Plant Growth Regulators Growth retardants(ABSCISIC ACID)

1
Plant Growth RegulatorsGrowth retardants(ABSCISIC
ACID)

• Prof. Dr./ Galal Ismail Eliwa
• Head Of Pomology Department

Faculty Of Agriculture Damietta University
E. mail/ geliwa2002_at_du.edu.eg
2
Discovery of Abscisic acid (ABC)

• Abscisic acid (ABA) was the last major hormone to
  be identified, although its existence had been
  forecast for some time.
• Groups lead by Addicott studying hormonal
  relationships in cotton (Ohkuma et al., 1963)
• And Wareing studying dormancy in woody perennials
  independently identified Abscisin II in cotton
  and Dormin in woody plants (Corniforth et al.,
  1965).
• The two compounds were ultimately determined to
  be identical and were given the name Abscisic
  acid in 1967 at a plant hormone conference in
  Ottawa, Canada.

3
ABSCISIC ACID (ABC)

• ABA is one of the hormone plant. Also called as
  Abscisin Dormin because of their regulatory
  effect on abscission and dormancy.
• Growth retardant (inhibits).
• Inhibition of bud growth and shoot formation.
• Promotes dormancy.
• Closes stomata.
• Produced in response to environmental stress,
  such as heat stress, water stress, salt stress.

(C15H20O4)
4
ABSCISIC ACID

• Unlike animals, plants cannot flee from
  potentially harmful conditions like
• drought
• The approach of winter
• They must adapt or die.
• The plant hormone Abscisic Acid (ABA) is the
  major player in mediating the adaptation of the
  plant to stress.

5
ABSCISIC ACID Function

• In preparation for winter, ABA is produced in
  terminal buds. This slows plant growth and
  directs leaf primordia to develop scales to
  protect the dormant buds during the cold season.
• ABA also inhibits the division of cells in the
  vascular cambium, adjusting to cold conditions in
  the winter by suspending primary and secondary
  growth.

6
ABSCISIC ACID Function

• Abscisic acid is also produced in the roots in
  response to decreased soil water potential and
  other situations in which the plant may be under
  stress.
• ABA then translocate to the leaves, where it
  rapidly alters the osmotic potential of stomatal
  guard cells, causing them to shrink and stomata
  to close.
• The ABA- induced stomatal closure reduces
  transpiration thus preventing further water loss
  from the leaves in times of low water
  availability.

7
ABSCISSIC ACID

• Sites
• Plastids by Mevalonic acid pathway
• (The Shikimic Acid Pathway)
• Most tissues, especially leaves and seeds
• Transport
• Xylem and phloem (greater amounts).

8
????? ???? ????????Biosynthesis of ABA

• ??? ????? ABA ?? Mevalonate ?? ????
  pyrophosphate Farnesyl ??? ?????? ??????? ??
  ???? ????? ??????????????? isoprenoids ??? ???
  ?????????? ??? ?? ????? ????? ??????????? ?? ??
  ????????? ??????????? ???????????? ??? ?? GA ?
  ABA ?????? ??????? .

9

• ABA appears to be an internal factor inducing
  dormancy in the buds of at least some temperature
  zone woody plants.
• ?????? ????? GA ABA ??? ??? ???? ??????? ????
  ????? ??? ??????? ??? ??? ????? GA ?? ??? ?????
  ??????? ????? ?? ??? ????? ??????? ????? ABA
  ?????? ?????? ?? ??????? ??? ???? ?? ??? ?????? (
  ??? ??????) ?? ??????? ??????? ???????.
• ???? ???? ????????? ??? ????? ????? ???????
  ????????? ??????? (?????? ????????) ?? ??? ??????
  ??????? ?? ??? ?????? ????? ?????? ????? ?? ????
  ????? ??????.(????? ABA- Bud dormancy)

10
Abscisic acid actions

• 1- ABA- drought resistance
• Abscisic acid is the key internal signal that
  facilitates drought resistance in plants.
• Under water stress conditions, ABA accumulates in
  leaves and causes stomata to close rapidly,
  reducing transpiration and preventing further
  water loss.
• ABA causes the opening of efflux K channels in
  guard cell plasma membranes, leading to a huge
  loss of this ion from the cytoplasm.
• The simultaneous osmotic loss of water leads to a
  decrease in guard cell turgor, with consequent
  closure of stomata.

11
ABA in roots that elongate the root for water
absorption
12
Abscisic acid actions

• 2- ABA- Seed Dormancy
• ABA plays a major role in seed dormancy
• During seed maturation, ABA levels increase
  dramatically.
• This inhibits germination and turns on the
  production of proteins that enable the embryo to
  survive dehydration during seed maturation

13
Abscisic acid actions

• 2- ABA- Seed Dormancy
• As dormancy can only be broken by specific
  environmental cues, it ensures that a seed will
  germinate only under suitable conditions of
  moisture, light and temperature
• The breaking of dormancy is associated with a
  decline in the level of ABA.

14
ABA prevents or delays the germination of seeds.

• (vivipary) ????? ????? ?????? ???? ?????? -
• - ???? ??????? ??? ???????? ?? ?????? ????- ????
  ??????? ???? ???? ??? ?? ???? ????? ??? ???????
  1- ??? ?????? ????? ????? ????? ??????? ((over
  mature) ???? ??????? ??????? ?????? ??????
  ?????????? ?????? ???????2- ?????? ???????
  ??????? ??? ????????? ((abscisic acid ?? ??????
  ??????? ? ??????? ?????? ?????? ??? ?????? ????
  ?????? ?????? ?????? ?????? ?????? ?? ??? ?????
  ??????3- ???? ??? ?? ?????? ????????? ????????
  ?? ??? ?????? ????? ???? ?????? ?????? ??????
  ???? ?????? (?????? ?????????? ??? ??????? ???
  ????????? (Coumarin ) ? ?? ??????? ?? ???
  ?????? ????????? ???? ??????? ??? ????? ?????? ??
  ?????? ??????

15
(No Transcript)
16
(No Transcript)
17
Abscisic acid actions

• 3- ABA- Bud dormancy
• ABA mediates the conversion of the apical
  meristem into a dormant bud. The newly developing
  leaves growing above the meristem become
  converted into stiff bud scales that wrap the
  meristem closely and will protect it from
  mechanical damage and drying out during the
  winter.
• ABA in the bud also acts to enforce dormancy so
  if an unseasonably warm spell occurs before
  winter is over, the buds will not sprout
  prematurely, only after a prolonged period of
  cold or the lengthening days of spring
  (photoperiodism) will bud dormancy be lifted.

18
Abscisic acid actions

• 4- ABA- Abscission
• ABA also promotes abscission of leaves and
  fruits (in contrast to auxin, which inhibits
  abscission).
• It is, in fact, this action that gave rise to the
  name abscisic acid.
• It promotes senescence through leaf abscission,
  degeneration of excised leaves and acceleration
  of decomposition of chlorophyll.

19
Abscisic acid actions

• 5- ABA- chemical thinner
• ABA has appeared on the horizon as a new and
  potentially useful chemical thinner.
• It has been shown to be an effective thinner on
  both apples and pears (Greene, 2007, 2009).
• The mode of action has not been defined but
  undoubtedly, closing of stomata, thus restricting
  carbohydrate supply will prove to be a
  contributing factor.

20
Abscisic acid actions

• 6- ABA- Freezing resistance
• Elevated ABA levels are associated with increased
  freezing resistance.
• ABA appears to mediate a plants response to
  environmental stresses, such as freezing by
  regulating gene expression.
• Certain genes are switched on by ABA while others
  are switched off.

21
Physiological effects of Abscisic acid
1. Stomata Closure Water shortage brings about increase in ABA level, leading to stomata closure as a response to water stress.
2. Growth Inhibiters ABA inhibits shoot growth but has less effect on root growth
3. GA Counteracts ABA counteracts the effect of gibberellins on alpha amylase synthesis in germinating seeds.
4. Induced Dormancy ABA affects induction or maintenance of dormancy in seeds.
22
Thank you for your attention