Lecture 4
Plant Development and Physiology
2106
Neal Stewart
Overview
• Know key plant anatomy and developmental
stages of plant growth
• Understand the importance of plant
hormones in plant biology
• Know the major plant hormones
Plant development
• Growth: irreversible increase in the size of
plant cells and organscells grow by division
and expansion
• Differentiation: specialization of cells into
tissues and organs
• Development: life cycle progression of plants
– Seed
– Organogenesis
– Reproduction
http://www.slideshare.net/bcbgarcia/bio-130microsporogenesis-gametogenesis-2013
Figure 4.2
Figure 4.2 Gametogenesis. Schematics of (a) an Arabidopsis flower with the floral
organs identified; (b) a cross section through the male organs (anther, filament) showing
the site of male gamete formation; (c) the female ovule contained within the carpels of
the flower showing the site of female gamete development. [Reprinted from Wilson and
Yang C (2004), with permission from the Society for Reproduction and Fertility.]
Figure 4.4
Figure 4.4 Embryo development. (a) Schematic of embryo stages. [Reprinted from Lenhard
and Laux (1999), with permission by Elsevier Science Ltd.] (b) Scanning electron micrograph of
Arabidopsis embryos in the globular and heart stages. The white lines indicate the cell division
planes. [Reprinted from Costa and Dolan (2000), with permission from Elsevier Science Ltd.]
Germination
Figure 4.1
Figure 4.1 Plant anatomy and morphology. The seedling shoot and root systems are
indicated, as are the shoot and root apical meristems, tissues that direct the major growth
and differentiation of plants. Active cell division within the meristem is shown in the last
panel; note the presence of two nuclei in some cells. Modified with permission from Dr. Dale
Bentham’s Website (http://biology.nebrwesleyan.edu/benham/plants/index.html).
Leaf cross section and physiology
Plant cell
Celldiagram.net
Figure 4.7
Figure 4.7 Leaf
development. (a, b)
Scanning electron
micrographs of leaf
primordia. Note the
presence of trichomes in (b).
(c) Schematic of leaf cross
section showing the
different leaf cell types. (d)
Cross section through leaf
vascular tissue. [Reprinted
from Byrne (2006), with
permission from the Public
Library of Science.]
Figure 4.8
Figure 4.8 Flower development. Arabidopsis (a) wild-type, (b) ap2, (c) pi, (d) ag, and (e) sep
flowers. Below each photo is a rendering of the ABC model as it functions in that flower.
[Reprinted from Krizek and Fletcher (2005), with permission from Nature Publishing.] See
color insert.
Hormone
Figure 4.10
Signal Cascade
DNA
RNA
Biological Responses
New Proteins
Figure 4.10 A paradigm plant hormone signal transduction pathway. Hormone on the
outside of a plant cell may be perceived by proteins present at or near the plasma membrane.
Alternatively, the hormone may be transported across the plasma membrane. Signal cascade
proteins are then activated. Once activated, these proteins can transmit signaling information
(arrows) to the interior of the cell. Many signal transduction pathways converge on the
stimulation of gene expression within the nucleus that results in the production of new
proteins in the cytoplasm that can affect specific biological responses.
What is a hormone?
• Biochemical which regulates growth based on
biological and environmental influences
• Synonyms: Plant hormones, plant growth
regulators (PGRs), phytohormones
• Regulate growth and development
• Mobile throughout plant
• Environment and stress responsive
Major plant hormones
•
•
•
•
•
•
•
Auxin – Greek: auxein; to grow or increase
Cytokinin – cytokinesis (cell division)
Abscisic acid – abscission
Jasmonic acid – found in jasmine oil
Gibberellic acid – pathogen Gibberella
Ethylene – chemical brother to ethanol
Brassinosteroids – derived from Brassica spp.
Figure 4.9 Plant hormones. Similarit
between some plant and animal
hormones. [Reprinted from Chow and
McCourt (2006), with permission from
Cold Spring Harbor Laboratory Press.]
Finding plant hormones
Observational:
Darwin stumbles on auxin
– Noticed grass tips grow toward light
– With tip growth responded to light
– Without tip growth had no response
Mutation screening: (aka forward genetics)
– Dwarf plants are can be hormone deficient
ABRC teaching tools website
General hormone biochemistry
• Present in all cells at various levels
• Classes of hormones work in signal cascades
– Hormone-receptor interactions
– Respond to a host of factors and biological needs
• Abiotic
– Water stress
– Light
– Nutrient deficiency
• Biotic
– Growth
– Development
– Herbivore stress
Hormone biosynthesis
Made from four biosynthetic pathways:
– Terpenoids
•
•
•
•
AMP + IPP (cytokinins)
Carotenoid breakdown (abscisic acid)
Diterpene (gibberellic acid)
Triterpene (brassinosteroids)
– Fatty acids (jasmonic acid)
– Tryptophan (auxins)
– Methionine (ethylene)
EGG database:
tp://www.genome.jp/kegg/
Auxins
•
•
•
•
Greek: auxein; to grow or increase
Apical dominance growth
Cell elongation
Hormone level very important
2, 4-dichlorophenoxyacetic Acid
http://pubchem.ncbi.nlm.nih.gov/
http://www.nsf.gov/news/news_images.jsp?cntn_id=104205
Taiz and Zeiger. 2002. Plant Physiology, 3rd Ed.
Auxin: Apical dominance
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Auxin.html
Cytokinin
•
•
•
•
•
Cytokinesis (cell division)
Organization and development of xylem tissue
Response to light
Lateral growth of shoots
Kinetin
Open stomata
http://pubchem.ncbi.nlm.nih.gov/
Application: cotton spraying
• Adding cytokinins to young cotton increase drought-resistance
• Arizona – 31% US cotton, highest yield acre-1
Auxin and cytokinin ratio importance
• Auxin alone = Large cells (no division)
• Cytokinin alone = Cells have no change
• Auxin + Cytokinin = Normal cell growth and
division
• Auxin + >Cytokinin = Shoot growth
• >Auxin = Cytokinin = Root growth
Auxin
Cytokinin
http://users.ugent.be/~p
debergh/pri/pri4ez04.jpg
Abscisic acid (ABA)
•
•
•
•
•
Originally implicated in leaf and fruit abscission
Involved in leaf senescence
Maintains seed dormancy (opposed to GA)
Involved in stomata regulation (closes)
Single hormone unit
http://pubchem.ncbi.nlm.nih.gov/
Jasmonic acid
• First identified in jasmine oil
• Response to biotic stress
– Wounding induces JA biosynthesis
– Microbial and fungal invasion
• Plant growth effects similar to auxin
– Specialty growth structures
http://pubchem.ncbi.nlm.nih.gov/
Jasmonic acid: Plant-insect co-evolution
Tri-trophic interactions
Degenhardt (2009)
Plant Physiology
149:96-102
Jasmonic acid: Pathogen response
http://park.itc.u-tokyo.ac.jp/biotec-res-ctr/kampo/eng/research_plant.html
Gibberellic acid
• Originally found in Gibberella (rice pathogen)
– Responsible for ‘foolish seedling’ phenomenon
– Uninhibited growth until breaking
• Involved in cell elongation
• Flowering and seed germination
http://pubchem.ncbi.nlm.nih.gov/
Modification of GA in rice
Miyako Ueguchi-Tanaka 2005 Nature 437, 693-698
Spraying GA for increased fruit yield
GA induces fruiting
in absence of seed
http://www.extension.org/pages/31607/using-plant-growth-regulators-toincrease-the-size-of-table-grape-berries#.Ut9EYbROmM8
Ethylene: the cell phone of PGRs
•
•
•
•
A hydrocarbon gas
Involved in fruit ripening, stress response
Inhibition of growth in dark conditions
Excess ethylene inhibits callus growth
Brassinosteroids
• Stress responses
– Switchgrass suspension cells have minor amounts
of lignin (small amounts of H monolignols)
– Addition of brassinolide induces normal lignin
formation and composition
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•
•
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Stem elongation
Seed germination
Pollen tube growth
Cell differentiation control
Brassinolide
http://pubchem.ncbi.nlm.nih.gov/
Overview of hormone mutants
Cytokinin
mutant
Brassinosteroid
mutant
Cytokinin
mutant
closer look
Ethylene
mutant
grown in dark
Abscisic acid
mutant
Bishopp A et al. Development 2006;133:1857-1869
Hormones (PGR) pathways
• PGRs work in complex cascades to produce signals
– Synergistic
– Anatognistic
• Variety of actions in cell
– Gene transcription
– Protein degradation
http://chriscarterart.wordpress.com/2010/05/09/mo
thers-day-2/mikado-plant-watercolor-sketch-chriscarter-050910/
Arabidopsis histidine kinase sensing and signaling; 2) A histidine
phosphotransferase protein nuclear translocation; 3) A response regulation
transcription activation; and 4) a negative feedback loop through cytokinininducible ARR gene products.
http://molbio.mgh.harvard.edu/sheenweb/cytokinin_signaling.html
Introduction: the importance of manipulation
of hormones for tissue culture
• Auxins and cytokinins are very important
– Higher auxin induces root growth
– Equal ratio induces callus and cell enlargement
– Lower auxin induces shoot growth
• Gibberellic acid germinates difficult seeds
• Add brassinosteroids for cell wall induction
Lecture summary
• Plant growth and responses under hormonal
control
• Auxin and cytokinin are key for plant growth
• Cell signaling is regulated by specific receptors
on cell membranes