Effects of Hydrostatic Pressure on Photosynthetic Systems. I. Preferential Destruction of the O2-Evolving Center

The effects of hydrostatic pressure treatments on the photosyntheticactivities of isolated thylakoids and PSII membranes were studied,and the following results were obtained. (1) The O₂-evolvingactivity was selectively inhibited by treatment at 200 MPa andabove, while the electron transport in the PSII reaction center,as measured by the photoreduction of 2,6-dichlorophenolindophenol(DCIP) with 1,5-diphenylcarbazide (DPC), was markedly enhanced.(2) The activity of PSI, as measured by the photoreduction ofmethylviologen with reduced DCIP, was not much affected evenafter treatment at 500 MPa, whereas this electron transportbecame uncoupled from phosphorylation at 200 MPa and above.(3) In pressure-treated PSII membranes, the EPR signal of Y⁺_zbecame photoinducible with the concomitant appearance of anEPR signal for Mn²⁺. (4) The 33-kDa extrinsic protein was retainedin inhibited PSII membranes, but the 17- and 23-kDa extrinsicproteins were lost. (5) Cross-linking of PSII proteins by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide(EDC) suppressed the pressure-induced inactivation of the evolutionof O₂. (6) In pressure-treated PSII membranes, higher concentrationsof DCMU were required to inhibit the photoreduction of DCIP.Features of the pressure-induced inhibition of various reactionsin photosynthetic membranes are discussed on the basis of theseresults. ¹On leave from Advanced Research Laboratory, Hitachi Ltd., Hatoyama,Saitama, 350-03 Japan.     

Automatic rearing system of mice and transmission of pseudomonas aeruginosa]

Mice either excreting or not excreting Pseudomonas aeruginosa in feces were maintained in stainless steel mesh cages on an automated rearing apparatus with automatic water-supply nozzles and intermittently flusing metal racks. No evidence of transmission of the organisms from positive mice to negative ones was obtained during at least eight weeks.     

An Improved Method for Determining the Ionic Conductance and Capacitance of the Membrane of Chara corallina

The assumption of a single exponential change for the voltageresponse caused by a square current of subthreshold intensityis not necessarily an adequate explanation of the situationin the Chara membrane. By improving the speed of electronicsfor current clamping and the accuracy of data simulation, itwas found that an additional process, which can be generallysimulated with another exponential function, was superimposedon the voltage response. Such an additional exponential processmay be partly atributed to the response of the tonoplast, ifthe internal potential measuring microelectrode is in the vacuole.However, this additional process still remained in the voltageresponse of the plasmalemma of the Chara internode when thetonoplast and a large amount of endoplasm were removed by internalperfusion with an glycol ether diaminetetraacetic acid solution.The additional exponential component arose from the change ofthe electromotive force of the single membrane during applicationof the test current pulse. The increase of the conductance of the plasmalemma alone waslarge during excitation, while that of the elecrostatic capacitancewas negligible. On the other hand, the conductance and capacitancewhich reflect an additional exponential ionic process duringthe test pulse both increased greatly around the peak of excitation.This rise is the main reason for an apparent large increaseof membrane capacitance which was deduced from a simple approximationof the membrane with a single time constant model. (Received January 6, 1982; Accepted June 23, 1982)