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Phospholipid fatty acid (PLFA) profiles provide a robust measure that can be used to fingerprint the structure of soil microbial communities, and measure their biomass. A replicated field trial, with gradients in substrate and O2 availability created by straw incorporation and flooding was used to test the ability of PLFA to discriminate soil microbial communities in different management regimes. Another objective was to test the usefulness, on a large scale, of some of the proposed interpretations of PLFA biomarkers. Using a direct gradient statistical analysis method, PLFA profiles were found to be very sensitive to flooding and straw treatments. Relative abundances of monounsaturated fatty acids were reduced with flooding and increased with added carbon, consistent with their proposed interpretations as indicators of aerobic conditions and high substrate availability. The cyclopropyl fatty acids were not useful as taxonomic indicators of respiratory type, although their responses were consistent with their proposed use as growth condition indicators. Branched fatty acids decreased, as a group, in response to high substrate conditions. A specific biomarker for Type II methanotrophs was not found in this rice soil, even under high carbon, low O2 conditions, which resulted in methane exposure in the soil. Direct comparison of PLFA and substrate utilization patterns indicated that Biolog patterns are highly selective, and do not reflect compositional changes in soil communities

Mitogen-activated protein kinase (MAPK) is activated by various biotic and abiotic stresses. Salt stress induces two well-characterized MAPK activating signaling molecules, phosphatidic acid (PA) via phospholipase D and phospholipase C, and reactive oxygen species (ROS) via nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase. In our previous study, the activity of soybean MAPK, GMK1 was strongly induced within 5 min of 300 mM NaCl treatment and this early activity was regulated by PA. In this study, we focused on the regulation of GMK1 at the later stage of the salt stress, because its activity was strongly persistent for up to 30 min. H₂O₂ activated GMK1 even in the presence of PA generation inhibitors, but GMK1 activity was greatly decreased in the presence of diphenyleneiodonium, an inhibitor of NADPH-oxidase after 5 min of the treatment. On the contrary, the n-butanol and neomycin reduced GMK1 activity within 5 min of the treatment. Thus, GMK1 activity may be sustained by H₂O₂ 10 min after the treatment. Further, GMK1 was translocated into the nucleus 60 min after NaCl treatment. In the relationship between GMK1 and ROS generation, ROS generation was reduced by SB202190, a MAPK inhibitor, but was increased in protoplast overexpressing TESD-GMKK1. However, these effects were occurred at prolonged time of NaCl treatment. These data suggest that GMK1 indirectly regulates ROS generation. Taken together, we propose that soybean GMK1 is dually regulated by PA and H₂O₂ at a time dependant manner and translocated to the nucleus by the salt stress signal.

Constitutive expression of the cold-regulated COR15a gene of Arabidopsis thaliana results in a significant increase in the survival of isolated protoplasts frozen over the range of -4.5 to -7 degree C. The increased freezing tolerance is the result of a decreased incidence of freeze-induced lamellar-to-hexagonal II phase transitions that occur in regions where the plasma membrane is brought into close apposition with the chloroplast envelope as a result of freeze-induced dehydration. Moreover, the mature polypeptide encoded by this gene. COR15am, increases the lamellar-to-hexagonal II phase transition temperature of dioleoylphosphatidylethanolamine and promotes formation of the lamellar phase in a lipid mixture composed of the major lipid species that comprise the chloroplast envelope. We propose that COR15am, which is located in the chloroplast stroma, defers freeze-induced formation of the hexagonal II phase to lower temperatures (lower hydrations) by altering the intrinsic curvature of the inner membrane of the chloroplast envelope

Phospholipid fatty acid (PLFA) profiles were measured in soils from organic, low-input, and conventional farming systems that are part of the long term Sustainable Agriculture Farming Systems (SAFS) Project. The farming systems differ in whether their source of fertilizer is mineral or organic, and in whether a winter cover crop is grown. Sustained increases in microbial biomass resulting from high organic matter inputs have been observed in the organic and low-input systems. PLFA profiles were compared to ascertain whether previously observed changes in biomass were accompanied by a change in the composition of the microbial community. In addition, the relative importance of environmental variables on PLFA profiles was determined. Redundancy analysis ordination showed that PLFA profiles from organic and conventional systems were significantly different from April to July. On ordination plots, PLFA profiles from the low-input system fell between organic and conventional systems on most sample dates. A group of fatty acids (i14:0, a15:0, 16:1 omega7c, 16:1 omega5c, 14:0, and 18:2 omega6c) was enriched in the organic plots throughout the sampling period, and another group (10Me16:0, 2OH 16:1 and 10Me17:0) was consistently lower in relative abundance in the organic system. In addition, another group (15:0, a17:0, i16:0 17:0, and 10Me18:0) was enriched over the short term in the organic plots after compost incorporation. The relative importance of various environmental variables in governing the composition of microbial communities could be ranked in the order: soil type time specific farming operation (e.g., cover crop incorporation or sidedressing with mineral fertilizer) management system spatial variation in the field. Measures of the microbial community and soil properties (including microbial biomass carbon and nitrogen, substrate induced respiration, basal respiration, potentially mineralizable nitrogen, soil nitrate and ammonium, and soil moisture) were...

For investigating the flavor contribution of phospholipids and triglycerides to pork, the longissimus muscle of Rongchang (RC) and PIC (bred by PIC Company of England) pig were selectively removed of intramuscular triglycerides or total intramuscular lipids. After cooking, the flavor of different samples was compared by sensory evaluation, gas chromatographymass spectrometry (GC-MS), and electronic nose. The results showed that removing triglycerides had little effect on the aroma of the cooked meat, but when total intramuscular lipids were removed a remarkable difference was observed. The control samples covaried strongly with some lipid-derived products, and the petroleum ether defatted samples also positively related to these compounds, but to a lesser extent, both of them negatively covaried with chloroform-methanol extracted samples which associated with some Maillard reaction products. Moreover the flavor difference between 2 breeds would decrease when triglycerides were removed, and reduce further when phospholipids and triglycerides were removed simultaneously. These results suggested that intramuscular lipids especially phospholipids contributed significantly to pork flavor, the flavor difference between 2 breeds resulted mainly from different intramuscular lipids content and composition.

Cold shock elicits an immediate rise in cytosolic tree calcium concentration ([Ca2+]cyt) in both chilling-resistant Arabidopsis and chilling-sensitive tobacco (Nicotiana plumbaginifolia). In Arabidopsis, lanthanum or EGTA caused a partial inhibition of both cold shock [Ca2+]cyt elevation and cold-dependent kin1 gene expression. This suggested that calcium influx plays a major role in the cold shock [Ca2+]cyt response and that an intracellular calcium source also might be involved. To investigate whether the vacuole (the major intracellular calcium store in plants) is involved, we targeted the calcium-dependent photoprotein aequorin to the cytosolic face of the vacuolar membrane. Cold shock calcium kinetics in this microdomain were consistent with a cold-induced vacuolar release of calcium. Treatment with neomycin or lithium, which interferes with phosphoinositide cycling, resulted in cold shock [Ca2+]cyt kinetics consistent with the involvement of inositol trisphosphate and inositide phosphate signaling in this response. We also investigated the effects of repeated and prolonged low temperature on cold shock [Ca2+]cyt. Differences were observed between the responses of Arabidopsis and N. plumbaginifolia to repeated cold stimulation. Acclimation of Arabidopsis by pretreatment with cold or hydrogen peroxide caused a modified calcium signature to subsequent cold shock. This suggests that acclimation involves modification of plant calcium signaling to provide a \"cold memory\"

Membrane disruption has been proposed to be a key event in plant senescence, and phospholipase D (PLD; EC 3.1.4.4) has been thought to play an important role in membrane deterioration. We recently cloned and biochemically characterized three different PLDs from Arabidopsis. In this study, we investigated the role of the most prevalent phospholipid-hydrolyzing enzyme, PLDalpha, in membrane degradation and senescence in Arabidopsis. The expression of PLDalpha was suppressed by introducing a PLDalpha antisense cDNA fragment into Arabidopsis. When incubated with abscisic acid and ethylene, leaves detached from the PLDalpha-deficient transgenic plants showed a slower rate of senescence than did those from wild-type and transgenic control plants. The retardation of senescence was demonstrated by delayed leaf yellowing, lower ion leakage, greater photosynthetic activity, and higher content of chlohphyll and phospholipids in the PLDalpha antisense leaves than in those of the wild type. Treatment of detached leaves with abscisic acid and ethylene stimulated PLDalpha expression, as indicated by increases in PLDalpha mRNA, protein, and activity. In the absence of abscisic acid and ethylene, however, detached leaves from the PLDalpha-deficient and wild-type plants showed a similar rate of senescence. In addition, the suppression of PLDalpha did not alter natural plant growth and development. These data suggest that PLDalpha is an important mediator in phytohormone-promoted senescence in detached leaves but is not a direct promoter of natural senescence. The physiological relevance of these findings is discussed

Ethylene has been implicated in signaling cell death in the lysigenous formation of gas spaces (aerenchyma) in the cortex of adventitious roots of maize (Zea mays) subjected to hypoxia. Various antagonists that are known to modify particular steps in signal transduction in other plant systems were applied at low concentrations to normoxic and hypoxic roots of maize, and the effect on cell death (aerenchyma formation) and the increase in cellulase activity that precedes the appearance of cell degeneration were measured. Both cellulase activity and cell death were inhibited in hypoxic roots in the presence of antagonists of inositol phospholipids, Ca2+-calmodulin, and protein kinases. By contrast, there was a parallel promotion of cellulase activity and cell death in hypoxic and normoxic roots by contact with reagents that activate G-proteins, increase cytosolic Ca2+, or inhibit protein phosphatases. Most of these reagents had no effect on ethylene biosynthesis and did not arrest root extension. These results indicate that the transduction of an ethylene signal leading to an increase in intracellular Ca2+ is necessary for cell death and the resulting aerenchyma development in roots of maize subjected to hypoxia

Abstract Microbial biomass and community structure were investigated in two composts using the phospholipid fatty acid technique. The composts consisted of shredded straw of Miscanthus with the addition of pig slurry to give an initial C:N ratio of about 25. Samples were taken following changes in the compost temperature (at 5°C intervals) during the first month of composting and additionally after 2 and 3 months. The total microbial biomass, measured as total amount of phospholipid fatty acid, peaked after 1 day with about six times the initial values. The temperature also peaked after 1 day, being above 60°C, and then slowly declined to around 25°C over 3 months. Microbial biomass was approximately halved during this time. When the total amount of phospholipid fatty acid was separated into indicator phospholipid fatty acids for different groups of microorganisms, these groups showed different patterns during the composting process. Gram-positive bacteria increased rapidly with increasing temperature and decreased with decreasing temperature. Gram-negative bacteria and fungi increased initially up to a temperature around 50°C, but decreased during the extreme heating phase. When the temperature declined to about 50°C, the amounts of phospholipid fatty acids indicative of these two groups increased again. The phospholipid fatty acid indicative of actinomycetes, 10Me18:0, was at a low level during the whole experiment, but increased slightly during the last month of composting. The development of the microbial community in the two composting systems was similar during the initial thermophilic phase of the composting process, but the communities after 3 months differed.