Oxygen-evolving diatom thylakoid membranes

Two protocols were developed that yielded purified oxygen-evolving thylakoi d membranes from the diatom Cylindrotheca fusiformis. One protocol employed sonication, while the second involved French press lysis of protoplasts fo rmed by brief culture of cells in a cation-depleted medium. Regardless of t he method of cell breakage, some damage to electron transport components oc curred. For preservation of both light-dependent electron transport activit y and in vivo fluorescence properties, 2 M sorbitol proved to be more effec tive than I M sorbitol, regardless of the method used for cell lysis. Thyla koids purified in 2 M sorbitol using the protoplast/French press method sho wed the best preservation of in vivo fluorescence emission signals and Phot osystem II activity with ferricyanide was completely inhibited by DCMU. Thy lakoids purified in 2 M sorbitol using sonication had higher rates of Photo system II activity with ferricyanide, but this activity was less sensitive to DCMU. Whole-chain electron transport activity was low in all preparation s. This is the first report of O-2 evolution and of long-wavelength fluores cence in purified thylakoids of any chromophytic alga. (C) 1998 Elsevier Sc ience B.V. All rights reserved.