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