Transcript Control Systems in Plants

Control Systems in Plants
Chapter 26
I. Control of Plant Development
A. plant hormones
1. chemical messengers within organisms
2. each has a very specific function
3. auxins
a.
b.
promote growth at apical meristems
cause growth in different directions
4. gibberellins
•
promote stem elongation
5. cytokinins
a.
b.
promote cell division
prevent premature aging (senescence)
6. ethylene
a.
b.
causes dropping of leaves and fruit (abscission)
ripens fruit
7. abscisic acid
a.
b.
promotes seed and bud dormancy
closes stomata
B. Plant Responses to the Environment
1.
tropisms
a.
b.
c.
growth toward or away from a variable
•
positive vs. negative
causes growth in different directions
phototropism, chemo-, thigmo-, gravi-
An example of positive phototropism
Fig. 26.11 (a) Negative gravitropism in
stem growth. (b) Positive gravitropism
in root growth.
2.
circadian rhythms
a.
b.
c.
activities that occur in 24-hour cycles
biological clocks
i.
internal (genetic) mechanism that maintains circadian rhythms
ii. strongly influenced by photoperiod
sleep movements
Fig. 26.13 Coiling response is
an example of thigmotropism.
Fig. 26.15
Examples of sleep
movements in
prayer plants and
morning glories.
d.
photoperiodism
i.
responses caused by changes in day-length
ii. controlled by the pigment phytochrome
•
acts as a photoreceptor
iii. best example is flowering
•
short-day vs. long-day vs.
day-neutral plants
Fig. 26.5
Graph of circadian rhythms in
morning glories.
The influence of photoperiod on flowering in
long-day and short-day plants.
II. Plant Defenses
A. like animals, plants have defenses against disease
1.
2.
3.
bacterial, viral, and fungal infections
much of their defense is based on genetics
chemical attacks against pathogens
a. often localized in more vulnerable areas
b. phytoalexins, alkaloids, glycosides, etc.
B. plants also protect themselves from herbivores
1.
2.
structural defenses
•
spines, thorns, hair layers, tough bark, etc.
chemical defenses
•
toxins, inedible substances, sticky substances, etc.
Fig. 26.19
Examples of plant
herbivores
Fig. 26.19 Plant fungal
infection