Lecture 6 Abscisic acid

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Lecture 6 - Abscisic acid

• Reference Taiz Zeiger (1998) Ch. 23
• Background to ABA
• ABA synthesis transport
• Physiological effects of ABA

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Background to ABA

• Historical
• Paul Wareing (1949)
• discovered dormin
• in buds ash, potato

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Background to ABA

• Historical cont.
• Addicott (1960s)
• discovery of abscisin in leaves, fruits.
• dormin abscisin chemically identical
• called abscisic acid.

Taiz Zeiger (1998) Fig 23.2
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Background to ABA

• General
• found in all vascular plants
• some mosses fungi
• not liverworts.

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Background to ABA

• General cont.
• ABA not actually involved with abscission.
• stims. ethylene prodn
• negative growth regulator.

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ABA synthesis transport

• Synthesis
• synth. plastids leaves, roots, fruits, seeds
• from carotenoid pigments.
• molybdenum required for biosynth.

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ABA synthesis transport

• Transport
• transported both xylem phloem
• also parenchyma cells (outside vasc. bundle).
• bidirectional.

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Physiological effects of ABA

• Seed development
• cell division phase
• dehydration phase
• ABA levels fluctuate during seed development.

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Physiological effects of ABA

• Embryo dessication tolerance
• promotes protein synth.
• stabilize membranes, proteins.

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Physiological effects of ABA

• Accumulation of storage proteins
• late embryogen.
• translocation?
• synth. storage proteins.

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11
Physiological effects of ABA

• Seed dormancy
• temporal delay germination
• dispersal
• seed survival.

Raven et al. (1999) Fig 23.18
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Physiological effects of ABA

• Coat imposed dormancy
• prevention water uptake
• mechanical constraint
• gas exchange
• inhibitors.

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13
Physiological effects of ABA

• Embryo dormancy
• cotyledon influence
• involves ABAGA ratio

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Physiological effects of ABA

• ABA seed dormancy
• ABA mutant non dormant
• breaking dormancy many seeds correlated with
  ?ABA, ?GA levels
• vivapary.

Raven et al. (1999) Fig 23.18
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Physiological effects of ABA

• ABA bud dormancy
• Wareing dormin inc. concn. leaves, buds end
  summer.
• applicn. ABA to non dormant buds caused dormancy.
• suggested ABA moved in from leaves after
  detection short day length.

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Physiological effects of ABA

• ABA bud dormancy cont.
• not inv. formn bud scales.
• no transport from leaves.
• short day treatments no rise in bud ABA.

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Physiological effects of ABA

• ABA GA seed enzymes
• affects synth. seed enzymes
• inhibits transcription.
• no endosperm breakdown.

Taiz Zeiger (1998) Fig 20.17
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Physiological effects of ABA

• ABA stomata
• stim. closing stomata most plant sp.
• 50X inc. ABA drought conditions
• applicn of ABA to leaves causes closing.

Taiz Zeiger (1998) Fig 23.3
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Physiological effects of ABA

• ABA stomata cont.
• 20X inc concn single guard cell.
• water-stressed roots form more ABA
• xylem transport to leaves.
• restoration turgor.

Taiz Zeiger (1998) Fig 23.4
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Physiological effects of ABA

• ABA stomata cont.
• mechanism
• increase in cytosolic Ca2
• increase in pH
• both lead to drop in cytosolic K.

Taiz Zeiger (1998) Fig 23.10
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Physiological effects of ABA

• ABA stomata cont.
• inhibition K and water leaks out, stomata
  close.
• signal loss of turgor signals enhanced ABA
  synthesis
• ABA deficient mutants cannot survive in dry
  environments.

Raven et al. (1999) Fig 28.24
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Physiological effects of ABA

• ABA roots/shoots
• low water potential root ABA may inhibit shoot
  growth and enhance root growth.
• may inc. movement of water through roots.

Taiz Zeiger (1998) Fig 23.5
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Physiological effects of ABA

• ABA leaf senescence
• leaf spotted with ABA, spot turns yellow,
  opposite from cytokinin.
• effects independ. ethylene.

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Physiological effects of ABA

• Stress hormone
• Universal stress hormone?
• evidence that ABA levels inc. by saline soils,
  cold, frost (possibly high temps.).
• most of these related to water stress.

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Physiological effects of ABA

• Stress hormone
• not nec. related to loss turgor
• reductn growth, metab., conservn of resources.
• preventn wall acidification?
• applied ABA can reduce plants reaction to stress,
  eg. freezing

Salisbury Ross (1992) Fig 18.18
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Physiological effects of ABA

• Stress hormone
• salt stress causes formation of osmotin in
  tobacco
• osmotin formed by plants with ABA and in the
  absence of salt.

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Physiological effects of ABA

• Mode of action
• various effects, depends on sp. plant part
• may specifically activate and deactivate certain
  genes
• calcium.

Taiz Zeiger (1998) Fig 23.8