Salt-stress-induced ABA accumulation in maize root tissues was compared with that in leaf tissues. While salt stress with NaCl resulted in a significant ABA accumulation in root tissues (up to 10-fold), the same stress only led to a small ABA accumulation in leaf tissues (about 1-fold). Pretreatment with ethylene glycol (EG), a permeable and inert monomer of PEG, could prevent the shrinkage of cell volume and completely block the ABA accumulation in leaf tissues under salt stress, but substantial salt-induced ABA accumulation was still observed in root tissues following such pretreatment. Hypotonic salt solutions, i.e. below 100 mM NaCl, still induced a significant ABA accumulation (more than 3-fold) in roots, but showed no effect on that in leaf tissues. Results suggest that the salt-stress-induced ABA accumulation in roots may also be triggered by an osmosensing mechanism, which is in addition to the perception of the changes in reduced cellular volume or plasmalemma tension that leads to ABA accumulation in leaves. When leaf and root tissues were immersed into salt solutions, salt entered into the cells as a function of time and salt concentrations. Such entrance apparently led to a loss of sensitivity of leaf tissues to accumulate ABA under the salt stress, and also prevented the leaf tissues from responding to further air-drying in terms of ABA accumulation. Roots showed no such responses. Results suggest that the entrance of salt into leaf cells brought about some toxic effect that might have reduced the capability of leaf cells to produce ABA under dehydration.

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Artemisinin is a widely used antimalarial drug. To evaluate the pharmacokinetics of artemisinin in rats, a sensitive and specific liquid chromatography/tandem mass spectrometric (LC/MS/MS) method was developed and validated for the determination of artemisinin in rat plasma. For detection, a Sciex API 4000 LC/MS/MS instrument with an electrospray ionization (ESI) TurboIonSpray inlet in the positive ion multiple reaction monitoring (MRM) mode was used to monitor precursor ([M+NH4]+) --> product ions of m/z 300.4 --> 209.4 for artemisinin and m/z 316.4 --> 163.4 for artemether, the internal standard (IS). The plasma samples were pretreated by a simple liquid-liquid extraction with ether. The standard curve was linear (r > 0.99) over the artemisinin concentration range of 1.0-200.0 ng/mL in plasma. The method had a lower limit of quantification of 1.0 ng/mL for artemisinin in 100 microL of plasma, which offered a satisfactory sensitivity for the determination of artemisinin. The intra- and inter-day precisions were measured to be within +/-5.3% and accuracy between -2.6% and 1.2% for all quality control samples, lower limit of quantification and upper limit of quantification samples. The extraction recoveries of artemisinin and the IS were 95.4 +/- 4.5% and 92.8 +/- 3.9%, respectively. This present method was successfully applied to the characterization of the pharmacokinetic profile of artemisinin in rats after oral administration.

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A detailed analysis of the product ion spectrum generated from the protonated molecule of sildenafil (Viagra(R)) under multiple tandem mass spectrometry (ESI-MS(n)) conditions using an ion-trap mass spectrometer is reported. Molecular composition data of the fragment ions were obtained with the aid of comparisons of the multiple tandem mass spectra of eight sildenafil derivatives in two series, the structures of which are identical except for some substituted alkyl groups. Attempts have been made to provide rational pathways for the formation of the fragment ions from these protonated sildenafil derivatives. The structure-fragmentation relationships will facilitate the characterization of the structures of other sildenafil analogs.

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The unique roles of individual cells may be critical to the physiology of an organism. In such cases, micromethods are essential to elucidating the molecular biology, biochemistry and biophysics of the specialized cells or even subcellular compartments of the important cells. The great proliferation of micromethods testifies to their value and no single review can be comprehensive. This review therefore provides only a generalized overview of one approach, namely dissection that provides a pure sample for subsequent extraction and analysis by microdroplet chemistry. As a means of illustrating the utility of this approach, an application-study of the interaction of cytosolic malate concentration and guard-cell phosphoenolpyruvate carboxylase-is provided.