Physiology of Seed PlantsRegulating Growth and Development: The Plant HormonesHormonesThree basic elements of HormonesPhytohormonesFive classes of plant hormones The “Classic Five”AuxinsPowerPoint PresentationSlide 9Slide 10Slide 11Slide 12Slide 13Slide 14Auxin promotes fruit developmentSlide 16Slide 17Slide 18Other characteristics of AuxinCytokininsDiscovery had two affectsBasic medium used for tissue culture of plant cellsGrowth factor from DNAKinetinSlide 25Slide 26Slide 27In tobacco stem tissueSlide 29Slide 30SummarySlide 32Slide 33Cytokinins delay leaf senescenceEthyleneAbscisic Acid (ABA)/DorminAbscisic AcisGibberellinAdditional chemicals used by plantsPhysiology of Seed PlantsRegulating Growth and Development: The Plant Hormones•Auxins•Cytokinins•Ethylene•Abscisic Acid•GibberellinsHormones•Chemical signals that help both plants and animals regulate and coordinate metabolism, growth, and differentiation.•Phytohormones- plant hormonesThree basic elements of Hormones1. Synthesis of the hormone in one part of the organism2. Transport of the hormone to another part (target tissue)3. Induction of chemical responsePhytohormones •Produced in tissues or glands•Very active in small quantities–Pineapple Ananas comosus for example are only 6 micrograms of indoleacetic acid (IAA) a common plant hormone per kg of plant material. (analogous to a needle in 20 metric tons)–Can stimulate or inhibit depends on chemical structure and how it is read by the target tissueFive classes of plant hormonesThe “Classic Five”•Auxins-•Cytokinins- •Ethylene- •Abscisic acid- •Gibberellins-Auxins•Charles Darwin and Francis Darwin- The Power of Movement in Plants 1881In response to lightan “influence” that causesbending is transmitted from the tip to area belowthe tipThe Principle naturally occuring Auxin- Indoleacetic AcidIn plants variety of pathways to produce-tryptophan usually precursor-All tissue produces IAA but typicallyfound in shoot apical meristems, young leaves and developing fruit and seeds.Mutants lacking either auxin or cytokininHave yet to be found- mutations eliminatingThem are lethalAuxin synthesis- the site of auxin synthesis along the margin of a young leafSite corresponds to the location of cells that will differentiate into a hydothode (gland like structure)GIS reporter gene detects auxinsynthesisAuxin transport- experimental demo of polar auxin transport in stems represented here by a segment of hypocotyl from a seedlingIn the root, nonpolar transport of IAA takes place in the phloem of the vascular cylinder whereas the polar transportoccurs in the epidermis and cortical parenchyma cellsIAA induced xylem regeneration around a woundArrowhead- vascular regenerationAcropetal polar movement of auxin from Above the arrow and then around the wound•- When the apical bud is cut off a plant, the development of axillary buds in lateral branches is observed. •- If the apical bud is replaced by cotton impregnated with auxin, no axillary bud development is observed. •- So the auxin replaces the apical bud. - It can be deduced that this hormone is produced in the apical part of the plant.The inferior part of the plant including roots ( or root cap) is cut off and the plant isput in a medium containing auxin or free of it. Without auxin, adventitious roots can developed. This is the principle of cuttings.However, with auxin, root development is much better.Auxin promotes fruit development•Auxin is involved with the formation of fruit•Parthenocarpic fuit- by treating a female flower parts (carpels) of certain species with auxin it is possible to produce a fruit (without fertilization- a virgin fruit) i.e. seedless tomatoes, cucumbers and eggplants.•Developing seed is a source of auxinAuxin and fruit development- Normal strawberryStrawberry with all seeds removedStrawberry with horizontal band of seeds removedOther characteristics of Auxin•Auxin provides chemical signals that communicate information over long distances•Promotes the formation of lateral and adventitious roots•Synthetic auxin (2,4 dichlorophenoxyacetic acid) are used to kill weeds (broad leaf)–Mechanism unk.Cytokinins•In 1941 Johannes van Overbeek found that coconut milk (liquid endosperm) contained potent growth factors•Factors greatly accelerated the development of plant embryos and promoted the growth of isolated tissue and cells in vitro (test tube)Discovery had two affects –It gave impetus to studies of isolated plant tissues–Launched the search for another major group of growth regulatorsBasic medium used for tissue culture of plant cells•Contained sugar•Vitamins•Various salts•Grown in this culture, growth slowed or stopped•Thus some growth stimulus declined and the addition of IAA had no affects•Adding coconut milk encouraged the cells to divide and growth to resumeGrowth factor from DNA•Isolation of growth factor from DNA identifying its chemical nature called kinetin and the group of regulators called cytokinins because its involvement with cytokinesisKinetin•Resembles purine- adenine (a nitrogenous base)•Probably does not occur naturally in plants•Has relatively simple structure•Chemist able to synthesize a number of related compounds–Zeatin- most active naturally occurring cytokinin (maize)Cytokinins•Found in active dividing structures, seeds, fruits, leaves and root tips•Found also in SVP horsetail, fern•Central to tissue culture methods and extremely important in biotech.•Tx of lateral buds causes growth even in the presence of auxin thus modifying apical growth.•The cytokinin/auxin ratio regulates the production of roots and shoots in tissue cultures•Undifferentiated plant cell has two courses open to it–It can enlarge, divide, enlarge and divide again (undifferentiate) –without undergoing cell division, it can differentiate for example it can elongate then divide to form different type of cellsIn tobacco stem tissue•Application of IAA causes rapid cell expansion- giant cells are formed•Kinetin alone has little or no effect•IAA + Kinetin results in rapid cell division, so that large numbers of relatively small, undifferentiated cells are formed.•High IAA, callus tissue- a growth of undiff. Cells in tissue culture frequently gives rise to roots.Callus development- effects of increasing [IAA] at various kinetin•- At the top, the apical dominance have been annulled by cutting the apical bud.- At the