Figure 4.

Activation of LHCII kinase decreases the sensitivity of LHCII phosphorylation to thiol reagents. Thylakoids isolated from dark-adapted leaves were incubated for 5 min either in darkness (gray bars) or in light (striped bars). Thiol reagents were subsequently added, and incubation continued for 5 more min before initiation of the phosphorylation assay. Activation of the kinase and phosphorylation of thylakoid proteins were also conducted in total darkness in the presence of NADPH and ferredoxin (hatched bars). The sequential order of the addition of thiol reagents and NADPH + ferredoxin is indicated in the figure. In all cases, the thylakoid protein phosphorylation was initiated by the addition of ATP. Phosphorylation levels of LHCII and D1 proteins were identical in the control assays without thiol reagents, regardless of the activation of the kinase in darkness or in light before the initiation of phosphorylation. DTT (2 mM) and thioredoxins (2 μM) were used in the assay medium. The phosphorylation levels of the D1 and LHCII proteins were analyzed as described in Fig. 2. Results are means ± SD, n = 2–4.