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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

processes and promote growth. Endophytes those especially colonizes the

plant root, induce production of indole acetic acid (IAA) an auxin which

have several physiological functions like shoot growth, seed germination,

root growth, vascular tissue differentiation and promote photosynthesis

(Ahmad & Kibert, 2013). In Solanum nigrum bacterial endophytes improved

growth by the activity of 1-aminocyclopropane-1-carboxylate (ACC)

deaminase enzyme and increased production of IAA. IAA also induces

plant-endophytes interaction thus promoting better plant growth (Suzuki

et al., 2003). During stress condition endophytes limits the production of

ethylene, ABA, JA, and gibberellic acid (GA) and promote growth. Endo­

phytic fungi Phoma herbarum isolated from salt stressed root of Glycine

sp. showed improved growth by production of GA. Plants that have poor

nutrient uptake machinery in the normal condition, endophytes interaction

improved nutrients uptake and promote growth in these plants. Thus, endo­

phyte promotes plant growth and development through three major steps,

production of secondary metabolites and phytohormones, improved nutrient

acquisition and providing tolerance against biotic and abiotic stresses.

3.4.1 ENDOPHYTES-MEDIATED ABIOTIC STRESS TOLERANCE IN

PLANTS

Endophyte is an essential element of plant symbiosis which helps to mitigate

several abiotic stresses in plants. The beneficial roles of endophytes are well

studied, and several reports exhibited that under abiotic stress condition these

microorganisms alter several biochemical, physiological, and molecular

events inside the plant tissue proving better resistance (Nagata et al., 2015;

Cherif et al., 2015). For optimal growth in plants, several environmental

factors play a key role and alteration of any of these factors can retard growth.

Drought, salinity, and temperature are the main abiotic stressors which limits

growth. Moreover, these primary stressors can also initiate some secondary

stress condition like oxidative and osmotic stresses. Endophytes activate

different stress responsive system as soon as the plant receives stress stimuli.

Endophyte also induces the expression of different stress responsive genes,

biosynthesis of stress related biochemicals including secondary metabolites

and phytohormones which minimizes the adverse impact. In pepper plants

under stress condition, Bacillus sp. and Arthrobacter sp. downregulated

several genes which promote stress and upregulated several stress defen­

sive genes that protect the plant from harmful effects (Lata et al., 2018). In