Chapter 11Growth

I. Introduction A. 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

B. Development Defined • the process of growth and differentiation of cells into tissues,

organs, and organisms

II. Plant Hormones A. Auxins 1. Early experiments by Darwin 2. Discovery of auxin by Frits Went (1926) 3. Characteristics of auxins

a. Sites of production 1) Apical meristems 2) Buds 3) Young leaves 4) Other active young plant parts

b. Polar movement • flow of auxins away from their source of synthesis

4. Naturally occurring auxins a. Indoleacetic acid (IAA) b. Phenylacetic acid (PAA) c. 4-chloro-indoleacetic acid (4-chloro-IAA)

5. Synthetic auxins and their uses a. Fruit retention b. Herbicides (2,4-D) • Agent Orange

B. Gibberellins

1. Discovery of "foolish seedling" disease

2. Effects of gibberellins

a. Increase stem growth

b. Breaking of dormancy of buds and seeds

C. Cytokinins

1. Discovery of enhancement of cell division

2. Stimulants to cell division called "cytokinins"

3. Found in meristems and developing tissues, e.g., young fruit

4. Effects of cytokinins

a. Enlarging of cells b. Differentiation of tissues c. Development of chloroplasts d. Stimulation of cotyledon growth e. Delay of aging in leaves

D. Abscisic Acid (ABA)

1. Discovery (1963)

2. Location in the plant

a. Synthesized in plastids from carotenoid pigments b. Common in fleshy fruits 1) Prevents seeds from germinating while still on the

plant 2) ABA inhibits cell growth

3. Other effects of ABA

a. Induces bud dormancy b. Regulates stomatal opening

E. Ethylene

1. Discovery (1934)

2. Produced by fruits, flowers, seeds, leaves, roots

3. Hastens ripening of fruits

F. Other Hormones or Related Compounds

1. Oligosaccharins a. Influence cell differentiation, reproduction and growth b. Released from cell walls

2. Brassosteroids a. Have gibberellinlike effect on stem elongation b. Found in legumes and several other plants

3. Batasins a. Promote dormancy in bulbils b. Produced in axillary buds of lilies

III. 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. Defined • breakdown of cell components and membranes that leads

to cell death

2. Why do plant parts senesce?

C. Other Interactions

IV. 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

2. Movements resulting from external stimuli a. Phototropism b. Gravitropism c. Other tropisms

B. Turgor Movements

1. "Sleep" movements (Circadian Rhythms)

2. Water conservation movements

3. Contact 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. Phototaxis

D. Miscellaneous Movements

1. Gliding movements

2. Dehydration movements

3. Explosive movements

V. Photoperiodism

A. Discovery

B. Critical Day-length

1. Short-day plants

2. Long-day plants

3. Intermediate-day plants

4. Day-neutral plants

VI. Phytochrome

A. Characteristics and Location in Plant

B. Phytochrome Interconversions

• Pred (Pr) and Pfar-red (Pfr)

C. Functions of Phytochrome

VII. A Flowering Hormone?

A. Defined

• hypothetical hormone that induces flowering in plants

B. Chailakhyan's Experiments with Flowering

VIII. Temperature and Growth

A. Optimum Temperature

B. Thermoperiodism

IX. Dormancy and Quiescence

A. Definition of Terms

1. Dormancy

2. Quiescence

B. Breaking of Dormancy

1. After-ripening

2. Stratification