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There has been very little research on the response to SO2 of plants which grow in Mediterranean climates; the vast majority of research has been on plants grown in cooler, moister climates. Vegetation grown in a Mediterranean climate, however, possesses certain biological features that enable success in such a climate; evidence presented suggests that the vegetations' response to SO2 may be different from that of other vegetation types. More particularly, as a most distinctive feature common to plants grown in Mediterranean climates is their drought stress resistance, it is possible that common mechanisms underlie the resistance of both drought stress and SO2 stress; this is explored at a theoretical level. As a consequence of biological differences, extrapolation from studies on plant species successful in cool, moist climates may be inappropriate in predicting the response to SO2 of Mediterranean climate vegetation; this has important implications for policy formulation and the development of Air Quality Standards.

This research investigated the response to SO2 exposure of three sclerophyllous tree species of the genus Eucalyptus, a genus well known for its adaptation to water-limited environments, allowing prediction of growth response across a range of SO2 concentrations. In addition, the response of the three Eucalyptus species was compared with that of another tree genus (Pinus) exposed to SO2 under identical conditions, thus providing the opportunity to explore response differences attributable to biological differences. Ten open-top chambers were used to expose 1-year-old saplings to less than 5, 50, 122, 175 and 332 nl 1−1 SO2 for 4 h day−1, 7 days a week, for 107 days. Response variables measured included various growth parameters and sulphur accumulation. Significant reductions in growth and increases in sulphur accumulation occurred in the eucalypt species, but the Pinus studied showed no significant response to the SO2 concentrations used. Despite its sclerophylly, the genus Eucalyptus is less resistant to SO2 than many other tree species.

The TMS-mapped representations of two intrinsic hand muscles, abductor pollicis brevis (APB) and abductor digiti minimi (ADM), were quantified using a transcranial magnetic stimulation (TMS) mapping technique in 10 right handed and 6 left handed subjects. A 50 mm diameter figure eight coil was used. Stimulus sites were located using a latitude/longitude based coordinate system, stimulus intensity was threshold-adjusted and stimuli were applied during controlled low-level (10%) voluntary contraction of the target muscles. Maps of the corticomotor representation were generated by fitting a continuously defined three dimensional function to the data obtained from stimulation at specific scalp sites, and projecting this function onto a two dimensional surface using a radial projection. It was found that the mapped representations of APB and ADM were large and overlapping but that there was a statistically significant separation of the two areas, the APB area being more laterally placed than the ADM area. The TMS-mapped representations of the two muscles showed no significant interhemispheric differences and were similar in left and right handed subjects. Rotation of the magnetic coil through 90 degrees resulted in medial shift and elongation of the TMS-mapped representations but there was no change in the relative positions of the two areas. The TMS-mapped representations were found to be very reproducible when mapping was repeated after intervals of up to 181 days. The present technique of TMS mapping allows the representation of individual hand muscles in the primary motor cortex to be reliably and reproducibly mapped and should prove useful for further studies of the physiology and pathophysiology of the motor cortex in man.

Transcranial magnetic stimulation (TMS) of the motor cortex during tonic muscle contraction produces a motor evoked potential followed by a silent period in the electromyogram. We sought to characterise the TMS induced silent period and to compare it to the silent period induced by supramaximal peripheral nerve stimulation. TMS was delivered to the motor cortex using a 9 cm diameter circular coil and the surface electromyogram was recorded from the contralateral abductor pollicis brevis muscle in six normal subjects. Increasing TMS stimulus intensity from 10 to 50% above threshold resulted in an increase in the duration of the silent period from a mean of 50 ms to 185 ms. Increasing the level of tonic muscle contraction from 5% of maximum to maximum resulted in a decrease in silent period duration from a mean of 155 ms to 133 ms. In contrast, the duration of the silent period following supramaximal median nerve stimulation showed greater shortening under similar conditions, from a mean of 160 ms at 5% of maximum contraction to 99 ms at 75% of maximum contraction. The TMS induced silent period was present during a TMS induced increase in the reaction time for a ballistic movement, the onset of movement being delayed until the end of the silent period. Peripheral nerve stimulation did not produce a delay in movement onset. The present findings favour a cortical origin for the TMS induced silent period, probably on the basis of intracortical inhibition, rather than peripheral inhibition of spinal motoneurones which is considered to be the basis for the silent period following peripheral nerve stimulation.

Ten open-top chambers were used to obtaine SO2 concentration-response relationships for growth in subterranean clover cv. ‘Trikkala’, and to study the associated sulphur accumulation. Four-week-old seedlings were exposed to 4, 41, 120, 255 or 515 nl l−1 of SO2 for 77 days, 4 h day−1. Response variables measured included leaf dry weight, stem weight, runner length, leaf number, average leaf weight, leaf: stem ratio and leaf sulphur concentration. Significant reductions in growth and changes in assimilate distribution occurred at 120 nl l−1 and higher concentrations; leaf sulphur concentration increased by ∼70 and 100% at 41 and 120 nl l−1, respectively.