TwoOldGuys Study Guides
response to environment
- shoots tend to grow [curve] toward light source
roots do not grow away from light source
- shoot apical meristem produces auxin
which is photo-oxidized
(blue light [460 nm] sensor may trigger enzyme responsible for photo-oxidation)
- shoots tend to grow [curve] away from gravity source
roots tend to grow toward gravity source
- auxin [or amyloplast] concentration may be higher on bottom of shoot or root
gravity pulls it downward
- auxin stimulates shoot elongation
auxin inhibits root eleongation
- estimate day-of-year
- spring germination & growth, spring blooming
- fall leaf colors & leaf loss, autumn blooming
- phytochrome: Pr ↔ Pfr
- Pr absorbs red light [660 nm] → Pfr
Pfr concentration estimates amount of day light
- Pfr absorbs infra-red light [730 nm] → Pr
Pr concentration estimates amount of night light
- elevated Pfr may trigger response
- elevated Pfr may suppress response
Some plants respond to touch by curling tendril toward touch.
Venus flytraps close leaf in response to touch.
Sensitive plant wilts in response to touch (harder touch → more wilt).
Many plant exhibit circadian changes in leaf position, or flower opening.
Many plants become dormant in response to actual adverse conditions (winter, seasonal
drought, non-seasonal drought), or even anticipated adverse conditions (photoperiodism).
Temperate and Boreal Zone species produce 'anti-freeze' during winter.
Some plants which are subject to sudden, large temperature swings
produce heat shock proteins.
Seed dormancy allows seeds to survive decades to centuries until dormancy is
broken usually by sufficient water present.
For those species with cork under the bark, the cork itself is a cushion to minimize
mechanical injury from falling limbs or small rocks. Most plants exude some substance
out of any injury which penetrates to the vascular tissue. This substance loses water
to the air, and effectively closes the wound [analogous to a animal scab]. Some species
exude oils, waxes or resins [pines]; while some [rubber tree, milkweed, dandelion) produce
latex [the raw material for natural rubber]. Others exude unidentified chemicals.
- other chemicals in the material which 'plugs' the injury:
- toxins to repel, disable, or kill invertebrates
- growth stimulating hormones [cause growth of shoot tissues over the injured area]
- toxins to induce cell death in surrounding tissue [further isolates wound]
- complex cell-to-cell signaling pathway
- produce proteinase inhibitors throughout plant
- proteinase inhibitors block digestive enzymes in gut of invertebrate herbivore
- hydrogen peroxide, nitric oxide, and [generic] antimicrobial agents plus
antigen-specific antibodies against microbes and fungi (effective against some
- toxins routinely circulate
- induce allergy-like response in vertebrate [poison ivy - 4 oils]
- respiratory arrest in insects [tobacco - nicotine]
- neurotoxins usually target Central Nervous System, incapacitating vertebrates
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© 2004-2005 TwoOldGuys
revised 19 aug 2006