I. SUMMARY/REVIEW
Four major stages in the life cycle of a plant
SEEDLING
A
B
SEED
VEGETATIVE PLANT
D
C
REPRODUCTIVE PLANT
A. Seed germination
B. Development of the vegetative body
C. Development of the reproductive organs-flowers, pollination, fertilization
D. Embryogenesis to form a seed
ORDERLY DEVELOPMENT DEPENDS ON COORDINATION AND ARE SUBJECT TO CONTROL
AT THREE LEVELS.
1. Programmed sequence
of gene expression
2. A balance of hormones
3. Environmental signals
A. SEED --> SEEDLING (Seed Germination)
a) BREAKING OF DORMANCY
Temperature
Water
Light
Hormones: ABA
Decr., GA increase. (e.g. BARLEY)
b) REQUIREMENTS FOR GROWTH
Water
Oxygen
Temperature
Mineral nutrients
Initially heterotrophic, mature seedling becomes photosynthetically-competent.
B. SEEDLING ---> VEGETATIVE PLANT (Vegetative development)
GROWTH & DIFFERENTIATION TO A PLANT WITH SPECIFIC ORGANS, TISSUES, CELL TYPES. Growth & Differentiation DEPENDS ON the genetic program, environmental conditions (e.g. light) & intrinsic hormones.
a) Shoot apical meristem gives rise to leaves and stem.
LEAF development: into cell types with particular structure and function. e.g.
mesophyll cell with chloroplasts
STEM
b) Root apical meristem gives rise to the root.
REQUIREMENTS FOR AUTOTROPHIC GROWTH
Light
Water
Essential mineral
nutrients
Oxygen
CO2
UPTAKE AND TRANSPORT of Water and Nutrients
Ability to synthesize all the complex organic biomolecules using inorganic
ions and simple compounds.
Photosynthesis
N assimilation
SYNTHESIS OF NEW ORGANIC COMPOUNDS NEEDED FOR GROWTH & DEV.
CARBOHYDRATES : CELLULOSE,
STARCH
PROTEINS: ENZYMES
NUCLEIC ACIDS: DNA,
RNA
C. MATURE VEGET. PLANT ---> REPROD. PLANT
(Reproductive Development)
ENVIRONMENTAL STIMULI :
LIGHT, TEMP, PHOTOPERIOD
HORMONES
NEW GENES ARE EXPRESSED
Transition from shoot apical meristem to Formation of the floral apical meristem
FORMATION OF FLOWER: sepals, petals, stamen, carpel
POLLINATION,
FERTILIZATION
D. REPRODUCTIVE PLANT ---> SEED (Embryogenesis)
AFTER FERTILIZATION, SEED DEVELOPMENT BEGINS