Respected Sir,

The difination of secondary/primary metabolism is a functional one. It also has a distributional component. Primary metabolites are universally present. They have to be present in the given organism to sustain life at the very basic level. However, secondary metabolites have no such requirement. Taxol, e.g. has only a restricted distribution but its absence from other species does not affect their survival. Thinking differently we can also say they are expendibles, meaning other compounds can take their place to perform the same function.

Fragrance, e.g. performs the same function, but their are many types of it, all performing the same function. Secondary metabolism is a variable component which allows  a particular species to perpetuate its lineage under changing evolutionary pressures, e.g. a change in the pollinator types. The component remains dormant and when the need arises it starts producing the required compounds.

Finally I beleive all the metaolome is essential for the producing organism, the secondary metbolome is just a subset that is dynamic in its composition and primary has fixed/predictable composition.

Dear sir,

Secondary metabolites are the compounds derived from primary metabolites. Thus it is named so. Also they are not required for normal growth and development of plants. in plant kingdom they are limited in occurrence and also very specific and restricted in particular taxonomic groups. secondary metabolites are accumulated in smaller quantities than primary one.

Dear Kulkarni, Aldallal and Ekambaram

Thank you very much for sharing your valuable thoughts. 

Can secondary metabolites be converted back to primary metabolites in times of need by the plant and by what biosynthetic methods?

Best wishes.

Let me add some papers more for evaluation this question.

Dear Dr. Vladimir

Thank you very much for your highly informative articles.

Regards.

Secondary metabolites are NOT inferior to primary metabolites.

Primary metabolites include carbohydrates, lipids, proteins, and nucleic acids, found universally in the plant kingdom because they are the components or products of PRIMARY or fundamental metabolic pathways or cycles such as glycolysis, the Krebs cycle, and the Calvin cycle.  These primary pathways are needed in enabling a plant to synthesize, assimilate, and degrade organic compounds, primary metabolites are essential to the life of the plant.

Secondary metabolites include alkaloids, terpenoids, and phenolics. But, these compounds also include primary metabolites, 'so whether a compound is a primary or secondary metabolite is a distinction based not only on its chemical structure but also on its function and distribution within the plant kingdom.'  Secondary metabolites are important in plant defense, also essential to the life of the plant, and used as medicines in humans.  (There is no inferiority or superiority.  I paraphrased from the link below.)

http://lifeofplant.blogspot.com/2011/03/metabolites-primary-vs-secondary.html

Dear Miranda

I agree with your opinion that neither of them are superior or inferior and are important for not only the plants but also to human beings and animals as medicines, colors, aromas etc. and other living beings like insects as attractants. They provide researchers excellent opportunity to study different biosynthetic pathways and the gene clusters involved in the pathways.

Best wishes.

Both are important for growth and survival of plants. Primary metabolites are structural chemical required for growth and development  wheresas secondary metabolites are essential for various physiological functions like self defense, etc

Dear Dr. Tripathi

Thank you for your valuable information. Do you have any references where secondary metabolites were converted back to primary metabolites and under what conditions such conversion takes place?

Best wishes.

Dear Dr Rao,

Primary and secondary metabolites cannot readily be distinguished on the basis of precursor molecules, chemical structures, or biosynthetic origins. For example, both primary and secondary metabolites are found among the diterpenes (C20) and triterpenes (C30). In the diterpene series, both kaurenoic acid and abietic acid are formed by a very similar sequence of related enzymatic reactions; the former is an essential intermediate in the synthesis of gibberellins, i.e., growth hormones found in all plants, whereas the latter is a resin component largely restricted to members of the Fabaceae and Pinaceae. Similarly, the essential amino acid proline is classified as a primary metabolite, whereas the C6 analog pipecolic acid is considered an alkaloid and thus a secondary product. Even lignin, the essential structural polymer of wood and second only to cellulose as the most abundant organic substance in plants, is considered a secondary product rather than a primary metabolite. Biotechnologically manipulating the interface between committed steps in primary and secondary metabolism pathways has only recently emerged. Neither I have any definite idea nor have any reference on this aspect. I am not sure whether metabolic engineering interventions at primary-secondary metabolism interface which is being fruitfully applied for yield enhancements of specific secondary products, can be applied other way round.

Dear Dr. Tripathi

Many thanks for adding your highly informative and thought provoking response. I do not have the soft copy of the following publication:

Croteau, R. (1987) Biosynthesis and catabolism of monoterpenoids. Chem. Rev. 87, 929-954.

Prof. Croteau stated that essential oil constituents can be catabolised and metabolised back to primary metabolites. One of the stated reasons for the synthesis of secondary metabolites by plants is to convert them back to primary metabolites in times of need i.e. akin to a bank account where we save the money in times of surplus and draw the money when we need it. We can also think of investing a part of earnings in assets like gold, ornaments, house, land etc. as a security for use in times of need.

Best wishes.

Respected Sir, Plants produces metabolites classified as primary and secondary metabolites. While metabolites likee proteins, carbohydrates, lipids are essential for grown and development therefore also regarded as primary, while secondary metabolites are derived from primary and do not directly contribute to plant growth and development. No, these secondary metabolites are not inferior but species specific, perform some major functions like antimicrobial, tolerance to stress responses, biosynthesis of therapeutic metabolites etc.

I m not very sure, but in vitro conversion may be possible by biotransformation method by employing a biological agency like cell culture for biological conversion of compounds

Dear Ms. Pragya Tiwari

Thank you for your useful views. Secondary metabolites do take part in the growth and development of a plant but are not required for completing its life cycle.

Best wishes.