Department of Biology, University of Dayton, Dayton, Ohio 45469.
Plant Physiol. 1973 Feb;51(2):372-7. doi: 10.1104/pp.51.2.372.
Arrhenius plots of translocation velocity as a function of petiole temperature show a marked increase in temperature dependence below 10 C in bean (a chilling-sensitive species) but not in sugar beet (chilling-resistant). The increased temperature dependence below 10 C was not observed for cytoplasmic streaming or oxygen uptake in bean. Bean petioles were served to release pressure in order to determine whether sieve tubes are obstructed in cold-treated petioles. The resulting pressure release caused serious displacement of the crystalline protein bodies in the sieve tubes of petioles at 25 C, but in those locally cooled to 0 C for 30 minutes little displacement occurred, indicating obstruction in the latter. An ultrastructural study of sieve tubes in tissue frozen rapidly in situ and dehydrated by freeze substitution revealed that treatment at 0 C for 30 minutes caused structural alteration and displacement of the cytoplasmic material lining the sieve tube wall resulting in occlusion of sieve plates. The sieve plates of the control petioles at 25 C were generally clear of obstructions. The results indicate that inhibition of translocation by chilling in chilling-sensitive plants results from physical blockage of sieve plates rather than from direct inhibition of a metabolic process which drives translocation.
Arrhenius 图显示，豆科植物（对冷敏感的物种）叶柄温度低于 10°C 时，转运速度对温度的依赖性明显增加，而甜莱（抗冷）则不然。在豆科植物中，细胞质流动或耗氧量对 10°C 以下温度的依赖性增加并没有被观察到。为了确定冷处理叶柄中的筛管是否受阻，对豆科植物的叶柄进行了去压力处理。在 25°C 下，由此产生的压力释放导致筛管中结晶蛋白体严重移位，但在局部冷却至 0°C 并保持 30 分钟的情况下，几乎没有发生位移，表明后者存在阻塞。对原位快速冷冻和冷冻替代脱水组织中的筛管进行超微结构研究表明，在 0°C 下处理 30 分钟会导致筛管壁内细胞质物质的结构改变和移位，从而导致筛板堵塞。25°C 下对照叶柄的筛板通常没有阻塞物。结果表明，冷敏感植物中冷胁迫对转运的抑制是由于筛板的物理阻塞，而不是直接抑制驱动转运的代谢过程。
