2b Growth and Development
Plant Growth and Development Overview
Page 1: Introduction to Plant Growth
Page 2: Definition of Growth
Growth is the irreversible increase in volume due to cell division and enlargement.
Cells differentiate into specialized forms as they mature.
Page 3: Factors Influencing Growth and Development
Influenced by genetic factors, environmental factors, and chemical substances.
Plants respond to natural chemicals in their systems and synthetic plant growth regulators (PGRs).
Page 4: Tropisms and Nastic Movements
Tropism: Response to unidirectional stimuli.
Phototropism: Response to light.
Geotropism: Response to gravity.
Thigmotropism: Response to touch.
Nastic Movements: Non-directional response to stimuli.
Includes epinasty (leaf droop), stomatal closure, photoperiodism, vernalization, and leaf abscission.
Page 5: Plant Growth Regulators (PGRs)
Auxins: Indole acetic acid (IAA) and synthetic auxins (e.g., NAA).
Gibberellins (GA3): Involved in various growth processes.
Cytokinins: Promote cell division.
Abscisic Acid (ABA): Inhibits growth and promotes dormancy.
Ethylene: Involved in fruit ripening and senescence.
Page 6: Functions of Auxins
Promotes cell elongation, shoot and bud growth, and root initiation.
IAA and NAA are common forms.
Page 7: Effects of Auxins
Stimulation:
Cell elongation and differentiation in stems.
Initiation and growth of flowers and fruits.
Inhibition:
Cell elongation in roots, lateral bud development, senescence, fruit and leaf abscission (dependent on balance with other PGRs).
Page 8: Roles of Gibberellins
Break dormancy and initiate germination.
Enhance starch breakdown in seeds and promote stem elongation and internode length in plants.
Page 9: Functions of Cytokinins
Promote cell division and differentiation, leaf formation, and chloroplast development.
Zeatin isolated from corn kernels is a type of cytokinin.
Page 10: Abscisic Acid (ABA) Functions
Induces dormancy in apical meristems and seeds.
Triggers leaf abscission and stomata closure.
Page 11: Ethylene Functions
Breaks dormancy, stimulates flower opening and fruit ripening, and induces abscission processes.
Page 12: Apical Dominance
Inhibition of lateral buds by shoot tip presence.
Removal of the shoot tip or addition of auxins can stimulate growth of lateral buds, impacting agricultural practices.
Page 13: Application of Auxins in Gardening
Manual removal of shoot tips promotes bushier growth.
Use of formulated auxins can maintain dominance of main shoots after pruning.
Page 14: Auxins in Fruit Development
Auxins help vascular activity and fruit development—applied auxins can trigger development even without fertilization.
Page 15: Use of NAA and 2,4-D
NAA prevents sprouting in potato tubers.
2,4-D selectively kills broadleaf weeds without harming monocots like cereal crops.
Page 16: Rooting Formulations
Rooting powders often contain IBA and occasionally NAA, aiding in root formation and development.
Page 17: Phototropism Explained
Tropisms indicate plant growth responses to environmental stimuli.
Positive tropism: Growth towards a stimulus; negative tropism: Growth away from a stimulus.
Page 18: Phototropism Details
Light from one direction causes shoots to grow positively while roots exhibit negative phototropism.
Page 19-21: Auxin Role in Phototropism
Auxins redistribute in light conditions; light affects curvature in seedlings causing differential growth.
Page 23: Other Types of Tropisms
Gravitropism: Response to gravity.
Chemotropism: Response to chemical stimuli.
Thigmotropism: Response to contact (common in climbing plants).
Hydrotropism: Growth response to moisture gradients.
Page 24-25: Photoperiodism
Plants respond to the length of day and night affecting development stages like flower and bud dormancy.
Page 26-27: Flowering via Photoperiodism
Night length determines flowering; certain plants require specific night lengths to bloom.
Page 28-29: Short-Day vs Long-Day Plants
Short-Day Plants: Flower during short day lengths (e.g., asters, chrysanthemums).
Long-Day Plants: Flower in long days (e.g., lettuce, spinach).
Page 30: Impact of Light Exposure
Different durations of light and dark periods modulate plant responses concerning flowering.
Page 31-35: Seasonal Growth Patterns
Plant flowering and cropping vary geographically; plant species may respond specifically to northern or southern hemispheres.
Page 36-37: Artificial Light Manipulation
Artificial light can be used to control flowering times in plants like poinsettias, often using low intensity lighting.
Page 40-42: Tuber Hybrids and Flower Induction
Tuber hybrids propagate through tubers and seeds and are affected by night length and leaf formation for flowering.
Page 43-44: Induction of Tuber Formation
Tuber induction relies on short day processes, where specific conditions terminate flowering.
Page 45: Saleable Plant Production
Long days promote leaf and flower formation, while extended night lengths trigger tuber formation or dormancy.
Page 46-49: Light and Photoperiodic Response
Light consists of various wavelengths affecting plant responses; phytochromes distinguish between red and far-red light.
Page 50-53: Flowering Mechanism
Photoperiodic flowering is regulated by light exposure and internal circadian rhythms; the ratio of Pr to Pfr signals the flowering response.