Abstract
Plants respond to various abiotic and biotic stress conditions through accumulation of phenolic compounds. The specificity of these phenolic compounds accumulation depends on the type of stress condition and the response of plant species. Light stress induces biosynthesis of phenolic acids and flavonoids in plants. Temperature stress initially induces biosynthesis of osmoprotective compounds and then later stimulates synthesis of antioxidant enzymes and antioxidant compounds such as flavonoids, tannins and phenolic acids in plant cells. Salinity causes oxidative stress in plants by inducing production of reactive oxygen species. To resist against oxidative stress plants produce polyphenols, flavonoids, anthocyanins, phenolic acids and phenolic terpenes. Plants biosynthesize phenols and flavonoids during heavy metal stress.to scavenge the harmful reactive oxygen species and to detoxify the hydrogen peroxide. Plants accumulate phenols at the infection sites to slow down the growth of microbial pathogens and restrict them at infected site. Plants also accumulates salicylic acid and H2O2 at the infection site to induce the systemic acquired resistance (SAR) against microbial pathogens. Plants accumulate phenolic compounds which act as inhibitor or toxicant to harmful nematodes, insects and herbivores. Hence, phenols regulate crucial physiological functions in plants to resist against different stress conditions.
Highlights
Plants have developed various metabolic pathways which respond to different abiotic and biotic stress conditions through biosynthesis of secondary metabolites
The variations in the transcription level of genes encoding for phenylalanine ammonia lyase (PAL) regulates the activity of the enzyme and in turn specific phenolic compounds are synthesized in response to biotic or abiotic stress
During temperature stress activity of phenylalanine ammonia lyase enzyme increases which results in accumulation of phenols in plants
Summary
Plants have developed various metabolic pathways which respond to different abiotic and biotic stress conditions through biosynthesis of secondary metabolites. These metabolic pathways are linked with the primary metabolic pathways which are the integral part of growth regulating programmes in plants. Some phenolic compounds are widely available in many plant species while others are available only in certain plants species [10] These phenolic compounds help in regulating various types of physiological functions in plants during growth and development but are involved in plant defense mechanisms. They are known to have defensive function against abiotic and biotic stress conditions. Nematicide iridoid glycosides accumulation was observed in roots of plant Plantago lanceolata when it was infected with nematodes [21]
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