistance, and plant development (Naveed
et al. 2014; Noumavo et al. 2016).
b. Indirect plant growth promotion
Bacterial indirect plant growth promotion is achieved by limiting abiotic stresses
or preventing the deleterious effects of pathogenic organisms, via (i) biological
control of pathogens (producing inhibitory allelochemicals, antibiotics, and cell walldegrading enzymes), (ii) parasitism, (iii) competition for niches and bioavailable
nutrients, (iv) signal interference (quorum sensing), (v) volatile compounds synthesis
(VOCs), and (vi) inducing systemic resistance (ISR) (Glick 2012; Alvin et al. 2014;
Sheoran et al. 2015).
8.6.5 Production of Cell Wall-Degrading Enzymes
Microbial cell wall-degrading enzymes play a major role in host plant protection from
biotic stresses (Goswami et al. 2016). Extracellular enzymes produced by endophytic strains include chitinases, dehydrogenases, β-glucanases, amylases, cellulases, lipases, etc. (Gupta et al. 2015). Both chitinase and β-glucanase are effective
in inhibiting the proliferation of hyphal by lysis and detangling of mycelia and other
morphologies of fungal pathogens (Vejan et al. 2016).
8.6.6 Hydrogen Cyanide Production (HCN)
Volatile compounds production include hydrogen cyanide (HCN), aldehydes, alcohols, ketones, etc. (Ulloa-Ogaz et al. 2015). Particularly, HCN is a key factor of
disease proliferation (Ramette et al. 2003), since cyanide is a metabolic inhibitor
that acts by protecting plants from colonization or competition (Passari et al. 2016).
8.6.7 Volatile Organic Compounds (VOCs)
The low molecular weight volatile organic compounds (VOCs) involve phenylpropanoids, terpenoids, and fatty acid derivatives, they are endowed with