Plant Responses to the Environment

  1. Plants
    and Environment
    • Hormones are used by plants to control
    • Growth
    • Development
    • Responses to environmental stimuli
    • Plants have adapted to many aspects of
    • their environment
    • Physical, or abiotic,
    • part
    • of environment such as light, temp, nutrients
    • Biotic such as predators, pollinators

  2. Hormones
    • Hormones are found in all multicellular
    • organisms
    • Chemical “coordinators” of organisms
    • Required in only minute amounts
    • Produced in one part of the organism and
    • are then transported to another part where they trigger a response

  3. Plant Hormones
    • Auxin
    • Cytokinins
    • Gibberellins
    • Abscisic Acid
    • Ethylene
    • Florigens
  4. Auxin
    • Controls growth and response to light
    • Promotes or inhibits cell elongation
    • Stimulates cell differentiation in xylem
    • and phloem of developing plants
    • Stimulates maturation of fruits
    • Influences timing of germination
    • Auxin is produced in the apical meristem

  5. Phototropism
    • Growth toward light
    • Controlled by auxin
    • production in shoot tip
    • Increase in auxin
    • causes cells in the stem to elongate
    • If stem is vertical, auxin is
    • evenly distributed and cell growth is equal

  6. Phototropism and Gravitropism
    • Work together to encourage vertical plant
    • growth
    • Auxin causes roots to grow toward gravity
    • because at very high concentrations it inhibits cell elongation
    • Root cells contain specialized plastid
    • cells with starch grains, called statoliths
    • As statoliths fall, auxin accumulates
    • Cell growth is inhibited on that side

  7. Cytokinins
    • Stimulates cell division, budding
    • Produced in actively growing tissues
    • Roots, embryos, fruits
    • Cytokinins travel through plant via xylem
    • It is the ratio of cytokinins
    • to auxin that
    • determines cell division and differentiation
    • Ratio helps a
    • plant maintain “weight” at the level of soil
    • Apical dominance occurs when high auxin
    • suppresses the formation of branches
    • Removing the apical meristem results in
    • more branching
    • High cytokinins in roots inhibits root growth
    • Cytokinins prevent cell death

  8. Gibberellins
    • Produced by the embryo and in young
    • plants’ roots and leaves
    • Activates the genes for enzymes that
    • break down the starch in the seed
    • Sugars are used by embryo for energy
    • Promotes growth of leaves and stems
    • Stimulates growth of flower stalk
    • Encourages fruit growth (fig 45-10)

  9. Abscisic Acid
    • Slows/suspends plant growth
    • Prepares plant for winter
    • Promotes dormancy of seeds (i.e. over the
    • winter)
    • Helps plant cope with stress
    • Water loss triggers abscisic
    • acid, which triggers the closure of stomata

  10. Ethylene
    • Senescence- irreversible changes leading
    • death
    • Can happen at the cell, structure, or
    • plant level
    • Leaves dropping in fall, break down of
    • chlorophyll
    • Flowers dying
    • Fruit ripening
    • Cell walls break down making fruit
    • “softer”

  11. Florigens
    • Leaves produce signaling hormones to
    • indicate lengthening day
    • A single leaf can detect changing light
    • and induce flowering on other areas of the plant
    • The actual molecule responsible is still
    • unknown
    • Scientists refer to these hypothetical
    • flowering hormones as florigens

  12. Biological Clocks and Rhythms
    • Circadian rhythm
    • Many plant functions change throughout
    • the day
    • Depends on environmental conditions
    • Ex: opening/closing of stomata
    • Photoperiodism
    • Increasing day length signals flowering
    • Varies by plant species
    • Plants can be:
    • Day-neutral, long-day, short-day

  13. Photoperiod

    • It is night length that is important
    • Interrupting night will prevent flowering
    • of short day plants, even if the day length is appropriate

  14. Phytochromes
    • Pigments in plants that detect varying
    • wavelengths of red light
    • Ratio of red (666nm) to far red (730nm)
    • wavelengths informs plant about light availability
    • Example:
    • Sunlight has a R:FR ratio of 1.2
    • Light under a canopy of leaves has a R:FR ratio
    • of 0.13
    • Light under 5 mm of soil has a R:FR ratio of
    • 0.88
    • Cue hormones that control daylight
    • dependent reactions
Card Set
Plant Responses to the Environment
Plant Responses to the Environment