Formation of the Photosynthetic Electron Transport System during the Early Phase of Greening in Barley Leaves

The development of photochemical activity in isolated plastids during the early phase of greening of 5-day-old etiolated barley seedlings was studied and related to the appearance of chlorophyll-protein complexes. Photochemical activities of PSI (DCIPH₂ → MV) and PSII (H₂O → DCIP, DPC → DCIP) appeared at 1 and 1.5 hours after the onset of illumination, respectively. However, PSI + PSII activity (H₂O → MV, H₂O → NADP) appeared at 4 hours. The functional plastoquinone pool was noticed, at the latest, from 4 hours. Chloroplast preparations from seedlings of 1 h of greening showed O₂ uptake upon illumination in the absence of MV (−MV activity). This activity peaked at 2 hours of greening, then fell to zero by 6 hours. In contrast to the −MV activity, MV-Hill activity began to increase at 2 hours. Although PSI activity appeared at 1 hour, it failed to reduce ferredoxin until 2 hours. NADP began to be photoreduced at 4 hours in accordance with the appearance of the ferredoxin:NADP reductase activity. After formation of PSI and PSII, electron transport systems between them and between PSI and NADP developed in coordination with each other. Thus, the whole electron transport from water to NADP began to operate at 4 hours.