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

PGPR, and AMF are symbionts, which promotes growth and induce tolerance

in plants against different biotic and abiotic stresses through the regulation of

different phytohormones, antioxidant enzymes, secondary metabolites, vola­

tile compounds, stress-related genes, and a number of signaling molecules

are activated by their interaction. PGPR and endophytic microbes stimu­

late the activity of 1-aminocyclopropane-1-carboxylate (ACC) deaminase

which lower ethylene levels and promotes growth in stress condition.

During stress period, association of PGPR, AMF, and endophytes elevate

the levels antioxidant enzymes like superoxide dismutase (SOD), catalase

(CAT) and ascorbate peroxidase (APX). Likewise, during biotic stress

situation, when pathogens attacks plants, these symbionts activate different

signaling molecules including cyclin dependent protein kinase (CDK),

mitogen-activated protein kinase (MAPK) and calcium-dependent protein

kinase (CDPK) which results in hypersensitive responses, rapid cell death

and induces PAMP-triggered immunity (PTI). In this chapter, we discussed

about how endophytes, PGPR, and AMF protects plants from different

biotic and abiotic stresses, which include drought, salinity, cold, flood, and

heavy metal stresses. Also enlightened different mechanism through which

endophytes, PGPR, and AMF confers tolerance and growth in plants during

adverse situations.

3.1 INTRODUCTION

The normal growth and development of the plant is supported by the different

environmental factors, mainly the climatic condition and the soil profile. Soil

is a dynamic and complex structure which is greatly influenced by the pres­

ence of a variety of stressors. The rapid climate change exhibited the severity

of different stress condition which affects the crop production and currently

it is a major problem of sustainable agriculture. These stresses can be catego­

rized into biotic such as attack of different pathogens and pests and abiotic

which mainly includes adverse climatic conditions like salinity, drought, cold,

flooding, heavy metal, and heat stress. However, abiotic stress is considered

as the main reason for yield losses, but biotic stressors also cause signifi­

cant effects to plants. Plants may cope with one or a combination of these

stresses. To deal with these stress conditions plants have evolved different

protective strategies both at cellular and molecular levels some of which are

phytohormonal regulation, production of antioxidant enzymes, changing of

architecture of plants root, transcriptional control, signal transduction, etc.