Salil Bose

P700 sensitization by low concentration of DCMU in isolated pea chloroplasts

Abstract Using steady-state relaxation spectrophotometric technique a P700 component ( t 1 2 ∼20 ms ) has been detected which was sensitized by low concentration (10−7M) DCMU in isolated broken chloroplasts of pea. The relative quantum yield of electron flux through DCMU-sensitized P700 was similar to that with methyl viologen or NADP as terminal electron acceptor and water as electron donor. Kinetic analysis showed that a small fraction (10%) of the total P700 reaction centers was sensitized by low DCMU.

Relationship between P700 turnover (m second) and NADP reduction as a function of ferredoxin concentration in isolated broken chloroplasts

Steady-state electron flux through P700 (t 12 20 msec) and concomitant rate of NADP reduction have been measured under weak actinic illumination as a function of concentration of ferredoxin added to broken chloroplasts isolated from peas. At suboptimal concentrations of ferredoxin this P700 is not sufficient to account for the NADP reduction. At high concentrations ferredoxin inhibits the rate of NADP reduction without affecting the P700 flux under short wavelength illumination. Under far red illumination P700 flux is also inhibited by ferredoxin at high concentrations. Addition of 5 mM Mg++ increases the rate of NADP reduction at all concentrations of ferredoxin under both kinds of illumination, while P700 flux is inhibited under short wavelength illumination and remains unchanged under far red illumination. The results indicate that the observed (20 msec) P700 is not involved in NADP reduction.

Inhibition of State Transition and Light-Harvesting Complex II Phosphorylation-Mediated Changes in Excitation Energy Distribution in the Thylakoids of SANDOZ 9785-Treated Plants

Abstract Thylakoids isolated from SAN 9785 (4-chloro-5-dimethylamino-2-phenyl-3(2H)-pyridazi-none)-treated pea plants showed an inhibition of “state transition” and the light-harvesting complex II (LHC II) phosphorylation-mediated changes in the energy distribution between photosystem II (PS II) and photosystem I (PS I) as measured by a decrease in PS II and an increase in PS I fluorescence yield. Interestingly, in these thylakoids the extent of phosphorylation-induced migration of light-harvesting complex (LHC II-P) to non-appressed membrane regions was only marginally inhibited. We propose that the suppression in the ability for “state transition” by SANDOZ 9785 (SAN 9785) treatment occurs due to a lack of effective coupling of the migrated LHC II-P and PS I. Since we observed a decrease in the antenna size of PS I of the treated plants, the lack of effective coupling is attributed to this decrease in the antenna size of PS I.

Mg2+-H+ Exchange in Chloroplast Membranes in Dark

Abstract Protons are released from unilluminated chloroplasts after the addition of Mg2+. The greatest number of protons was measured at pH 6.5 and corresponded to 0.6 mol protons per mol chlorophyll.