Sommerville Karen D, Hill Lisa, Offord Catherine A, Walters Christina
Australian PlantBank, Botanic Gardens of Sydney, Locked Bag 6002, Mount Annan NSW 2567 Australia.
National Laboratory for Genetic Resources Preservation, United States Department of Agriculture, Fort Collins, Colorado USA.
Ann Bot. 2025 Aug 6. doi: 10.1093/aob/mcaf181.
Recent studies on desiccation-tolerant Australian rainforest seeds demonstrated that some were short-lived in storage. We sought to understand structural changes of storage lipids that might occur during storage at -20°C that could contribute to a short lifespan.
We used differential scanning calorimetry (DSC) to examine exothermic and endothermic transitions during freezing and thawing in dry seed samples of 23 species. Seed samples and extracted triacylglycerols (TAGs) were cooled to -150°C and rewarmed to 50°C at 10°C min-1; slower and faster rates of cooling/warming were used for a subset of species to examine lipid crystallisation and melting kinetics. Thermograms were analysed for temperature and enthalpy of observed peaks, and these were compared with expected values to detect anomalies. Extracted lipids were further analysed using gas chromatography (GC) to characterize fatty acid composition. The thermal profiles of six species were used to design experiments comparing the impact of storage at -20°C to storage at temperatures outside the range of thermal transitions.
Thermal activity was detected in 22 samples within the narrow temperature range of -30 and -10°C; activity at broader temperature ranges was also detected depending on species, cooling protocol and fatty acid composition. A profound interaction between DSC parameters and time at low temperature, as well as fatty acid composition, suggested that TAG crystallisation rates contribute to low temperature sensitivity. We confirmed that damage from TAG crystallisation could be avoided by storing seeds at temperatures above TAG crystallisation and melting events; storage at cryogenic temperatures improved survival over storage at -20°C but requires further optimisation to maintain pre-storage germination potential.
We conclude that the crystallisation and melting of TAGs during storage may negatively impact seed longevity. Seed thermal profiles and rate of TAG crystallisation may serve as predictive tools for sensitivity to storage at -20°C.
近期对澳大利亚耐旱雨林种子的研究表明，有些种子在储存过程中寿命较短。我们试图了解在-20°C储存期间可能发生的储存脂质结构变化，这些变化可能导致种子寿命缩短。
我们使用差示扫描量热法（DSC）来检测23个物种干燥种子样品在冷冻和解冻过程中的放热和吸热转变。将种子样品和提取的三酰甘油（TAGs）以10°C/min的速率冷却至-150°C，然后再升温至50°C；对一部分物种采用较慢和较快的冷却/升温速率来研究脂质结晶和熔化动力学。分析热谱图中观察到的峰的温度和焓，并将这些值与预期值进行比较以检测异常。使用气相色谱法（GC）进一步分析提取的脂质，以表征脂肪酸组成。利用六个物种的热谱图设计实验，比较-20°C储存与热转变范围之外温度储存的影响。
在-30°C至-10°C 的狭窄温度范围内，在22个样品中检测到热活性；根据物种、冷却方案和脂肪酸组成，在更宽的温度范围内也检测到了热活性。DSC参数与低温下的时间以及脂肪酸组成之间存在显著相互作用，这表明TAG结晶速率会影响低温敏感性。我们证实，将种子储存在高于TAG结晶和熔化温度的条件下，可以避免TAG结晶造成的损害；在低温下储存比在-20°C储存能提高种子存活率，但需要进一步优化以维持储存前的发芽潜力。
我们得出结论，储存期间TAGs的结晶和熔化可能会对种子寿命产生负面影响。种子热谱图和TAG结晶速率可作为预测种子对-20°C储存敏感性的工具。
