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Abscission

Abscission. Remarkable ability to discard parts/ organs that may be re-made later Leaves Fruits Anthers Floral whorls after fertilization Bark Eucalyptus Birch. Abscission program. Highly programmed series of events: Mobilization Formation of cork Detachment. 1. Mobilization.

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Abscission

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  1. Abscission Remarkable ability to discard parts/ organs that may be re-made later • Leaves • Fruits • Anthers • Floral whorls after fertilization • Bark • Eucalyptus • Birch

  2. Abscission program Highly programmed series of events: • Mobilization • Formation of cork • Detachment

  3. 1. Mobilization Transport the most valuable materials, esp. N, back to the main body: • Proteins • Chlorophyll • Starch • DNA signal aa Proteins, DNA, starch, etc + + enzymes aa, glucose

  4. 2. Cork formation • Under abscission zone: • Layers of parenchyma on both sides of abscission zone make and inject suberin and lignin into walls (protective cork).

  5. 3. Detachment • At abscission zone: • Layers of parenchyma cells secrete cell wall enzymes (glucanases and pectinases); self digest • Take up water, swell and weaken, part falls off

  6. C2H4 is the primary internal signal C2H4 causes cells to read genes for: • Amylases, glucanases, pectinases that weaken walls • Glucose and oligos increase – change in osmotic potential causes water to enter • PAL synthesis • Directly stimulated by C2H4 or by oligos • Makes? • Defensive compounds (phytoalexins) • Lignin (hardening & defensive agent) & suberin (waterproofing) of cork cells • Anthocyanin purplered color in leaves and ripe fruit

  7. Met + IAA C2H4 - + Abscission Hormonal controls on abscission • IAA can stimulate C2H4 production • IAA reduces organ’s sensitivity to abscission signal (C2H4) • Cocks abscission ‘gun’ but puts on the safety • If [IAA] declines, abscission zone sensitive to C2H4; abscission ABA increases [C2H4]; thus?? CK + affects [IAA]; thus??

  8. Environ. signals + - Alter [IAA, ABA, CK] + - C2H4 + Abscission Environmental signals for abscission • Injury • Water stress • Aging • Shading • Competition • Flooding • Fertilizer Three tier signal system:

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