Chapter 22 Control Systems in Plants. 22.1 Hormones Charles and Francis Darwin Plant tip...
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Transcript of Chapter 22 Control Systems in Plants. 22.1 Hormones Charles and Francis Darwin Plant tip...
Chapter 22
Control Systems in Plants
22.1 Hormones
Charles and Francis Darwin Plant tip experiments
AuxinsPromote plant growthProduced in apical meristem of shootsCell elongation
Auxin builds up on shaded side Elongation on shaded side causes plant to bend
toward lightStimulate secondary growth Secreted by seeds to stimulate development
of ovary to fruit Farmers use this to grow seedless plants
Cytokinins
Stimulate cell divisionProduced in embryos, roots, and fruitsSlow aging of flowers and fruitsAffected by auxins
High levels of auxins inhibits branching Travels from terminal bud Bushier plant = “pinch back”
Gibberellins
Stimulate growth of stems Cell division and elongation(similar to
auxins)
With auxins, influence fruit developmentPromotes seed germination
Abscisic Acid (ABA)
Halts primary and secondary growth Promotes dormancy during winter or
drought More likely to survive when it becomes
dormant
Stress hormone Dehydration - ABA causes stomata to close
Ethylene
Stimulates fruit ripeningPromote “leaf drop”
Adaptation helps trees from drying out in the winter
High ethylene; low auxins - cooler temps and shorter days
22.2 Plant Response
Tropisms: growth responses that cause parts of a plant to grow slowly toward or away from a stimulus
Rapid plant movements Plants can respond quickly to touch to
avoid being eaten Leaf folding
Thigmotropism
Change in plant growth due to touchClimbing plants
Tendrils coil and grasp objects
Mechanical stress Bend to avoid damage
Leaf folding
PhototropismGrowth of a plant part toward or away
from lightLight on a shoot tip
Protein with light-absorbing molecule Signals molecules that affect
auxin transport Auxin lengthens shade side
Gravitropism
Response to gravitySeedling’s shoot grows
upward, root downwardHypothesis: gravity pulls
organelles to low points of cells Uneven distribution may
signal cells to move auxins
Drought
Causes wilting and reduces photosynthesis Respond by conserving water
Succulents (cacti) Thick cuticle and fleshy stems Spines instead of leaves
Arctic Plants Small leaves and low to the ground Reduce transpiration
Flooding
Overwatered plants can suffocate Lack of oxygen spaces in soil
Plants in wet areas Mangroves
Roots partially above ground to provide oxygen
Release ethylene Some cells die to form air tubes
Salt Stress
Too much salt; lose water to soil through osmosis
halophytes: salt-tolerant plants Salt glands
Pump out salt across leaf epidermis Rain washes salt away
Pickleweed Excess salt to stems; shed stems
Disease Defense
Epidermis - barrier to pathogens Pathogens cross by wounds or stomata
Chemicals Antimicrobial Signal lignin production- seals off invader
Ability to recognize and attack certain pathogens
22.3 Light and Seasons
circadian rhythm: biological cycle that occurs about every 24 hours Daily signals; light
Plants produce flowers during different times of the year based on day/night length
PhotoperiodismAbility to use lengths of day to time seasonal
activities short-day plants: flower in fall or winter when
darkness is a certain length Long-day plants: flower in spring or summer when
days are longer Spinach, irises
day-neutral plant: flowers when it reaches a certain stage of maturity Dandelions, tomatoes, rice
Florists can change this by flashing light in the night
Phytochromes
Pigment proteins that detect sunrise and sunset
Sunrise= red light Change to active form that triggers
responses
Sunset - change back to inactive form