Photosystem 2 efficiency and thylakoid protein pattern in DCMU-treated wheat seedlings during senescence

Changes in various components of photosynthetic apparatus during the 6-d da rk incubation at 25 degreesC of detached control and DCMU-treated Triticum aestivum L. leaves were examined. The rate of photosystem 2 (PS2) activity was decreased with increase of the time of dark incubation in control leave s. In contrast to this, DCMU-treated leaves demonstrated high stability by slowing down the inactivation processes. Diphenyl carbazide and NH2OH resto red the PS2 activity more in control leaves than in DCMU-treated leaves. Mn 2+ failed to restore the PS2 activity in both control and DCMU-treated samp les. Similar results were obtained when F-v/F-m was evaluated by chlorophyl l fluorescence measurements. The marked loss of PS2 activity in dark incuba ted control leaves was primarily due to the loss of D1, 33, and 23 kDa extr insic polypeptides and 28-25 kDa LHCP2 polypeptides.