1. Lecture 5 Plant hormones and Signal transduction
PLSC 452/552
1/23/14
Department of Plant Sciences
Neal Stewart Lab

2. 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?

3. 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

4. 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

5. 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.

6. 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

7. ABRC teaching tools website

8. 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

9. 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)

10. KEGG database:

11. Auxins Greek: auxein; to grow or increase Apical dominance growth
Cell elongation
Hormone level very important
2, 4-dichlorophenoxyacetic Acid

13. Taiz and Zeiger. 2002. Plant Physiology, 3rd Ed.

14. Auxin: Apical dominance

15. 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
Kinetin

16. Application: cotton spraying
Adding cytokinins to young cotton increase drought-resistance
Arizona – 31% US cotton, highest yield acre-1

17. 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

18. Auxin
Cytokinin

19. 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

21. 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

22. Jasmonic acid: Plant-insect co-evolution
Tri-trophic interactions
Degenhardt (2009)
Plant Physiology
149:96-102

23. Jasmonic acid: Pathogen response

24. 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

25. Modification of GA in rice
Miyako Ueguchi-Tanaka 2005 Nature 437,

26. Spraying GA for increased fruit yield
GA induces fruiting
in absence of seed

27. 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

28. Conversational Plants?
Ethylene production increases during stress
Drought
Heat
Perceived by neighboring plants
Unstressed plants induce stress pathways

29. Brassinosteroids Stress responses Stem elongation Seed germination
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

30. Overview of hormone mutants
Cytokinin
mutant
Brassinosteroid
mutant
Cytokinin
mutant
closer look
Phenotypes associated with the brassinosteroid, ethylene, cytokinin and abscisic acid receptor mutants. All images are shown against wild type for comparison. (A) The brassinosteroid receptor mutant bri1-301 (bottom) shows a dwarf phenotype. (B) The dark-grown ethylene receptor mutant ein4 (right) lacks the triple response (left; see main text). (C) The triple cytokinin receptor mutant cre1 ahk2 ahk3 (right) shows reduced growth. (D) The root vascular bundle normally consists of xylem, phloem and procambium cell files, whereas in wol (bottom), or in cre1 ahk2 ahk3 (not shown), there are fewer vascular cell lineages, all of which differentiate as protoxylem. The vascular bundle is encircled by a layer of pericycle cells (asterisks) (E) The abscisic acid receptor mutant fca (right) flowers later than wild type, as demonstrated by increased leaf number at flowering. Scale bars: in C, 2 mm; in D, 10 μm. [A is reprinted, with permission, from Cano-Delgado et al. (Cano-Delgado et al., 2004); B is reprinted, with permission, from Hua et al. (Hua et al., 1998); E is reprinted, with permission, from Amasino (Amasino, 2003).]
Ethylene
mutant
grown in dark
Abscisic acid
mutant
Bishopp A et al. Development 2006;133:

31. Hormones (PGR) pathways
PGRs work in complex cascades to produce signals
Synergistic
Anatognistic
Variety of actions in cell
Gene transcription
Protein degradation

33. 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.

34. 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

35. 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