ORGANIC COMPOUNDS

Growth Defined 1.Increase in mass due to the division and enlargement of cells 2.Types of growth in plants a.Determinate growth b.Indeterminate growth 3.Differentiation of cells

Development Defined The process of growth and differentiation of cells into tissues, organs, and organisms

Plant Hormones Auxins a.Early experiments by Darwin b.Discovery of auxin by Frits Went (1926) c.Characteristics of auxins 1)Sites of production a)Apical meristems b)Buds c)Young leaves d)Other active young plant parts e) Monocots less sensitive to auxins than dicots 2)Polar movement flow of auxins away from their source of synthesis

Frits Went (1926)

d.Naturally occurring auxins 1)Indoleacetic acid (IAA) 2)Phenylacetic acid (PAA) 3)4-chloro-indoleacetic acid (4-chloro-IAA) e.Synthetic auxins and their uses 1)Fruit retention 2)Herbicides (2,4-D) Agent Orange uncontrolled growth leads to death

2.Gibberellins a.Discovery of "foolish seedling" disease b.Effects of gibberellin 1) Increase stem elongation 2) Breaking of dormancy of buds and seeds 3) Similar to functions of auxins, enhanced when used together

Gibberellins increase stem growth

3.Cytokinins a.Discovery of enhancement of cell division b.Stimulants to cell division called "cytokinins" c.Found in meristems and developing tissues, e.g., young fruit d.Effects of cytokinins 1)Enlarging of cells 2)Differentiation of tissues 3)Development of chloroplasts 4)Stimulation of cotyledon growth 5)Delay of aging in leaves

3.Cytokinins – The first cytokinin was isolated from herring sperm in 1955 by Miller and his associates (Miller et al., 1955). – This compound was named kinetin because of its ability to promote cytokinesis. – Cytokinin is ubiquitous to all plant species in one form or another.

4.Abscisic Acid (ABA) a.Discovery (1963) b.Location in the plant 1)Synthesized in plastids from carotenoid pigments 2)Common in fleshy fruits a)Prevents seeds from germinating while still on the plant promoted dormancy b) ABA inhibits cell growth c. Other effects of ABA 1)Induces bud dormancy 2)Regulates stomatal opening (water stress brings about an increase in ABA synthesis).

5.Ethylene a.Ethylene has been used in practice since the ancient Egyptians, who would gas figs in order to stimulate ripening b.Produced by fruits, flowers, seeds, leaves, roots c.Hastens ripening of fruits

Hormonal Interactions A.Apical Dominance 1.Defined suppression of the growth of lateral or axillary buds 2.Auxin and/or cytokinin mediated B.Senescence 1.breakdown of cell components and membranes that leads to cell death 2.Why do plant parts senesce? C.Other Hormonal Interactions

Review 1. growth inhibitors - abscisic acid, ethylene 2. stress hormone, protects plants - abscisic acid 3. closes the stomata - abscisic acid 4. growth promotors - auxin, cytokinin, giberellins 5. a gas – ethylene 6. produces dormancy in seeds and buds - abscisic acid 7. breaks dormancy in seeds and buds – gibberellin 8. stimulates the ripening of fruit – ethylene 9. prevents plant tissues from senescing or aging – cytokinin 10. is produced by the apical bud and inhibits the growth of lateral buds - auxin

Plant Movements A.Growth Movements 1.Movements resulting primarily from internal stimuli a.Helical (Spiraling) movements b.Nodding movements c.Twining movements d.Contractile movements e.Nastic movements: Venus flytrap, sensitive plant 2.Movements resulting from external stimuli a.Phototropism b.Gravitropism c.Thigmotropism

Plant Movements cont. B.Turgor Movements 1.“Sleep” movements (Circadian Rhythms) 2.Solar Tracking 3.Water conservation movements C.Taxes (Taxic Movements) 1.Defined a.Type of movement that involves either the entire plant or its reproductive cells b.Does not occur in flowering plants 2.Types a.Chemotaxis b.Phototaxi

Plant Movements cont. D.Miscellaneous Movements 1.Gliding movements 2.Dehydration movements 3.Explosive movements

Photoperiodism A.Discovery B.Critical Day-length 1.Short-day plants 2.Long-day plants 3.Intermediate-day plants 4.Day-neutral plants

END