Department of Biology, University of Waterloo, Waterloo, Ontario, Canada.
Plant Physiol. 1977 May;59(5):803-7. doi: 10.1104/pp.59.5.803.
Lipid transition temperatures for rough and smooth microsomal membranes isolated from bean (Phaseolus vulgaris) cotyledon tissue at various stages of germination were determined by wide angle x-ray diffraction. The transition temperatures were established by recording diffraction patterns through a temperature series until a sharp x-ray reflection centered at a Bragg spacing of 4.15 A and denoting the presence of crystalline lipid was discernible. For rough and smooth microsomes from 2-day-old tissue, the transitions occurred at 0 C and 3 C, respectively, indicating that at this early stage in the germination sequence the membrane lipid is entirely liquid-crystalline at physiological temperature. By the 4th day of germination, the transition temperatures had increased to 32 C for smooth microsomes and 35 C for rough microsomes, indicating that at 29 C, which was the growth temperature, portions of the membrane lipid were crystalline. During the later stages of germination, the transition temperature for smooth microsomes continued to rise through 44 C at day 7 to 56 C at day 9, by which time the cotyledons were extensively senescent and beginning to abscise. There was also a dramatic increase in the proportion of membrane lipid in the crystalline phase at 29 C. By contrast, the rough microsomes showed little change in transition temperature and only a slight increase in the proportion of crystalline lipid during this late period in germination. The data indicate that substantial amounts of the lipid is senescing membranes are crystalline even at physiological temperature. Moreover, there is a temporal correlation between the appearance of this crystallinity and loss of membrane function, suggesting that the two may be causally related.
利用广角 X 射线衍射技术，测定了不同发芽阶段菜豆子叶组织中粗糙型和光滑型微粒体膜的脂类转变温度。通过在一系列温度下记录衍射图谱，直到能辨认出一个位于布拉格间距 4.15Å 处的尖锐的 X 射线反射，确定了转变温度，该反射表示结晶脂质的存在。对于来自 2 日龄组织的粗糙型和光滑型微粒体，转变分别发生在 0°C 和 3°C，表明在发芽序列的这个早期阶段，膜脂质在生理温度下完全呈液晶态。到第 4 天发芽时，光滑型微粒体的转变温度上升到 32°C，粗糙型微粒体的转变温度上升到 35°C，表明在 29°C（生长温度）时，部分膜脂质呈结晶态。在发芽的后期阶段，光滑型微粒体的转变温度继续上升，在第 7 天达到 44°C，在第 9 天达到 56°C，此时子叶已严重衰老并开始脱落。在 29°C 时，膜脂质处于结晶相的比例也显著增加。相比之下，在这个后期的发芽阶段，粗糙型微粒体的转变温度变化不大，结晶态脂质的比例也只是略有增加。这些数据表明，大量的脂类是衰老的膜呈结晶态，即使在生理温度下也是如此。此外，这种结晶度的出现与膜功能的丧失之间存在时间上的相关性，表明两者可能存在因果关系。
