Endogenous Rhythms/ Plant Movements

• Many aspects of plant behavior exhibit periodic oscillations that appear to be controlled by an internal time measuring system: the endogenous biological clock
• Criteria to distinguish simple periodic phenomena and rhythm driven by an endogenous clock

  1. Persists in the absence of external clues
  2. Can be reset by external signals such as light and temperature
  3. No lasting effect of temperature on the timing of the clock-driven rhythm
• Classification of Biological Rhythms

  1. Circadian Rhythm
  2. Lunar rhythm
  3. Annual rhythm
  4. Ultradian rhythm
• Classification of Biological Rhythms

  
  

  Circadian Rhythm (circa=about+diem=day)

  • 24 hours eg bean movement (hyponasty, epinasty) (example: Portulaca, Calathea, rain tree or Fertility Tree of UPLB)
• Classification of Biological Rhythms

  
  

  Lunar rhythm

  • 28 days, between one full moon to the next
• Classification of Biological Rhythms

  
  

  Annual rhythm

  • flowering of fire trees, cherry blossoms and kapok every summer
• Classification of Biological Rhythms

  
  

  Ultradian rhythm

  • <24 hrs
• Classification of Biological Rhythms

  Ultradian rhythm

  • <24 hrs
• Plant Movements

  • Growth movements
  • Turgor movements
• Plant Movements

  • Growth movements - result of differential growth within an organ or between 2 different organs (irreversible)
• Plant Movements

  • Turgor movements - Results from volume changes in certain cells due to changes in osmotic potential (water) pressure due to the influx or efflux of ions which in turn cause water to move in and out of the cells (reversible, but not all the time)
• Tropism

  • Growth towards or away from an environmental stimulus
  • Result from differential growth of specific organds of a plant
• Nastic movement

  • Movement not oriented towards or away from an environmental stimulus
• Plant Responses to Stimuli

  A) Phototropism

  B) Photonasty

  C) gravitropism

  D) Thigmotropism

  E) Thigmonasty

  F) Thermotropism

  G) Thermonastly

  H) Chemotropism

  I) Chemonasty

  J) Hydrotropism

  K) Hydronasty

  
• Tropism

  1. Positive tropisms
  2. Negative tropisms
• Tropisms

  • Positive tropisms
  • the plant moves toward the stimulus
  • ex. bending toward light
• Tropisms

  • Negative tropisms
  • movements away from the stimulus
• Phototropism - movement in response to light

  
• Gravitropism - Growth movements in response to gravity
• Gravitropism

  • Shoots
  • negatively gravitropic, away from the center (-)
  • plant shoots exhibit negative gravitropism because they grow away from gravity
• Gravitropism

  • Roots
  • positively gravitropic, towards the earth’s center(+)
• Thigmotropism

  • directional response of a plant organ to touch or physical contact with a solid object
  • curling of threadlike appendages in vines

  
• Heliotropism

  • changing position and facing normal to the sun throughout the day
  • the solar tracking of plant organs- example: sunflowers

  
• Photoperiodism

  • Long-day plants
  • Short-day plants
  • Day-neutral plants
• Photoperiodism

  • Long-day plants
  • Flower when daylength is longer than a critical value
• Photoperiodism

  • Short-day plants
  • Flower when the daylength is shorter than a critical value
• Photoperiodism

  • Day-neutral plants
  • Flower when they become mature regardless of daylength
  • Long day – malunggay, aster, gladiola, fire tree, golden shower
  • Short-day – beans, poinsettia
• Flowering

  • Mode of Reproduction (self, cross, asexual)
  • Mode of Pollination – insect, wind, water, birds
  • Fertilization • Fruit/seed setting
  • Harvesting
  • Postharvest Handling
  • Types of seeds based on storage behavior
• Dormancy - a slowdown in an organisms metabolic rate
• Seed dormancy – inability of viable seed s to germinate given favorable conditions for germination.
• Parthenocarpy - fruit development without fertilization
• SENESCENCE

  • the collective term for aging processes that lead to the death of a plant or plant part
  • Leaf colors are an example that results from changes in light quality and photoperiod that trigger chlorophyll destruction, unmasking the other pigments in the leaf
• Phytohormones

  • Organic substances other than nutrients
  • Effective at low concentrations
  • Naturally-occuring
  • Modify plant growth and development (quantitative/qualitative)
  • More than one hormone is involved in the control of physiological processes but only one tends to dominate the control process
• Hormones

  • organic substances effective at low concentrations that modify plant growth and development
  • produced naturally by plants
• Plant Growth Regulators

  • may be synthetic compounds (e.g., IBA and Cycocel) that mimic naturally occurring plant hormones, or
  • may be natural hormones that were extracted from plant tissue (e.g., IAA)
• Auxin

  A) Indoleacetic acid

  B) Dichlorophenoxyacetic acid

  C) Naphthaleneacetic acid

  
• Auxins

  • synthesized in shoot apical meristems, young leaves, seeds and fruits
  • promote growth in molar concentrations of 10-3 to 10-8
• Indoleacetic Acid (IAA)

  • Auxin produced chemically
  • synthesized from indole or tryptophan
• Auxins

  • Auxin produced in apical buds - inhibit the activation of buds lower on the stems (apical dominance)
  • Promote lateral and adventitious root development
• Auxin

  • Fruit development requires auxin produced by the developing seed.
  • Auxin pastes applied to developing ovaries can promote:
  • parthenocarpy - fruit development in the absence of fertilization