More Hormones

1. More Hormones • Aims: • Must be able to state what pheromones are, with examples. • Should be able to state some examples of how pheromones can be used. • Could be able to outline the use of hormones as plant regulators.

2. Pheromones • Pheromones are chemical signalling molecules secreted by animals, particularly insects. • Influence the behaviour of members of the same species – Species specific. • A male insect will only respond to a pheromone released by a female of the same species. • E.g. Moths produce pheromones as a sex attractant to attract males.

3. Using Pheromones • Pheromones can be used to reduce insect pests in commercial crops. • Artificial chemicals that mimic particular pest pheromones are used. • Traps are set containing the artificial pheromone, to attract and contain the male pests.

4. Activity • Complete page 107 in Biozone book.

5. Plant Hormones • Unlike animals, plants do not have a nervous system. • Plant growth and regulation is controlled by internal and external factors: • Fruit growth and ripening • Flowering • Germination • Formation of buds • Lengthening of stems • Downward growth of roots • Plant dormancy • etc

6. External Factors influencing Growth • Light intensity • Gravity • Water • Light direction • Day Length • Temperature

7. Plant Responses • Plants are able to respond to physical parameters in their environment: • Light – Grow towards = (phototropism) • Gravity - Shoots upwards = (negative geotropism) Roots down = (positive geotropism) • Changing day lengths – trigger for flowering in many species (phototropism) • Periods of cold (vernalisation)

8. Plant Hormones • Plant hormones are mainly produced in the growing regions called the meristems • Plant hormones are transported throughout the plant via the xylem and/or Phloem • Plant hormones do not act in isolation, with the presence of one influencing the action of another.

9. Auxins • Transported from tip to base through parenchyma cells • Involved in controlling elongation and enlargement of plant cells • Stimulate elongation of Stems • Stimulate growth of lateral and adventitious roots (but at high concentrations inhibit roots growth) • Promote growth of flowers and fruits • Influence the differentiation of unspecialised cells into vascular tissue (xylem/ phloem) • Eg: IAA (Indoleacetic acid)

10. Effect of Auxin In strawberries, auxin is produced by the “seeds” on the surface of the fruit. If removed, the strawberry does not develop, however normal development occurs if the auxin is replaced

11. Phototropism is the bending of a plant towards light (=stimulus) Auxin in the cells moves to the dark side of the coleoptile. Cells on the dark side to elongate. Uneven elongation leads to bending Also occurs in roots in response too gravity (geotropism) Phototropism and Geotropism

12. Cytokinins • Cytokinins act on shoots, roots and fruits. • High concentrations of Cytokinins are found in young, growing plants • Promote cell reproduction • Transported via xylem

13. Gibberellins promote cell elongation and cell reproduction in tissues of stems and leaves Eg: Gibberellic Acid Transported via xylem and phloem Gibberellins Plants with (left) and without (right) the influence of gibberellins

14. Abscisic Acid • Abscisic acid inhibits growth and influences stomatal closure. • Also inhibits germination of seeds, promotes seed dormancy and seasonal dormancy. • Causes abscission of leaves and fruits • Transported via vascular tissue

15. Ethylene • Promotes fruit ripening, senescence, and abscission of leaves and flowers. • Also promotes germination • Ethylene and fruit production works on a Positive Feedback mechanism • Transported throughout plant by diffusion through intercellular spaces. • Ethylene is not technically a hormone but a gas produced by the metabolism of a plant

16. Activity • Complete page 91 and 92 in Biozone books.