Three major distinct metabolic pathways that can supply osmotically active solutes to guard cells have been clearly characterized:

1.The uptake of K+ and Cl– from the apoplast, coupled to the biosynthesis of malate2– within the guard cells.

2. The production of sucrose in the guard cell cytoplasm from precursors originating from starch hydrolysis in the guard cell chloroplast

3. The production of sucrose from precursors made in the photosynthetic carbon fixation pathway at the guard cell chloroplast

TLS Online TPP Program

#Id: 7147

#Unit 6. System Physiology – Plant

There are three pathways for the synthesis of JAs, including the octadecane pathway starting from α-linolenic acid (18:3) and the hexadecane pathway starting from hexadecatrienoic acid (16:3). 

All three pathways require three reaction sites: the chloroplast, peroxisome, and cytoplasm. 

TLS Online TPP Program

#Id: 7148

#Unit 6. System Physiology – Plant

In plants, mechanical damage or insect feeding can cause rapid and transient accumulation of JA and JA-Ile at the site of injury, thereby activating the expression of defense genes surrounding the wound and producing a local defense response

TLS Online TPP Program

#Id: 7149

#Unit 6. System Physiology – Plant

In the local defense response, there are two ways of short-distance transmission of the JA signal. First, the systemin produced by the wounding acts as a signaling molecule, which is transmitted to the adjacent site through the apoplast and phloem to activate the JA cascade reaction pathway. Second, JA and JA-Ile induced by systemin act as signals and are transported to adjacent sites for defensive responses

TLS Online TPP Program

#Id: 7150

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 7151

#Unit 6. System Physiology – Plant

The defense response triggered by a traumatic signal can result in a local defense response near the wound and/or a systemic acquired resistance (SAR) at the uninjured site, and/or even induced defense responses from adjacent plants. 

TLS Online TPP Program

#Id: 7152

#Unit 6. System Physiology – Plant