lecture 6 Light and plant development Flashcards
What is light needed for with plants?
Light is needed as a source of energy in the process of photosynthesis. Additionally it is a source of information for plants.
What does light provide plants?
It provides plants critical information about its light environment, which they needs in order to:
Germinate
Grow to a certain size or shape
Induce protective substances
Initiate flowering
What are plants senstive and react to?
quality of light
intensity of light
duration of light
the direction of light
How do plants respond to the light stimuli?
by growing, differentiating, tracking time of day and even seasons, and moving toward or away from the light.
What do plants use the evolved highly sensitive mechanisms for perceiving light for?
regulating developmental changes.
What do plants need in order to initiate development from dark to light growth?
Light energy
Explain etiolated growth
Seedling grown in dark have a pale, unusually tall appearance, known as etiolated growth.
What is the appearance of seedlings grown in light?
vigorous, green appearance
In relation to seedling growth why wan’t photosynthesis drive this transformation?
chlorophyll is not present during that time.
What induces the initial rapid changes for de-etiolation?
distinctly different light response called photomorphogenesis.
What are the light-mediated changes in plant growth and development called?
Photomorphogenesis
What are the important pigments that can promote the responses in plants called?
Photoreceptors
What do Photoreceptors absorb?
Red, Far-red and blue light
List the different parts of the flowering plants from top to bottom
Terminal bud containing shoot apex
Flower
Flower shoot
Node
Axillary bud
Internode
Vegetative shoot
Blade
Petiole
Taproot
Lateral roots
Root apex, covered with root cap
What is a Phytochrome?
Phytochrome is a protein pigment that absorbs red light (650 – 680 nm) and far-red light (710 – 740 nm); plays a key role in light-regulated vegetative growth and reproductive development.
What do spectrophotomete studies indicate?
that the phytochromes are concentrated in meristematic regions of plants.
What do the different phytochromes regulate?
distinct processes in plants and their response can be classified according to the amount and quality of light required to produce the effect.
Where is phytochrome present in dark-grown or etiolated plants?
in a red-light absorbing form (Pr), is converted by red light to a far-red light-absorbing form (Pfr), whichis physiologically active form of phytochrome.
What can Pfr be converted to?
Pr
What is the conversion of Pfr to Pr?
This conversion/ reconversion is a distinctive property of phytochrome and known as photoreversibility.
What does Phytochrome regulate?
Phytochrome regulates the transcription and expression of several genes mainly involved in greening (de-etiolation).
The complete reversal of etiolation symptoms by light involves?
long term alteration in metabolism that can be brought about by changes in gene expression.
Phytochrome also regulates the?
sleep movement of leaves referred to as nyctinasty and is a well described example of plant response regulated by light.
In nyctinasty leaves extend horizontally (open) to?
face the light during day and fold together vertically (close) at night.
Nyctinastic leaf movements are exhibited by?
many legumes such as Mimosa and Albizia.
Phytochrome brings about leaflet closure by?
regulating membrane potentials and ion fluxes.
What is Photoperiodism?
Photoperiodism is the ability of the plant to detect day length, which makes it possible for an event to occur at a particular time of the year, showing a seasonal response.
Plant photoperiodic responses utilize phytochrome as?
a primary photoreceptor, with subsequent specific signal transduction pathways to regulate different responses.
The classification of plants according to their photoperiodic response is usually based on the flowering time: For Short-day plants?
Flower only in a short days
The classification of plants according to their photoperiodic response is usually based on the flowering time: For long-day plants?
Flowers only in long days
The classification of plants according to their photoperiodic response is usually based on the flowering time: For day-neutral?
plants are insensitive to day length and flowering is under autonomous regulation through internal control.
The classification of plants according to their photoperiodic response is usually based on the flowering time: For kidney beans?
is a day-neutral species evolved near equatorwhere the day-length is constant throughout the year.
The classification of plants according to their photoperiodic response is usually based on the flowering time: For some desert plants?
evolved to germinate, grow, and flower quickly whenever sufficient water is available.
Explain Phototropism
- A common observation is that house plants placed near a window grow towards the incoming light.
- This response is called phototropism, a classical example of how plants alter their growth pattern in response to the direction of incident radiation.
What is phototropism an example of?
light as an environmental signal.
What does blue light stimulate?
blue light stimulates asymmetric growth and subsequent bending. It can be observed in fungi, ferns and higher plants.
What is blue light also used for by plants?
Blue light signals are used by plants in many other responses, allowing the plant to sense the presence of light and its direction.
What is a blue light photoreceptor?
Phototropin is a blue light photoreceptor.
When do leaves have the highest light absorption?
when the leaf lamina is perpendicular to the incident light.
How do many crop plants control light absorption?
by continuously adjusting orientation of their laminae, commonly known as solar tracking.
What is Heliotropism?
The solar-tracking plants can move their leaves in response to the sun light which is called heliotropism.
What is diaheliotropic?
Leaves that maximize light interception by solar tracking are called diaheliotropic.
What happens when you keep leaves perpendicular to the sun?
solar tracking plants maintain maximize photosynthetic rate throughout the day.
What is paraheliotropic?
Plants that move their leaves to avoid full exposure of sun light, thus minimize heating and water loss called paraheliotropic.
What is the coleoptile?
The shoot of grass when grows through the soil is protected by a modified leaf that covers it, called coleoptile.
Unequal light perception in the coleoptile results in?
unequal growth and bending due to concentrations of auxin in the lighted and shaded sides of the coleoptile.
Studies on blue light photoreceptor using Arabidopsismutants lacking in the blue light stimulated inhibition of hypocotyl showed that?
cryptochrome-1 (cry 1) a protein, acts as blue-light photoreceptor mediating the inhibition of stem.
The stomatal response to blue light regulates?
stomatal movement throughout the life of plant.
The carotenoid zeaxanthin mediates blue light photo-reception in the?
guard cells
Select the phrase that most closely defines phototropism:
a) plant curvature in light
b) the control of the direction of plant growth by light
c) the response of plants to different light intensities
d) the control of plant growth by light
e) none of the above
b)the control of the direction of plant growth by light
Which of these characteristics would help most to identify phytochrome?
a) demonstrates photoreversibility
b) located in the chloroplast
c) in solution in the cytoplasm
d) membrane bound
e) none of these
a)demonstrates photoreversibility
Is a dark grown potato shoot typified by:
a) expanded leaves
b) green coloration
c) increased node number
d) extended internodes
e) curled shoot apex
a)extended internodes
In heliotropism, the orientation of the plant stem is influenced most by:
a) the direction of unilateral light
b) the movement of the sun across the sky
c) the direction of gravity during the day
d) the spectral properties of the light
e) none of these
b)the movement of the sun across the sky
In phototropism, the most likely effector mechanism (i.e. that produces the response) in a curving shoot is:
a) an auxin gradient across the shoot
b) synthesis of a growth hormone on the dark side
c) destruction of auxin on the light side
d) production of ethylene in the shoot
e) increase in gibberellin levels in the shoo
a)an auxin gradient across the shoot
