Chapter 9 : Growth and Development
Overview
This chapter introduces growth phenomena with a discussion of the distinctions among growth, differentiation, and development. This is followed by a discussion of plant hormones
(auxins, gibberellins, cytokinins, abscisic acid, ethylene) their roles in plant growth and development, and the role of signal transduction in plant responses to the environment. The chapter explores plant movements, including spiraling, twining, contraction, nastic, tropic, turgor, taxic, and miscellaneous other movements. The discovery and functions of phytochrome and photoperiodism are briefly surveyed. The chapter concludes with a discussion of the relationship of temperature to growth and dormancy.
Detailed Lecture Outline
I. Introduction
A. Growth Defined
1. An irreversible 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. Nutrients, Vitamins, and Hormones
A. Nutrients Defined
·necessary for plant growth and maintenance
B. Vitamins Defined
·Organic molecules that participate in catalyzed reactions
C. Hormones
1. .Produced and are active in smaller amounts than vitamins and enzymes
2. Usually produced in actively growing regions of plants
3. Ordinarily transported from point of origin to other parts of plants
4. Plant growth response: signal transduction pathway
D. Types of Plant Hormones
1. Structure
2.Three major groups promote plant growth
3. Auxins
a. Early experiments by Darwin
b. Discovery of auxin by Frits Went (1926)
c. Characteristics of auxins
1) Production pathways
2) 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
3) Polar movement
• flow of auxins away from their source of synthesis
4) Effects of auxins
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
2. Gibberellins
a. Discovery of "foolish seedling" disease
b. Effects of gibberellin
1) Increase stem growth
2) Breaking of dormancy of buds and seeds
3) Similar to functions of auxins, enhanced when used together
4) Can hasten conversion of juvenile leaves to adult foliage
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
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
b) ABA inhibits cell growth
c) Movement of ABA, like gibberellins and cytokinins, is non polar
c. Other effects of ABA
1) Induces bud dormancy
2) Regulates stomatal opening
5. Ethylene
a. Discovery (1934)
b. Produced by fruits, flowers, seeds, leaves, roots
c. Hastens ripening of fruits
d. Ethylene accumulation in spaceships
B. Other Hormones or Related Compounds
1. Bind to receptors on cell surfaces
2. Oligosaccharins
a. Influence cell differentiation, reproduction and growth
b. Released from cell walls

III. Hormonal Interactions
A. Apical Dominance
1. Defined
• suppression of the growth of lateral or axillary buds
2. Auxin and/or cytokinin mediated
3. Auxins control cytokinin concentration
B. Senescence
1. Defined
• breakdown of cell components and membranes that leads to cell death
2. Why do plant parts senesce?
C. Other Hormonal Interactions: PGRs promote, inhibit or modify plant processes
IV. Plant Movements
A. Growth Movements
1. Movements resulting primarily from internal stimuli
a. Helical (Spiraling) movements or Nutations
b. Nodding movements
c. Twining movements
d. Contractile movements
e. Nastic movements
2. Movements resulting from external stimuli
a. Phototropism
· Photoreceptor proteins in plasma membrane
b. Gravitropism
c. Other tropisms
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
c. Requires motility
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 and Cryptochromes
A. Characteristics and Location in Plant
B. Phytochrome Interconversions

• Pred (P r
) and Pfar-red (P fr
)
C. Functions of Phytochrome
D. Cryptochromes
E. Further studies
VII. A Flowering Hormone?
A. Defined
• hypothetical hormone that induces flowering in plants
B. Chailakhyan's Experiments with Flowering
C. CONSTANS gene in Aradapsis thalliana
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