PubMed · 11843876
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S K Jankelowitz, A S Zagami. 2001. Cold-stimulus headache.. https://doi.org/10.1046/j.1468-2982.2001.00301.x
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Methods to collect, transport, and store samples of snow and ice have been developed that enable detailed observations of these samples with a technique known as low-temperature scanning electron microscopy (LTSEM). This technique increases the resolution and ease with which samples of snow and ice can be observed, studied, and photographed. Samples are easily collected in the field and have been shipped to the electron microscopy laboratory by common air carrier from distances as far as 5,000 miles. Delicate specimens of snow crystals and ice grains survive the shipment procedures and have been stored for as long as 3 years without undergoing any structural changes. The samples are not subjected to the melting or sublimation artifacts. LTSEM allows individual crystals to be observed for several hours with no detectable changes. Furthermore, the instrument permits recording of photographs containing the parallax information necessary for three-dimensional imaging of the true shapes of snowflakes, snow crystals, snow clusters, ice grains, and interspersed air spaces. This study presents detailed descriptions of the procedures that have been used successfully in the field and the laboratory to collect, ship, store, and image snow crystals and ice grains.
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Oxygen evolution is inhibited when leaves of chilling-sensitive plants like cucumber are treated at 0 degrees C in the dark. The activity is restored by moderate illumination at room temperature. We examined the changes in the redox state of the Mn-cluster in cucumber leaves in the processes of dark-chilling inhibition and subsequent light-induced reactivation by means of thermoluminescence (TL). A TL B-band arising from S(2)Q(B)(-) charge recombination in PSII was observed upon single-flash illumination of untreated leaves, whereas four flashes were required to yield the B-band after dark-chilling treatment for 24 h. This three-step delay indicates that over-reduced states of the Mn-cluster such as the S(-2) state were formed during the treatment. Fitting analysis of the flash-number dependence of the TL intensities showed that the Mn-cluster was more reduced with a longer period of the treatment and that S(-3) was the lowest S-state detectable in the dark-chilled leaves. Measurements of the Mn content by atomic absorption spectroscopy showed that Mn atoms were gradually released from PSII during the dark-chilling treatment but re-bound to PSII by illumination at 30 degrees C. Thus, dark-chilling inhibition of oxygen evolution can be ascribed to the disintegration of the Mn-cluster due to its over-reduction. The observation of the S(-3) state in the present in vivo system strongly suggests that S(-3), which has been observed only by addition of exogenous reductants into in vitro preparations, is indeed a redox intermediate of the Mn-cluster in the processes of its disintegration and photoactivation.