Pergamon www.elsevier.com/locate/asr Adv. Space Rex Vol. 27, No. 5, pp. 1007-1010,200l 0 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-l 177/01 $20.00 + 0.00 PII: SO273-1177(Ol)OOl93-4 EFFECTS OF SLOW CLINOROTATION ON LIPID CONTENTS AND PROTON PERMEABILITY OF TH-YLAKOID MEMBRANES OF PEA CHLOROPLASTS N. F. Mikhaylenko’, S. K. Sytnik’, and E. K. Zolotareva’ ‘MG. Kholodny Institute of Botany, National Academy of Sciences of the Ukraine 2 Tereschenkivska Str., Kyiv 01004, Ukraine 21nstitute of Plant Physiology and Genetics, National Academy of Sciences of the Ukraine, 31/l 7 Vasylkivska Str., 03022, Kyiv, Ukraine ABSTRACT Photochemical characteristics and lipid composition of thylakoid membranes from 12 day-old pea leaves that were exposed to slow clino-rotation were examined and compared with a vertical control. Proton permeability of thylakoid membranes was estimated from light-induced proton uptake (AH’) and post-illumination proton efflux in chloroplast suspensions. The ApH magnitude was calculated from the level of light-induced quenching of 9-aminoacridine fluorescence. Proton permeability of thylakoid membranes increased during exposure to clino-rotation. When subsequently transferred to darkness, proton efflux increased almost 2-fold in clino- rotated leaves. The results were compared with data on pigment and polar lipid composition of photosynthetic membranes in clino-rotated and control plants. It was concluded that both the increase of proton permeability and the decrease of polar lipid content in chloroplasts were induced by clino-rotation. 0 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved. INTRODUCTION Adaptation of plants to clino-rotation or microgravity conditions is well documented (Laurinavichius et al., 1984; Kordyum et al., 1994; Kordyum, 1997). However, little is known about the effects of altered gravity conditions on the status of photoactive membranes and on the photochemical activity of the photosynthetic apparatus of seedlings. The photosynthetic apparatus is located in thylakoid membranes of the chloroplast, and characteristics such as ion selectivity and proton permeability are of fundamental importance for photosynthetic efficiency. An increase of proton permeability of photosynthetic membranes results in the uncoupling of photophosphorylation and electron transfer. Insulating properties of biological membranes are determined by lipid components of their bilayers. Data (Rumjanceva et al., 1990; Adamchuk et al., 1999) suggest that lipid composition of photosynthetic membranes as well as their ultrastructure are changed under spaceflight conditions. The aim of this study was to evaluate how proton permeability characteristics of thylakoids that were isolated from pea plants that were exposed to clino-rotation correlate with lipid composition of thylakoid membranes. MATERIALS AND METHODS Pea (Pisum sativum Z,.) plants were grown on a horizontal clinostat (2 rpm) and in vertical control for 12 days at 22 to 24°C and low illumination (143 umol rns2s-‘, 16 h light period). Chloroplasts (class II) were isolated from leaves as described earlier by Zolotareva et al. (1997) and resuspended in isotonic storage buffer (pH 8.0) containing 10 mM tricine-NaOH, 200 mM sorbitol, 10 mM KCl, 10 mM NaCl, and 2.5 mM MgC12. The solution was adjusted to a chlorophyll (Chl) concentration of 4 mM and kept on ice in darkness. The Chl concentration was measured according to Vernon (1960). The ApH magnitude was estimated by light-induced quenching of 9-aminoacridine fluorescence according to Schuldiner et al. (1972). Each reaction solution was adjusted to the appropriate pH before initiation of the assay. 1007