Gap junctions permit the passage of molecules as large as 1.2 nm in diameter (molecules smaller than 1200 Da).

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#Unit 6. System Physiology – Plant

AUXIN SIGNAL TRANSDUCTION PATHWAYS

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#Id: 7527

#Unit 6. System Physiology – Plant

The auxin receptor is composed of two proteins: the SCF complex component TIR1 and the repressor protein AUX/IAA. Ubiquitin moieties are first activated by E1 ligase and added to target proteins by E2 ligase. 

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#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.

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#Unit 6. System Physiology – Plant

PHYSIOLOGICAL EFFECTS OF AUXIN:

Three main guidance systems control the orientation of plant growth:

Phototropism, 

Gravitropism, 

Thigmotropism

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#Id: 7530

#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: 7531

#Unit 6. System Physiology – Plant