physiological effects of auxin ¤ cell elongation ¤ phototropism: lateral distribution of auxin ¤...
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Physiological effects of auxin
¤ cell elongation
¤ phototropism:
lateral distribution of auxin
¤ gravitropism:
¤ thigmotropism:
less is known, probably involves auxin gradient
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Evidence that the lateral redistribution of auxin
The shaded side is more acidic
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How do plant cells detect gravity
A gravity sensor: the large, dense amyloplasts Statoliths;
Statocytes – the specialized gravity-sensing cells in the central
cylinder of root cap, columella
In shoots: starch sheath
a layer of cells that surrounds the vascular tissues of the shoot
Fig. 19.13a
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Starch-statolith hypothesis:
columella
Nodal ER
(5~7 rough ER sheets)
Starch-deficient mutants: no gravitropic response
Starch-less mutants: some gravitropism
Exist some starch-independent gravity
perception mechanism
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Tensegrity model for gravitropism (02)
Tensional integrity: structural integrity created by interactive tension between
the structural components.
Web Topic 19.10 The giant-celled fresh water alga Chara the entire protoplast acts like a statolith, and that gravity is perceived at
the interface between plasma membrane and cell wall
Plasmalemma Central Control (PCC) model, stretch-activated calcium
channels are clustered around attachment centers connecting the
cytoskeleton and the cell wall.
Gravity sensing: calcium and pH dependent
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Gravity sensing may involve pH changes
A cytosolic pH-sensitive fluorescent dye
The cytoplasmic pH , apoplastic pH 10 min delay tropic curvature
(7.27.6) (5.54.5)
columella
activate H+-ATPase
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Gravity sensing – calcium and pH dependent
¤ + EGTA: agravitropism
+ Ca2+ agar: bend to the agar side
intracellular [Ca2+]
¤ thigmotropism
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Auxin is redistribution laterally in the root cap
Bending occur
Protection, perception
Cap produces root growth inhibitor affect gravitropism