Chloroplast coupling factor 1: A species-specific receptor for tentoxin

Area of Science:

• Plant biochemistry
• Molecular biology
• Phytopathology

Background:

• Tentoxin is a phytotoxin known to induce chlorosis in susceptible plants.
• The precise molecular mechanism of tentoxin's action, particularly its interaction with energy transduction pathways, requires further elucidation.

Purpose of the Study:

• To investigate the molecular basis of tentoxin's phytotoxicity.
• To determine the interaction between tentoxin and coupling factor 1 (CF(1)) ATPase in sensitive and insensitive plant species.

Main Methods:

• Assessing the effect of tentoxin on photophosphorylation and CF(1) ATPase activity in lettuce (sensitive) and radish (insensitive).
• Quantifying tentoxin binding to CF(1) using affinity constants.
• Correlating tentoxin sensitivity with chlorosis induction across multiple plant species.

Main Results:

• Tentoxin inactivated photophosphorylation and CF(1) ATPase in sensitive lettuce by binding to CF(1) with high affinity (1.3–20 x 10^7 M⁻¹).
• Insensitive radish required 20-fold more tentoxin for 50% photophosphorylation inhibition, with unaffected CF(1) ATPase and weak tentoxin binding (< 1 x 10⁴ M⁻¹).
• Tentoxin sensitivity of photophosphorylation correlated with chlorosis sensitivity in six other plant species.

Conclusions:

• Tentoxin exerts its phytotoxic effects by inhibiting CF(1) ATPase activity, a process dependent on high-affinity binding to CF(1).
• Differential binding affinity of tentoxin to CF(1) explains the varying sensitivity observed in different plant species.
• The study establishes a direct link between tentoxin's molecular interaction with CF(1) and its physiological impact, chlorosis.