The overall effect is a significant net dipole for the a helix that gives a partial positive charge at the amino end and a partial negative charge at the carboxy end of the a helix. 

TLS Online TPP Program

#Id: 10143

#Unit 6. System Physiology – Plant

Phototropism Is Mediated by the Lateral Redistribution of Auxin

In response to a directional light stimulus, the auxin produced at the tip, instead of being transported basipetally, is transported laterally toward the shaded side. Two flavoproteins, phototropins 1 and 2, are the photoreceptors for the blue-light signaling pathway that induces phototropic bending in Arabidopsis

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#Id: 10144

#Unit 6. System Physiology – Plant

Amyloplasts that function as gravity sensors are called statoliths, and the specialized gravity-sensing cells in which they occur are called statocytes

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#Id: 10145

#Unit 6. System Physiology – Plant

EGTA [ethylene glycol-bis(b-aminoethyl ether)- N,N,N′,N′-tetraacetic acid], a compound that can chelate (form a complex with) Ca2+, prevents Ca2+ uptake by cells and inhibits root gravitropism.

TLS Online TPP Program

#Id: 10146

#Unit 6. System Physiology – Plant

According to the starch–statolith hypothesis, columella of the root cap cells represent statocytes, or gravity-sensing cells

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#Id: 10147

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 10148

#Unit 6. System Physiology – Plant

According to the current hypothesis, the gradient in phototropin phosphorylation induces the movement of auxin to the shaded side of the coleoptile. Once the auxin reaches the shaded side of the tip, it is transported basipetally to the elongation zone, where it stimulates cell elongation. The acceleration of growth on the shaded side and the slowing of growth on the illuminated side (differential growth) give rise to the curvature toward light.