Lipids are the major form of carbon storage in arbuscular-mycorrhizal fungi. We studied fatty acid synthesis by Glomus intraradices and Gigaspora rosea. Our data strongly suggest that the fatty acid synthase activity of arbuscular-mycorrhizal fungi is expressed exclusively in the intraradical mycelium and indicate that fatty acid metabolism may play a major role in the obligate biotrophism of arbuscular-mycorrhizal fungi.

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Our purpose was to determine initial microbial populations in shredded Iceberg lettuce (Lactuca sativa L.) cv 'Great Lakes', and to study their changes under different controlled atmospheres. Lettuce was shredded, washed, disinfected, water rinsed and centrifuged before being stored for 12 days under air, 3% 02, 3% O2 + 5% CO2 or 3% 0, + 10% CO*. Microbiological analysis and assessment of visual quality were carried out every 3 days. No human pathogens were found. Controlled atmospheres had little or no effect on the microbiological populations studied. A 3% O2 + 10% CO* atmosphere maintained acceptable visual quality of lettuce, without appreciably affecting microbial development.

Wide-angle x-ray diffraction has provided evidence for lipid phase separations in microsomal membranes from chill-injured tomato (Lycopersicon esculentum Mill. cv Caruso) fruit. Maturegreen fruit stored for 20 d at 5'C had not begun to ripen and were essentially free of chilling injury symptoms. Within 4 d of being returned to 25"C, however, the fruit displayed characteristic symptoms of chilling injury, including translucent water-soaked patches, surface pitting, and irregular pigmentation. Membrane damage measured as electrolyte leakage from pericarp discs intensified after the fruit were returned to ambient temperature. Wide-angle x-ray diffraction patterns recorded at 25°C for microsomal membranes isolated from untreated, mature-green fruit indicated that the membrane bilayers were exclusively liquid-crystalline. Diffraction patterns for microsomal membranes from fruit stored for 20 d at 5°C showed only trace amounts of gel phase lipid, but within 4 d of subsequent exposure of the fruit to ambient temperature, there was evidence for a pronounced lateral phase separation of lipids within the membranes that would render them leaky. Inasmuch as the phase separations were detectable at 25'C and became pronounced only subsequent to the chilling episode, they appear to be an indirect rather than direct effect of exposure to low temperature. The diffraction data thus support the notion that the lipid phase changes observed here are not directly induced by low temperature but rather reflect subsequent biochemical changes in the bilayers that may contribute to the development of chilling symptoms.

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