Plants are capable of synthesizing anoverwhelming variety of low-molecular-weight organic compounds, termed“secondary metabolites”, usually with very unique and complex structures. Theyrepresent one of the most diverse and intriguing organic compounds that natureoffers. These are molecules that are not essential for cell viability, butnevertheless play a very important role in the survival and fitness of theplant. Plant secondary metabolitesprovide a battery of chemical defences against insect, pathogen and herbivoreattacks, as well as play an important role in attracting pollinatinginsects. In addition, plant secondaryproducts have served mankind as medicines and poisons since the dawn ofcivilization; early examples include the poisoning of Socrates through theadministration of hemlock and the alkaloid atropine that Cleopatra secretlyused as a cosmetic for dilating her pupils. Nowadays, plant secondary products represent an indispensable source ofcommercially important compounds, including pharmaceuticals, natural flavours,fragrances, dyes and gums. Plant secondary metabolites of industrialsignificance include pharmaceuticals (alkaloids such as ajmalicine, berberine,atropine etc.; steroids such as diosgenin; cardenolides such as digitoxin anddigoxin), flavours (sweeteners such as stevioside and thaumatin; bitteringagents such as quinine), pigments (shikonin), fragrances (rose oil, lavenderoil etc.) and agrochemicals (azadirachtin).
Secondary metabolites are a very broadgroup of metabolites with no distinct boundaries, and grouped under no singleunifying definition. Though extensive work has been performed, plant secondarymetabolism remains poorly characterized. Knowledge about biosynthetic pathwaysand their regulation would be crucial to help bypass the low yield of varioussecondary metabolites in plants or plant-cell cultures.
In
BIOTECHNOLOGICALASPECTS OF SECONDARY METABOLITE PRODUCTION
Bopana Nishrithaa and Saxena Sanjayb*
eds Ashwani Kumar and Sudhir Sopory
