Plant Hormones. There are five major types of plant hormones: Gibberelins Cytokinins Ethylene...
-
Upload
jonah-harvey -
Category
Documents
-
view
225 -
download
0
Transcript of Plant Hormones. There are five major types of plant hormones: Gibberelins Cytokinins Ethylene...
Plant Hormones
Plant Hormones There are five major types of plant
hormones: Gibberelins Cytokinins Ethylene Abcisic Acid Auxins
The structure and function of each type of hormone will be described
Gibberellins
Overview
Gibberellins (GAs) regulate and influence: cell elongation seed germination dormancy flowering sex expression enzyme induction leaf and fruit senescence.
Germination
Signal starch hydrolysis through inducing the synthesis of the enzyme α-amylase in the aleurone cells
Gibberellins produced in the scutellum diffuse to the aleurone cells where they stimulate the secretion α-amylase
α-Amylase then hydrolyses starch into glucose
Gibberellins cause higher levels of transcription of the gene coding for the α-amylase enzyme
Gibberellins: Chemical Structure
Gibberelins have complex ring structures Typically contain carboxylic acid groups Many specific gibberelins exist
Numeric naming system (i.e. GA#) May be classified into two structural
types: C-19 Gibberelins (19 carbon) C-20 Gibberelins (20 carbon)
Gibberellins: Chemical Structure
Type 1: 19 Carbon Gibberelins
OH
O
O
O
A C-19 Gibberellin GA9
Gibberellins: Chemical Structure
Type 2: 20 Carbon Gibberelins
O
HO
O
HO
A C-20 Gibberellin
GA12
Cytokinins
Cytokinins Cytokinins
Found in a variety of plants and have many functions
Synthesized in meristematic tissues in roots and transported to aboveground organs
Regulate growth and development of tissue primarily by promoting cell division Involved in germination, shoot differentiation, leaf
senescence Interacts with other plant hormones for some
functions
Cytokinins Function
Regulates apical dominance and lateral root initiation
Slows down senescence (plant aging) and chlorophyll degradation in aging leaves
Regulates growth of dicot seedlings in the dark (in combination with ethylene)
Involved in development of sex organs and male sterility
Synthesized in meristematic tissues in roots and transported to aboveground organs
Cytokinins
Cytokinins contain adenine:
Two structure types: Isoprenoid
Isoprene structural units: Aromatic
Contain aromatic groups
N
NNH
N
Cytokinins: Isoprenoid
N
NNH
N
HNCH2
H2C
OH
CH3
Zeatin
N
NNH
N
HNCH2
H2C
OH
CH3
H
H
Dihydrozeatin
Isoprene units
adenine
Cytokinins: Aromatic
N
NHN
NHN
benzyladenine
adenine
Aromatic group
Cytokinins: Aromatic
CH2
NH
N
NN
HN
HO
orthotopolin
adenine
Aromatic group
Ethylene
EthyleneEthylene
Universally produced by all plants Angiosperms, Gymnosperms, Ferns, Mosses,
Liverworts Also found in some fungi, yeast and
bacteria Important roles in:
Abscission Germination Senescence Stress response to pathogens
Ethylene and Fruit Ripening
Helps fruits go through color change, softening of walls, conversion of starch to sugar
Ethylene is produced in low amounts throughout plant life some “climacteric” plants
have sudden peaks in ethylene synthesis which signals ripening changes
Ethylene gas is sprayed on fruit crops to ripen at same time
Some stress situations trigger ethylene production exposure to heat/cold physical damage attack by fungal or bacterial pathogens flooding that limits oxygen
Similar to Abscisic acid’s stress response
Ethylene and Stress
Growth and Messaging
Ethylene and growth Promotes root growth and root hair growth Can cause asymmetric growth in stems and
leaves Ethylene regulates seedlings’ horizontal growth
& apical hook formation…= “Triple response” of seedlings grown in dark
Can act as second messenger Auxin, cytokinin can cause ethylene production
in seedlings
Ethylene’s “triple response”Ethylene’s “triple response”
Apical hook formation
Ethylene: Chemical Structure
Ethylene is a very small, simple molecule compared to other plant hormones
Two carbons sharing a double bond Ethylene is a gas at room temperature
C C
H
H
H
H
Ethylene
Abscisic Acid
Abscisic Acid (ABA)Abscisic Acid (ABA)
Found universally in plants and algae Many functions! Important roles in:
plant development bud & seed dormancy Germination cell division leaf senescence Abscission cellular response to stress
Abscisic Acid
Acts as a general inhibitor of growth and metabolism Inhibits growth in hypocotyls, epicotyls,
leaves, coleoptiles Seed dormancy
ABA promotes seed dormancy so plant seeds can withstand desiccation
ABA as a Stress Hormone ABA increases with various
environmental or biological plant stresses Excess heat, pests, excess salt
and/or dehydration Wilted plants have high levels of
ABA In a drought, ABA increases in
some plants, causing the stomata to close, preventing water loss
ABA can also produces osmolytes that protect cell membranes from dehydration
Abscisic Acid Chemical Structure
Abscisic acid is a carboxylic acid
Abscisic Acid
CH3
OH
O
CH3H3C
O OH
Carboxylic acid
Auxins
It’s All in the Name
“Auxins” from the Greek word αυξανω = "I grow or increase".
They were the first of the major plant hormones to be discovered.
Overview
essential for cell growth affects both cell division and cellular
expansion. may promote axial elongation (as in
shoots), lateral expansion (as in root swelling), or isodiametric expansion (as in fruit growth)
auxin-promoted cellular expansion occurs in the absence of cell division.
auxin-promoted cell division and cell expansion may be closely sequenced within the same tissue (root initiation, fruit growth)
Important Functions
coordination of many growth and behavioral processes in the plant life cycle
stimulate or inhibit the expression of specific genes.
coordinate development at all levels in plants, from the cellular level through organs and ultimately the whole plant.
Master Hormone
indole-3-acetic acid (IAA). the most important member of the
auxin family the most potent native auxin generates the majority of auxin
effects in intact plants
Working Together
patterns of active transport are complex
typically act in concert with, or in opposition to other plant hormones
auxins and other plant hormones nearly always interact to determine patterns of plant development.
Auxin Shared Functions
stimulates cell elongation by stimulating wall loosening factors, such as elastins, to loosen cell walls (with gibberellins)
stimulates cell division (with cytokinins) applied to callus, rooting can be
generated (with cytokinin) xylem tissues can be generated (with
cytokinins)
More Auxin Shared Functions
promotes femaleness in dioecious flowers (with ethylene)
inhibits or promotes leaf and fruit abscission (with ethylene)
stimulate cell division in the cambium andin tissue culture (with cytokinins)
Auxin Functions
Stimulate cell elongation
stimulate differentiation of phloem and xylem
Stimulate root initiation on stem cuttings and lateral root development in tissue culture
mediate the tropistic response of bending in response to gravity and light
suppresses growth of lateral buds
delay leaf senescence
More Auxin Functions
can induce fruit setting and growth in some plants
involved in assimilate movement toward auxin, possibly by an effect on phloem transport
delay fruit ripening promote flowering in Bromeliads stimulate growth of flower parts stimulate the production of ethylene at high
concentrations inhibit growth by closing the stoma during
water stress.
Auxins: Chemical Structure
Many naturally occurring auxins exist, along with many synthetic auxins used in agriculture
Most naturally occurring auxins contain an indole ring group or a phenyl group
Auxins (natural and synthetic) are carboxylic acids
Halides are also seen in both natural and synthetic auxins
Naturally Occurring Auxins
NH
O
OH
indole-3-acetic acid
NH
Cl
OH
O
4-chloroindole-3-acetic acid
Carboxylic acid
=IAA, the most important member of the auxin family
Naturally Occurring Auxins
phenylacetic acid
OH
O
Synthetic Auxins
NH
O
OH
indole-3-butyric acid
napthalene acetic acid
O
OH
Synthetic Auxins
O
Cl
Cl
OHO
2,4-dichlorophenoxy-acetic acid
Ether linkage
halogens
SourcesSources Wikipedia, Auxin, 2010, http://en.wikipedia.org/wiki/Auxin Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston:
Benjamin-Cummings Company, 2001. Delker, C., Raschke, A. and Quint, M., 2008, Auxin dynamics: the
dazzling complexity of a small molecule’s message, Planta, vol 227, 929-941.
Gibberellins: A Short History, from http://www.plant-hormones.info, the home since 2003 of a website developed by the now-closed Long Ashton Research Station
Wikipedia, Gibberellin, 2010, http://en.wikipedia.org/wiki/Gibberellin Koning, Ross E. 1994. Auxins. Plant Physiology Information Website.
http://plantphys.info/plant_physiology/auxin.shtml. (4-7-2010). Litwak, G. 2005. Plant hormones. Elsevier Academic Press: San Diego,
CA. Raghavan, V. 1997. Molecular embryology of flowering plants.
Cambridge University Press. New York, NY. Srivastava, LM. 2002. Plant growth and development: hormones and
environment. Elsevier Science: San Diego, CA. http://www.plant-hormones.info/auxins.htm the home since 2003 of a
website developed by the now-closed Long Ashton Research Station
Photo credits: http://humankinetics.files.wordpress.com/2009/07
/fresh-fruit.jpg http://www.nature.com/emboj/journal/v22/n6/
thumbs/7595043f4.jpg http://plantphys.info/plant_physiology/images/
tripleresponse.gif http://farm4.static.flickr.com/
3657/3513022448_e7bb1c305e_m.jpg http://www.hiltonpond.org/images/
FreezeHackberry01.jpg