Plant Growth Regulators/Plant Hormone PDF

Plant Growth Regulators/ Plant Hormone Week 3  What is Plant Growth Regulators?  hormones (from the  Endogenous organic Greek word hormaein, meaning "to excite") compounds active at  Other names; Plant very low Growth Regulators/...

Plant Growth Regulators/ Plant Hormone Week 3  What is Plant Growth Regulators?  hormones (from the  Endogenous organic Greek word hormaein, meaning "to excite") compounds active at  Other names; Plant very low Growth Regulators/ concentration Phytohormone  Internal and external signals that regulate plant growth are mediated, at least in part, by plant growth-regulating substances Difference of plant hormone to animal hormone ❖1. Fundamental actions are difference ❖2. Plant hormone not came from specialized tissue for hormone production, unlike animal hormone (e.g., sex hormones made in the gonads, human growth hormone - pituitary gland) ❖3. Plant hormones do not have definite target areas (e.g., auxins can stimulate adventitious root development in a cut shoot, or shoot elongation or apical dominance, or differentiation of vascular tissue, etc.).  Each has a Multiplicity of Effects  Depending on site of action  Developmental stage of plant  Concentration of hormone  Tissue specificity  Hormone – naturally occurring plant growth regulators  Synthetic growth regulators – not considered to be plant hormones  Type of Plant Growth Regulator 1. Auxin (indoleacetic acid) : cell elongation 2. Cytokinins (zeatin, zeatin riboside, isopentenyl adenine): (cell division + inhibits senescence) 3. Gibberellins (GAx...125): (cell elongation + cell division - translated into growth)  4. Abscisic acid (ABA): (abscission of leaves and fruits + dormancy induction of buds and seeds) 5. Ethylene: (promotes senescence, epinasty, and fruit ripening) 6. others (real and fabled; jasmonic acid, brassinolide, florigen, juvenone)  Auxin Stimulate shoot  Eg. IAA, IBA, cell elongation NAA Produced in apical and root meristems, young leaves, seeds in developing fruits. Stimulate growth but too much inhibits growth  Functions  1) Root initiation, stem elongation  2) Retard abscission (loss) of leaves & fruits 3) stimulates cell differentiation  4) Apical dominance  5)Inhibit bud formation 6) Embryogenesis ▪ Discovered as substance associated with phototropic response. ▪ Occurs in very low concentrations. ▪ Isolated from human urine, (40mg 33 gals-1) ▪ In coleoptiles (1g 20,000 tons-1) ▪ Differential response depending on dose.  Auxin promotes activity of the vascular cambium and vascular tissues.  plays key role in fruit development  Cell Elongation: Acid growth hypothesis  auxin works by causing responsive cells to actively transport hydrogen ions from the cytoplasm into the cell wall space  Auxin Discovery  Auxin increases the plasticity of plant cell walls and is involved in stem elongation.  Arpad Paál (1919) - Asymmetrical placement of cut tips on coleoptiles resulted in a bending of the coleoptile away from the side onto which the tips were placed (response mimicked the response seen in phototropism).  Frits Went (1926) determined auxin enhanced cell elongation. Discovery of auxin Signal-transduction pathways in plants Cell elangotion: Auxins works by causing responsive cells to actively transport hydrogen ions from cytoplasm into the cell wall space (Acid growth hypothesis) Biosynthesis of auxin Type of auxins in plant tissue culture Indolebutyric acid (IBA) Indoleacetic acid (IAA) 2, 4 dichlorphenoxyacetic acid (2,4D) 2, 4, 5 trichlorophenoxyacetic acid (2, 4, 5 T) picloram Application of auxin in tissue culture  0.01 – 10 mg L-1 IAA;  Low auxin → Synthetic auxins (2,4- adventitous root D, NAA) - relatively formation predominates; high more active: 0.001 auxin → callus – 10 mg L-1 formation  0.01 – 10 mg L-1 IAA;  2,4-D – induce Synthetic auxins (2,4- mutation, inhibit D, NAA) - relatively photosynthesis more active: 0.001 – 10 mg L-1  Auxin and papaya callus induction Fig. 1. The endogenous auxin and cytokinin content in hypocotyl and morphological observation of callus at different media during in vitro organogenesis of papaya. A. Hypocotyl of papaya ‘Zhongbai’ grown under light and dark condition for 7 days, Scale =1 cm. B. Statistics of hypocotyl length. C. The absolute quantification of hormone levels in the dark-grown hypocotyl of papaya ‘Zhongbai’. The value was calculated by using the standard curve. D–I. The state of callus formed after explants grown on K5, K19~K32 media for 30 days. Scale =2 mm. Statistical significance was determined by SPSS (*P