Arabidopsis mutants containing gene disruptions in AHA1 and AHA2, the two most highly expressed isoforms of the In animals, the sodium pump is the primary active transport system and creates a membrane potential and sodium gradient that are used by all ion channels and cotransporters (1, 2). In higher plants and fungi, however, the transport of all solutes across the plasma membrane is coupled to a proton gradient rather than a sodium gradient. Thus, in these organisms, a plasma membrane proton pump creates a protonmotive force at the plasma membrane that drives all channels and cotransporters. Given the known importance of transport at the plasma membrane for life functions, it is not surprising that genetic studies of the sodium pump in nematodes, fruit flies, zebrafish, and mice, as well as with the proton pump of yeast, all conclusively demonstrate the lethal effects of loss-of-function mutations for a gene encoding the primary active transporter (Table 1) (3-11). In contrast, although there have been several reports of altered growth of mutant plants containing genetic alterations in the plasma membrane proton pump (12-17), none of these studies have provided evidence indicating that this enzyme performs an essential function for plant life. In this study, we present evidence clearly demonstrating that the plasma membrane proton pump is essential for plant growth. We show that AHA1 and AHA2 (for Arabidopsis H ϩ -ATPase isoforms 1 and 2), the two most highly expressed members of the AHA gene family, perform overlapping functions that mask the lethality in single gene loss-of-function mutants. We also describe phenotypic screening that supports the in planta role of the proton pump in generating a protonmotive force and mass spectrometric methods that allow a more detailed and quantitative analysis of the in vivo regulation of these proteins at the post-translational level. (aha1-6, SALK016325; aha1-7, SALK065288; and aha1-8, SALK118350) and AHA2 (aha2-4, SALK082786, and aha2-5, SALK022010) were obtained from the Arabidopsis Biological Resource Center (Ohio State University) (18). Seeds were germinated on plates containing half-strength M&S 3 salts, 1% (w/v) sucrose, and 0.7% (w/v) agar. Plants that were transferred to soil/perlite mixture (Jiffy-Mix, Jiffy Products of America, Lorrain, OH; horticultural perlite, The Schundler Co., Metuchen, NJ) were grown at 21°C under constant light or 22°C with a regime of 16 h of light/8 h of dark. EXPERIMENTAL PROCEDURES Plant Materials and Growth Conditions-Mutants (ecotype Columbia) carrying T-DNA insertions in AHA1T-DNA Mutant Identification and Plant Genotyping-Plant genomic DNA was extracted using the method of Krysan et al. (19), with the elimination of the phenol/chloroform extraction step. The location of the T-DNA insertion in AHA1 or AHA2 was determined by sequencing PCR fragments containing the * This work was supported by grants from the Department of Energy and the National Science Foundation (to M. R. S.) and by National Science Foundation Grant MCB-0619...

Niemann–Pick disease, type C1 (NPC1) is a fatal, autosomal recessive, neurodegenerative disorder caused by mutations in the NPC1 gene. As a result of the genetic defect, there is accumulation of unesterified cholesterol and sphingolipids in the late endosomal/lysosomal system causing both visceral and neurological defects. These manifest clinically as hepatosplenomegaly, liver dysfunction, and neurodegeneration. While significant progress has been made to better understand NPC1, the downstream effects of cholesterol storage and the major mechanisms that drive these pathologies remains less understood. In this study, it is sought to investigate free fatty acid levels in Npc1−/− mice with focus on the polyunsaturated ω‐3 and ω‐6 fatty acids. Since fatty acids are the main constituents of numerous lipids species, a discovery based lipidomic study of liver tissue in Npc1−/− mice is also performed. To this end, alterations in fatty acid synthesis, including the ω‐3 and 6 fatty acids, are reported. Further, alterations in enzymes that regulate the synthesis of ω‐3 and 6 fatty acids are reported. Analysis of the liver lipidome reveals alterations in both storage and membrane lipids including ceramides, fatty acids, phosphatidylcholamines, phosphatidylglycerols, phosphatidylethanolamines, sphingomyelins, and triacylglycerols in Npc1−/− mice at a late stage of disease.