Lecture 3: Photobiology Flashcards
Cycle of High Quality sustainably produced grain
- Plant sciences (leads to both 2&3):
(2)- Phenotypic selection of low N requirements varieties
-Genetic markers for low N requirement
—–
(3)-Optimal timing for N application
-Translation
-outreach and extension - Genetics (leads to high-quality sustainably produced grain):
-Pre-breeding
-Breeding program
-Low N requirement high yielding wheat varieties - Agronomy (leads to HQSPG)
-Informed agronomic practices
-Variety specific recommendations
Etiolation
-Mechanism that increases the probability of the plant to reach the light
-Stems of plants raised in the dark elongate much more rapidly than normal
-Once light shines:
1. the cotyledons spread apart
2. the primary leaves grow to full size+ turn green
3. production of normal-size internodes
4. photosynthesis CANNOT be the driving force because chlorophyll is not present during this time
Photobiology: developmental programs
-Plants employ two contrasting developmental programs to succeed in ambient light conditions:
- Skoto-morphogenesis
- Photo-morphogenesis
Skoto-morphogenesis
Allows young seedlings to grow rapidly in darkness using the energy present in the seed reserves:
-Elongated hypocotyl
-Closed cotyledons
-Apical hook
Photo-morphogenesis
- Process where light signals:
-inhibit the rapid elongation of hypocotyl
-expand the cotyledons
-promote greening - Allows the seedling body to adjust for:
-optimal light-harvesting capacity
-Autotrophic growth - Multiple photoreceptors to track a wide spectrum of light wavelengths in a local environment
Photoreceptors
Plants:
-Photosynthetic pigments
-Phytochromes
-Cryptochromes
-Phototropins
Phytochrome Structure
-Similar to cyclic tetrapyrroles such as heme and chlorophyll
-Chromophore: photo reactive prosthetic group
-Phytochrome protein structure includes:
1. Photosensory region
2. Regulatory domain
3. Hinge between them
-Phytochrome spatial structure:
1. Dimer= 2 molecules (subunits) assembled together
2. PR both subunits are folded at the hinge
3. PFR the structure opens up
Phytochrome Interacting Factors (PIFs)
-Transcription factors with a central role in photomorphogenesis
-Large changes in the patterns of gene expression
PIF3:
1. promotes the transcription of skotomorphogenic genes and suppresses photomorphogenesis SUPPRESSOR
- binds at the C-terminal domain of the regulatory region of PHYB
PIFs: PIF3
PIF3:
-promotes the transcription of skotomorphogenic genes and suppresses photomorphogenesis SUPPRESSOR
- binds at the C-terminal domain of the regulatory region of PHYB
PIFs: PFR and PIFs mode of action
Events in chronological order:
1. PR (cytosol) is converted to PFR
2. PFR moves into nucleus
3. PFR interacts with PIFs
PIFs: EVENTS in the nucleus
- PFR complexes with PIF3
- Phosphorylation of PIF3
- Degradation via proteasome
- PFR removes the transcription factors that promote skoto-and rebalances transcription in favour of photomorphogenesis
Photoperiodism
Day/night duration: processes start with a definite amount of sunlight
Photoperiodism controls:
-Initiation of flowering
-Onset of tuber development
-Bulb initiation
-Entry into dormancy
Dark length:
-Short-day plants (SDPs)
-Long day plants (LDPs)
-Day neutral
Photoreceptors respond to both the amount+quality of light:
-Stability of key proteins expressed according to the circadian rhythms must NOT be degraded!
-These proteins regulate other genes
Case-study: Flower induction
-Leaf (and not the shoot apex) perceives the inductive stimulus COMPETENCE
-Photoinduction: continuous source of a mobile flowering stimulus
-Florigen: translocating factor promoting flowering
Case-study: Vernalization
-Cold requirement
-Acts as a kind of time-computing mechanism
-Vernalization is an example of an epigenetic switch
-Even after chilling (0C<temp<7C) treatment has been discontinued, vernalisation-mediated change in competence to flower is retained.
