Flowering Flashcards
Explain Floral development
Describe the meristem region
How is the transition to flowering achieved?
Flowers are the reproductive structures of angiosperms and can be defined in terms of developmental programming.
When and where flowers are made are the most important “decisions” plants make.
*Meristems are actively growing regions of the plant and give rise to new tissues and organs. In order to reproduce, angiosperms make a transition from vegetative to reproductive meristem identity
*The transition to flowering is achieved via the differential expression of homeotic genes
Give the steps of a classical forward genetics approach
*formulate biological question
*Design genetic screen
*Mutagenize - chemical (e.g. EMS), radiological (e.g. rays), biological (e.g. T-DNA insertional mutagenesis in plants)
*Screen -i.e. look for mutants of the desired class(es)
*Investigate further
*at last! Answer those biological questions!
Why is floral timing important?
It is all about reproduction and economics!
Coincide with pollinators
Coincide with flowering of sexual partners
Maximize seed number and quality
Avoid exposure of flowers to harsh environmental conditions (e.g. frost)
How is floral timing achieved?
Plants weigh up environmental, developmental and endogenous influences and “decide” when to flower.
Vernalization (L. vernalis, of the spring) is the name given to the process that occurs when the barrier to flowering is removed in plants via an exposure to an extended cold period.
e.g a cabbage that had been growing without ever having a vernalization treatment will stay in its vegetative state and keep growing nonstop.
What are the 3 classes of photoreceptors described in Arabidopsis? (circadian clock)
5 Phytochromes (A-E) (these sense red and infrared light)
3 Cryptochromes (1,2 and 3)
2 Phototropins (1 and 2)
There is evidence that implies the existence of others e.g UVRA
Describe photoreceptor-mediated responses to light in plants?
Flavonoid biosynthesis (phy -seedlings, crys and UV-B)
Regulation of flowering time (phys, cry2)
Inhibition of hypocotyl elongation and Cotyledon expansion (phy, crys and UV-B)
Stomatal opening (phots)
Chloroplast movement (phots)
Phototropism (phots)
These are all involved in the light quality
long day plants
long day plants flower as the days get longer vice versa
arabidopsis can be short day and long day
Explain CO proteins
CO protein is produced in long days
CO protein is broken down in the light and is stabilised in the dark
coincidence of light and CO mRNA leads to stabilisation of CO protein and activation of FT under long days.
Describe florigen (plant hormone)
Graft-transmissible
Produced in leaves
Known since 1930s by Mikhail Chailakhyan
Graft assembly
Cuts are made perpendicular to the hypocotyl
Scions and rootstalks are joined and supported with a silicon collar
Grown 6 days in 25oC to promote wound healing
Transfer to soil or hydroponics
Micrografting -Wild-type shoots (scions) grafted onto Arabidopsis rootstocks expressing luciferase
Fluorescent proteins
Carefully mutagenised versions of
Green Fluorescent Protein (GFP)
have been engineered which fluoresce with various wavelenghts of emmission.
Floral timing
The transition to flowering is influenced by environmental, developmental and endogenous factors
There is complex interplay between competing factors
Genetic analysis has been very important in defining mechanisms of floral induction and the crosstalk between inductive pathways
Physiological data complements genetic data
Florigen is the message which leaves send to the floral meristem to initiate flowering
Genetic studies have lagged physiological studies of the florigen, but have recently caught up
Light, the circadian clock, and circadian [Ca2+] oscillations have roles in the photoperiodic pathway
Arabidopsis gene names related to function of genes and mutations found
VRN=mutants in vernalisation(requirement of cold treatment for seeds) don’t need cld
ZEITLUPE (or ZTL for short) =Helps it keep its circadian clock.
flowering locus t= mutants in that gene don’t flower
Gigantea= These plants get really as plant stays in vegetative growth without the switch to reproductive growth
Describe and explain the pathways that relate to the decision of flowering.
Photoperiodic,Vernalization,Autonomous,Gibberellin
Gibberellin=A hormonal interaction that will stimulate the expression of FT.
autonomous= safety net for the plant, if plant gets to a certain stage as its starting to senesce, it just uses all of its resources to produce flowers.
Vernalization=A plant will produce FLC which kind of sits in the nucleus and prevents the expression of FT (flowering) the way to remove FLC is to give it a cold treatment which breaks it down over time. Allows plants to measure length of cold period.
Photoperiodic=functions through circadian clock and through two protein GI (gigantea and CO (constance) where CO expresses FT.
What is stratification?
a process where seeds need to experience a cold period of winter before germination
