Loik Michael E, Nobel Park S
Department of Biology, University of California, 90024, Los Angeles, CA, USA.
Laboratory of Biomedical and Environmental Sciences, University of California, 90024, Los Angeles, CA, USA.
Oecologia. 1991 Nov;88(3):340-346. doi: 10.1007/BF00317576.
Thickness, relative water content (RWC), osmotic pressure, water potential isotherms, and mucopolysaccharide content were measured for the photosynthetic chlorenchyma and the water-storage parenchyma of the winter hardy cactus, Opuntia humifusa, after shifting from day/night air temperatures of 25° C/15° C to 5° C/-5° C. After 14 d at 5° C/-5° C, the average fraction of water contained in the symplast decreased from 0.92 to 0.78, the water potential of saturated (fully hydrated) tissue was essentially unchanged, but the osmotic pressure of saturated tissue decreased (by 0.15 MPa for the chlorenchyma and 0.12 MPa for the water-storage parenchyma). After 7 weeks at 5° C/-5° C, tissue thickness was reduced by 61% for the chlorenchyma and 65% for the water-storage parenchyma, and the RWC decreased by 42% and 68%, respectively; these changes contributed to an osmotic pressure increase of 0.55 MPa for the chlorenchyma and 0.34 MPa for the water-storage parenchyma. During the 7 week acclimation to low temperature, mucopolysaccharide increased by 114% for the chlorenchyma and by 89% for the water-storage parenchyma. The water potential of the extracted mucopolysaccharide was relatively constant for an RWC between 1.00 and 0.30, decreasing abruptly below 0.30. Changes in water relations parameters and in mucopolysaccharide content during low-temperature acclimation may reduce water efflux from the cells, and thus reduce damage due to rapid dehydration during extracellular freezing.
在将耐寒仙人掌平卧仙人掌从昼夜气温25℃/15℃转移至5℃/-5℃后，对其光合薄壁组织和储水薄壁组织的厚度、相对含水量（RWC）、渗透压、水势等温线以及粘多糖含量进行了测定。在5℃/-5℃下放置14天后，共质体中所含水分的平均比例从0.92降至0.78，饱和（完全水合）组织的水势基本未变，但饱和组织的渗透压降低（光合薄壁组织降低0.15 MPa，储水薄壁组织降低0.12 MPa）。在5℃/-5℃下放置7周后，光合薄壁组织的厚度减少了61%，储水薄壁组织的厚度减少了65%，相对含水量分别降低了42%和68%；这些变化导致光合薄壁组织的渗透压增加了0.55 MPa，储水薄壁组织的渗透压增加了0.34 MPa。在7周的低温驯化过程中，光合薄壁组织的粘多糖增加了114%，储水薄壁组织的粘多糖增加了89%。对于相对含水量在1.00至0.30之间的情况，提取的粘多糖的水势相对恒定，在低于0.30时突然下降。低温驯化过程中水分关系参数和粘多糖含量的变化可能会减少细胞中的水分外流，从而减少细胞外结冰期间快速脱水造成的损伤。
