Plant Hormones and Growth Regulators Quiz
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Questions and Answers

Which of the following is NOT a recognized group of plant hormones?

  • Auxin
  • Gibberellins
  • Cytokinins
  • Salicylic acid (correct)

    • Plant hormones can only promote cellular activities.

    False (B)

    What is the primary function of plant growth regulators?

    To alter growth patterns and/or maintenance of the plant.

    The effectiveness of a plant hormone depends on maintaining a closely regulated ______ size.

    <p>pool</p> Signup and view all the answers

    Match the plant hormone with its primary function:

    <p>Auxin = Promotes cell elongation and root development Gibberellins = Promote stem elongation and seed germination Cytokinins = Promote cell division and delay leaf senescence Abscisic acid = Promotes dormancy and stress tolerance Ethylene = Promotes fruit ripening and leaf abscission Brassinosteroids = Promote cell elongation and vascular tissue development</p> Signup and view all the answers

    What is the pointed protective sheath covering the emerging shoot in monocotyledons called?

    <p>Coleoptile (B)</p> Signup and view all the answers

    Plant hormones are only found in meristems and buds.

    <p>False (B)</p> Signup and view all the answers

    Who was the first scientist to discover a plant hormone?

    <p>Frits Went</p> Signup and view all the answers

    Auxin promotes the development of lateral buds.

    <p>False (B)</p> Signup and view all the answers

    The ______ is a plant hormone that promotes fruit development.

    <p>auxin</p> Signup and view all the answers

    Which of the following is NOT a function of auxin?

    <p>Inhibit leaf abscission (A)</p> Signup and view all the answers

    What is the name of the phenomenon where auxin produced in apical buds inhibits the development of lower buds?

    <p>Apical dominance</p> Signup and view all the answers

    Match the plant hormones with their primary functions:

    <p>Auxin = Promote fruit development Cytokinins = Promote lateral bud development Gibberellins = Promote stem elongation Ethylene = Promote leaf abscission</p> Signup and view all the answers

    What is the primary chemical structure of gibberellins?

    <p>Terpenoids (C)</p> Signup and view all the answers

    The discovery of gibberellins was linked to a fungal disease that caused abnormal growth in rice seedlings.

    <p>True (A)</p> Signup and view all the answers

    Gibberellins are produced in the ______ and ______ of plants.

    Signup and view all the answers

    Which of the following is NOT a function of brassinosteroids?

    <p>Promote fruit ripening (C)</p> Signup and view all the answers

    Salicylic acid is a phenolic compound involved in activating defense genes against pathogens.

    <p>True (A)</p> Signup and view all the answers

    What is the name of the most biologically active brassinosteroid?

    <p>Brassinolide</p> Signup and view all the answers

    The ______ is a small peptide found in wounded tissues and acts as a signal molecule for defense responses.

    <p>Systemin</p> Signup and view all the answers

    How are brassinosteroids deactivated in plants?

    <p>By epimerization of α-hydroxyl groups and subsequent esterification or glucosylation (C)</p> Signup and view all the answers

    Oligosaccharins are short-chain sugars found in cell walls and primarily play a role in plant defense against herbivores.

    <p>False (B)</p> Signup and view all the answers

    What is the term used for the production of secondary metabolites that poison predators or attract their predators in response to being attacked?

    <p>Inducible defences</p> Signup and view all the answers

    Cytokinins work to counter the effects of auxin, promoting lateral bud development.

    <p>True (A)</p> Signup and view all the answers

    The fungus ______ was responsible for the "foolish seedling" disease in rice plants, leading to the discovery of gibberellins.

    <p>Gibberella fujikuroi</p> Signup and view all the answers

    Which of the following is a characteristic of gibberellins?

    <p>They are related to carotenes and other isoprene derivatives (C)</p> Signup and view all the answers

    Gibberellins work independently of auxin to promote stem elongation.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the chemical produced by the fungus Gibberella fujikuroi that causes the "foolish seedling" disease in rice plants?

    <p>Gibberellin</p> Signup and view all the answers

    The application of auxin pastes to developing ovaries can promote ______, the development of fruit without the presence of viable seeds.

    <p>parthenocarpy</p> Signup and view all the answers

    Auxin is the only plant hormone involved in promoting fruit development.

    <p>False (B)</p> Signup and view all the answers

    What is one effect of gibberellins on plant growth?

    <p>Accelerates flowering in biennials (A)</p> Signup and view all the answers

    Gibberellins are used to shorten the stalk length of seedless grapes.

    <p>False (B)</p> Signup and view all the answers

    What is the primary natural cytokinin found in plants?

    <p>Zeatin</p> Signup and view all the answers

    Cytokinins are primarily found in ______ tissues of seeds, fruits, and root tips.

    <p>actively dividing</p> Signup and view all the answers

    Match the following gibberellin applications with their effects:

    <p>Bolting of biennials = Accelerates flowering Malting of barley = Speeds up malting process Gibberellins on dwarf tomatoes = Reverses genetic dwarfism Fruit production = Increases stalk length of grapes</p> Signup and view all the answers

    Which of the following is a commercial application of gibberellins?

    <p>Increasing sugar yield in sugarcane (C)</p> Signup and view all the answers

    Cytokinins are synthesized only in the root tips of plants.

    <p>False (B)</p> Signup and view all the answers

    What are the two main functions of gibberellins in plant physiology?

    <p>Promote cell elongation and influence floral initiation</p> Signup and view all the answers

    Ancymidol and paclobutrazol are examples of gibberellin ______ used to limit plant growth.

    <p>biosynthesis inhibitors</p> Signup and view all the answers

    The auxin to cytokinin ratio influences which aspect of plant growth?

    <p>Morphogenesis in cultured tissues (B)</p> Signup and view all the answers

    What is the primary effect of high concentrations of auxin and low concentrations of kinetin?

    <p>Development of roots (D)</p> Signup and view all the answers

    Ethylene is only produced in flowers and fruits.

    <p>False (B)</p> Signup and view all the answers

    Name a gas produced by plants that has significant effects on root and shoot development.

    <p>Ethylene</p> Signup and view all the answers

    Ethylene biosynthesis is controlled by the enzyme _______.

    <p>ACC synthase</p> Signup and view all the answers

    Match the following effects of ethylene with their corresponding descriptions:

    <p>Promotes fruit ripening = Causes softening and flavor enhancement Induces leaf senescence = Increases the rate of leaf aging Promotes root formation = Stimulates adventitious root development Breaks seed dormancy = Initiates growth from a dormant state</p> Signup and view all the answers

    What role does cytokinin play in plant physiology?

    <p>Delays leaf senescence (A)</p> Signup and view all the answers

    Cytokinins promote chloroplast development.

    <p>True (A)</p> Signup and view all the answers

    What is the phenomenon called when nutrients are mobilized into leaves from other parts of the plant?

    <p>Cytokinin-induced nutrient mobilization</p> Signup and view all the answers

    Ethylene can be synthesized from the amino acid _______.

    <p>methionine</p> Signup and view all the answers

    What effect does ethylene have on submerged aquatic species?

    <p>Encourages elongation growth (D)</p> Signup and view all the answers

    What effect does ethylene have on fruits?

    <p>It synchronizes flowering and fruit set. (C)</p> Signup and view all the answers

    Abscisic acid promotes seed germination.

    <p>False (B)</p> Signup and view all the answers

    What is the primary role of abscisic acid in relation to water stress?

    <p>Promotes stomata closure.</p> Signup and view all the answers

    Abscisic acid is synthesized from the carotenoid __________.

    <p>violaxanthin</p> Signup and view all the answers

    Match the following plant hormones with their effects:

    <p>Ethylene = Fruit ripening and flower abscission Abscisic Acid = Seed and bud dormancy Gibberellins = Promote seed germination Auxins = Promote growth and cell elongation</p> Signup and view all the answers

    Which of the following processes does abscisic acid regulate?

    <p>Seed dormancy (A)</p> Signup and view all the answers

    Abscisic acid only functions in the roots of plants.

    <p>False (B)</p> Signup and view all the answers

    How does abscisic acid affect guard cells during water deficit conditions?

    <p>It activates K+ ion transport out of guard cells.</p> Signup and view all the answers

    Abscisic acid levels are high when seeds are __________.

    <p>mature</p> Signup and view all the answers

    Which plant hormone is responsible for female sex expression in cucumber?

    <p>Ethylene (A)</p> Signup and view all the answers

    Study Notes

    Plant Growth Regulators

    • Plant hormones are chemicals produced by plants that modify growth and maintenance.
    • These hormones are found in various plant cells and tissues, but are most concentrated in growing areas and buds.
    • Hormones control cellular activities by sending chemical signals.
    • Plant hormones regulate cell division, elongation, and differentiation.
    • Plant hormones frequently interact with each other, and their impact overlaps. The effectiveness of a hormone depends on maintaining a stable amount.
    • This stability is achieved through a complex interplay of biosynthesis, storage as inactive conjugates, and molecule degradation.
    • Six primary plant hormone groups are recognized: auxins, gibberellins, cytokinins, abscisic acid, ethylene, and brassinosteroids.

    Classification of PGR

    • Growth-promoting hormones increase plant growth (e.g., auxins, gibberellins, cytokinins).
    • Growth-inhibiting hormones reduce plant growth (e.g., abscisic acid, ethylene).

    Hormone Action

    • Apical meristem: Hormones like auxin, cytokinins, and gibberellins impact cell division and elongation. Abscisic acid influences dormancy.
    • Flower: Auxins and gibberellins are involved in flower initiation and differentiation.
    • Fruit: Auxin and cytokinins affect fruit growth and ripening; ethylene affects ripening.
    • Leaf: Gibberellins promote growth, while ethylene contributes to leaf senescence.
    • Lateral bud: Auxin inhibits lateral bud growth, but cytokinins encourage it.
    • Stem: Auxin and gibberellins promote stem elongation.
    • Root: Auxin promotes root initiation and growth, but inhibits growth in some cases. Gibberellins also affect root development.

    Auxin

    • Auxin was the first plant hormone discovered.
    • Key experiments on auxin were conducted by Darwin (1880), Peter Boysen-Jensen (1913), Paál (1919), and Frits Went (1926).
    • Coleoptiles are the pointed protective sheaths, present in the emerging shoots of monocots.
    • Auxin is synthesized in meristematic regions, apical buds, young leaves, and the embryo after pollination.
    • This hormone moves down the stem primarily through the parenchyma cells by polar transport.
    • Auxin enters cells as IAAH (passively) or IAA- (active cotransport).
    • Transport proteins are present at a cell's basal end, assisting in moving auxin through the plasma membrane to adjacent cells.
    • Auxin plays a role in cell elongation by triggering the expansion of cell walls through proton pumps. This increases the concentration of H+ which activates proteins called expansins.
    • Expansins disrupt hydrogen bonds, breaking down cellulose bridges in cell walls which leads to expansion when water is absorbed.
    • Auxin is important in tropic responses (plant growth response to stimuli), particularly in the uneven elongation of cells on the shaded side of light-exposed plants.
    • Auxin triggers production of secondary xylem by stimulating cambium cell division.
    • This hormone plays a key role in wound tissue repair.
    • Apical dominance is the effect of auxins produced in apical buds inhibiting the growth of lower buds on the stem.
    • Auxin promotes lateral bud formation, but this effect diminishes with distance from the plant's shoot tip.

    Gibberellins

    • Gibberellins were discovered by E. Kurosawa when he observed "foolish seedling disease", caused by the fungus Gibberella fujikuroi.
    • Gibberellins are produced in roots, shoot tips, and young leaves, and concentrated in seeds.
    • Gibberellins are a family of molecules (more than 125 known) based on a 20-carbon ent-gibberellane structure.
    • Gibberellins promote rapid stem elongation and cell division, coordinating with auxins.
    • Gibberellins align microtubules in preprophase bands, influencing cellulose expansion in cells.
    • Effects of gibberellins include bolting (growth of stems that result in producing flowers). This occurs in biannual plants during the first growing season.
    • Gibberellins reverse genetic dwarfism.
    • This hormone regulates juvenile-to-adult transitions, floral initiation, and sex determination. Gibberellins also promote fruit set and seed germination.
    • Gibberellins are used in commercial applications like fruit production (longer stalks for seedless grapes), barley malting, and sugarcane yield enhancement.
    • Gibberellin biosynthesis inhibitors (e.g., ancymidol, paclobutrazol) are commercially used to stop plant growth, resulting in shorter, more compact plants.

    Cytokinins

    • Cytokinins are synthesized by a condensation of an isopentenyl group with the amino group of adenosine monophosphate.
    • Cytokinins are found in actively dividing plant tissues, including seeds, fruits, leaves, root tips, and wound sites.
    • Root tips appear to be the core locations for cytokinin production; these hormones are transported throughout the plant via the xylem.
    • Localized cytokinins at lower concentrations are needed to release buds out of dormancy.
    • Cytokinins regulate cell division in shoots and roots, affecting cell cycle components.
    • High zeatin levels are observed in synchronized tobacco cells at the end of the S phase, during mitosis, and in the G₁ phase.
    • The auxin/cytokinin ratio influences morphogenesis in plants.

    Ethylene

    • Ethylene is a gaseous hydrocarbon with effects on root and shoot development.
    • It's synthesized from the amino acid methionine through S-adenosylmethionine to 1-aminocyclopropane-1-carboxylic acid (ACC).
    • The production of ethylene is limited in some plants; sulphur is conserved and recycled in the Yang cycle.
    • Ethylene production is governed by transcriptional regulation, primarily through the enzyme ACC synthase.
    • Ethylene is released from the plant to the environment and in some cases it is deactivated through oxidation.
    • Ethylene promotes fruit ripening, lateral cell expansion, seed/bud dormancy break.
    • Ethylene promotes growth elongation in submerged aquatic species.
    • Ethylene influences flowering, root and root hair development in plants.
    • Applications for ethylene include hastening fruit ripening of apples and tomatoes, degreening citrus fruits, and synchronizing flowering and fruit set in pineapples.
    • Ethylene accelerates abscission of flowers and fruit; and induces fruit thinning in cotton, cherry, and walnut trees.
    • Ethylene promotes female expression in cucumbers thereby enhancing self-pollination and yield.

    Abscisic Acid (ABA)

    • ABA plays a critical role in seed and bud dormancy and responding to water stress.
    • ABA is a 15-carbon terpenoid, produced from the terminal section of carotenoids and is released in the process of cleaving the 40-carbon xanthophyll violaxanthin.
    • This hormone is degraded by oxidation into phaseic acid, and then further reduced to dihydrophaseic acid.
    • ABA is produced in virtually every part of a plant including the root cap and apical bud, and is mostly found in chloroplasts and amyloplasts.
    • ABA promotes winter bud scaling in woody plants.
    • ABA derivatives called dormins are used in nurseries to maintain dormant conditions in plants.
    • ABA promotes dormancy reversal with the help of gibberellins.
    • ABA promotes stomata closure when there is a water deficiency in leaves and triggers the activation of potassium ion transport out of guard cells.
    • Signal transduction pathways associated with calcium secondary messengers are needed.
    • ABA is produced in roots by detecting low water levels in tissues. This causes ABA to upwardly transport into leaves and activates stomata closure.
    • ABA helps in reducing transpiration to prevent water loss in times of scarcity.

    Brassinosteroids

    • Brassinosteroids are triterpene plant steroid hormones produced in pollen, immature seeds, shoots and leaves.
    • The most biologically active form is brassinolide.
    • Brassinosteroids are synthesized from the sterol campesterol.
    • They are deactivated by epimerization of the a-hydroxyl groups or esterification with fatty acids, or glucosylation.
    • Brassinosteroids promote stem elongation and ethylene production.
    • Brassinosteroids inhibit root growth and development.

    Other Plant Hormones (OTHERS)

    • Salicylic acid (phenolic): Activates defense genes, resulting in defense against pathogens, triggered by a hypersensitive reaction.
    • Oligosaccharins-Short chain sugars found in cell walls, play a vital role in defense against pathogens, and in the regulation of growth, differentiation, and flower development; acting as signaling molecules.
    • Systemin: A small peptide that stimulates defense activities as a ligand (signal molecule). It stimulates defense activation by initiating the signal transduction pathway.
    • Jasmonates (fatty acid derivatives): Play a part in regulating seed germination, root development, and protein storage. These hormones are produced in response to wound signals; they also regulate signal transduction pathways that result in the development of secondary metabolites like protease inhibitors or volatile compounds.

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    Test your knowledge on plant hormones, their functions, and key discoveries in the field of plant physiology. This quiz covers various aspects including definitions, functions, and classifications of plant growth regulators. Dive into the fascinating world of plant biology with questions that challenge your understanding.

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