H Lochmann | PubMed Health

PubMed2001

Determination of tobacco alkaloids in single plant cells by capillary electrophoresis.

A new capillary electrophoresis system with direct UV detection for the analysis of the tobacco alkaloids nicotine, nornicotine and anabasine in plant microsamples was developed. An electrolyte containing a high concentration of citric acid to provide good buffer capacity at pH 3.6 was found to be most suitable in terms of sensitivity and separation efficiency. At this low pH the tobacco alkaloids are present in cationic form, showing high mobility and increased UV absorption. This system was used for the analysis of nicotine in single epidermal leaf cells of tobacco plants. Only vacuolar concentrations of nicotine were determined, as the vacuole occupies >95% of the entire volume in epidermal cells. The procedure of sample acquisition and preparation for nicotine analysis of vacuolar samples in the pl range is shown. The results indicate a gradient of nicotine from the leaf base to the tip with higher concentrations present in the cells at the tip. Compared to simultaneously measured bulk leaf samples containing all types of cells, tissues and compartments, the concentrations in epidermal cells are much higher. As nicotine is the major defence substance against insects in tobacco and the epidermis is the most exposed leaf tissue this result is physiologically plausible.

Electrophoresis, Capillary↗

PubMedDate not supplied

Dual response audiometry: a time-saving technique for enhanced objective auditory assessment.

The effectiveness of objective audiometric assessment can be improved by simultaneously recording transient evoked otoacoustic emissions (TEOAE) and auditory brainstem responses (ABR). Using a stimulation paradigm based on sequences of linearly balanced click stimuli (as described by Kemp et al.) acoustical and electrical responses of the auditory system can be obtained in one single run (dual response audiometry, DRA). The click stimuli are presented via an ear canal probe containing a speaker and a miniature microphone. EEG activity is recorded from surface electrodes fixed at the vertex and the mastoid ipsilateral to stimulus presentation. Microphone output and voltage difference between electrodes are fed into a dual-channel data acquisition system, where they are separately amplified and filtered into appropriate frequency ranges. After each stimulus, sweeps of 256 samples within a time window of 17 ms are taken of both signals. They are subject to artefact rejection and averaging of amplitude and polarity. The electrical responses to low and high level clicks within one stimulus sequence are processed separately, whereas the acoustical responses are summated across levels in order to eliminate stimulus-related contamination. As the result of one single run, ABR at two levels and non-linear TEOAEs are obtained within approximately 1 min. The signal quality is estimated by correlation analysis and binomial statistics. Among various features of DRA, the most important advantage is the improvement of the success rate. The influence of perturbations is limited since muscle artefacts due to motor activity affect only the ABR, whereas noise contamination affects only the TEOAE. The accuracy of threshold determination is better than with conventional ABR since the stimulus level is measured in situ. One DRA examination provides complete information about the functional integrity of the cochlea and neural pathways without additional time. It appears ideal for the application as a second stage infant screen.

Acoustic Stimulation↗