Question

Some herbicides inhibit the electron transport chain in the thylakoid membrane. Without the movement of electrons, hydrogen ions would not be pumped from the stroma to the thylakoid space and the hydrogen ion gradient would not be established. How would this affect the Calvin cycle reactions?

Answer 1

Calvin cycle consist in three steps: 1) CO2 fixation 2) CO2 reduction 3) Regeneration of RuBP.

After fixation of CO2 we have 3-phosphoglycerate and start the CO2 reduction step, where it receives a phosphate group from ATP getting ADP through Phosphoglicerate kinase obtaining 1,3 phophoglycerate. Then, it receives protons from NADPH + H getting NADP+ and Glyceraldehyde 3-phosphate through Glyceraldehyde 3-phosphate enzyme. Electron transport chain which produce NADPH is pumped thanks to thylakoids. So, when a herbicide inhibit the electron transport chain doesn’t allow obtain Glyceraldehyde 3-phosphate in Calvin cycle, stopping the cycle.