The light responses of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) activation and light scattering, a measure of the transthylakoid ΔpH, were found to be similar in Arabidopsis leaves. Methyl viologen lowered the light requirements for both activation and scattering, indicating that rubisco activation is related to thylakoid energization status. Nigericin inhibited rubisco activation in spinach protoplasts, providing further evidence for an association between rubisco activation and thylakoid energization. Light scattering and fluorescence quenching signals indicated an overenergization of the thylakoids in an Arabidopsis mutant defective in light activation of rubisco.
