biology 11of organisation and function of...
TRANSCRIPT
BIO1PS 2012Plant Science
Lecture 5Hormones Pt. II
Dr. Michael EmmerlingDepartment of BotanyRoom [email protected]
Learning Objectives – Part 2Describe the major roles of cytokinins
Describe the interaction between auxin and cytokinins
Describe the major roles of ethylene
Plant Tissue CultureCommercially important:
tea micropropagation
•micropropagation of plants
Nepenthes edwardsiana
•production of plants e.g. pitcher plants
Plant Tissue CultureScienti!cally important:
uniform experimental material
regeneration of whole plants
ME
Plant Tissue Culture
Ladiges et al. (2010), 4th ed., Fig. 14.16
tomato infected withAgrobacterium
Agrobacterium Infection
Taiz and Zeiger (2010), 5th ed., Fig. 21.1
IAAMIPT
Cytokinins• originally discovered as a cell-division
promoting substance in coconut milk extracts (zeatin)
• later puri!ed from denatured DNA (kinetin in autoclaved herring sperm)
cytokinin (mg/l)
0 0.2 1.0
Different CytokininsKinetin
Zeatin
Adeninecytokinin found in most plants
synthetic analog, from herring sperm
zeatin ribosidezeatin ribonucleotide
zeatin ribotide
Conjugated Zeatin
trans!!
zeatin ribotide
basesugar
phosphate
Cytokinin Activities• stimulation of cell division
• promotion of shoot outgrowth in tissue culture
• regulation of senescence
• promotion of growth of axillary buds (with auxin)
Cytokinin and Auxin• Cytokinin and auxin together promote cell
division and expansion
• Agrobacterium induces the proliferation of plant cells, leading to crown gall disease
It's All About Ratios
Taiz and Zeiger (2010), 5th ed., Fig. 21.16 tobacco callus
mg/lm
g/l
More About Ratios
cytokinin 1auxin 0
cytokinin 0auxin 0
cytokinin1auxin 0.5
cytokinin 0auxin 0.05
http://plantphys.info/plant_physiology/images/tissuehormones.gif
cytokinin
10
1
0.1
0
auxin0 0.05 0.5 5
all values mg/l
cytokinin
auxin
Auxin and Cytokinin Ratios
Auxin and Cytokinin Ratios
Ladiges et al. (2010), 4th ed., Fig. 18.14
auxin+
cytokinin
auxin+
cytokininauxin
Auxin and Cytokinin Ratios
Ladiges et al. (2010), 4th ed., Fig. 18.13
Cytokinin and Senescence
http://www.uwsp.edu/biology/courses/botlab/images/Lab12Growth/12E%20cytokinin%20wheat.jpg
Taiz and Zeiger (2010), 5th ed., Fig. 21.19
tobacco expressing ipt gene:delayed senescence
Cytokinin Production
emerging lateral root
GFPpromoter
"gene construct"
promoter
+ cytokinin
GFP
pAIPT::GFP
Adenylate IsoPentenyl Transferase
Green Fluorescent Protein
Discovery of Ethylene
Coal gas used for street lamps
defoliated trees
Ethylene•C2H4
• very small molecule
• volatile gas
• very low concentrations
• 0.01 ml/l
• only one ethylene – no variants or other molecules
Ethylene• rapid diffusion throughout plant tissues
• rapid diffusion between individual plants
• very rapid effects
• even distribution within a plant
• associated with stress responses, wounding and ripening
Ethylene Effects• fruit ripening – climacteric fruits
• abscission
• senescence
• nodule formation
• shoot elongation
• germination
Ethylene• used extensively in horticulture, fruit and
vegetable growth, harvesting and production
• particularly on bananas and tomatoes
• speeds up the climacteric phase, increased respiration upon fruit ripening
Ethylene ResponseClimactericEthylene can induce ripening in:
apples, pears, apricot, nectarine, tomato sapodilla
quince
passionfruit
mangoavocado
rockmelon
bananapeach
Ethylene Response
Ethylene can't induce fruit ripening:
cherry, pepper, lemon, orange, grape
Non-climactericlychee
blackberry
eggplant
watermelon
strawberry
honeydew
mandarin
Ethylene and Ripening• Unripe fruit is often easier to pick, process,
transport and store than fully ripened fruit
• Ripening can be induced by adding ethylene, or the chemical agent ethephon
pH>4-5 +H2PO4- + Cl-
RipeningUntreated
Ethephon
• Breakdown of chlorophyll
• Increased synthesis of coloured pigments
• Increased synthesis of sugars
"Senescence"
Ichimura et al. (2002), Bull. Natl. Inst. Flor. Sci. 2, 1
STS: silver thiosulfate1-MCP: 1-methylcyclopropene
Abscission
ripening tomato
Deepwater Rice
Grown in river #ood plains of SE Asia
Rice must grow very rapidly when #oods arrive
Some varieties can elongate ~25cm per day
SNORKEL genes are ethylene response factors triggering internode elongation via GA
SK1 and SK2:"SNORKEL"
Ethylene and NodulationMedicago truncatula
Penmetsa and Cook (1997), Science 275, 527
wild type
sickle mutant
defect in ethylene signalling