HOW TO RIPEN GREEN TOMATO?

Plant Hormones

12.6 UNDERSTANDING PLANT HORMONES

A.k.a phytohormonesA group of naturally occurring organic compounds that influence physiological process at low concentration

Usually produced in one part of the plant

Translocated to another part of plant when they act

PLANT HORMONES

Plant need hormones to:Allow them to respond to environmental factors

Environmental factors CO2

O2

Toxins Gravity Temperature Sunlight Parasites Pathogens

Control plant growth, development and movement

Example of plant hormones:AuxinsGibbrellinsCytokininsAbscisinsEthylene or ethene

AUXIN

Greek (to grow)E.g. indoleacetic acid (IAA), zeatin

(natural) & kinetin (synthetic)Promote cell elongation & cell

enlargementProduce at stem tips, root tips (root

caps), stems & budsRequired by plants almost all the timeInvolved in phototropism & geotropism

AUXINS

POP QUIZ

AUXIN IN GEOTROPISM

Major effect is on stem elongation ; important in the regulation of height

Have little effect on rootsProduce at seeds, fruits & young leaves

Only required at certain times to induce major developmental changes (stem elongation)

GIBBERELLINS

Stimulate cytokinesis (cell division) & influence cell differentiation

Produced in all actively growing tissues (meristematic tissue)

Often act together with auxins

CYTOKININS

Promote stomatal closure, prolong seed dormancy & stimulate shedding of leaves, flowers and fruits

Mostly synthesized in mature leaves

ABSCISINS

A gas; transported by diffusionPromotes flower opening and fruit ripening

Also stimulates:Defence response to wounding/ infection of disease

Shoot growth & differentiationRoot growth & differentiationLeaf & fruit abcission

ETHYLENE OR ETHENE

THE USE OF HORMONES IN AGRICULTURE

1. Promote growth of roots

2. Stimulate parthenocarpy – formation of fruits without fertilisation

3. Herbicide4. Prevent fruit from

dropping before harvest is due

AUXINS

1. Promote fruit ripening2. Induce flowering in pineapple3. Increase latex flow – rubber

trees4. Promote female flower

production

ETHYLENE / ETHENE

1.+ auxins = stimulate the production of shoots & roots in tissue culture

2.Prolong the storage life of vegetables

CYTOKININS

1. Increase production of bigger & more uniform bunches of seedless grapes

2. Increase sugarcane yield3. Increase flower bud production

and stimulate their early flowering

GIBBERELLINS