Plants: Hormones Flashcards
Plants hormones drive tropsisms, what is tropisms?
Any growth response that results in plant organs curving toward or away
from stimuli
What is phototrpism?
growth of a shoot in response to light
* Moving toward sunlight helps a growing plant use sunlight to drive
photosynthesis
* Can result when the cells on the dark side of a plant stem elongate
faster than those on the light side
What are hormones?
chemical signal
* produced in one part of the body
* transported to other parts,
* acts on target cells to change their functioning
What are the five major plant hormones?
Auxins, Cytokinins, Givvverellins, Abscicic acid and Ethylene
Describe plant hormones?
- produced in very low concentrations
- can have a profound effect on growth and development
- The binding of hormones to cell-surface receptors triggers a signal
transduction pathway - amplifies the hormonal signal
- leads to a response or responses within the cell
What is auxin?
any chemical substance that promotes seedling elongation
* Indoleacetic acid (IAA)
* Auxin is produced in apical meristems at the tips of shoots
* Hormone moves down the plant
* Known as “apical dominance”
What does auxin concentrations do?
- stimulates or inhibits the elongation of shoots and roots
- may act by weakening cell walls
- allows them to stretch when cells take up water
- stimulates the development of vascular tissues and cell
division in the vascular cambium, promoting growth in stem
diameter - produced by developing seeds and promotes the growth of fruit
What is cytokinin?
Stimulates cell division
* produced in actively growing organs
such as roots, embryos, and fruits
* move upward from roots through a
plant
* balancing the effects of auxin
from apical meristems
* causing lower buds to develop
into branches
What is gibberellins?
affects stem elongation and cell division in stems and leaves
What is abscisic acid?
inhibits many plant processes (growth)
* act as a “stress hormone” – close
stomata when plant is dehydrated
* High concentrations of ABA promote seed
dormancy
* ABA must be removed for germination
to occur
* Ratio of ABA to gibberellins controls
germination
What is ethylene?
triggers fruit ripening
* gaseous by-product of coal combustion
* naturally occurring plant hormone
* Plants produce ethylene
* fruit ripening and programmed cell
death
* also produced in response to stresses
such as drought, flooding, injury, or
infection
What causes a plant to grow in response to an envrinmental stimuli?
tropisms
What are the three stimuli plants respond to?
Phototropsim (light), gravitropism (gravity), thigmotropism (touch)
What are circadian rhythms?
internal clocks that are influenced by environmental cues such as
light, but they are controlled by biological clocks
* In plants, this is likely the result of rhythmic production of proteins
that influence gene expression
What is a photoperiod?
- relative lengths of day and night
- environmental stimulus plants most often use it to detect the
time of year
What are short day plants?
flower when dark period > critical length
What are long day plants?
flower when dark period > critical length
