Control Systems in Plants

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 • Cytokinins • Abscisic acid • Ethylene • Gibberellins • Abscisic acid • Auxins and cytokinins • Auxins • 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: • 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. 3. Thigmotropism • growth in response to touch • tendrils contacts solid and coils • increased production of ethylene • ` 4. Hydrotropism • growth toward water • willow tree