Plant HormonesPlant Hormones
Types of hormonesTypes of hormones
Like animals, plants use hormones to Like animals, plants use hormones to produce functional and structural changes. produce functional and structural changes.
Types of hormones includeTypes of hormones include AuxinsAuxins GibberellinsGibberellins CytokininsCytokinins EthyleneEthylene
AuxinAuxin
Auxins are a type of hormone that produces Auxins are a type of hormone that produces cell elongation and allows the plant to cell elongation and allows the plant to grow grow in length and to develop.in length and to develop.
The natural Auxin is a compound called The natural Auxin is a compound called indoleacetic acid or IAAindoleacetic acid or IAA
AuxinAuxin
Auxin associated with phototropism - early experimentsAuxin associated with phototropism - early experimentsdemonstrate tip as receptor.demonstrate tip as receptor.
Auxin continuedAuxin continued
Auxin is made at the apical meristem of a Auxin is made at the apical meristem of a shoot and moves down at a rate of 10 mm shoot and moves down at a rate of 10 mm per hour to the region of elongation and per hour to the region of elongation and stimulates cell growth. stimulates cell growth.
Question???? At this speed, how do you think it is At this speed, how do you think it is
transported through the cell? transported through the cell?
Auxin moves down the plantAuxin moves down the plantAnswer Too slow for phloem transportationToo slow for phloem transportation It is carried by the parenchyma tissue It is carried by the parenchyma tissue
from one cell to the next.from one cell to the next.
Auxins do two things to help with cell Auxins do two things to help with cell elongation: elongation:
1.1. Soften the cell walls so the plant can Soften the cell walls so the plant can expandexpand
2.2. Increase the rate of cell divisionIncrease the rate of cell division
Demonstration of transported chemicalDemonstration of transported chemical
Loosening of cell wallLoosening of cell wall
Lateral growthLateral growth
Auxins produced in the meristem inhibits growth Auxins produced in the meristem inhibits growth of side branches (lateral stems)of side branches (lateral stems)
CytokininsCytokinins
CytokininsCytokinins
You will remember from Mor 4 that cytology You will remember from Mor 4 that cytology is the study of cells. is the study of cells.
The hormone, Cytokinins stimulate cell The hormone, Cytokinins stimulate cell division (mitosis and division (mitosis and cytokinesis)cytokinesis)
Cytokinins are produced by actively growing Cytokinins are produced by actively growing tissue and can move throughout the plant in tissue and can move throughout the plant in the xylem, phloem and parenchyma cells. the xylem, phloem and parenchyma cells.
Function of cytokininsFunction of cytokinins
Promotes cell division.Promotes cell division.Lateral bud development.Lateral bud development.Delay of senescence (AGING).Delay of senescence (AGING).Stomata opening.Stomata opening.Rapid transport in xylem stream.Rapid transport in xylem stream.
Cytokinins are used with Auxins to Cytokinins are used with Auxins to help plants to grow and develop help plants to grow and develop
GibberellinGibberellin
Effects of GibberellinsEffects of Gibberellins
General cell elongation.General cell elongation.Breaking of dormancy.Breaking of dormancy.Promotion of flowering.Promotion of flowering.
GibberellinsGibberellins
Gibberellins are growth hormones that allow the Gibberellins are growth hormones that allow the plant to plant to grow in lengthgrow in length..
Gibberellins were discover in Asia when some Gibberellins were discover in Asia when some farmers noticed that rice would grow too fast and farmers noticed that rice would grow too fast and tall which was caused by a fungus called tall which was caused by a fungus called Gibberella. Gibberella.
Gibberellins are usually produced in roots and Gibberellins are usually produced in roots and young leaves and stimulate a growth in leaves and young leaves and stimulate a growth in leaves and stems but not in roots. stems but not in roots.
Gibberellins are also found to increase Gibberellins are also found to increase seed seed germination and flower developmentgermination and flower development
Discovered in association with Foolish Discovered in association with Foolish disease of rice (disease of rice (Gibberella fujikuroi)Gibberella fujikuroi)
infecteduninfected
Gibberellins and plant growthGibberellins and plant growth
EthyleneEthylene
H H \ / C = C / \ H H
Functions of ethyleneFunctions of ethylene
Gaseous in form.Gaseous in form.Rapid diffusion.Rapid diffusion.Affects adjacent individuals.Affects adjacent individuals.Senescence (Senescence (agingaging) and abscission () and abscission (the naturthe natur
al process by which leaves or other parts are al process by which leaves or other parts are shed from a plantshed from a plant).).
Interference with auxin transport.Interference with auxin transport. Initiation of stem elongation and bud Initiation of stem elongation and bud
development.development.
Ethylene gasEthylene gas Years ago, farmers use to heat fruit in a Years ago, farmers use to heat fruit in a
kerosene oven to make them ripen faster. kerosene oven to make them ripen faster. Scientist learnt that it was not the heat but the Scientist learnt that it was not the heat but the ethylene gas byproduct that made it ripenethylene gas byproduct that made it ripen
We now know that plants develop their own We now know that plants develop their own ethylene as a hormone that makes fruit ripenethylene as a hormone that makes fruit ripen
EthyleneEthylene Scientist also discovered that ethylene is the Scientist also discovered that ethylene is the
opposite to Auxin and opposite to Auxin and inhibits cell growthinhibits cell growth
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Have a great day!!!Have a great day!!!
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