PCG 202 (HERBARIUM AND PLANT PRIMARY METABOLISM).pdf

 Herbarium is a storehouse of plant specimens which are collected, dried and mounted on handmade paper sheets.  They are arranged in plant families and kept in pigeon holes of steel or wooden cupboards and maintained carefully for current and future studies.  Herbarium is a...

 Herbarium is a storehouse of plant specimens which are collected, dried and mounted on handmade paper sheets.  They are arranged in plant families and kept in pigeon holes of steel or wooden cupboards and maintained carefully for current and future studies.  Herbarium is a reference material for naming, identification and classification of plants.  The herbaria are indexed with unique codes. Each herbarium is assigned an official code that is used as a standard reference for citation. ▪The Voucher herbarium specimen is pressed plant sample deposited for future reference and it will be verify the identity of the specific plant used in a study. The vouchers are crucial in authenticating the taxonomy of an organism, as a tool for identifying localities of the taxon, and for additional taxonomic, genetic, ecological, and/or research. Preparation of herbarium specimens: The preparation of the specimens is followed by: ▪i) Collection: The specimen material (plants) is collected as whole (if they are herbs) or part of plant along with flowers and fruits/carpels. Before putting your specimens in the collection bag remove all the insects, spider-webs and foreign bodies attached to your specimens. Then the specimens mounted in 42 cm x 29 cm (16 ½” x 11 ½”) size blotting paper. The leaves mounted in dorsiventral position. The half-size of the regular newspaper can fit this size. Put the mounted specimens in between cardboards/ wooden frames. ▪ii) Poisoning and drying the specimen: Poisoning kills the plants and prevents the formation of abscission layer and thereby the leaves, flowers and fruits will be intact with the specimen (twig) will not be getting detached from the plant. The poisoning is generally done by dipping the whole plant in a saturated solution of mercuric chloride in ethyl alcohol (usually 20 gm in a litre of alcohol). The plant is again put between the blotters/ newspaper in the presser till it gets completely dried. ▪iii) Mounting and labelling: The dried plant specimens are now mounted on herbarium sheets. Fixing the processed plant specimen on herbarium sheet is called mounting. A standard herbarium sheet is 28 cm (breadth) x 42 cm (length) and usually made up of heavy long-lasting white handmade paper or thick sheet. The sheet is usually stiff and flexible so as to prevent damage during the handling of mounted specimens. The common technique is pasting specimens to sheet with natural glue (usually Gum Arabic). The herbarium specimen sheet is now ready for deposition/reposition in the one of the indexed herbaria for the plant identification as well as to acquire a “Voucher Specimen” number. Voucher specimens provide a permanent, physical record and form the foundation on which all natural product research stands.  Metabolism can be defined as the sum of all the biochemical reactions carried out by an organism. Plant metabolism is the set of life-sustaining chemical transformations within the plant cell.  Metabolites are the intermediates and products of metabolism and are usually restricted to small molecules. Metabolite are also chemical compounds which take part in the process of metabolism.  A plant cell produces two types of metabolites: (1) Primary metabolites 2) Secondary metabolites  Figure 1: Primary metabolites ▪Primary metabolism comprises all metabolic pathways that are essential to the plant's survival, generating compounds (metabolites) that are directly involved in the growth and development of the organism. ▪The role of primary plant metabolites in basic life functions are cell division and growth, respiration, storage and reproduction. ▪They include the components of processes such as glycolysis, the Krebs or citric acid cycle, photosynthesis and associated pathways. ▪Primary metabolites include small molecules such as sugars, amino acids, tricarboxylic acids, or Krebs cycle intermediates, proteins, nucleic acids and polysaccharides which are essential for plant growth, development, reproduction, stress adaptation, and defense. Figure 2: Examples of Primary metabolites  Biological Significance of Carbohydrate  a) Saccharides play a role as structural elements and cell wall polysaccharides, e.g. cellulose  b) In energy storage, e.g. starch  c) As constituents of various metabolites, e.g. nucleic acid  d) In protecting tissues against dehydration Biological Significance of Proteins  a) Proteins can be part of a structural element of a cell  b) Enzymes and many receptors are also proteins Biological Significance of Lipids ▪a) The main biological function of lipids is energy storage ▪b) As structural components of cell membranes ▪c) As important signaling molecules Biological Significance of Organic Acids Some of the organic acids play a role in the kreb cycle. These are citric, malic, succinicc, fumaric, oxaloacetic, ketoglutaric, and pyruvic acid. This cycle plays a role in synthesis within the plant cells, while it is mainly an energy source in animals. Figure 3: Roles of some plant primary metabolites ▪Secondary metabolism produces a large number of organic compounds that are not essential to the functioning of the plant (growth, development and reproduction) but are required for the plant to survive in its environment. ▪Secondary metabolites are compounds biosynthetically derived from primary metabolites. ▪ Secondary plant metabolites are useful for defence purposes (against insects of fungi), they give plants characteristics colour, they also attract pollinators. ▪Secondary metabolites have shown to possess various biological and pharmacological effects (antibiotic, antifungal, antiviral, anti-inflammatory, anti-cancr etc.) which provide the scientific base for the use of plants in the traditional medicine. ▪Some primary metabolites are precursors of secondary metabolites. ▪Secondary metabolites have shown to possess various biological and pharmacological effects(antibiotic, antifungal, antiviral, anti-inflammatory, anti-cancr etc.) which provide the scientific base for the use of plants in the traditional medicine. ▪Secondary metabolites are used commercially as biologically active compounds as pharmaceuticals, flavors, fragrances, and pesticides. ▪Examples of secondary metabolites are alkaloids, phenolics, tannins, flavonoid, anthraquinones, essential oils, steroids etc.  There are four different pathway used by plants to produce secondary metabolites and each is responsible for the synthesis of different classes of compounds.  1.) Shikimic acid pathway: simple phenolics glycosides, lignans, coumarins and napthoquinones  2.) Acetate-malonate pathway: anthraquinone, flavonoids, tannins  3.) Mevalonate pathway: tannins  4.) Amino acid pathway: alkaloids