The transmembrane distribution of monogalactosyldiacylglycerol and digalactosyldiacylglycerol was determined in chloroplast thylakoids from a range of temperate climate plants. These plants included dicotyledons, monocotyledons, C16:3 and C18:3 plants and herbicide-resistant species. In all the thylakoids examined monogalactosyldiacylglycerol was enriched in the outer leaflet (53-65%) while digalactosyldiacylglycerol was highly enriched in the inner leaflet (78-90%). The non-bilayer forming monogalactosyldiacylglycerol represented 55-81% of the total acyl lipids of the outer monolayer. The relative acyl lipid composition of both leaflets of the thylakoid membrane indicates that the lamellar structure is strongly favored in the inner monolayer, whereas the outer one presents a metastable character which allows the probable coexistence of both lamellar and non-lamellar phases. The consequence of this asymmetry for the stability and function of the thylakoid membrane is discussed.
The transmembrane distribution of phosphatidylglycerol was determined in thylakoids from barley (Hordeum vulgare), lettuce (Lactuca sativa) and pea (Pisum sativum) chloroplasts. Phospholipase A2 and phospholipase D digestion and chemical-labelling methods were used. Phosphatidylglycerol was preferentially localized in the outer (stromal) leaflet. The proportion of the phospholipid in this leaflet ranged from about 66% in pea to about 75% for barley and lettuce thylakoids. One of the main fatty acids, trans-delta 3-hexadecenoic acid, was exclusively located in the outer leaflet in all three plant types. The data are discussed in relation to suggested roles for phosphatidylglycerol in thylakoid function.
Physiological tests were devised and used to compare 15 strains representing five species of soil and freshwater amoebae assigned to the genus Acanthamoeba. The tests gave an acceptable level of reliability and the pattern of responses was not affected by the differing growth rates of the organisms. There was some degree of overlap between the strains, as shown by the high level of inter-species similarities in relation to those between strains of the same species. Previous classifications of Acanthamoeba, which are based solely on morphological criteria, do not adequately reflect the diversity of these amoebae. I N T R O D U C T I O NSmall amoebae, variously assigned to the genera Acanthamoeba, Hartmannella and Mayorella, occur widely in soil and aquatic habitats and are probably some of the most common protozoa (Page, 1967(Page, , 1976. Some cause certain pathological conditions (Culbertson, 1971). As they are one of the few groups of protozoa which can be isolated and grown in axenic culture they are also being used increasingly in fundamental studies of cell physiology and biochemistry. However, their ecological relationships are poorly understood, due, in part, to the confusion of some of the existing classifications of the group which are based entirely on morphological criteria.At present the most important taxonomic characters are: pseudopodial form; type of amoeboid movement; occurrence of a flagellate stage in the life-cycle; nuclear structure; cyst morphology and method of excystation. The use of such characters can be criticized on several grounds, for example, descriptions of pseudopodial form are often imprecise and cyst morphology can be extremely variable or modified significantly by the environment (Pussard, 1966;Stratford & Griffiths, 1978).The DNA base compositions of representative strains range from 50 to 62 yo GC (Adam & Blewett, 1974) suggesting that existing classifications may not adequately reflect the diversity of this group of organisms. Physiological characters could be used more extensively (Adam, 1964b), and in this present study, methods have been devised to examine further the physiological diversity of 15 strains of amoebae now included in the genus Acanthamoeba. M E T H O D SStrains and their routine maintenance. Fifteen strains representing five species of Acanthamoeba were examined (Table 1). All cultures were axenic and, after receipt, were maintained in PGY medium [0.75 % (w/v) peptone, 0.75 % (w/v) yeast extract, 1.5 % (w/v) glucose; Difco or Oxoid peptones and yeast extracts could be used in this medium with equal effect]. Stock cultures (5 ml) were kept at laboratory temperature in small, screw-capped bottles. These were inoculated with 0.5 ml of a culture which had been maintained similarly and subcultures were made every 4 to 6 weeks.Tests used to characterize cultures of trophozoites. Tests devised for this study are listed in Table 2. PGY
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