biology 11of organisation and function of...

BIO1PS 2012Plant Science

Lecture 5Hormones Pt. II

Dr. Michael EmmerlingDepartment of BotanyRoom 410m.emmerling@latrobe.edu.au

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