Cell Biology international Reports, Vol. 6, No. 9, September 1982 851 DISTRIBUTION OF INTRAMEMBRANOUS PARTICLES IN THE PLASMALEMMA OF PHYSARUMPOLYCEPHALUM DURING SCLEROTIZATION, SPORE-FORMATION AND SPORE-GERMINATION Z. Shraideh' , J. Kukulies, K. V. Wolf, K. E. Wohlfarth-Bottermann and W. Stockem Institute for Cytology, University of Bonn D-5300 Bonn 1, Ulrich-Haberland-Str. 61 a Federal Republic of Germany ABSTRACT The distribution and density of intramembranous particles (IMP) in the plasma membrane of the acellular slime mold Physarum polyce- phalum during sclerotization, sporulation and germination was inve- stigated by means of freeze-etching. The total number of IMP on bo h the PF and EF of young as w 11 2 wetted spores (1,550 IMP&m ) as dry spores (2,100 - 2,2p IMP/,um 5 ), and sclerotia (2,300 IMP/,um ) is remark- ably reduced in comparison to the IM -density of migrating plasmodia (3,680 IMP&m 5 in the plasma membrane ). The most obvious decrease in IMP-density can be observed in EF, i. e., the asymmetry of the cell membrane as expressed by the PF : EF ratio shifts from about 2.5 : 1 to 10 : 1. The cell surface of spores and sclerotia shows a regular pattern of elevations on the PF and corresponding indenta- tions on the EF. On the PF the elevations display a distinct accumu- lation of IMP. The significance of the fine structural changes of the cell membrane during sclerotization, sporulation and the early stage of spore germination is discussed with regard to altered physiologi- cal conditions. INTRODUCTION Comparative studies on the distribution and density of intramem- branous particles (IMP) in plasmodia of the acellular slime mold Phy- sarum polycephalum revealed a2total amount of IMP in the peripheral plasmalemma of about 3,6OO/pm , whereas in plasmalemma invaginations, the number of IMP is reduced to 3,292 (Wolf et al., 1980). 1) Supported by a fellowship of the Deutscher Akademischer Austauschdienst and 2) by a grant from the Deutsche Forschungsgemeinschaft. Editor (provided this paper is accepted): Please arrange this ms in such a way in the journal that it begins with an uneven page number (in order to avoid a page turnover for simultaneous reading of the legends and corresponding figures). 0309-1651/82/090851-07/$03.00/O @ 1982 Academic Press Inc. (London) Ltd.