Production of Plant Secondary Metabolites: MCQ for DBT BET, GPAT, GATE, & CSIR NET

Production of Plant Secondary Metabolites: MCQ for DBT BET, GPAT, GATE, & CSIR NET

What are Plant secondary metabolites? The plant produces certain chemical compounds known as phytochemicals. Secondary metabolites are the chemical compounds that do not participate in plant metabolism. As secondary metabolites do not possess any physiological function in plants and they are not directly needed instead they have a major role in plant adaptation. It is found that during plant growth cells undergo morphological differentiation and maturation, cells produce secondary metabolites.  They are generally derived from primary metabolites such as amino acids, nucleic acids, etc. plant tissue culture techniques are preferred for the production of secondary metabolites for commercial interest. They are important sources of drugs, dyes, pigments, food additives, flavors, fragrances, and pesticides, hence they gain economic importance for pharmaceutical companies. Secondary metabolites Examples: Alkaloids, Glycosides including steroids and Phenolics, latex, tannins, terpenoids, etc. Secondary metabolites can be classified into three major groups based on their origin 1) Terpenoids: all terpenoids including, all secondary compounds and primary metabolites are derived from 5-carbon precursor isopentenyl diphosphate (IPP). 2) Alkaloids: they are derived from amino acids, hence they have one or more nitrogen atom. 3) Phenolics: they are formed by either the shikimic acid pathway or the malonate/acetate pathway.   Steps involved in Production of Secondary metabolites 1. Cell line selection for high yield: it is a critical step to separate producer cells from nonproducer cells which can produce large amounts of desired metabolites. This can be done by: a. Cell Cloning: in this procedure, there is the growth of single cells taken from suspension culture and these cells are screened for the secondary metabolites. Cells having high yield are maintained by sub-cloning. It can be either single-cell cloning or cell aggregate cloning. b. Visual or chemical analysis: cell lines that produce colored metabolites like dyes can be identified visually e.g. beta carotene Shikonin, which helps in selecting high-yield cells. For quantitative analysis, analytical methods like Radioimmunoassay, microspectrophotometry, HPLC, and fluorescent antibody techniques, are used for colonies from single-cell culture. c. Selection for resistance: mutant cells are found in a culture that is resistant to toxic compounds and overproduces metabolites. Such mutants can be selected to produce large quantities of metabolites.   2. Large-scale cultivation of plant cells: for large Industrial production of metabolites, a large number of cells are required, and hence large cultivation of plant cells is needed. Cultured plant cells vary in volume, shape, and size, further, low growth rate and genetic stability is seen in cultured cells. Based on these considerations large-scale cultivation of plant cells can be done by free cell suspension culture, Immobilized cell culture, two-phase system culture, and hairy root culture.   3. Composition of culture media and effects of nutrients: composition of culture media plays important role in the Invitro growth of plant cells. Two medium approach in which the first medium is required for desirable growth of cells and second media for good production of secondary metabolites is preferred for optimum production of secondary metabolites. The effects of nutrients such as Sucrose is more preferred than fructose or galactose as a carbon source. Ammonia is used as a nitrogen source, as nitrogen is utilized by cells to produce primary metabolites like proteins, amino acids nucleic acid enzymes, etc, hence the production of secondary metabolites is depended on primary metabolites. Inorganic phosphate is used, as it essential for respiration i.e. glycolysis and photosynthesis, even phosphorylated intermediates release phosphates like terpenes, terpenoids, and phenylpropanoids which are secondary metabolites. The selection of plant growth regulators like auxins and cytokinins is also essential as it has a direct effect on cell growth, metabolism, and differentiation. Precursors which are substrates molecules incorporated into secondary metabolites are added to the medium which can enhance the product formation 4. Elicitor-induced production of secondary metabolites: Elicitors are the compounds like pectin, pectic acid, (endogenous elicitors produced by plant cells) chitin, chitosan, (exogenous elicitors produced by a microorganism), ethylene, fungicides, antibiotics (abiotic elicitors chemical agents) and cold, heat UV light (physical abiotic elicitors) are used to promote or stimulate the production of secondary metabolites. This elicitor’s act by gene activation and increase synthesis of mRNAs encoding enzymes, responsible for secondary metabolite production. 5. Effect of environmental factors: environmental factors like light is essential for photosynthesis and light-mediated enzymatic reactions, indirectly affect the production of secondary metabolites. Generally, a temperature of 250 to 300 is essential for the optimum growth of cultured cells as cell growth is increased with an increase in temperature. the pH of the culture medium should be 5 to 6 for the good growth of cultures. Continuous aeration is needed for good growth of culture and ultimately production of secondary metabolites. 6. Biotransformation using plant cell culture: it is a conversion of one chemical molecule into another i.e. substrate into the final product by using a biological system i.e. cell suspension known as biotransformation or bioconversion. Free or immobilized Enzymes as biocatalyst are used for the purpose. The reactions like hydroxylation, reduction or glycosylation may be involved in bioconversions. In brief, the bioconversion involves the conversion of less important substances to valuable medicinal or commercial products like digitoxin to digoxin obtained for digitalis. 7. Release and analysis of secondary metabolites: this involves purification and separations of secondary metabolites from cell culture. Isolation and analysis are easy when product form is released in medium or else permeabilizing agents such as dimethyl sulfoxide (DMSO) is used to disrupt two cell membranes i.e. plasma membrane and tonoplast to release the product stored in vacuoles of the cell.

Advantages for production of secondary metabolites

  1. Production of compounds can be done in controlled conditions as per market demand.
  2. Environmental factors, seasonal variations, pest, and microbial diseases, and geographical constraints can be avoided by the in-vitro cultural system
  3. Product formation can be facilitated by control over cell growth.
  4. The consistency of quality products can be achieved as they are produced from a specific cell line.
  5. Product recovery is easy
  6. In-vitro cultures are important when plants are expensive or difficult to grow in fields.
  7. Mutant cell lines can be developed for the production of novel compounds.
  8. Plant tissue culture techniques can minimize time and labor cost

Disadvantages

  1. In compared to intact plants, production of secondary metabolites is lower in Invitro culture
  2. There are chances of cell damage during culture due to vigorous stirring
  3. Strict aseptic conditions have to be maintained, otherwise, any infection to the culture can affect production.
 

Examples of secondary metabolites used as drugs

Secondary metabolite (drug)

Use

Vincristine

Anti-cancer

Podophyllotoxin

Anti-neoplastic

vinblastine

Anti-neoplastic

digoxin

Cardiotonic

Morphine

Analgesic

Codeine

Analgesic

Quinine

Anti-malarial

Nicotine

Insecticidal

Sennosoides (Anthraquinone)

Laxatives

 

   

Multiple-choice questions

  1._____________is the source for Production of secondary metabolite a) Primary metabolite b) DNA c) RNA d) Carbohydrates   2. Secondary metabolites are used by plant cells for__________ a) Production of nucleic acids b) For making plasma membrane c) Morphological differentiation d) All   3. Secondary metabolite is source for ____________ a) Drugs b) Fragrances c) Dyes d) All   4. Which one of the following is NOT secondary metabolite a) Proteins b) Alkaloids c) Terpenes d) Terpenoids   5. _______________is one of the function of secondary metabolite a) As drug b) To attract birds c) To make disease free plant d) all     6. _______________is visually identified secondary metabolite a) Digitoxin b) Digoxin c) Beta carotene d) Quinine   7. Elicitors are the compounds used to enhance the growth, size, and shape of plant cells in tissue culture a) True b) False c) Partially True d) None of the above   8. ___________is Endogenous type of elicitor a) Temperature b) Pectin c) Chitin d) Fungicide   9. __________ range of temperature is required for in-vitro culture a) 200 to 250 b) 300 to 350 c) 250 to 300 d) 350 to 400   10. Production of secondary metabolites by plant tissue culture technique is preferred because a) Production yield is very high b) Product recovery is easy c) Aseptic conditions can be easily maintained d) No skilled person is required Answer Key
  1. a
  2. b
  3. d
  4. a
  5. a
  6. c
  7. b
  8. b
  9. c
  10. b
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Reference

  1. U. Satyanarayana, biotechnology, 1st e.d. Kolkata, books & allied (p) ltd publishers, 2005  page:507-516
   

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