1. Control Systems in Plants

2. Plant Hormones What is a Plant Hormone ?
Compound produced by one part of an organism that is translocated to other parts where it triggers a response in target cells and tissues.

3. Functions of Plant Hormones
Control plant growth and development by affecting division, elongation, and cell differentiation
Effect depends on size of action, stage of plant growth and hormone concentration
Hormonal signal is amplified by gene expression, enzyme activity, or membrane properties

4. Table 39.1 An Overview of Plant Hormones

5. Auxins (IAA) indoleacetic acid: natural auxin in plants
Promotes elongation & secondary growth
Apical meristem is the major site of auxin production
Inhibits lateral growth
Induces female floral parts & fruit

6. Figure 39.8 Apical dominance: with apical bud (left), apical bud removed (right)

7. Figure 39.7 Cell elongation in response to auxin: the acid growth hypothesis

8. Cytokinins Move from the roots to tissues by moving up xylem
Stimulates protein synthesis
Made in roots
Functions:
1. Cell division and differentiation
2. Apical dominance
3. Anti-aging hormones
slow protein deterioration

9. Gibberellins Stimulate elongation of cells Inhibits root growth
Stimulate flower part development- bolting
Signals seeds to break dormancy and germinate

10. Figure 39.9 “Foolish seedling disease” in rice

11. Figure 39.11 The effect of gibberellin treatment on seedless grapes

12. Abscisic Acid (ABA) Growth inhibitor returns seeds to dormancy
inhibits cell division in vascular cambium
causes rapid closing of stoma during dry periods
promotes positive geotropism

13. Figure 39.12 Precocious germination of mutant maize seeds

14. Ethylene Gaseous hormone High [auxin] induces release of ethylene
Causes senescence (aging)
Fruit ripening – one bad apple does spoil the whole bunch
Abscission – loss of leaves on
deciduous trees

15. Figure 39.16 Abscission of a maple leaf

16. Which hormones cause the following….
Apical dominance from apical bud
Abscission
Stimulates growth of axillary buds
Root growth
Stimulates closing of stomata
Causes fruit ripening
Stimulates seeds to break dormancy and germinate
Growth inhibitor
Cell division and differentiation
Cell elongation
Seedless fruit

17. Answers to Previous Slide:
Auxin
Ethylene
Cytokinins
Abscisic acid
Gibberellins
Auxins and cytokinins
Auxins

18. Which hormone is made at each location?
Made in roots and transported upwards
Found in meristems of apical buds and seed embryos
Found in tissues of ripening fruit
Leaves stems, roots and green fruit

19. Answers to Previous Slide:
Cytokinins
Auxins
Ethylene
Abscisic Acid

20. Plant Movement A. Tropisms: 1. Phototropism
growth response toward or away from stimuli
1. Phototropism
cells on darker side of shoot elongate faster than cells on bright side due to auxin distribution
auxin move laterally across the tip from the bright to dark side by an unknown mechanism.
Cells on the dark side grow

21. 2. Gravitropism (geotropism)
gravity
roots --> positive geotropism
stems---> negative geotropism
Statoliths
starch grains in root cap cells, they trigger calcium redistribution which results in auxin movement in root
auxin inhibits cell elongation
upperside of root elongates faster than bottom

22. growth in response to touch tendrils contacts solid and coils
3. Thigmotropism
growth in response to touch
tendrils contacts solid and coils
increased production of ethylene `
4. Hydrotropism
growth toward water
willow tree