Figure 1.

DTT restores DBMIB-inhibited light-regulated translation of chloroplast mRNAs but not activity of PS II. (A) Dark-adapted intact chloroplasts were treated in the dark with or without 2.5 μM DBMIB, then an aliquot was transferred for 5 min to the light (150 μmol m⁻²⋅sec⁻¹). The translational activities of the dark- and light-incubated chloroplasts were then assayed by labeling newly synthesized proteins for 5 min with [³⁵S]methionine, in the presence or absence of 5 mM DTT. Translation reactions were chased by incubating for an additional 5 min in the presence of 5 mM nonradioactive methionine and stopped by placing tubes in liquid N₂. Chloroplasts were lysed, and extracted proteins were fractionated by SDS/PAGE, blotted onto nitrocellulose membranes, and visualized by autoradiography. (B) Net oxygen exchange was measured in C. reinhardtii cw15 cells with an oxygen electrode. Measurements were performed for 5 min in the dark or light (150 μmol m⁻²⋅sec⁻¹) in the presence or absence of 2.5 μM DBMIB, and then for an additional 5 min with or without 5 mM DTT. (C) Initiation of translation is required for light-regulated translation of chloroplast mRNAs. Dark-adapted intact chloroplasts were treated with or without 15 μM lincomycin (Lync.), then an aliquot was transferred for 5 min to the light (150 μmol m⁻²⋅sec⁻¹), and treatment followed as in A.