Trehalose 6-P (T6P) is a sugar signal in plants that inhibits SNF1-related protein kinase, SnRK1, thereby altering gene expression and promoting growth processes. This provides a model for the regulation of growth by sugar. However, it is not known how this model operates under sink-limited conditions when tissue sugar content is uncoupled from growth. To test the physiological importance of this model, T6P, SnRK1 activities, sugars, gene expression, and growth were measured in Arabidopsis (Arabidopsis thaliana) seedlings after transfer to cold or zero nitrogen compared with sugar feeding under optimal conditions. Maximum in vitro activities of SnRK1 changed little, but T6P accumulated up to 55-fold, correlating with tissue Suc content in all treatments. SnRK1-induced and -repressed marker gene expression strongly related to T6P above and below a threshold of 0.3 to 0.5 nmol T6P g 21 fresh weight close to the dissociation constant (4 mM) of the T6P/ SnRK1 complex. This occurred irrespective of the growth response to Suc. This implies that T6P is not a growth signal per se, but through SnRK1, T6P primes gene expression for growth in response to Suc accumulation under sink-limited conditions. To test this hypothesis, plants with genetically decreased T6P content and SnRK1 overexpression were transferred from cold to warm to analyze the role of T6P/SnRK1 in relief of growth restriction. Compared with the wild type, these plants were impaired in immediate growth recovery. It is concluded that the T6P/SnRK1 signaling pathway responds to Suc induced by sink restriction that enables growth recovery following relief of limitations such as low temperature.

An overview of the use of CE-MS in the field of metabolomics is provided. Metabolomics is concerned with the comprehensive analysis of endogenous low-molecular-weight compounds in biological samples. CE-MS has demonstrated to be a powerful technique for the profiling of polar metabolites in biological samples. This review covers the use of various CE separation modes, capillary coatings, MS analyzers, sample preparation techniques, and data analysis methods used in CE-MS for metabolomics. The applicability of CE-MS in metabolomics research is illustrated by giving examples of the analysis of bacterial extracts, plant extracts, urine, plasma, and cerebrospinal fluid samples. The relevant CE-MS metabolomics studies published between 2000 and 2008 are presented in tabular form, including information on sample type and pretreatment and MS detection mode. Future developments with regard to the use of alternative ionization techniques, the use of coupled separation systems and the potential of microchip CE systems for metabolomics are discussed.

Trehalose 6-phosphate (T6P) is a sugar signal that regulates metabolism, growth, and development and inhibits the central regulatory SNF1-related protein kinase1 (SnRK1; AKIN10/AKIN11). To better understand the mechanism in wheat (Triticum aestivum) grain, we analyze T6P content and SnRK1 activities. T6P levels changed 178-fold 1 to 45 d after anthesis (DAA), correlating with sucrose content. T6P ranged from 78 nmol g 21 fresh weight (FW) pregrain filling, around 100-fold higher than previously reported in plants, to 0.4 nmol g 21 FW during the desiccation stage. In contrast, maximum SnRK1 activity changed only 3-fold but was inhibited strongly by T6P in vitro. To assess SnRK1 activity in vivo, homologs of SnRK1 marker genes in the wheat transcriptome were identified using Wheat Estimated Transcript Server. SnRK1-induced and -repressed marker genes were expressed differently pregrain filling compared to grain filling consistent with changes in T6P. To investigate this further maternal and filial tissues were compared pre-(7 DAA) and during grain filling (17 DAA). Strikingly, in vitro SnRK1 activity was similar in all tissues in contrast to large changes in tissue distribution of T6P. At 7 DAA T6P was 49 to 119 nmol g 21 FW in filial and maternal tissues sufficient to inhibit SnRK1; at 17 DAA T6P accumulation was almost exclusively endospermal (43 nmol g 21 FW) with 0.6 to 0.8 nmol T6P g 21 FW in embryo and pericarp. The data show a correlation between T6P and sucrose overall that belies a marked effect of tissue type and developmental stage on T6P content, consistent with tissuespecific regulation of SnRK1 by T6P in wheat grain.

Over the last two decades, coupled capillary electrophoresis (CE)-mass spectrometry (MS) has developed into a generally accepted technique with a wide applicability. A growing number of CE-MS applications make use of capillaries where the internal wall is modified with surface coating agents. In CE-MS, capillary coatings are used to prevent analyte adsorption and to provide appropriate conditions for CE-MS interfacing. This paper gives an overview of the various capillary coating strategies used in CE-MS. The main attention is devoted to the way coatings can contribute to a proper CE-MS operation. The foremost capillary coating methods are discussed with emphasis on their compatibility with MS detection. The role of capillary coatings in the control of the electroosmotic flow and the consequences for CE-MS coupling are treated. Subsequently, an overview of reported applications of CE-MS employing different coating principles is presented. Selected examples are given to illustrate the usefulness of the coatings and the overall applicability of the CE-MS systems. It is concluded that capillary coatings can enhance the performance and stability of CE-MS systems, yielding a highly valuable and reproducible analytical tool.