THE CONTROL OF FLOWERING
PLANTS FLOWER AT DIFFERENT TIMES OF THE YEAR.
HOW DO PLANTS KEEP TRACK OF THE SEASONS?
WHICH ENVIRONMENTAL SIGNALS CONTROL
FLOWERING?
HOW DO ENVIRONMENTAL SIGNALS BRING ABOUT THE
TRANSITION TO FLOWERING?
FLOWERING IN ARABIDOPSIS
(B)
VEGETATIVE VS. FLOWERING SHOOT APEX IN
ARABIDOPSIS
VEGETATIVE
APEX
FLOWERING
APEX
FLORAL EVOCATION
THE EVENTS OCCURRING IN THE SHOOT APEX
THAT SPECIFICALLY COMMIT THE APICAL
MERISTEM TO PRODUCE FLOWERS
FLORAL ORGANS ARE INITITATED IN SUCCESSIVE
WHORLS
MUTATIONS IN FLORAL ORGAN IDENTITY GENES
THE ABC MODEL FOR FLORAL ORGAN IDENTITY
QUADRUPLE MUTANT (ap1, ap2, ap3/pi, ag) RESULTS IN
THE PRODUCTION OF LEAF-LIKE STRUCTURES IN
PLACE OF FLORAL ORGANS
THE SHOOT APEX AND PHASE CHANGES
THE SHOOT APICAL MERISTEM PASES THROUGH THREE
DEVELOPMENTAL PHASES:
1. THE JUVENILE PHASE
2. THEADULT VEGETATIVE PHASE
3. THEADULT REPRODUCTIVE PHASE
JUVENILE AND ADULT FORMS OF ENGLISH IVY (Hedera
helix)
JUVENILE
ADULT
(GIBBERELLIN
CAUSES
REVERSION OF
ADULT FORM TO
JUVENILE FORM
IN ENGLISH IVY)
FLORAL EVOCATION: COMPETENCE AND
DETERMINATION
PHOTOPERIODISM: MONITORING DAY
LENGTH
PLANTS CAN USE CIRCADIAN
RHYTHMS TO MEASURE
DAYLENGTH
PLANTS CAN USE CIRCADIAN RHYTHMS TO MEASURE
TIME
Entrained rhythm
Free running rhythm
DAY LENGTH VARIES WITH LATTITUDE
DAY LENGTH VARIES WITH THE MONTH OF THE YEAR
AND THE LATTITUDE, EXCEPT AT THE EQUATOR
Day length = night length all
year at the equator
THE DISCOVERY OF PHOTOPERIODISM
1. GARNER AND ALLARD (1920s) AT USDA LAB AT
BELTSVILLE, MD STUDIED FLOWERING IN
MARYLAND MAMMOTH TOBACCO PLANT.
2. MARYLAND MAMMOTH WAS A SINGLE GENE
MUTANT TOBACCO THAT DIDN’T FLOWER IN
THE SPRING OR SUMMER, LIKE WILD TYPE.
3. IT ONLY FLOWERED WHEN BROUGHT INTO
THE GREEN HOUSE IN THE WINTER.
PLANTS CAN BE CLASSIFIED ACCORDING TO THEIR
PHOTOPERIODIC RESPONSES
1. Short Day Plants (SDPs) flower when day length
is shorter than a critical day length.
2. Long day plants (LDPs) flower when the day
length is longer than a critical daylength.
3. Long-short-day plants (LSDPs) flower after a
sequence of long days followed by short days.
4. Short-long-day plants (SLDPs) flower after a
sequence of short days followed by long days.
5. Day-neutral plants (DNPs) are insensitive to
daylength, Flowering is under internal
developmental control.
THE SITE OF PERCEPTION OF THE
PHOTOPERIODIC STIMULUS IS THE
LEAF
EFFECT OF DAY LENGTH ON FLOWERING IN SDPs AND
LDPs
Critical day langth
Critical day langth
NIGHT BREAK EXPERIMENTS DEMONSTRATE ROLE OF
NIGHT PERIOD IN SDPs
NIGHT BREAK EXPERIMENTS ALSO DEMONSTRATE
ROLE OF NIGHT PERIOD IN LDPs
THE LENGTH OF THE DARK PERIOD REGULATES THE
PHOTOPERIODIC RESPONSES IN BOTH SDPs AND LDPs
NIGHT BREAKS GIVEN AT DIFFERENT TIMES DURING
THE NIGHT PERIOD REVEAL CIRCADIAN RHYTHMICITY
ACCORDING TO THE COINCIDENCE MODEL, THE
EFFECT OF THE NIGHT BREAK DEPENDS ON THE
RHYTHM OF LIGHT SENSITIVITY
(SDP Soybean)
PHYTOCHROME IS THE PIGMENT INVOLVED IN
MEASURING THE NIGHT LENGTH
AS IN THE CASE OF SDPs, ACCORDING TO THE
COINCIDENCE MODEL, THE EFFECT OF THE NIGHT
BREAK DEPENDS ON THE RHYTHM OF LIGHT
SENSITIVITY
LDP Arabidopsis
VERNALIZATION: PROMOTING FLOWERING WITH COLD
TREATMENT (40 DAYS AT 4C)
Winter-annual Arabidopsis
without vernalization
Winter-annual Arabidopsis
with vernalization
VERNALIZATION: SITE OF PERCEPTION
THE SITE OF PERCEPTION OF
VERNALIZATION IS THE SHOOT TIP
DEVERNALIZATION
THE EFFECT OF COLD TEMPERATURE IN
PROMOTING FLOWERING CAN BE REVERSED
BY WARM TEMPERATURE (DEVERNALIZATION)
VERNALIZATION BLOCKS THE EXPRESSION OF THE
GENE FLOWERING LOCUS C (FLC)
Winter annual
without cold
Winter annual
after 40 cold
days
FLC mRNA
Winter annual
without cold,
but with FLC
mutation
GRAFTING STUDIES
GRAFTING STUDIES HAVE
DEMONSTRATED THE ROLE OF A
TRANSMISSIBLE STIMULUS PRODUCED BY
LEAVES WHEN PHOTOPERIODICALLY
INDUCED.
DEMONSTRATION OF LEAF-GENERATED FLORAL
STIMULUS (FLORIGEN) IN THE SDP PERILLA
Induced
graft donor
leaf
Uninduced graft
donor leaf
SUCCESSFUL TRANSMISSION OF FLORAL STIMULUS
BY INTERGENERIC GRAFTING
Stock: Nonvernalized,
cold-requiring LDP
Hyascyamus niger
(henbane)
Scion: LDP Petunia
hybrida, induced with
long days.
THE PHENOMENON OF INDIRECT INDUCTION
MULTIPLE INDUCTION BY A SINGLE INDUCED LEAF