PubMed · 5777151
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1969. Cold and colds.. https://pubmed.ncbi.nlm.nih.gov/5777151/
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In contrast to most temperate woody species, apple and pear and some other woody species of the Rosaceae family are insensitive to photoperiod, and no alternative environmental seasonal signal is known to control their dormancy. We studied growth and dormancy induction in micropropagated plants of four apple (Malus pumila Mill.) and one pear (Pyrus communis L.) commercial rootstock cultivars in controlled environments. The results confirm that growth cessation and dormancy induction in apple and pear are not influenced by photoperiod, and demonstrate that low temperature (< 12 degrees C) consistently induces both processes, regardless of photoperiodic conditions. Successive stages of the autumn syndrome (growth cessation, formation of bud scales and winter buds, leaf senescence and abscission, and dormancy induction) occurred in response to low temperature. Long days increased internode length at higher temperatures, but had no significant effect on leaf production in any of the cultivars. Chilling at 6 or 9 degrees C for at least 6 weeks (about 1000 h) was required for dormancy release and growth resumption, whereas treatment at 12 degrees C was marginally effective, even after 14 weeks of exposure. We are thus faced with the paradox that the same low temperature conditions that induce dormancy are also required for dormancy release in these species.
The purpose of this in vitro study was to compare quantitatively the density of standard cold lateral gutta-percha compaction and warm vertical compaction by using the continuous wave of condensation technique. Forty transparent acrylic blocks with 30-degree, curved root canals were instrumented using Gates Glidden burs and Profile 0.06 taper rotary nickel-titanium files in a crown-down manner. The blocks were weighed and randomly assigned to two evenly distributed groups. Group A was obturated with the cold lateral-compaction technique using medium-fine, gutta-percha accessory points until the canal was completely filled. Group B was obturated with the continuous wave of condensation technique until the canal was completely filled. The blocks were weighed again after obturation. Data were analyzed using a two-sample t test at the 5% significance level. Results demonstrated that the continuous wave of condensation technique resulted in a significantly greater density compared with cold lateral compaction. Warm vertical compaction using the continuous wave of condensation technique in acrylic blocks resulted in a greater gutta-percha fill by weight compared with standard cold lateral compaction.
The photosensitized oxidation of 2',3',5'-tris-(O-tert-butyldimethylsilyl)-8-oxo-7,8-dihydroguanosine (8-oxoG) with singlet oxygen was studied by low-temperature NMR. A stable intermediate was characterized at -60 degrees C by (13)C, 2D NMR HMBC spectra, and chemical shifts calculated by hybrid Hartree-Fock density functional theory which agreed with the structure 5-hydroperoxy-8-oxo-7,8-dihydroguanosine. Reduction of this intermediate at low temperature afforded the corresponding alcohol, the long-postulated 5-hydroxy-8-oxo-7,8-dihydroguanosine, the last intermediate in the formation of spiroiminodihydantoin. Upon warming to room temperature, this alcohol rearranges to form the spiroiminodihydantoin in good yield within 2 h.