Lecture 5Plant hormones

andSignal transduction

PLSC 452/5521/23/14

Department of Plant SciencesNeal Stewart Lab

Brain teaser

• Little Johnny nails a sign 90 cm off the ground to a tree outside of his clubhouse that says “no girls allowed.” If the tree grows 12 cm every year, at what height will the sign be when Little Johnny returns as Big Johnny in 15 years?

Overview

• Define “hormone” as a functional compound. What is the function and importance of hormones?

• Know the major plant hormones• Understand real-world application of

hormones• Importance of hormones for tissue culture:

introduction

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.

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)

KEGG database: http://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)• Accidently added degraded DNA to medium• Organization and development of xylem tissue• Response to light• Lateral growth of shoots• Open stomata

http://pubchem.ncbi.nlm.nih.gov/

Kinetin

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/~pdebergh/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/

http://www.rikenresearch.riken.jp/eng/research/6121

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-evolutionTri-trophic interactions

Degenhardt (2009) Plant Physiology 149:96-102

http://park.itc.u-tokyo.ac.jp/biotec-res-ctr/kampo/eng/research_plant.html

Jasmonic acid: Pathogen response

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 yieldGA induces fruiting in absence of seed

http://www.extension.org/pages/31607/using-plant-growth-regulators-to-increase-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

Conversational Plants?

• Ethylene production increases during stress– Drought– Heat

• Perceived by neighboring plants

• Unstressed plants induce stress pathways

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• Stem elongation• Seed germination• Pollen tube growth• Cell differentiation control

Brassinolide

http://pubchem.ncbi.nlm.nih.gov/

Brassinosteroidmutant

Bishopp A et al. Development 2006;133:1857-1869

Overview of hormone mutants

Ethylenemutant

grown in dark

Cytokininmutant

Cytokininmutant

closer look

Abscisic acidmutant

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/mothers-day-2/mikado-plant-watercolor-sketch-chris-carter-050910/

http://molbio.mgh.harvard.edu/sheenweb/cytokinin_signaling.html

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 cytokinin-inducible ARR gene products.

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

• Hormones are biochemicals that regulate plant growth based on biological and environmental cues

• Auxin and cytokinin are key for plant growth• Abiotic and biotic stress response is regulated

by hormones• Cell signaling is regulated by specific receptors

on cell membranes