Plant Growth Regulators PDF

Plant Growth Regulators  Plant hormones/ growth regulators Are chemicals produced by plants that alter growth patterns and/or maintenance of the plant Found in many cells and tissues, although plant hormones seem to be concentrated in meristems and buds...

Plant Growth Regulators  Plant hormones/ growth regulators Are chemicals produced by plants that alter growth patterns and/or maintenance of the plant Found in many cells and tissues, although plant hormones seem to be concentrated in meristems and buds (which are dormant shoot meristems) Control cell activities by sending chemical signals or messages to cells to do something or to not do something, including activating the genes that code for specific enzymes Inhibit as well as promote cellular activities Hormones identified in plants most often regulate division, elongation and differentiation of cells RH10203 PLANT PHYSIOLOGY RH10203 PLANT PHYSIOLOGY  Most hormones have multiple effects in plants Plant hormones work in very small concentrations Often work in conjunction with each other, and have overlapping effects Also work with environmental stimuli Effectiveness of a hormone depends on maintaining a closely regulated pool size – accomplished by A balance of biosynthesis Storage as inactive conjugates Catabolic degradation of the molecule RH10203 PLANT PHYSIOLOGY  Presently there are six recognized groups of plant hormones: Auxin Gibberellins Cytokinins Abscisic acid Ethylene Brassinosteroids RH10203 PLANT PHYSIOLOGY  Classification of PGR On the Basis of Nature of Function Growth promoting hormones/Growth promoter: Increase the growth of plant. e.g. Auxins. Gibberellins, Cytokinins Growth inhibiting hormones/Growth retardant: Inhibit the growth of plant. e.g. ABA, Ethylene RH10203 PLANT PHYSIOLOGY RH10203 PLANT PHYSIOLOGY  The first hormone Auxin to be discovered in plants Summary of early experiments in auxin research Darwin, 1880 Peter Boysen-Jensen (1913) Paál (1919) Frits Went (1926) Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as oats and grasses. RH10203 PLANT PHYSIOLOGY  Where produces/ found in plant [] Meristematic regions & actively growing organs: coleoptile apices, root tips, the apical buds of growing stems, germinating seed Major site Young, rapidly growing leaves of synthesis Developing inflorescence Embryo following pollination and fertilization RH10203 PLANT PHYSIOLOGY  Auxin always moves down the stem parenchyma cells towards roots by polar (charged) transport (auxin becomes negatively charged) using proton pumps, an ATP requiring process Auxin enters cells as IAAH passively, or as IAA- via active cotransport IAAH dissociates within the cytosol and special auxin transport proteins in the basal end of the cell are needed to carry auxin through the plasma membrane to the top of the adjacent cell Auxin destined for root tissue, however, moves through phloem sieve tubes RH10203 PLANT PHYSIOLOGY  The chemiosmotic model for polar auxin transport (From Jacobs and Gilbert 1983) Shown here is one cell in a column of auxin-transporting cells RH10203 PLANT PHYSIOLOGY  Auxin functions Promotes elongation and cell enlargement For cell elongation, proton pumps increase the H+ concentration in cell walls, which stimulates expansins, proteins that disrupt hydrogen bonds and break cross linkages in cellulose This facilitates wall expansion when cells take in more water RH10203 PLANT PHYSIOLOGY  Auxin role in cell wall expansion RH10203 PLANT PHYSIOLOGY  Involved in tropic responses Auxins migrate away from light, which accounts for the uneven elongation of cells on the shaded side of a plant unevenly exposed to light, as studied by Darwin RH10203 PLANT PHYSIOLOGY  Auxin stimulates the production of secondary growth by simulating cambium cells to divide and secondary xylem to differentiate Wound tissue repair is initiated by auxin when portions of vascular bundles are damaged IAA-induced xylem regeneration around the wound in cucumber (Cucumis sativus) stem tissue (A) Method for carrying out the wound regeneration experiment. (B) Fluorescence (courtesy of R. Aloni.) micrograph showing regenerating vascular tissue around the wound. RH10203 PLANT PHYSIOLOGY  Auxin produced in apical buds tends to inhibit the activation of buds lower on the stems This is known as apical dominance This effect lessens with distance from the shoot tip Cytokinins (another group of plant hormones) counter the apical dominance effect of auxins and promote lateral bud development RH10203 PLANT PHYSIOLOGY  Promote lateral and adventitious root development Auxin applied to shoots on left and center Promote other hormone production, especially ethylene when auxin concentration increases Promote flower initiation Loss of auxin initiates leaf abscission RH10203 PLANT PHYSIOLOGY  Promotes fruit development Fruit development requires auxin produced by the developing seed Auxin pastes applied to developing ovaries can promote parthenocarpy (fruit development in the absence of viable seeds) Normal Fruit No fruit with seeds One row of seeds removed removed RH10203 PLANT PHYSIOLOGY  Gibberellins Normal Foolish rice The discovery of gibberellins – Ewiti Kurosawa when he determined that a fungus was responsible for abnormal rice seedling growth, called the "foolish seedling" disease The fungus secreted a chemical that caused the rice plants to grew abnormally long, and then collapse from weakness The fungus was Gibberella fujikuroi, hence the hormone name RH10203 PLANT PHYSIOLOGY RH10203 PLANT PHYSIOLOGY  Where produces/ found in plant Produced in roots and shoot tips and younger leaves, but have their highest concentration in seeds An extensive family of molecules with more than 125 now known 11 12 20 13 Diterpenes – based on the 20-C1 CH C 3 CH 3 19 ent-gibberellane structure 2 D A H 8 15 3 7 18 19 CH3 CH3 CH 3 RH10203 PLANT PHYSIOLOGY  Induce dramatic internode elongation in certain types of plants, such as dwarf and rosette species and grasses Related biosynthetically to carotenes and other isoprene derivatives RH10203 PLANT PHYSIOLOGY  Gibberellins functions Gibberellins work with auxins to promote rapid elongation and division of stem tissue. Gibberellins determine microtubule alignment in the preprophase band that determines the plane of cellulose expansion. Microtubule alignment in hypocotyl (Red dots are chloroplasts) RH10203 PLANT PHYSIOLOGY  The effects of gibberellins on elongation are seen in: Bolting of biennials, to produce flowers during the first growing season Reversal of genetic dwarfism GA on dwarf tomato and dwarf peas GA and bolting cabbage RH10203 PLANT PHYSIOLOGY  Regulate the transition from juvenile to adult phases Influence floral initiation and sex determination Promote fruit set Promote seed germination RH10203 PLANT PHYSIOLOGY  Gibberellins: commercial applications Fruit production to increase the stalk length of seedless grapes The bunch on the left is an untreated control The bunch on the right was sprayed with gibberellin during fruit development Malting of barley to speed up the malting process Increasing sugarcane yields to increase sugar yield in sugarcane RH10203 PLANT PHYSIOLOGY  Uses in plant breeding Reduce the time to seed production by inducing cones to form on very young trees Promotion of male flowers in cucurbits Stimulation of bolting in biennial rosette crops such as beet (Beta vulgaris) and cabbage (Brassica oleracea) RH10203 PLANT PHYSIOLOGY  Gibberellin biosynthesis inhibitors ancymidol (known commercially as A-Rest) or paclobutrazol (known as Bonzi) commercially to prevent to produce elongation growth in some plants shorter, more to further reduce stem length and compact plants lodging the restriction of growth in roadside shrub plantings RH10203 PLANT PHYSIOLOGY  Cytokinins A group of phenyl urea derivatives of adenine First chemically isolated in 1913 Were studied using coconut endosperm for a number of years starting in the 1940’s This isolate was shown to be a potent growth promoter and was used in tissue culture and embryo development studies RH10203 PLANT PHYSIOLOGY  Kinetin (N6-furfuryl adenine) The first molecule to be discovered with cytokinin activity However, is a synthetic cytokinin that was originally isolated from autoclaved DNA HN CH 2 O CH2 OH Amino purine N N N N N CH 2 CH3 H Zeatin is the most abundant N N natural cytokinin N N H trans-Zeatin (Z) RH10203 PLANT PHYSIOLOGY  Synthesized by a condensation of an isopentenyl group with the amino group of adenosine monophosphate (AMP) Also form conjugates with sugars Metabolized by oxidation RH10203 PLANT PHYSIOLOGY  Where produces/ found in plant Cytokinins are found in actively dividing tissues of seeds, fruits, leaves and root tips, and wound tissue sites Studies indicate that root tips are most likely the location for cytokinin production and cytokinins are transported through xylem to the rest of the plant However, localized cytokinins are needed to release buds from dormancy RH10203 PLANT PHYSIOLOGY  Cytokinin functions Regulate cell division in shoots and roots Regulate specific components of the cell cycle Zeatin levels were found to peak in synchronized culture tobacco cells at the end of S phase, mitosis, and G1 phase RH10203 PLANT PHYSIOLOGY  The auxin: cytokinin ratio regulates morphogenesis in cultured tissues At low auxin and high kinetin concentrations (lower left) buds developed. At high auxin and low kinetin concentrations (upper right) roots developed. At intermediate or high concentrations of both hormones (middle and lower right) undifferentiated callus developed. (Courtesy of Donald Armstrong.) RH10203 PLANT PHYSIOLOGY  Modify apical dominance and promote lateral bud growth Induce bud formation in a moss (Courtesy of H. Kende.) Control protonemal filaments Protonemal filaments treated with benzyladenine Overproduction has been implicated in genetic tumors Expression of genetic tumors in the hybrid Nicotiana langsdorffii × N. glauca. (From Smith 1988.) RH10203 PLANT PHYSIOLOGY  courtesy of R. Amasino Delay leaf senescence probably by stimulating RNA and protein synthesis and delaying degradation of chlorophyll Promote movement of nutrients into leaves from other parts of the plant, a phenomenon known as cytokinin-induced nutrient mobilization Plant expressing Age-matched ipt gene remains control: advanced green and senescence, no photosynthetic photosynthesis RH10203 PLANT PHYSIOLOGY  Promote chloroplast development Promote cell Expansion in leaves and cotyledons Regulate growth of stems and roots RH10203 PLANT PHYSIOLOGY  H H Ethylene C C A gaseous hydrocarbon H H Has significant effects on the development of roots and shoots Synthesized from the amino acid methionine via S- adenosylmethionine (SAM) and 1-aminocyclopropane-1- carboxylic acid (ACC) Because there are limited amounts of methionine in most plants, the sulphur is salvaged and recycled by the Yang cycle Ethylene biosynthesis is controlled by transcriptional regulation of the rate-limiting enzyme, ACC synthase Is readily given off to the atmosphere, but can also be deactivated by oxidation RH10203 PLANT PHYSIOLOGY  Ethylene biosynthetic pathway and the Yang cycle RH10203 PLANT PHYSIOLOGY  Where produces/ found in plant Produced in large amounts by tissues undergoing senescence or ripening Formed in all plant organs – roots, stems, leaves, bulbs, tubers, fruits, seeds … Rate of production – vary Stage of development From tissue to tissue within the organ – peripheral RH10203 PLANT PHYSIOLOGY  Ethylene functions Promotes the ripening of some fruits Induces lateral cell expansion Breaks seed and bud dormancy in some species Cereals/ Potato & other tubers Promotes the elongation growth of submerged aquatic species Dicots: Ranunculus sceleratus, Nymphoides peltata, and Callitriche platycarpa Fern: Regnellidium diphyllum Cereal deepwater rice RH10203 PLANT PHYSIOLOGY  Induces the formation of roots and root hairs Capable of inducing adventitious root formation in leaves, stems, flower stems, and even other roots Induces flowering in the pineapple family & mango May change the sex of developing flowers The promotion of female flower formation in cucumber Enhances the rate of leaf senescence RH10203 PLANT PHYSIOLOGY  Ethylene: important commercial uses Ethephon (2-chloroethylphosphonic acid) or Ethrel sprayed in aqueous solution readily absorbed and transported within the plant. releases ethylene slowly by a chemical reaction, allowing the hormone to exert its effects: hastens fruit ripening of apple and tomato degreening of citrus, synchronizes flowering and fruit set in pineapple RH10203 PLANT PHYSIOLOGY  accelerates abscission of flowers and fruits induce fruit thinning or fruit drop in cotton, cherry, and walnut promote female sex expression in cucumber, to prevent self-pollination and increase yield inhibit terminal growth of some plants in order to promote lateral growth and compact flowering stems RH10203 PLANT PHYSIOLOGY  Abscisic acid (ABA) Abscisic acid plays major roles in seed and bud dormancy, as well as responses to water stress A 15-C terpenoid compound derived from the terminal portion of carotenoids Synthesized by cleavage from a 40-C xanthophyll violaxanthin Degraded by oxidation to phaseic acid and subsequent reduction to dihydrophaseic acid RH10203 PLANT PHYSIOLOGY RH10203 PLANT PHYSIOLOGY  Where produces/ found in plant Detected in every major organ or living tissue from the root cap to the apical bud Synthesized in almost all cells that contain chloroplasts or amyloplasts CH3 H3 C CH3 H OH H COOH O CH 3 Abscisic acid RH10203 PLANT PHYSIOLOGY  Abscisic Acid functions Promotes seed dormancy activities ABA levels are high when seeds mature, promoting lowered metabolism and synthesis of proteins needed to withstand the dehydration associated with dormancy Seeds germinate when ABA is degraded by some environmental action Desert seeds must have the ABA washed out of the seed coat, as do plants of marshy areas; temperate area plants have ABA degraded by light-stimulated enzymes In other cases breaking dormancy is relative to the ratio of ABA (which keeps seeds in dormancy) and gibberellins (which promote germination) RH10203 PLANT PHYSIOLOGY  Promotes winter bud scale formation on woody plants in preparation for winter dormancy ABA derivatives, called dormins, are used in commercial nurseries to keep materials to be shipped in dormant conditions The dormancy can be reversed with gibberellins RH10203 PLANT PHYSIOLOGY  Promotes stomata closure during leaf water deficit conditions by activating K+ ion transport out guard cells This involves signal transduction pathways with Calcium secondary messengers ABA in this case originates in roots, and detects low water level in root tissues ABA moves upward into leaves and activates stomatal closure RH10203 PLANT PHYSIOLOGY  Abscisic acid is produced in the roots in response to decreased soil water potential and other situations in which the plant may be under stress. ABA then translocates to the leaves, where it rapidly alters the osmotic potential of stomatal guard cells, causing them to shrink and stomata to close. The ABA-induced stomatal closure reduces transpiration thus preventing further water loss from the leaves in times of low water availability. RH10203 PLANT PHYSIOLOGY  Brassinosteroids Triterpene derivatives with a chemical structure similar to animal steroid hormones Brassinolide The most biologically active brassinosteroid Synthesized from the sterol campesterol Deactivated by epimerization of the α-hydroxyl groups on the A ring and subsequent esterification with fatty acids or by glucosylation RH10203 PLANT PHYSIOLOGY  Where produces/ found in plant Pollen, immature seeds, shoots, leaves Brassinosteorid functions Promote shoot elongation Ethylene production Inhibit root growth and development RH10203 PLANT PHYSIOLOGY  OTHERS Salicylic Acid (phenolic)- Activate defense genes for resistance against pathogen invaders, known as the hypersensitive response Oligosaccharins (Short chain sugars in cell walls) – Play role in defense against pathogens; help regulate growth, differentiation and flower development; signaling molecules RH10203 PLANT PHYSIOLOGY  OTHERS (cont.) Systemin (small peptide in wound tissue) - Stimulate defense activities as the signal molecule (ligand) that activates the signal transduction pathways that include the jasmonates Jasmonates (fatty acid derivatives) – Play role in seed germination, root growth, and the storage of protein (especially in seeds); Synthesized in response to signal molecules produced in wound areas; involved signal transduction pathways that result in secondary metabolites (protease inhibitors) that poison the predator, or synthesis of volatile molecules that attract the predator’s predators RH10203 PLANT PHYSIOLOGY