A:T base pairs are thus favored because they are more readily distorted to allow the initial opening of the minor groove. There are also extensive interactions between the phosphate backbone and basic residues in the b sheet, adding to the overall binding energy of the interaction.

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

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