Transcript PLANT RESPONSES TO SIGNALS

Plant Responses to Signals
Chapter 39
• Plants have to respond to gravity
and other stimuli in environment.
• Growth pattern in plants reaction to light.
• Shoot reaches sunlight - starts
process called greening.
• Shoots start to grow - entire
plant begins to make chlorophyll.
• Begins signal transduction
pathway like one seen in animal
cells.
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• Signal transduction pathway
promotes cell activity in plant.
http://www.ercim.org/publication/Ercim_News/enw44/sillion.jpg
Hormones
• Plants produce hormones that
regulate growth and development.
• Hormones - chemical signals
produced in one part of body,
transported to other parts.
• Growth towards or away from
stimuli (regulated by hormones) tropism.
http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/tropism.gif
• Growth of shoot towards light phototropism (positive).
• Hormone responsible for growth auxin.
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• Auxin produced in large
quantities in apical meristem growth occurs.
• Auxin used on cut stems to
promote root growth.
• Auxins used as growth inhibitor
for some plants - used as
pesticides.
http://botit.botany.wisc.edu/images/130/Growth_Substances/Auxins/root_formation/
• Cytokinins stimulate cytokinesis
(cell division)
• Cytokinins produced in actively
growing tissues, particularly
roots, embryos, and fruits.
• Both cytokinins and auxins
present, cells divide.
Shoots forming with
addition of cytokinins
http://trilliumresearch.org/images/htr_web_images_research/05_rp_03_30_md.jpg
• Cytokinin levels raised, shoot
buds form.
• Auxin levels raised, roots form.
• Cytokinins also slow down aging
process of some plant organs florists use sprays to keep
flowers fresh.
http://www.gbpetalpusher.com/flowers/flower5-big.jpg
• Gibberellins stimulate growth in
leaves and stems - little effect
on root growth.
• Stems, gibberellins stimulate cell
elongation and cell division.
• Gibberellins applied to dwarf
plants - grow to normal height.
• Applied to normal plants - nothing
happens.
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• Many plants - both auxin and
gibberellins must be present for
fruit to set.
• Seeds have large amount of
gibberellins - signals seed to
break dormancy.
http://www.science.org.au/sats2004/images/helliwell2.jpg
• Abscisic acid promotes plant to
become dormant; thought to help
leaves drop in fall.
• Sometimes seed will need to have
all abscisic acid removed (through
washing) to break dormancy.
• Also helps to withstand drought sends plant into dormancy until
the conditions are favorable
again.
http://www.eco-systems.org/images/Premature_sugar_maple_leaf_drop_along_town_road_in_August_2000_.jpg
• Ethylene promotes leaf dropping
as well as fruit ripening.
• If fruit producing ethylene
placed with fruits that are not,
those fruits will also ripen in
response to hormone.
• By losing leaves during fall, plants
prevent drying out during winter.
http://www.pakupaku.info/knowledge/images/ethylene.gif
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Responses to light
• Plants require light to grow; can
absorb various aspects of
spectrum of light.
• Respond differently to different
wavelengths of light.
• 2 different types of plants, short
day and long day.
http://oceancolor.gsfc.nasa.gov/SeaWiFS/ICONS/spectrum.gif
• Short-day plants - long-night
plants -require minimum length of
uninterrupted darkness.
• Long-day plans - short-night
plants - require period of
continuous darkness interrupted
by few minutes of light.
• Response to light photoperiodism.
http://www.berrypropco.co.nz/variety_pics/par.gif
http://plantfacts.ohio-state.edu/hcs300/devel2.htm
• Typically, red light used to
interrupt nighttime cycle.
Tropisms
• Roots - positive gravitropism
(grow in direction of gravity);
shoots - negative gravitropism
(grow against direction of
gravity).
• Thigmotropism - response to
touch; in some plants, causes
plant to coil around an object
(like tendril).
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• Some plants cannot grow in
extreme temperatures or
salinities; others thrive in them.
• Freezing of cytoplasm can kill
plant because excess ions can
accumulate.
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http://www.learnnc.org/lp/media/collections/cede/resized/cedebwr07.jpg
Marsh grasses are often tolerate of
extreme salinities
Plant defenses
• Plants susceptible to many
different bacteria and viral
infections because of place in
food chain.
• Eaten by herbivores - need
protection against excess
herbivory – use physical
defenses, such as thorns, and
chemical defenses, such as
production of toxic compounds.
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http://www.learner.org/jnorth/images/graphics/monarch/PlantDefense01.jpg
• Some plants able to secrete
compounds that kill insect eating
it.
• Most plants resistant to
pathogens automatically because
they are able to detect infection
and kill it off right away.
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http://138.23.152.128/images/leaf.jpg