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Chloroplastal damage as trigger to hydra-alga endosymbiosis breakdown

CHLOROPLASTAL DAMAGE AS TRIGGER TO HYDRA-ALGA ENDOSYMBIOSIS BREAKDOWN G. KOVACEVIC(1), N. LJUBESIC(2), M. KALAFATIC(1) (1)Faculty of Science, University of Zagreb, Department of Zoology, HR-10000 Zagreb, Croatia, (2) Ruder Boskovic Institute, Department of Molecular Genetics, Bijenicka 54, HR-10000 Zagreb, Croatia The deleterious effect of herbicide SAN 9789 on hydra-alga endosymbiosis was studied. The aim of this study was to observe the changes on chloroplast in endosymbiotic green alga and on other ultrastructural components in both endosymbionts, and from this point of view to draw out the conclusion about (in)dependence of both endosymbionts and maintaining of the endosymbiosis. Green hydra (Hydra viridissima Pallas, 1776) is an excellent example of endosymbiosis. In its gastrodermal myoepithelial cells it contains the individuals of unicellular green alga Chlorella vulgaris(1). Endosymbiosis is possible because of the specific preadaptations of both endosymbiont and its host. Green alga contains the characteristic huge kidney-like chloroplast with dense thylakoides that form numerous grana. Chloroplast envelopes contain carotenoids that have protective photooxidative role. Individuals of green hydra were treated in high-light (1372 lx) and low-light (294 lx) laboratory conditions (21oC, 10 hs daylight and 14 hs dark) for 72 hs with 2x10-4 mol/L and 2x10-5 mol/L of water solution of herbicide SAN 9789, active compound norflurazon, using aquarium water. They were compared to control groups of organisms. For cTEM standard preparation methods were used. Micrographs were made by using electron microscope Zeiss EM10A. The expected antichloroplastal effect was the most expressed since norflurazon is a bleaching agent that affects carotenoids especially in high-light conditions(2). The ultrastructural analysis of high-light conditions treatment in higher concentration showed irregularities to chloroplastal thylakoidal system that was changed in shape and position, with thylakoides thorn apart, ending with blind ends. Changes were observed also on other ultrastructures of green alga and hydra. Algal hard cell wall was wrinkled. Absence of symbiosomes and changed volume of perialgal space pointed out the extreme damages. Mitochondria were affected. Endoplasmic reticulum was torn apart, found only in fragments. Different kinds of membrane structures were formed in the shape of osmiophylic figures as the result of complete animal cell degradation, while white globules and dark spots appeared in algal vacuoles. Inside chloroplast plastoglobules appeared (Fig. 1). This is known response to the xenobiotic treatment(3). In concentration 2x10-5 mol/L occurred similar changes but of weaker intensity (Fig. 2). Described but milder damages occurred also in low-light conditions treatment.

chloroplasts; cellular ultrastructures; herbicide

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