Responses of superoxide dismutase (EC 1.15.1.1) and glutathione reductase (EC 1.6.4.2) activities were evaluated in leaf tissue from intact cotton plants (Cotton Branch 1697) H202 and O2(3, 20) and concludes with the ultimate reduction of H202 (4, 13, 16). This cycling of 02 leads to no net evolution or uptake but results in a transport of electrons or 02 intermediates to locations removed from the '

Managing the fatty acid composition of grazing ruminant diets could lead to meat and milk products that have higher conjugated linoleic acid (CLA) concentrations, but forage fatty acid dynamics must be more fully understood for a range of forages before grazing systems can be specified. The fatty acid profiles of 13 different forages, including grasses, legumes, and forbs, grown under greenhouse conditions, were determined. Three separate harvests, at 3-week intervals, were made of each plant material. alpha-Linolenic [C18:3, 7.0-38.4 mg g(-1) of dry matter (DM)], linoleic (C18:2, 2.0-10.3 mg g(-1) of DM), and palmitic (C16:0, 2.6-7.5 mg g(-1) of DM) acids were the most abundant fatty acids in all species at each harvest, together representing approximately 93% of the fatty acids present. Concentrations of fatty acids declined as plants developed, but the fractional contribution of each fatty acid to total fatty acids remained relatively stable over time. Grasses had a uniform composition across species with a mean of 66% of total fatty acids provided by C18:3, 13% by C18:2, and 14% by C16:0. The fractional contribution of C18:3 to total fatty acids was lower and more variable in forbs than in grasses. Intake of fatty acid by grazing ruminants would be affected by the forage species consumed.

Mesembryarnhemnam crystafiinm, a halophilic, inducible Crassulacean acid metabolism (CAM) species, was grown at NaCI concentrations of 20 and 400 milimlar in the rooting medium. Plants from the low salinity treatment showed exclusively C3-photosynthetic net CO2 fixation, whereas plants exposed to the high salinity level exhibited net CO2 dark fixation involving CAM. Mesophyll protoplasts, isolated from both tissues, were gently ruptured, and the intracelular localization of enzymes was studied following differential centrifugation and Percoll density gradient centrifugation of protoplast extracts. Both centrifugation techniques resulted in the separation of intact chloroplasts, with up to 90% yield, from other organelles and the nonparticulate fraction of cels. Enzymes were identified by determination of activity and by sodium dodecyl sulfate gel electrophoresis of enzyme protein.Experiments established the extraorganelar (cytoplasmic) location of phosphoenolpyruvate carboxylase, enolase, phosphoglyceromutase, and NADP-malic enzyme; the mitochondrial location of NAD-malic enzyme; and the chloroplastic location of pyruvate, Pi dikinase. NAD-glyceraldehyde-3-phosphate dehydrogenase, phosphohexose isomerase, and phosphoglycerate kinase were associated with both cytoplasm and chloroplasts.NADP-dependent malate dehydrogenase activity was found in both the chloroplastic and extrachloroplastic fractions; the activity in the chloroplast showed an optimum at pH 8.0 and was dependent upon preincubation of enzyme with dithiothreitol. The extrachloroplastic activity showed an optimum at pH 6.5 and was independent ofpretreatment with dithiothreitol. In the paper presented here, the intracellular distribution of 16 enzymes was studied in the halophilic, inducible CAM plant Mesembryanthemum crystallinum (26). Leaves of M. crystallinum are apparently low in phenolic compounds, and high extractable activities of several enzymes have been reported for this species (9). Experimental plants were manipulated to show either exclusively C3-photosynthetic net CO2 fixation during the light (growth at low salinity levels in the rooting medium) or to exhibit nocturnal net CO2 uptake involving CAM (growth at high salinity levels). Mesophyll extracts with almost all chloroplasts intact were routinely obtained from plants of both salinity treatments by gentle rupture of enzymically isolated protoplasts. Two techniques, differential centrifugation and Percoll density gradient centrifugation, were used to study the intracellular localization of enzymes. Chloroplast integrity was preserved during these procedures, and the two methods gave identical results. MATERIALS AND METHODS Growth

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