ACTION OF THE ALLELOCHEMICAL, FISCHERELLIN-A, ON PHOTOSYSTEM-II

The cyanobacterium, Fischerella muscicola, produces a secondary metabo lite named fischerellin A (FS) that strongly inhibits the growth of cy anobacteria and other photosynthetic organisms. The compound exhibits a unique structure and is composed of two cyclic amines and a C-15 sub stituent that contains a double bond in the (Z) configuration and two triple bonds [L. Hagmann, F. Juttner, Tetrahedron Lett., 37 (1996) 653 9-6542], The site of FS action is located in photosystem II (PSII). Th e chlorophyll fluorescence induction transient and O-2 evolution metho ds have been used to determine the site of action of FS in PSII. FS af fects the fluorescence transients, as well as O-2 evolution by the cya nobacterium, Anabaena P9. The green alga, Chlamydomonas reinhardtii, a nd higher plants were also affected by FS in a concentration-and time- dependent fashion. FS acts at several sites which appear with increasi ng half-time of interaction in the following sequence: (1) effect on t he rate constant of Q(A)(-) reoxidation; (2) primary photochemistry tr apping; (3) inactivation of PSII reaction center; and (4) segregation of individual units from grouped units. FS does not affect the photosy nthetic activity of purple bacteria, Rhodospirillum rubrum. (C) 1998 E lsevier Science B.V. All rights reserved.