BSCI 442
DEVELOPMENT = Sum of GROWTH & DIFFERENTIATION
GROWTH is an irreversible increase in size or volume.
DIFFERENTIATION occurs when cells take on a special form
and function.
Pattern formation (e.g. of an embryo) is determined by
the plane of division.
II. What controls development?
The orderly development of the plant depends on coordination
and are subject to control at 3 distinct levels:
1. Genetic control of the developmental program
2. Environmental stimuli
3. A balance of hormones
The developmental program is inherited. ie. it
is in the nucleus and is encoded by the specific sequences of the genes.
Plants use environmental cues, such as light, daylength,
cold to proceed from one developmental stage to another.
Plants also respond to several hormones.
Environmental cues and internal factors (hormones) can
regulate growth by controlling and modifying the developmental program.
III. Changes in gene expression is a principal
factor in regulating development.
Gene Expression refers to the synthesis of specific proteins
encoded by specific genes.
Information flows from DNA ---> RNA ---> protein.
How is gene expression regulated? Gene expression
can be regulated at many levels: :
*A. Transcription
B. RNA Processing
C. Translation
*D. Protein modification
Most (if not all) environmental and hormonal stimuli act in part on modifying gene expression.
Useful General Terms:
Transcription factors: are proteins that
bind to regulatory regions of a gene and so regulate the transcription
of that gene.
These factors can be activators or
repressors. The factors can bind directly to a regulatory DNA
sequence or bind to DNA-binding proteins to form a complex.
cis-acting elements (or sequences): refer to regulatory
DNA
sequences near the gene.
trans-acting factors: refer to proteins that bind
directly or indirectly with regulatory DNA sequences (including the cis-acting
elements).