APPEARANCE AND DEVELOPMENT OF PHOTOSYNTHETIC ACTIVITIES IN WHEAT ETIOPLASTS GREENED UNDER CONTINUOUS OR INTERMITTENT LIGHT—EVIDENCE FOR WATER‐SIDE PHOTOSYSTEM II DEFICIENCY AFTER GREENING UNDER INTERMITTENT LIGHT*

Abstract

Abstract— Etiolated wheat seedlings are greened under continuous or intermittent light. Under continuous light the onset of photosystem II (PS II) activity appears after 4 h of illumination. Under intermittent light (1 ms flashes alternating with 15 min dark periods), PS II activity cannot be detected after 300–400 flashes, although the pigment composition and structural development of these plastids are similar to those observed after 4 h of continuous light. However, the appearance of PS II activity in isolated plastids can be observed in two different ways: (1) in vivo by exposing the seedlings to a short period of continuous light after the intermittent light; or (2) in vitro by addition to the isolated plastids of an electron donor for PS II, such as diphenylcarbazide. It is concluded that the intermittent light induces development of the electron transport chain from PS II to PS I, but that a deficiency occurs on the water‐side of PS II.