Department of Biology, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801.
Appl Environ Microbiol. 1988 Jul;54(7):1678-81. doi: 10.1128/aem.54.7.1678-1681.1988.
A newly discovered form of biological ice nucleus associated with lichens is described. Ice nucleation spectra of a variety of lichens from the southwestern United States were measured by the drop-freezing method. Several epilithic lichen samples of the genera Rhizoplaca, Xanthoparmelia, and Xanthoria had nuclei active at temperatures as warm as -2.3 degrees C and had densities of 2.3 x 10 to more than 1 x 10 nuclei g at -5 degrees C (2 to 4 orders of magnitude higher than any plants infected with ice nucleation-active bacteria). Most lichens tested had nucleation activity above -8 degrees C. Lichen substrates (rocks, plants, and soil) showed negligible activity above -8 degrees C. Ice nucleation-active bacteria were not isolated from the lichens, and activity was not destroyed by heat (70 degrees C) or sonication, indicating that lichen-associated ice nuclei are nonbacterial in origin and differ chemically from previously described biological ice nuclei. An axenic culture of the lichen fungus Rhizoplaca chrysoleuca showed detectable ice nucleation activity at -1.9 degrees C and an ice nucleation density of 4.5 x 10 nuclei g at -5 degrees C. It is hypothesized that these lichens, which are both frost tolerant and dependent on atmospheric moisture, derive benefit in the form of increased moisture deposition as a result of ice nucleation.
一种与地衣有关的新发现的生物冰核形式被描述。采用滴冻法测量了来自美国西南部的多种地衣的冰核谱。几种附生地衣样本，如 Rhizoplaca、Xanthoparmelia 和 Xanthoria 属，其冰核活性温度低至-2.3°C，在-5°C 时的密度为 2.3 x 10 到 1 x 10 个核 g-1（比任何感染有冰核活性细菌的植物高 2 到 4 个数量级）。大多数测试的地衣在-8°C 以上都有核活性。地衣基质（岩石、植物和土壤）在-8°C 以上几乎没有活性。从地衣中未分离到冰核活性细菌，活性也不会被热（70°C）或超声破坏，表明地衣相关的冰核是非细菌来源的，并且在化学上与先前描述的生物冰核不同。地衣真菌 Rhizoplaca chrysoleuca 的无菌培养物在-1.9°C 时表现出可检测的冰核活性，在-5°C 时的冰核密度为 4.5 x 10 个核 g-1。据推测，这些地衣既具有抗霜性，又依赖大气水分，由于冰核作用，它们会获得更多的水分沉积，从而受益。
