HOW TO RIPEN GREEN TOMATO?

Plant Hormones 12.6 UNDERSTANDING PLANT HORMONES

 A.k.a phytohormones  A 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  CO 2  O 2  Toxins  Gravity  Temperature  Sunlight  Parasites  Pathogens  Control plant growth, development and movement

 Example of plant hormones:  Auxins  Gibbrellins  Cytokinins  Abscisins  Ethylene or ethene

AUXIN

 Greek (to grow)  E.g. indoleacetic acid (IAA), zeatin (natural) & kinetin (synthetic)  Promote cell elongation & cell enlargement  Produce at stem tips, root tips (root caps), stems & buds  Required by plants almost all the time  Involved in phototropism & geotropism AUXINS

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AUXIN IN GEOTROPISM

 Major effect is on stem elongation ; important in the regulation of height  Have little effect on roots  Produce 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 diffusion  Promotes flower opening and fruit ripening  Also stimulates:  Defence response to wounding/ infection of disease  Shoot growth & differentiation  Root growth & differentiation  Leaf & 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.Herbicide 4.Prevent fruit from dropping before harvest is due AUXINS

1.Promote fruit ripening 2.Induce flowering in pineapple 3.Increase latex flow – rubber trees 4.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 yield 3.Increase flower bud production and stimulate their early flowering GIBBERELLINS