Plant secondary compounds lecture note.pptx

Lecture note

1. REVIEW ON PLANT SECONDARY METABOLITES IN PLANTS AND THEIR SIGNIFICANCE Submitted By:- Hemlata Ph.D scholar Deptt . of Entomology

2. SECONDARY METABOLITES Plants synthesize different organic molecules called secondary metabolites. These compounds often differ between individuals from the same population of plants. They are involved in the normal growth, development, or reproduction of an organism. They protect plants against stresses, both biotic and abiotic .

3. Significance of Secondary Metabolites Secondary metabolites attract animals for pollination and seed dispersal. The plants used in their defence against herbivores and pathogens. They act as agents of plant-plant competition. They are used in making drugs, insecticides, flavours, pigments, scents, rubber, spices and other industrial materials like gums, resins for human welfare.

4. Types of Secondary Metabolites These are highly numerous in number, chemically diverse in nature and belong to three groups. Isoprenoids or Terpenes , e.g., rubber, steroids, essential oils, carotenoid pigments. Nitrogen containing compounds , e.g., alkaloids, glucosinolates , glycosides, non-protein amino acids. Phenolic compounds , e.g., lignin, tannins, coumarins , aflatoxins , flavonoids .

5. 1.TERPENES Terpenes are involved in defense as toxins and feeding deterrents to a large number of plant feeding insects. Terpenes are divided into : Monoterpenes Sesquiterpenes Diterpene Triterpenes Polyterpenes

6. Monoterpenes (C10) This pyrethroid occur in the leaves and flowers of Chrysanthemum species. It has a low persistence in the environment and low mammalian toxicity. In Gymnosperms (conifers) á- pinene , â- pinene , limonene and myrecene are found.

7. Sesquiterpenes (C15) It plays an important role in plant defense . Such as costunolides are antiherbivore agents having strong feeding repellence to many herbivorous, insects and mammals. ABA is also a sesquiterpene . It plays a roles in: Initation and maintenance of seed and bud dormancy. Plants response to water stress.

8. Diterpenes (C20) Abietic acid is a diterpene found in pines and leguminous tress. It is present in resin canals of the tree trunk. Phorbol found in euphorbiaceae work as skin irritants and internal toxins to mammals.

9. Triterpenes (C30) They are important component of plant cell membranes, especially in the plasma membrane. Milkweeds produce glucosides that protect them against herbivores by most insects and even cattle.

10. Limnoid , a group of bitter substances in citrus fruits and act as antiherbivore compounds. Azadirechtin acts as a feeding deterrent to some insects like insects in order Lepidoptera and diptera .

11. Polyterpenes (C5)n These polyterpenes occur in plants. Tetraterpenes are carotenoids family of pigments. Rubber is found in long vessels called laticifers , provide protection as a mechanism for wound healing and as a defense against herbivores .

12. 2.Nitrogen containing compounds They include alkaloids, cyanogenic glucosides , and non-protein amino acids. Most of them are biosynthesized from common amino acids. They play a great role in the antiherbivore defense and toxicity to humans.

13. Alkaloids Alkaloids are a group of naturally occurring chemical compounds. Most alkaloids are believed to function as defensive elements against predators, especially mammals because of their general toxicity and deterrence capability.

14. Cyanogenic glucosides They constitute a group of N-containing protective compounds usually occur in members of families viz., Graminae , Rosaceae and Leguminosae . The presence of cyanogenic glycosides deters feeding by insects and other herbivores such as snails and slugs.  

15. Amygdalin , the common cyanogenic glucoside found in the seeds of almonds, apricot, cherries and peaches. Lima bean is inducible indirect antiherbivore defences including the production of volatile organic compounds (VOCs).

16. Non-protein amino acids Many plants also contain unusual amino acids called non- protein amino acids. They are present in free forms and act as protective defensive substances. Canavanine and azetidine is a non-functional proteins its catalytic site is disrupted.

17. 3.Phenolic compounds A hydroxyl functional group on an aromatic ring called Phenol. These is an important part of the plants defence system against pests and disease including root parasitic nematodes.

18. Coumarin These phenolic compounds are present in vascular plants. They have a wide range of anti-microbial activity against both fungi and bacteria. It behave as natural pesticidal defense compounds for plants.

19. Halogenated coumarin derivatives inhibit fungal growth. 7-hydroxylated simple coumarins may play a defensive role against parasitism of Orobanche cernua .

20. Lignin Lignin vary among species, plant organs and even layers of a single cell wall. Its chemical durability makes it relatively indigestible to herbivores and insects pathogens. Lignifications block the growth of pathogens and are a frequent response to infection or wounding.

21. Flavonoids Flavonoids have different functions in plant system including pigmentation and defense . They are ubiquitous in photosynthesizing cells. Flavonoids protect plants from different biotic and abiotic stress.

22. It act as: 1. Phytoalexins 2. Unique UV- filter 3.Detoxifying agents 4. Allelopathic compounds 5. Function as signal molecules 6.Antimicrobial defensive compounds

23. Isoflavonoids Isoflavonoids are ubiquitously present in plants. They play a critical role in plant development and defense response. It promotes the formation of nitrogen-fixing nodules by symbiotic rhizobia . 

24. Tannins Tannins reduce the growth and survivorship of many herbivores. It act as feeding repellents to a great diversity of animals. In mammalian herbivores, they cause a astringent sensation in the mouth. Protocatechllic and chlorogenic acids have a special function in disease resistance.

25. They prevent smudge in onions, a disease caused by the fungus Colletotrichum circinans . Proanthocyanidins act as feeding deterrents against some insects such as, Lymantria dispar (L.), Euproctis chrysorrhoea (L.) and O. brumata .

26. 4.Sulphur containing secondary metabolites They include: GSH GSL Phytoalexins Thionins Defensins Allinin They linked with the defence of plants against microbial pathogens.

27. GSH The major forms of organic S in the soluble fraction of plants. It reduces S in the regulation of plant growth and development. Ascorbic acid is the integral weapon in the defense against ROS generated by O 3 .  

28. GSL A group of N and S containing glucosides that increase their resistance against the unfavourable effects of predators, competitors and parasites. They release volatiles defensive substances exhibiting toxic or repellent effects. Mustard oil glucosides in cruciferae and allyl cys sulfoxides in allium . Isothiocyanates and nitriles , function in defense as herbivorous toxins and feeding repellent.

29. Phytoalexins Phytoalexins are synthesized in response to bacterial or fungal infection. They help in limiting the spread of the invading pathogens by accumulating around the site of infection.

30. There are multiple responses involving several related derivatives such as: Orchinol in orchid tubers Trifolirhizin in red clover Glyceollins in Glycine max Wyerone forms in Vicia fava Pistin in Pisum sativum pods

31. Defensins , thionins and lectins Defensins genes are partly pathogen-inducible are involved in resistance. Accumulation of thionins in the cell wall of wheat involved in defense responses to infections and in spreading of Fusarium culmorum . Plant produce lectins as defensive proteins that bind to epithelial cell lining of the digestive tracts and interfere with nutrient absorption.

32. CONCLUSIONS The potential roles of Plant secondary metabolites in defence mechanisms and ecological adaptation. The N and S containing secondary metabolites enhance the capability of a plant to cope with biotic and abiotic stress. Additional research in area of natural pesticides development is needed in current scenario. This will improve their resistance against herbivores and microbial pathogens as well as various environmental stresses.