4. really cool stuff plants do Flashcards
tropisms
When a plant grows towards or away from and external stimulus
* Usually involves bending or curving
* Positive – response towards something
* Negative – a response away from something
phototropism
Growing towards light
* Cells on the shady side elongate
* Caused by auxins
Light drives auxin to the shady side
gravitropism
Response to gravity
* Roots grow down and shoots
grow up, even if plant is on its
side
Starch-Statolith Hypothesis
Amyloplasts (starch containing plastids) that sense gravity are called statoliths
* These occur in cells called statocytes
* In stems, these are in the starch sheath around the vascular tissues
* When a root is placed sideways, amyloplasts in statocytes slide downward so that
the root grows in that direction
hydrotropism
Growth towards water
* Hard to study because gravitropism is so pronounced
* Used a pea plant mutant that did not respond to gravity
thigmotropism
Growth in response to touch
* Plants will grow around rocks or wind around support structures
* Tendrils have memory of what supports them
Circadian Rhythms
Regular happenings in a plants life that occur on a 24 hour cycle
* Flowers open in the morning
* Controlled by Circadian Clocks at the cellular level
* These have 3 parts:
* Oscillator – generate rhythmic behavior
* Input – what carries environmental information to the oscillator (like morning sun)
* Output – What regulates biochemical and physical processes
Circadian Clocks – Environmentally
synchronized
The environment controls these – the light/dark cycle
* Adjusts seasonally
* Example: When insects are at a stage to pollinate flowers, flowers will open
based on the insects feeding behavior
Adjustments to Circadian Rhythms
Entrainment – when daylength changes, a plant must adapt to the
changing amount of light
Gating – There are differences in how a plant responds based on strength of the stimuli
Photoperiod
The effect of daylength on flowering
* A “biological response to a change in the proportions of light and dark on a 24
hour cycle”
* Because daylength changes with time of year, this allows plants to determine
what season it is and change behavior accordingly
short day plants
Flower early spring or fall
* Must have a light period shorter than a critical length
* Example: Poinsettias
long day plants
Flower in the summer
* Only if light period is longer than a critical length
* Examples: Spinach; lettuce; some potatoes
day neutral plants
Flower no matter what daylength
phytochrome
the primary photoreceptor
This is a pigment found in the cytoplasm of plants
* Occurs in very small amounts
* Detect using a spectrophotometer
* Absorbs red (660 nm) & far red (730nm) wavelengths of light
Phytochrome mediates photomorphogenesis
floral stimulus
Leaves perceive daylength and then form a substance that moves to
the shoot and induces flowering
* This substance was called “florigen” - a small protein (FT)
* This is produced in the companion cells of minor vein phloem of leaves,
transferred to the sieve tubes and transported to the shoot apical meristem
* FT works with another protein (FD) and activates genes that are floral
promotors
Vernalization
- When plants must be exposed to cold in order to flower
- This is common in winter annuals & biennials
- Also necessary for garlic – planted in the fall and grows and flowers in
the Spring - Usually these all require a certain long day photoperiod too
Dormancy
A special condition when growth will not occur unless the plant is
exposed to certain conditions
* Seed dormancy can be broken in various ways:
* Stratification – when a moist seed is exposed to low temperatures for many
days
* Scarification – Breaking the seed coat either physically or chemically
Seed banks
where seeds (which hold all the genetic characteristics
of plants) are held just in case
seed banks
where seeds (which hold all the genetic characteristics
of plants) are held just in case
Dormant Buds
Starts in mid-summer after forming
Acclimation – the process where a plant gets prepared to shut down
in the winter. This leads to cold-hardiness – the ability to survive in
less than ideal conditions
nyctinastic (nastic) movement
When a plant moves in response to
a stimulus
* Example: When leaves are oriented
horizontally during the day and
vertically at night
Thigmonastic movements
Nastic movements from mechanical stimulation
* Examples:
* Sensitive plant – Mimosa pudica
* Venus flytrap – leaves spring shut on insects
Heliotropism
Solar tracking – when leaves and flowers move diurnally, orienting themselves to the sun
* Examples: Sunflower; cotton; soybean
* Not like phototropism since it is not a result of uneven growth, rather it is like a nastic movement
