1. Hormone Function and Tropisms
Plant Growth
Hormone Function and
Tropisms

2. • protoderm • ground meristem • procambium Primary Meristems
Whether they are involved in primary or secondary growth, all plant cells and tissues arise from three primary meristems*:
• protoderm
• ground meristem
• procambium
*Meristem: plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth

3. Specialized Tissues in Plants
Plant Growth
Meristems – tissues responsible for growth
Undifferentiated cells
Apical Meristem
Produce growth increased length
Differentiation
Cells will assume roles in the plant
Flower Development
Starts in the meristem

4. Growth Hormones (Regulation)
Plants produce chemical substances called hormones that inhibit or promote growth.
Common plant hormones are….
Inhibitors
Cytokinins
Gibberellins
Auxins

5. Cytokinins
Hormones that work with auxins to stimulate cell division.

6. Gibberellins
Hormones that stimulate cell elongation, premature flowering, and breaking of dormancy.

8. Auxins
Hormones that speed plant growth by stimulating cell enlargement.

9. Tropisms
A tropism is a growth response involving bending or curving of a plant part toward or away from an external stimulus that determines the direction of movement
Response toward the stimulus is positive, and response away from the stimulus is negative

10. Phototropism
Phototropism is the growth of stems of plants toward light - it is probably the best known of the plant tropisms - phototropism is caused by elongation of the cells on the shaded part of the plant - so that entire plant bends or curves toward the light
This growth pattern is caused by the hormone auxin - auxin migrates to the shaded part of the plant and stimulates increased cell growth and elongation on the shaded part of the plant

12. Gravitropism
Gravitropism is a response to gravity - if a seedling is placed on its side, the root will curve to grow downward and the shoot will curve to grow upward
Auxin may play a role in the response of shoots

13. Gravitropism in plants

14. Thigmotropism
Thigmotropism is response to touch or contact with a solid object - this is most commonly seen in tendrils, modified leaves or stems depending on the species.
the tendrils wrap around any object they come in contact with and so enable the plant to cling and climb.