Plant Reproductive Physiology

1

• Plant Reproductive Physiology

2
Flowering

• Photoperiodism
• Temperature
• Nutrition

3
Fruiting

• Pollination
• Development after fertilization
• Maturity, ripening and senescens

4
Plant Growth Stages

• Juvenile stage
• Transitional stage
• Maturity stage
• Senescence stage

5
Juvenile stage

• Vegetative growth and unable to flower even if
  plant grows an environment for flowering
• a physiological state of plant before flower
  differentiation
• Flowering cannot be induced
• plants often differ in appearance from the adult.
• Phase length varies
• annual shorter eg. Weed will be at juvenile
  stage 4-5 d after germinated
• perennial longer at juvenile
  stage
• eg. in certain shrubs up to 40years
• Morphologies
• Simple primary leaf to trifoliate leaves
• beans adult compound leaf juvenile simple
  leaf
• leaves lobe
• rapid growth
• Usually, the basal part of tree is juvenility and
  the top is mature or adult in physiology.

6
Methods to shorten juvenility

1. Long-day treatment - shorten the juvenility form
   510 year to 1 year of birch
2. Grafting- speed up flowering of fruit crops in
   2-3 year.
3. GAs treatments- can induce flowering in
   juvenility of ivy, cypress and fir.

7
Transitional stage

• Have both juvenile and mature tissue
• May revert back to juvenile if environmental
  conditions are right.
• Involves the transition of a vegetative meristem,
  producing leaves and stems, into a floral
  meristem, producing flowers.

8

• Flower Initiation and Development
• a. Irreversible change in which to bud
  (meristem) changes from growing vegetative tissue
  to reproductive tissue
• b. Improper conditions can cause flower buds to
  abort
• 1. High temp
• 2. Moisture stress
• c. Flowers can be induced naturally or through
  PGR (plant growth regulators)

9
Maturity or reproductive stage

• Stage where plants are ready to flower.
• Flowering - ultimate expression of mature state
• Changes influence by environment
• Environment serve as expression changes regulator
• Changes in physiology and morphology
• Transformation of primodium of stem, leaf or
  vegetative part to primodium reproductive organ
• One way transformation
• Many plants produce flowers independent of
  environmental conditions

10

• Factors influence transformation of the juvenile
  into the mature
• Temperature Vernalization
• Photoperiodism
• Light intensity
• Drought stress
• Low fertility levels (especially N)

11
Senescens

• The final stage in a plants life cycle
• a. May occur naturally or accelerated by
  environmental conditions including pathogenic
  attack
• b. Cell and tissues deteriorate
• c. Partial senescence is when plant organs age
  and eventually die
• d. Complete senescence is when the whole plant
  dies.
• Monocarpic plant flowering and fruiting once
• Polycarpic plant many times/repeat

12
Flowering
13
Flower Production

• Four genetically regulated pathways to flowering
  have been identified
• 1. The light-dependent pathway
• 2. The temperature-dependent pathway
• 3. The gibberellin-dependent pathway
• 4. The autonomous pathway
• Plants can rely primarily on one pathway, but all
  four pathways can be present

14
(No Transcript)
15
Autonomous Pathway

• The autonomous pathway does not depend on
  external cues except for basic nutrition
• It allows day-neutral plants to count nodes and
  remember node location

16
-Tobacco plants produce a uniform number of nodes
before flowering- Upper axillary buds of
flowering tobacco remember their position if
rooted or grafted
Autonomous Pathway--Plants Can Count
17
Autonomous Pathway--Plants Can Remember
Not-Florally Determined Plants are said not to
remember...Florally Determined plants are said to
remember
18
Photoperiodism the response of plant to flower
to photoperiod (day length of 24h cycle)

1. Julien Tournois (1910) 1st found about LD in
   flowering
2. George Klebs (1918) observe the function of LD
   in flowering
3. Garner Allard (1920) found photoperiod
   ?relative duration of light and dark towards
   control flowering of certain crops. eg. tobacco
   flowering once expose to short light period
   (SDP)

19

• Hamner Bonner (1938) phenomena night break
  where dark disturbance during day time are not/a
  bit effect but light disturbance during night
  time inhibit flowering (SDP) or initiate
  flowering (LDP)
• Dark time more function in determine reaction in
  photoperiod

20
Flowering response of Japanese morning glory
(left) and black henbane (right) to daylength of
24-h period. Note the prominent flowers (arrows)
in Japanese morning glory under short days and in
black henbane under long days . Plants of
each species under both photoperiod regimes are
of the same age
Long days Short days
21
Plant types responsive to photoperiodism

• 1. Short day plant (SDP)
• The plant can only flower under day length
  shorter than its critical day length of 24 h
  cycle. eg. chrysanthemums
• ie. the critical day length to induce flowering
  must be less than some maximum.
• 2. Long day plant (LDP)
• The plant can only flower under daylength longer
  than its critical day length of 24 h cycle. eg.
  Chinese cabbage, beet etc.
• ie the critical day length must be longer than a
  minimum

22

• 3. Day neutral plant (DNP)
• Without critical daylength, they can flower in
  any day length of 24h cycle, if other conditions
  are satisfied. eg. tomato, cucumber, egg plant
  and bean. After bred for long time , most of
  crops are not sensitive to day length, eg. early
  rice, spring soybean, spring maize and cotton
• Critical Day Period
• It is the duration of the photoperiod or the dark
  period that ultimately determines whether the
  plant has to go through vegetative growth or to
  produce flowers. 
• referred as the day length of 24h cycle - the
  shortest day length for LDP flower and the
  longest day length for SDP flower.

23
(No Transcript)
24
(No Transcript)
25
Photochrome

• The chemical nature of the receptor is a the
  molecule PHYTOCHROME.
• - biological compound that absorbs light
• Two types -Phytochrome far red (PFR)
• -Phytochrome red (PR)
• - interconvertible

26
(No Transcript)
27
(No Transcript)
28

• Plants measure the ratio of Pfr/Pr.
• LDP would flower when the ratio is high
• SDP would flower when the ratio is low
• Since Pfr is labile and is broken down at night
  or reverts back to Pr - the longer the night, the
  lower the phytochrome (Pfr) content.
• Thus, phytochrome is like the sand in an egg
  timer the relative amount of Pfr remaining at
  the end of the night would be an indication of
  the day length.

29

• Flowering in SDP
• Short day plants flower when the night period is
  long.
• In day light or red light, phytochrome red (Pr)
  is converted to phytochrome far red (Pfr). The
  conversion actually only requires a brief
  exposure to white or red light.
• In the dark, Pfr is slowly converted back to Pr.
  A long night means that there is a long time for
  the conversion.
• Under short day conditions (long night) at the
  end of the night period the concentration of Pfr
  is low.
• In SDP, low Pfr concentration is the trigger for
  flowering.
• Flowering in LDP
• Long day plants flower when the night period is
  short.
• In day light (white or red) the Pr is converted
  to Pfr.
• During periods when the day light period is long
  but critically the dark period is short, Pfr does
  not have long to breakdown in the dark.
  Consequently there remains a higher concentration
  of Pfr.
• In LDP, high Pfr concentration is the trigger to
  flowering.

30
(No Transcript)
31
(No Transcript)
32

• Dark period more important in photoperiodism
  reaction because interruption during night will
  inhibit flowering in SDP but promote flowering in
  LDP
• In short day plants, Pr promotes flowering when
  Pfr suppresses it, when it is vice versa in long
  day plants.

33

• Flowering hormone?
• Leaves detected photoperiod (at least
• one leaf must be present for the plant
• to fllower)
• The receptor of photoperiod is located within
  the leaf.
• Photoperiodism sensor - leaf ? bud
• Buds produce flowers
• Bud meristem changes from vegetative to flower
  growth

34

• Stimulus transferred
• Cut off all leaves after expose to photoperiod
  ?inhibit flowering
• Cut off all leaves 20 -36hrs later ?promote
  flowering
• In 2005 a substance, mRNA (FL mRNA) was finally
  isolated that was found to be moving from leaf to
  flower meristem.
• This mRNA provides a link between the phytochrome
  system (the receptor), its activation of genes in
  the leaf (mRNA synthesis) and the differentiation
  of the meristem into the flower structure.
• Florigen - name given to the proposed flowering
  "hormone.

35
(No Transcript)
36
Commercially importance

• Flower industry eg. Chrysanthemum sdp
• Selection of variety/cultivar for vegetable and
  field crops
• Manipulating Flowering Response
• Use artificial light or dark to simulate
  daylength.
• Light at night to lengthen day.
• 10 pm to 2 pm.
• Cover with black cloth to shorten the day.

37
Temperature (T)

• Vernalization ? the process by which flowering is
  promoted by prolonged exposure to the cold of a
  typical winter
• plant expose to low T to initiate and promote
  flowering
• common in biennials and some perennial plants
• reactions are varies among spesies/variety

38
(No Transcript)
39

• eg. apple, cherry, pear, peaches
• carrots, cabbage,
• bulbs like tulip, onion
• a. cold storage is used to preserve (sets) bulbs
  during winter this causes the sets to flower and
  produce seed in spring
• b. to devernalize- sets are exposed to 27oC for
  2-3 weeks before planting

40

• Temperature and time of vernalization
• -4?12?. Most efficient 12 ?
• Reaction between temperature and time
• - in the range of vernalization temperature, the
  lower T, the shorter time.
• - the lower temperature for vernalization the
  plant needs, the longer time lasts.
• Table 8-1 Temperature and time for vernalization
  of wheat
• Types temperature range(?
  ) days
• Spring wheat 515
  58
• Semi winter wheat 3 6
  1015
• Winter wheat 0 3
  40 45

41

• Kinetics of the vernalisation
• effective on actively growing plant.
• ie. growing plant under gone vegetative
  stage, seed stage (annual) or bulb
• - Seeds must imbibed water (50 of seed dry
  weight) and the germination process has been
  initiated and exposed to low temperature (
  vernalized). The vernalized seeds are dried and
  stored.
• - other plants in particular the biennial eg.
  cabbage, must reach a certain minimum size or age
  before they can be vernalized ie. whole plant
• In general, the plant flowering need long day
  period and higher temperature after finishing
  vernalization, which induces flower
  differentiation

42

• The site/part of vernalization is the growing
  point (shoot apex)
• eg. celery
• - shoot apex exposed to low temperature, other
  part of plant to normal (higher) temperature,
  the plant can flower.
• -shoot apex to normal (higher)
  temperature, other part of plant low temperature,
  the plant remain vegetative
• The main part sensitive to low temperature is
  shoot apical meristem - bud, apex meristems

43

• Facultative (quantitative)
• Flowering will appear earlier (faster) once
  expose to low T eg. winter annual cereal
• Absolute (obligate)
• MUST expose to low T then flowering appear eg.
  biennial plants (cabbage)
• Exposure to desired period

44

• Lang (1957) found that GA function vernalin,
  where GA promote flowering without vernalisation
• Vernalin hypothesis After passing
  vernalization, plant can form vernalin,which can
  transfer from one part to others and promote
  flower.
• Vernalization only act the meristem of shoot
  apex. The effect can transfer form the cell to
  cell, not from organ to organ.

45
Low T vernalization and GA3 induce flowering in
carrot
Control GA3 Low T
46

• In relation to flowering and fruiting or duration
  of plant life, plants are group into
• Perennial plants
• Able to flower and produce seeds and fruit for an
  indefinite number of growing seasons
• - may be herbaceous or woody
• -in deciduous plants all the leaves fall, and
  the tree is bare, at a particular time of year
• -in evergreen plants, the leaves drop throughout
  the year, and so the plant is never completely
  bare
• Annual plants
• Grow, flower, and form fruits and seeds, and
  typically die within one growing season
• - usually herbaceous
• Biennial plants
• Have two-year life cycles
• -they store energy the first year and flower the
  second year
•  

47
Application of vernalization on production

• 1. Treatment with vernalization and
  devernalization
• eg. onion for seed production
• 2. Induced crops to flower
• forcing plants for earlier or late bloom
• blooms indoor
• 3. Selecting sowing date
• different types and characters

48
Interaction bet. T and photoperiodism

• SDP initiate flowering at low T. eg.
  Chrysanthemum
• As supplementary or complimentary to each other

49
Devernalisation

• Vernalisation cancellation
• Before finishing vernalization, the effect will
  lost under high temperature
• Devernalization - 2540??
• eg. vernalized onion bulbs expose to high
  temperature after vernalisation
• Direct planting ? flowering
• Keep in warm temperature (2-3wks) ? not flowering

50
Nutrition

• Klebs (1918) ratio of carbohydrate with
  inorganic nutrient esp N (CN) high will
  promote flowering
• Kraus Kraybill (US) flowering on tomato
  plants was controlled by CHON level
• CHON low delay flowering less flower (N
  high)
• CHO low, N low less vegetative part, less
  flower
• CHON high faster and no of flower increase
• ? there is no CN critical for flowering