Figure 1.

Induction of State I → State II Transition in De-Enveloped Chloroplasts.

(A) Transitions monitored by detecting the level of phosphorylated Lhcb1/2. Anti-phosphothreonine was used to probe immunoblots of the following thylakoid preparations. Lanes 1 to 6: thylakoids that were dark-adapted (1), dark-adapted with ATP (2), treated with duroquinol plus ATP (3), subjected to 30 μmol photons·m⁻²·s⁻¹ of 640-nm light for 30 min without ATP (4), or with ATP in the presence (5) or absence of 10 μM DCMU (6). Lanes 7 to 9: thylakoids subjected to 30 μmol photons·m⁻²·s⁻¹ of 640-nm light for 5, 10, or 30 min, respectively.

(B) Transitions monitored by low-temperature chlorophyll fluorescence measurements. The emission spectra shown were recorded at 77K using an excitation wavelength of 480 nm. Spectra were normalized to the area below the curves. Thylakoids were trapped in state I (solid line) and then induced to undergo two sequential transitions: first to state II (dashed line) and subsequently back to state I (dotted line). The increase of the 730-nm peak upon exposure to PSII-specific light is indicative of the association of LHCII with PSI. Inset: Fluorescence difference spectrum (F_I – F_II). The area below the positive and negative peaks is approximately the same, as expected.