PIN7 and PIN3 are thought to redirect auxin back into vascular parenchymal tissue, where polar transport takes place.

TLS Online TPP Program

#Id: 10142

#Unit 6. System Physiology – Plant

PHYSIOLOGICAL EFFECTS OF AUXIN:

Three main guidance systems control the orientation of plant growth:

1. Phototropism, 

2. Gravitropism, 

3. Thigmotropism

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

TLS Online TPP Program

#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

TLS Online TPP Program

#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

TLS Online TPP Program

#Id: 10147

#Unit 6. System Physiology – Plant