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Electrons produced by Chl-aIIin a short flash are finally transfered to Chl-ai after having passed several intermediates. The reaction between Chl-aIand its primary electron donators PD (probably Cyt-f and PC) has been studied by means of high time resolution flash photometry in isolated spinach chloroplasts with the following results:

New absorption changes with a life time of 2·10—4sec at ∼690 nm probably represent the chlorophyll-a light reaction in photosynthesis which promotes the cleavage of water.

1. The Chl-b reaction in chloroplasts is biphasic.

After the reduction of PQ in the light, PQ=is oxidized in the dark. Three types of reoxydation can be distinguished in isolated chloroplasts of spinach:

Plastoquinone PQ is engaged in photosynthesis 1. Difference spectra in the UV-region indicate that PQ is an intermediate in the electron transport chain 2. PQ is located as a pool between the two light reactions I and II 3. PQ is reduced by hνIIand oxidized by hνI3. In this paper the difference spectra which occur during light excitation of spinach chloroplasts and chlorella vulgaris were measured in the UV-region with high resolution by the high sensitive method of periodical flash photometry 6.

In order to test recent interpretations of field indicating absorption changes in photosynthesis, the influence of the electric field on the absorption spectrum of chlorophyll-b is measured in vitro.

A repetitive laser giant pulse photometer is described which can resolve absorption changes of 0.1% in the time range of 10 ns. With this instrument the following results have been obtained.

A repetitive ultra-short-flash photometer is described which can resolve absorption changes of 0,01% in the time range of 10-7sec. With this instrument the following results have been obtained.

1. Fluorescence changes of umbelliferone have been used as indicator for pH changes in the outer phase of the functional membrane of photosynthesis. In combination with the repetitive pulse technique it is possible to measure the pH change which is produced during one turn-over of the molecular machinery (Δ pH ≈ 10−4). The analysis of this primary pH changes gives insight in the primary ionic events in general.

Electrical field changes across the function membrane of photosynthesis have been measured via special absorption changes. These occur by the action of the field on pigments which are located within the membrane. - Proton translocation has been measured by absorption changes of added pH indicators. Repetitive flash technique has been used for the sensitive detection of these absorption changes.

1. The complete difference spectrum of the reaction of the photoactive chlorophyll-an is presented.

From action spectra of separated light reactions the function of different chlorophylls in photosynthesis have been estimated.

The primary reactions of photosynthesis are fast reactions. To get detailed informations we developed three different methods. 1. sensitive flash photometry 38, 2. periodically chemical relaxation51, 26a, 3. manometry in flashing light groups 26b. With the method of flash photometry fast absorption changes in suspensions of chlorella and spinach chloroplasts were studied. 7 different types of absorption changes have been separated and analysed (Fig. 2). Older results 28-49lead to a reaction scheme published in l. c. 13. This scheme was refined (s. Fig. 3) by results published in l. c. 14-26. In the following 6 papers these investigations are described in detail and supplement by new results.