Coordination & Control in Plants
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Which process would most likely be influenced by phytochromes in plants?

  • Regulating leaf color in autumn
  • Initiating flowering in response to daylight changes (correct)
  • Enhancing fruit ripening in the absence of light
  • Promoting root growth in the dark

    • What role do cytokinins play in the process of senescence in plants?

  • Delaying the breakdown of chlorophyll and prolonging leaf greenness (correct)
  • Promoting seed dormancy in low light conditions
  • Inducing earlier flowering in response to light
  • Accelerating the aging process of leaves

    • Which of the following is NOT a commercial use of gibberellins?

  • Inducing flowering in certain plants
  • Increasing fruit size
  • Stimulating cell division in tissue cultures (correct)
  • Delaying the ripening of citrus fruits

    • What is the primary effect of cytokinins in relation to apical dominance?

    <p>Promotion of lateral bud growth and reduced apical dominance</p> Signup and view all the answers

    How do photoperiodism and circadian rhythms relate to flowering induction?

    <p>Photoperiodism adjusts light duration, while circadian rhythms synchronize internal biological systems.</p> Signup and view all the answers

    Which statement regarding auxins is true?

    <p>The chemical messenger influences growth by asymmetrical distribution.</p> Signup and view all the answers

    What is a direct effect of gibberellins in plants?

    <p>Enhancement of fruit growth and parthenocarpy.</p> Signup and view all the answers

    Which compound is commonly used in agriculture as a herbicide?

    <p>Naphthaleneacetic acid.</p> Signup and view all the answers

    What role do gibberellins play in photoperiodism?

    <p>They can substitute red light to induce flowering in long-day plants.</p> Signup and view all the answers

    Which of the following is NOT a function of gibberellins?

    <p>Stimulating cell division in roots.</p> Signup and view all the answers

    The discovery of gibberellins involved isolating chemicals from which organism?

    <p>Gibberella fujikoroi.</p> Signup and view all the answers

    Auxins are particularly effective in which of the following applications?

    <p>Inducing root formation in stem cuttings.</p> Signup and view all the answers

    Which of the following statements about auxins and gibberellins is incorrect?

    <p>Auxins are synthesized in the roots of plants.</p> Signup and view all the answers

    What role do phytochromes play in plants?

    <p>They are responsible for responses to red light.</p> Signup and view all the answers

    Which plant hormone enhances seed germination and promotes apical dominance?

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

    How do oligosaccharins function in plants?

    <p>They signal defense responses.</p> Signup and view all the answers

    What is the primary effect of ethylene on ripening fruits?

    <p>It softens fruit and increases sugar levels.</p> Signup and view all the answers

    What is the function of phytochromes in resetting the biological clock of plants?

    <p>They activate and inactivate based on light exposure.</p> Signup and view all the answers

    What effect does carbon dioxide application have on fruit ripening?

    <p>It stops the ripening process during transport.</p> Signup and view all the answers

    In which way does light influence flowering in plants?

    <p>By regulating photoperiodism through phytochromes.</p> Signup and view all the answers

    What role does abscisic acid play during water stress in plants?

    <p>It removes K+ ions from guard cells causing stomatal closure.</p> Signup and view all the answers

    What is a significant characteristic of phytochromes?

    <p>They consist of two identical protein molecules.</p> Signup and view all the answers

    Which of the following statements about the synthesis and translocation of abscisic acid is correct?

    <p>Abscisic acid is synthesized in leaves, stems, fruits, and seeds primarily in the phloem.</p> Signup and view all the answers

    What physiological effect is NOT associated with brassinosteroids?

    <p>Facilitation of stomatal formation.</p> Signup and view all the answers

    What is the primary mechanism by which ethylene aids in seed dispersal?

    <p>It attracts animals that eat the ripened fruit.</p> Signup and view all the answers

    What is the primary effect of high levels of abscisic acid on plant parts?

    <p>It promotes abscission of fruits and leaves.</p> Signup and view all the answers

    Which of the following correctly describes the relationship between abscisic acid and seed dormancy?

    <p>It inhibits germination, allowing seeds to remain dormant in drought conditions.</p> Signup and view all the answers

    What commercial application leverages the properties of abscisic acid?

    <p>Inducing dormancy in nursery stock before shipping.</p> Signup and view all the answers

    Which is an antagonist of abscisic acid in plant growth regulation?

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

    How does abscisic acid affect stomata during periods of water stress?

    <p>It enables stomatal closure to conserve water.</p> Signup and view all the answers

    Which of these conditions promotes the germination of seeds that contain high concentrations of abscisic acid?

    <p>Heavy rainfall that washes out abscisic acid.</p> Signup and view all the answers

    What historical finding led to the identification of abscisic acid as a plant hormone?

    <p>Isolation of a substance from sycamore leaves called Dormin.</p> Signup and view all the answers

    What is primarily inhibited by abscisic acid during its function in plants?

    <p>Germination of seeds in adverse conditions.</p> Signup and view all the answers

    What is the primary factor that controls flowering in plants according to the given information?

    <p>Length of uninterrupted darkness</p> Signup and view all the answers

    Which type of plant will NOT flower if the dark period is shorter than its critical length?

    <p>Short-day plants</p> Signup and view all the answers

    How can a horticulturist induce flowering in long-day plants under unfavorable conditions?

    <p>By manipulating the duration of light periods</p> Signup and view all the answers

    What happens if a dark period intended for flowering is interrupted by a flash of light?

    <p>Flowering is inhibited if the interruption is short.</p> Signup and view all the answers

    Circadian rhythms in plants primarily relate to which of the following processes?

    <p>Flowering and seed germination</p> Signup and view all the answers

    In which situation would long-day plants exhibit flowering?

    <p>When the dark period is shorter than a critical length</p> Signup and view all the answers

    Photoperiodism is crucial for plants because it allows them to:

    <p>Synchronize flowering with environmental conditions</p> Signup and view all the answers

    Which of the following is NOT a typical consequence of photoperiodic flowering control?

    <p>Setting the duration of floral bud development</p> Signup and view all the answers

    What critical factor will ensure flowering in a short-day plant during an experiment?

    <p>A prolonged dark period</p> Signup and view all the answers

    In the experiments conducted, what is the conclusion regarding flowering in relation to light exposure?

    <p>Only uninterrupted darkness can induce flowering.</p> Signup and view all the answers

    Study Notes

    Coordination & Control in Plants

    • Plant hormones, also known as growth substances or plant growth regulators, are organic chemicals.
    • They exist in very low concentrations in plant tissues.
    • They act as messengers, stimulating, inhibiting, or modifying growth and development.
    • They are usually synthesized in specific regions of the plant, such as embryos, apical meristems of shoots and roots, and young growing leaves and developing seeds.

    Plant Hormones vs. Animal Hormones

    • Plants lack specialized glands for hormone synthesis.
    • Plant hormones are transported from the production site to other parts of the plant.
    • Plant hormones are active at their site of production.
    • Transport and action are generally slow in plants.
    • Plant hormonal actions are less specific, potentially affecting different tissues and organs.
    • Plant hormones are primarily involved in growth and development.
    • Animal hormones are produced by specialized endocrine glands.
    • Animal hormones are mainly transported by the bloodstream to target cells/organs.
    • Animal hormones are active primarily at their target cells/organs
    • Transport and action are generally rapid.
    • Animal hormonal actions are more specific, effecting only specific target cells/organs.

    Major Plant Hormones

    • Five major plant hormones recognized in modern plant biology: Auxin, Abscisic Acid, Cytokinin, Gibberellins, and Ethylene.
    • These hormones play crucial roles in plant growth and well-being.
    • Hormones may interact individually, have opposing effects (antagonism), or exhibit synergistic interactions (where the combined effect is greater than the sum of individual effects).

    1. Auxins

    • Plant hormones influencing cell division and elongation (via vacuolation and elongation).
    • Natural auxins, such as indole-3-acetic acid (IAA), are produced naturally by plants.
    • Auxin (IAA) binding to cells decreases cell pH, loosening cell walls, allowing for more water uptake.
    • This increased turgor pressure leads to cell swelling and elongation promoting plant growth.
    • Auxin effects depend on the target tissue.
    • Examples include auxin's role in shoot elongation, cell division and differentiation in vascular cambium, fruit development in ovaries, and lateral root formation in roots.
    • Phototropism - plant growth towards a light source
      • Auxin is produced more on the shaded side of a shoot or coleoptile.
      • Cells on the shaded side elongate faster than cells on the illuminated side.
    • Geotropism - Plant growth in response to gravity
      • Auxin gathers in the lower half of the stem and root, slowing growth in the root and curving downward.
      • Auxin stimulates growth in the shoot and stem, curving upward.
    • Promotes fruit development-stimulates fruit development and is used for parthenocarpy (fruit development without fertilization), producing seedless fruits.
    • Auxins also have inhibitory effects, suppressing lateral bud growth, which is known as apical dominance.
    • Inhibits abscission-causes dropping of leaves, flowers, and fruits from the plant
    • Young leaves and fruits produce auxins, and production of auxin reduces in an ageing leaf or ripened fruit, increasing production of abscisic acid.

    2. Gibberellins

    • Plant hormones promoting cell elongation and stem length growth.
    • Synthesized in meristems of apical buds, roots, young leaves and embryos in seeds.
    • Gibberellins have a terpene structure, a group of plant chemicals related to lipids.
    • Gibberellins stimulate stem growth by interacting with IAA and sometimes substituted for red light in promoting flowering in long-day plants and inhibits it in short-day plants.
    • Promotes fruit growth and parthenocarpy.
    • Used to break seed dormancy.
    • Inhibits root initiation
    • Stimulates leaf growth

    3. Cytokinesis

    • Plant hormones that promote cell division and differentiation in the presence of auxin.
    • Produced in actively growing tissues, such as embryos in seeds, fruits, and roots.
    • Transported in the xylem to various parts of the plant.
    • Promotes lateral bud growth (inhibition of apical dominance).
    • Delays senescence (aging) of plant cells.
    • Acts as a signal to shoots about the health and activity of roots.

    4. Abscisic Acid (ABA)

    • Plant hormone that slows metabolism and inhibits growth in most plant parts.
    • Works antagonistically to auxins, gibberellins, and cytokinins.
    • Synthesized in leaves, stems, fruits, and seeds.
    • Mainly translocated in the phloem and can diffuse from the root cap to the root cells.
    • Causes stomata closure during water stress by stimulating the removal of K+ ions from guard cells.
    • Causes dormancy in some seeds, particularly in desert plants; ABA inhibits germination which helps plants survive adverse conditions.

    5. Ethylene

    • Plant hormone in the form of a gas.
    • A metabolic by-product in most plant organs, especially ripening fruits and aging leaves.
    • Increased level of ethylene triggers fruit ripening (positive feedback).
    • Hydrolytic enzymes are released, breaking down cell wall components, chlorophyll, and softening fruits, converting starches and fruit acids to sugars.
    • The bright colors, scents, and sugars produced during fruit ripening help attract animals to eat the fruits and disperse the seeds.
    • Used commercially to allow the shipping of green, still-hard fruit (minimizing bruises and rotting) by applying ethylene after transportation.

    Other Hormones

    • Brassinosteroids - first discovered in Brassica pollen, stimulating cell division and elongation.
    • Broad spectrum of physiological effects on plants, promoting apical dominance, promoting leaf senescence, and enhancing seed germination, gravitropism.
    • Oligosaccharins - Oligosaccharides with hormone-like functions released from the cell wall by enzymes secreted by pathogens. The signal for defense responses.

    The Effect of Light on Flowering

    • Light is vital in directing plant growth and development.
    • Sunlight resets biological clocks in plants by activating and inactivating photoreceptors (phytochromes).

    Phytochromes

    • Phytochromes are photoreceptors for red light responses, present in low concentration in various plant organs, especially leaves.
    • Each phytochrome is a homodimer consisting of two identical protein molecules linked to a chromophore.

    Photoperiodism

    • Photoperiodism – response to the relative lengths of daylight and darkness.
    • Many plants flower at specific times of the year due to photoperiod differences.
    • Plants exhibiting this phenomenon are classified into short-day plants, long-day plants, or day-neutral plants.

    Phytochrome Roles in Controlling Flowering

    • Photoreceptor in photoperiodism is phytochrome.
    • The balance between Pr and Pfr forms of phytochrome controls flowering in short-day and long-day plants.
    • Pfr (active form) triggers or inhibits flowering in response to different light conditions.
    • Accumulation or high amounts of Pfr stimulates flowering in long-day plants, and inhibits flowering in short-day plants.
    • An accumulation of florigen( a chemical messenger that transmits information from leaves to flower buds) in the leaves is also needed for flowering. Florigen is secreted in response to relative amounts of Pr and Pfr in the leaves.

    Short-day Plants (SD)

    • Flower when the dark period exceeds a certain critical length.

    Long-day Plants (LD)

    • Flower when the dark period is less than a specific critical length.

    Day-neutral Plants

    • Plants unaffected by photoperiodism, such as tomatoes and cucumbers.

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    Description

    Explore the fascinating world of plant hormones in this quiz. Test your knowledge on how these growth regulators operate, their role in plant development, and how they differ from animal hormones. Delve into the intricate processes that guide plant growth and response to stimuli.

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