Chapter 26 Control of Plant Development plant hormones chemical messengers within organisms each has a very specific function auxins promote growth at apical meristems cause growth in different directions ID: 775552
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Control Systems in Plants
Chapter 26
Slide2Control of Plant Development
plant hormones
chemical messengers within organisms
each has a very specific function
auxins
promote growth at apical
meristems
cause growth in different directions
gibberellins
promote stem elongation
cytokinins
promote cell division
prevent premature aging (senescence)
ethylene
causes dropping of leaves and fruit (abscission)
ripens fruit
abscisic
acid
promotes seed and bud dormancy
closes stomata
Slide3Plant Responses to the Environmenttropisms growth toward or away from a variablepositive vs. negativecauses growth in different directionsphototropism, chemo-, thigmo-, gravi-
An example of positive phototropism
Fig. 26.11 (a) Negative
gravitropism
in stem growth. (b) Positive
gravitropism
in root growth.
Slide4circadian rhythmsactivities that occur in 24-hour cyclesbiological clocksinternal (genetic) mechanism that maintains circadian rhythmsstrongly influenced by photoperiodsleep movements
Fig. 26.13 Coiling response is an example of
thigmotropism.
Fig. 26.15 Examples of sleep movements in prayer plants and morning glories.
Slide5photoperiodismresponses caused by changes in day-lengthcontrolled by the pigment phytochrome acts as a photoreceptorbest example is floweringshort-day vs. long-day vs. day-neutral plants
The influence of photoperiod on flowering in long-day and short-day plants.
Fig. 26.5 Graph of circadian rhythms in morning glories.
Slide6Plant Defenses like animals, plants have defenses against diseasebacterial, viral, and fungal infectionsmuch of their defense is based on geneticschemical attacks against pathogensoften localized in more vulnerable areasphytoalexins, alkaloids, glycosides, etc.plants also protect themselves from herbivoresstructural defensesspines, thorns, hair layers, tough bark, etc. chemical defensestoxins, inedible substances, sticky substances, etc.
Fig. 26.19 Examples of plant herbivores
Fig. 26.19 Plant fungal infection
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