McLetchie D Nicholas, Stark Lloyd R
Department of Biology, 101 Morgan Building, University of Kentucky, Lexington, KY 40506-0225, USA.
Ann Bot. 2006 Apr;97(4):505-11. doi: 10.1093/aob/mcl011. Epub 2006 Feb 14.
Actively growing post-embryonic sporophytes of desert mosses are restricted to the cooler, wetter months. However, most desert mosses have perennial gametophytes. It is hypothesized that these life history patterns are due in part to a reduced thermotolerance for sporophytes relative to gametophytes.
Gametophytes with attached embryonic sporophytes of Microbryum starckeanum were exposed whilst desiccated to thermal episodes of 35 degrees C (1 hr), 55 degrees C (1 hr), 75 degrees C (1 hr) and 75 degrees C (3 hr), then moistened and allowed to recover for 35 d in a growth chamber.
All of the gametophytes survived the thermal exposures and produced protonemata, with the majority also producing shoot buds. Symptoms of gametophytic stress (leaf burning and discoloration of entire shoots) were present in lower frequencies in the 55 degrees C exposure. Sporophyte resumption of growth and maturation to meiosis were significantly negatively affected by thermal treatment. Not a single sporophyte exposed to the two higher thermal treatments (75 degrees C for 1 h and 75 degrees C for 3 h) survived to meiosis, and those sporophytes exposed to 75 degrees C that survived to the post-embryonic phenophase took significantly longer to reach this phase. Furthermore, among the thermal treatments where some capsules reached maturity (35 degrees C and 55 degrees C), maternal shoots that produced a meiotic capsule took longer to regenerate through protonemata than maternal shoots aborting their sporophyte, suggestive of a resource trade-off between generations.
Either (1) the inherent sporophyte thermotolerance is quite low even in this desert moss, and/or (2) a gametophytic thermal stress response controls sporophyte viability.
沙漠苔藓的胚后孢子体在生长活跃期仅限于较凉爽、湿润的月份。然而，大多数沙漠苔藓具有多年生配子体。据推测，这些生活史模式部分归因于孢子体相对于配子体耐热性降低。
将附着有星状小曲尾藓胚胎孢子体的配子体在干燥状态下暴露于35摄氏度（1小时）、55摄氏度（1小时）、75摄氏度（1小时）和75摄氏度（3小时）的热暴露中，然后湿润并在生长室中恢复35天。
所有配子体在热暴露后存活并产生原丝体，大多数还产生了芽。在55摄氏度暴露中，配子体应激症状（叶片灼伤和整个枝条变色）出现的频率较低。热处理对孢子体恢复生长和成熟至减数分裂有显著负面影响。暴露于两种较高热处理（75摄氏度1小时和75摄氏度3小时）的孢子体无一存活至减数分裂，而暴露于75摄氏度并存活至胚后物候期的孢子体到达该阶段所需时间明显更长。此外，在一些蒴果达到成熟的热处理（35摄氏度和55摄氏度）中，产生减数分裂蒴果的母枝通过原丝体再生所需时间比其孢子体败育的母枝更长，这表明两代之间存在资源权衡。
要么（1）即使在这种沙漠苔藓中，孢子体固有的耐热性也相当低，和/或（2）配子体热应激反应控制着孢子体的活力。
