The contents of chlorophyll (Chl), leaf biomass, and soluble proteins were markedly decreased in phytoplasma infected apple leaves. Similar results were also observed for ribulose-1,5-bisphosphate carboxylase, 14CO2 fixation, and nitrate reductase activity. In contrast, the contents of sugars, starch, amino acids, and total saccharides were significantly increased in phytoplasma infected leaves. In isolated chloroplasts, phytoplasma infection caused marked inhibition of whole photosynthetic electron chain and photosystem 2 (PS2) activity. The artificial exogenous electron donor, diphenyl carbazide, significantly restored the loss of PS2 activity in infected leaves. Similar results were obtained when Fv/Fm was evaluated by in vivo Chl a fluorescence kinetic measurements. and M. Bertamini ... [et al.].
Changes in various components of photosynthetic apparatus during the 6-d dark incubation at 25 °C 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 leaves. In contrast to this, DCMU-treated leaves demonstrated high stability by slowing down the inactivation processes. Diphenyl carbazide and NH2OH restored the PS2 activity more in control leaves than in DCMU-treated leaves. Mn2+ failed to restore the PS2 activity in both control and DCMU-treated samples. Similar results were obtained when Fv/Fm was evaluated by chlorophyll fluorescence measurements. The marked loss of PS2 activity in dark incubated control leaves was primarily due to the loss of D1, 33, and 23 kDa extrinsic polypeptides and 28-25 kDa LHCP2 polypeptides. and N. Nedunchezhian, K. Muthuchelian, M. Bertamini.
Photosynthetic electron transfer was studied in thylakoids isolated from control and DCMU-grown wheat (Triticum aestivum L.) seedlings. When exposed to high temperature (HT) and high iradiance (HI), thylakoids showed large variations in the photosynthetic electron transport activities and thylakoid membrane proteins. A drastic reduction in the rate of whole electron transport chain (H2O → MV) was envisaged in control thylakoids when exposed to HT and HI. Such reduction was mainly due to the loss of photosystem 2, PS2 (H2O → DCBQ) activity. The thylakoids isolated from seedlings grown in the presence of DCMU showed greater resistance to HT and HI treatment. The artificial exogenous electron donors MnCl2, DPC, and NH2OH failed to restore the HI induced loss of PS2 activity in both control and DCMU thylakoids. In contrast, addition of DPC and NH2OH significantly restored the HT induced loss of PS2 activity in control thylakoids and partially in DCMU thylakoids. Similar results were obtained when Fv/Fm was evaluated by chlorophyll fluorescence measurements. The marked loss of PS2 activity in control thylakoids was evidently due to the loss of 33, 23, and 17 kDa extrinsic polypeptides and 28-25 kDa LHCP polypeptides. and K. Muthuchelian, M. Bertamini, N. Nedunchezhian.