Phytochrome is most heavily concentrated in the regions where dramatic developmental changes are occurring: the apical meristems of the epicotyl and root.

TLS Online TPP Program

#Id: 10139

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 10140

#Unit 6. System Physiology – Plant

The auxin receptor is composed of two proteins: the SCF complex component TIR1 and the repressor protein AUX/IAA.

TLS Online TPP Program

#Id: 10141

#Unit 6. System Physiology – Plant

TIR1 recruits AUX/ IAA proteins to the SCF -TIR1 complex in an auxin-dependent manner. Once recruited by auxin, AUX/IAA proteins are ubiquitinated by the E3 ligase activity of the SCF-TIR1 complex, which marks the protein for destruction by the 26S proteasome.

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