January 26-27, 2012: Life Cycle

Behavior = the manner in which a person
behaves in reacting to social stimuli or to
an inner need or to a combination thereof;
OR = good manners
OR = an activity of a defined organism,
especially observable activity when
measurable in terms of quantifiable effects
on the environment whether arising from
internal or external stimuli
OR = anything that an organism does that
involves action and response to
OR = the response of an individual, group,
or species to the whole range of factors
constituting its environment
Plant Life Cycle:
includes stages of
processes of mitosis,
cell expansion,
fertilization (twice!)
Plant Development
is flexbile:
indeterminate, cells
Corn (Zea mays)
produces male flowers
and female flowers
(many make up the ear)
the plants can ‘self’ or
a pollen grain germinating
on a style must extend its
tube down the length of
the style (12 inches or so)
and fertilize the embryo
at the end of the style
in order to make a kernel
(ovule) develop
Once and embryo is formed, it can undergo
mitosis (cell division), and differentiation to
make all the different cell types, tissues and
organs of a plant. This process is called
Development is regulated at three levels:
Genetic – by control of the pattern of gene
expression, cells determine which
proteins, structures and processes
are active
Internal signaling – signals include ‘hormones’
other metabolites (sugars, peptides)
hydraulic and electric signals
External signaling
biotic interactions
Plant ‘hormones’ or growth
regulators are active at nM levels.
Their activity depends on:
1) rate of synthesis
2) rate of transport to active site
3) receptivity of target/presence
of receptor
4) rate of degradation
Seeds are like tiny space ships, launched from their mother into space, packed full
of food, primed to germinate if or when they land on suitable substrate.
• dormancy must be broken
• seed imbibes water
• tissues rehydrate
• embryo releases GA
• aleuroce cells respond to GA
• endosperm digested
• embryo begins to grow
• root elongation followed by
Some seeds require light as a cue for germination.
The photoreceptor responsible for this sensory process is Phytochrome
– red (660 nm)/far red (730 nm) photoreceptor ‘switch’
phytochrome is a
protein with enzyme
activity (kinase),
bound to a chromophore;
when the chromophore
absorbs R or FR light,
it changes the protein
conformation, thus
the enzyme