ABSTRACT
Plants are exposed to various abiotic (salinity, temperature extreme, water deficit, nitrogen loss, and heavy metals) and biotic (microbial and weeds) stresses. Plant biochemical pathways are impaired upon environmental stresses, and it becomes hard for plants to tolerate stresses. Photosynthesis and respiration are the most important processes on Earth and need to be regulated in an altered way to tolerate stress conditions. Plants withstand 214stress conditions by altering these mechanisms other than at normal conditions. Phytohormones and antioxidants display a significant role in the plant defense system. Phytohormones (auxins, abscisic acid, gibberellins, jasmonic acid, and salicylic acid) help plants to survive under various stresses by changing their endogenous levels, while the built-in antioxidant defense systems support the plants to tolerate environmental stresses by removing reactive oxygen species and reactive nitrogen species produced under such harsh conditions. An improved understanding of plant strategies in stress conditions is needed to make plants able to withstand changing environmental conditions to reduce massive damages to crops. This chapter will highlight the role of phytohormones and antioxidants in mitigating the ill effects of different abiotic and biotic stresses, especially with reference to photosynthesis and respiration.
