Mechanisms of Egg Activation

TLS Online TPP Program

#Id: 10172

#Unit 6. System Physiology – Plant

Three main classes of mutations affecting plant height have

been selected:

1. Gibberellin-insensitive dwarfs

2. Gibberellin-deficient mutants in which the gibberellin deficiency has been overcome by a second “suppressor” mutation, so the plants look closer to normal

3. Mutants with a constitutive gibberellin response (“slender” mutants)

TLS Online TPP Program

#Id: 10173

#Unit 6. System Physiology – Plant

GAI and RGA proteins normally act as repressors of gibberellin responses. Gibberellin acts indirectly through an unidentified signaling intermediate, which is thought to bind to the regulatory domains of the GAI and RGA Proteins. 

TLS Online TPP Program

#Id: 10174

#Unit 6. System Physiology – Plant

DELLA is feedback regulator

TLS Online TPP Program

#Id: 10175

#Unit 6. System Physiology – Plant

In the absence of gibberellin, 

the DELLA proteins positively regulate GID1, GA20ox, and GA3ox, and negatively regulate GA2ox. 

TLS Online TPP Program

#Id: 10176

#Unit 6. System Physiology – Plant

Conversely bioactive gibberellin and the GID1 receptor enhance DELLA repressor degradation, while GA2ox blocks DELLA repressor degradation

TLS Online TPP Program

#Id: 10177

#Unit 6. System Physiology – Plant

DELLA degradation results in the release and activation of phytochrome interacting factor (PIF) transcription factors, such as PIF3 and PIF4, as well as other bHLH transcription factors