Chap_7_Plant_Growth.pptx
- 1. PLANT GROWTH
- 2. Growth can be defined as irreversible increase in the dry weight & volume of an organism. Introduction Growth is due to cell division, cell enlargement & maturation The process marks completion by a) permanent change in size & b) increase in dry weight. Animal growth is uniform & limited but plant growth is not uniform (growth is seen at tips) & unlimited. Growth can be studied from the seed stage, a seed is made up of embryo enclosed by endosperm finally seed coat.
- 3. Introduction contd…. Embryo further can be differentiated into radicle, plumule & cotyledons (seed leaves). Radicle & Plumule form the embryo axis & is also called as tigellum. The point of attachment of cotyledons & embryo axis is called as first node. The part of embryo axis between first node & plumule is called Epicotyle similarly the part of embryo axis between first node & radicle is called Hypocotyle. If endosperm persists the seeds are called endospermic/albuminous & if the endosperm is used then the seed is called as non-endospermic/exalbuminous seed. Testa & Tegmen are the two seed coats.
- 4. Seed Dormancy (Rest) Dormancy may be defined as the condition of the viable seed when it fails to germinate even under favorable conditions. Quiscence It is defined as the condition of viable seed which fails to germinate because of unfavorable conditions Immature embryo’s Factors affecting Seed Dormancy Impermeable seed coat Presence of germination inhibitors, eg: Abscissic acid, Phenolics
- 5. Scarification of seed coat: Mechanical roughening of seed coat, to make it pervious to water Methods to induce germination Stratification of seeds: Moist seeds are subjected to temperature gradient, changing environmental conditions like light, pressure, temperature. Growth Regulators: Treating the seeds with Growth regulators like Auxins, Giberellins etc. Seed Germination The resumption of active growth of an embryo of seed after a period of dormancy is known as seed germination.
- 6. Cell enlargement (with the help of water) Changes during Seed Germination Hydrolysis Translocation of food Conversion of food into simpler forms. Types of Seed Germination Epigeal (Cotyledons above the ground): Cotyledons are pushed upwards above the soil due to elongation of hypocotyle. Hypogeal (Cotyledons remain below the ground): Cotyledons remain below the soil due to elongation of epicotyle.
- 9. Water: Increases permeability, essential for enzymatic activity. Factors affecting germination Oxygen: required for respiration & release of energy. Temperature: Optimum temperature is 26 to 300C. Light: Not an essential factor but some seeds germinate better when exposed to light. Characteristics of Growth Meristematic tissue or Growing tissue is responsible for growth. It is present in the apices of stem & root. According to the origin meristems are of two types’ primary (increase in length) & secondary. Secondary meristem is seen in vascular bundle & cork cambium.
- 10. Growth Curve It is a Sigmoid or S shaped curve. Growth curve shows following three phases Lag Phase – initial phase, slow growth Log Phase – rapid increase in growth Steady Phase – slow growth due to limitations of nutrients.
- 11. Phases of Growth Formative Phase or phase of cell division Phase of Elongation or enlargement Phase of Maturation or Differentiation Restricted to the apical meristems (root & stem) Cell divide continuously, they show abundant cytoplasm, distinct nucleus & thin cellulose wall. Cells increase in size; cells elongate & enlarge to reach maximum dimensions in this phase. Cells mature & differentiate to obtain permanent size; thickening of cell wall takes place The time interval from formative phase to maturation phase is called Grand period of Growth.
- 12. Factors affecting Growth Temperature: Optimum temperature required for proper growth should be 26 to 30oC, above 45oC protoplasm coagulates & is damaged hindering growth. Nutrients: They are required for synthesis of protoplasm provide energy. Water: Required to maintain turgidity of growing cells & also as a medium for chemical reactions. Oxygen: Indispensable for the process of respiration releasing energy Light: Not essential in initial stages but required later for photosynthesis & thus stimulates growth.
- 13. Growth Regulators Growth regulators are the main internal factors controlling growth, also called as plant growth hormones, Growth regulating substances. They are of two types namely Natural & Artificial. Properties of Hormones Hormones are other than nutrients They are required in less quantity. They move from place of production to the site of action. They have a broad action spectrum. An organic substance produced naturally & controls growth or other physiological process at a site away from its place of production is termed as plant hormone.
- 14. Auxins Tryptophan (Auxin precursor) is converted to form auxins. Auxins are found in two forms Free Auxins (easy for isolation or extraction) & Bound Auxins (Difficult to extract). Free & Bound Auxins are always in a dynamic equilibrium. Anti auxins inhibit the action of auxins. Chemical Nature Chemical formula of auxins is C10H9O2N Weak organic acids occurring in the form of Indole – 3 – Acetic acid (IAA),. Tryptophan Indole Pyruvic acid / Tryptoamine Indole acetaldehyde IAA Tryptophan is produced in leaves
- 15. Went Avena Coloeoptile Test 3 cm long seedling of Avena is selected. Tip is removed (decapitulation) & placed on Agar block. Agar agar is a polysaccharide which acquires a gelatin like consistency when dissolved in water & cooled. Agar block is cut in to pieces, tips are discarded. Agar block is placed asymmetrically on cut end of the coleoptile for 2 hrs. Curvature is observed. Characteristics Synthesis at shoot, root tips & young parts of plants. Moves from top to bottom Inactivated by light Higher concentration promotes stem growth & retards the growth of root & axillary buds & vice versa.
- 16. Role Stimulates cell division & elongation Promotes apical dominance Induces root formation Sex Expression – Increases number of female flowers Induces formation of seedless fruits (Parthenocarpy) Induces flowering in Litchi & Pineapple. Prevents sprouting of potatoes when need to be stored Prevention of lodging (falling of crops in windy season) Maintains the vegetative condition by inhibiting flowering which is required in crops like cabbage. Prevents formation of Abscission layer Prevents pre-harvest fruit drop Xylem differentiation Used in Tissue culture Weed Control – differential killing (2,4 D kills broad leaved dicot weeds without harming monocot crops)
- 17. Gibberellins Gibberellins were isolated from Gibberella fujikuroi (fungus) by Yabuta & Sumiki. Gibberella fujikuroi causes Foolish seedling of rice also called Bakanae’s disease. Such plants are unusually taller, seedless, thinner & paler. Chemical Nature Chemical formula of Gibberellic acids is as follows GA1 C19H24O6 GA2 C19H26O6 GA3 C19H22O6 GA4 C19H24O5 Acetyl Co A Kaurene Gibberellic Acid
- 18. Movement is non polar, lateral movement is also possible. Not influenced by light Characteristics They are concentrated in the growing regions like shoot apices, young leaves & embryos Role Stimulates rapid cell division & cell elongation leading to elongation of internodes Leaves become broader, increasing photosynthesis resulting in increase in height. Overcomes Dwarfism – Induces internodal growth in genetically dwarf varieties (Dwarfism is due to deficiency of Gibberellins, no additional internodes are produced but length of internodes increases).
- 19. Internodes strikingly increase just before flowering, this is termed as bolting, Gibberellins causes bolting & flowering. (In nature it is favoured by either cold nights/long days) Breaks dormancy & allows germination. Flowering – induces off season flowering. Role contd…. Modification of sex of flowers – induces production of male flowers. Formation of enzymes – mobilizes stored food during seed germination& early seedling growth by forming enzymes. (Proteases, Amylases, Lipases & Ribonucleases). Cold treatment is substituted Parthenocarpy Delay ripening
- 20. Kinetin was isolated from Herring sperm of DNA. Coconut Milk is a rich source of cytokinin. Basic in nature, amino purines or phenyl urea derivatives Cytokinins Zeatin (6-hydroxy 3-methyl trans 2-butenyl aminopurine) is the naturally occurring cytokinin & Kinetin (6 Furfuryl aminopurine) is an synthetic cytokinin. Chemical Nature C10H9N5O is the chemical formula, they are derivatives of purine base Adenine, & amino group in 6th position has many substitutes.
- 21. Synthesized in roots, movement is non polar. Characteristics Stimulates mitotic activity & found in areas of cell division. Counteracts apical dominance, delays senescence. Nutrient transport – regulates phloem transport. Cell Division – induces cell division & cell wall formation Role Flowering – induces flowering in few short day plants. Cell Enlargement – induces cell division in leaf discs & cotyledons Seed Dormancy – breaks dormancy & promotes germination.
- 22. Differentiation – induces plastid, trachied, interfascicular cambium differentiation. Role contd….. Senescence / Richmond Lang effect – Delays senescence by retention of chlorophyll & proteins. Apical Dominance – activates growth of lateral buds thus reducing apical dominance. Morphogenesis – Changing the balance of Cytokinins & Auxins initiates root/shoot growth.
- 23. Maximum production takes place in fruits before senescence (only growth regulator in gaseous form). Ethylene is a volatile gas produced through metabolic process & also called as ripening hormone. Ethylene Chemical Nature CH2=CH2 is a volatile gas. Methionine Methional Ethylene Methionine 4-methyl thio butyric acid Ethylene Movement is non polar, active in low temperature. Characteristics Synthesized in tissues undergoing senescence & ripening. Promotes abscission of leaves, flowers & fruits, inhibits root & stem elongation in dicots.
- 24. Sprouting of storage organs. Role Sex expression – feminizing effect. Epinasty – drooping of leaves. Senescence – enhances senescence Growth – stimulates horizontal growth in seedling Wound Response – reduces stress/withst& infection. Effect on flowering – stimulates flowering in pineapple. Activation of enzymes – activates the action of enzymes. Apical Dominance – promotes & prolongs dormancy of lateral buds. Fruit Ripening & climatic rise – production of ethylene increases 100 times.
- 25. Abscission – promotes the changes that occurs before abscission, enhances cell wall destroying enzymes. Role contd…. Root growth – At low concentration stimulates root growth, at high concentration root growth is inhibited. Triple response – reduction in elongation, swelling of epicotyl & change in direction of growth.
- 26. Production of this hormone is stimulated by drought, water logging & other adverse climatic conditions. Naturally occurring growth inhibitor, also called Stress hormone. Abscissic acid (ABA) Chemical Nature It is a 15 csron sesquiterpenoid, exists in positive (cis more active) & negative (trans) form. Trans form is converted in to cis in the presence of ultraviolet light. Synthesized in mature leaves & transported by vascular tissues Characteristics Effective in low concentration, movement is non polar. Inhibition of protein synthesis
- 27. Role Abscission – causes leaf fall, Senescence – accelerates leaf senescence Seed & Bud dormancy – maintains dormancy Release of Ethylene – stimulates release of ethylene. Growth inhibition – inhibits action of growth promoters. Flowering – promotes flowering in SDP & inhibits flowering in LDP. Water stress & antitranspirant – Causes closure of stomata & retains water. Resistance & tolerance – increases resistance to cold & enables to withstand dessication. Seed development & germination – inhibits development & germination by inhibiting activities of many enzymes.
- 28. Characters Gibberellins Examples Movement Auxins IAA Polar Cytokinins Developing seeds, roots Root, shoot tips Coconut milk Kinetin, Zeatin Gibberellic acids Site Main function Elongation of cells Cell division Mode of action Incr. O.P, permeability Activates DNA synthesis Induces auxin synthesis Non-Polar Non-Polar Elongation of internodes
- 29. Gibberellins Auxins Cytokinins P h y s i o l o g i c a l e f f e c t s Cell division Cell division Stem elongation Root initiation Apical dominance Prevents lodging Shortens internodes Initiates flowering promotes femaleness Parthenocarpy Breaks dormancy Prevention of abscission layer Weed control (2,4-D) Cell enlargement Reduces apical dominance Breaks dormancy Delays senescence Tissue differentiation Parthenocarpy Initiation of intra- fasicular cambium Bolting Flowering in biennial plants Induces male sterility Parthenocarpy Activates cell division Breaks dormancy Increases male flowers Delays ripening & Scenscence in Citrus
- 30. Characters Examples Movement Ethylene Non Polar Abscissic acid Fruits, Flowers, leaves Mature leaves Site Main function Post harvest ripening Inhibits buds, seed germination Mode of action Activates respiration Inhibts protein synthesis Non-Polar Ethylene Abscissic acid Causes Senescence Causes early leaf fall Causes abscission & leaf fall
- 31. P h y s i o l o g i c a l e f f e c t s Inhibits root & stem elongation Induces dormancy Ethylene Abscissic acid Initiation of flowering in Apple,Pineapple & Mango Forms adventitious roots Increases female flowers Epinsaty (downward rolling of leaves) Induces apical dominance Promotes abscission Breaks dormancy Promotes abscission Suppresses germination Closing of stomata (K+) Encourages leaf senescence by inducing loss of proteins & chlorophyll. Reduces rate of photosynthesis Induces flowering in few SDP Inhibition of shoot growth
- 32. Photoperiodism: The effect of duration of light hours on the growth & development of plants, especially flowering is called photoperiodism. On the basis of the photoperiod plants have been classified in to following categories: Short Day plants: They require shorter light period than their critical period. Uninterrupted dark period is more important & not the duration of exposure to light. If the uninterrupted dark period is less than critical length, flowering does not occur. Eg. Chrysanthemum, Potato, Sugarcane, Strawberry etc.
- 33. Long Day plants: They require longer period of light than their critical period. Photoperiod may vary from 14 to 18 hrs, best flowering occurs in continuous light. Darkness plays an inhibitory role. A flash of light during long dark periods can induce flowering even during short day periods. Shorter dark period is more important than light period. Eg. Spinach, Radish, Opium, Wheat etc. Day Neutral Plants: These plants flower irrespective of light & dark periods. Eg. Tomato, Cucumber, Sunflower, Maize etc.
- 34. Vernelization: The method of inducing early flowering by pretreatment of seeds with a certain low temperature is known as vernelization. Mostly biennials & perennials require need vernelization. Plants which can be vernelized are called inductive type & the one which cannot are called non inductive. In cold countries there are two types of cereals Winter & Spring. Winter cereals are sown in September/October flowering in following summer whereas Spring cereal is sown in Spring which flowers in Summer. If winter cereals are sown in Spring they will flower in next year’s summer i.e. they require chilling treatment.
- 35. Devernelization: When plants treated with cold treatment are exposed to higher temperature, the flowering did not occur this phenomenon is called devernelization. Physiology of flowering in Petkus rye: In cold countries there are two varieties of Petkus rye, winter rye & spring rye. Spring strain is annual, flowering & fruiting in one growing season but winter strain is biennial i.e. vegetative growth in the first season & flowering, fruiting in the next season. Thus Petkus rye the winter variety can be vernelized in the seed stage resulting in the production of flowers in the first acting as the spring strain.