Department of Crop and Soil Sciences, Washington State University, Pullman, Washington, United States of America, US Department of Agriculture, Agricultural Research Service, Wheat Health, Genetics and Quality Research Unit, Pullman, Washington, United States of America.
The Center for NMR Spectroscopy, Washington State University, Pullman, Washington, United States of America.
PLoS One. 2018 Jun 18;13(6):e0198042. doi: 10.1371/journal.pone.0198042. eCollection 2018.
The ability of winter wheat (Triticum aestivum L.) plants to develop freezing tolerance through cold acclimation is a complex rait that responds to many environmental cues including day length and temperature. A large part of the freezing tolerance is conditioned by the C-repeat binding factor (CBF) gene regulon. We investigated whether the level of freezing tolerance of 12 winter wheat lines varied throughout the day and night in plants grown under a constant low temperature and a 12-hour photoperiod. Freezing tolerance was significantly greater (P<0.0001) when exposure to subfreezing temperatures began at the midpoint of the light period, or the midpoint of the dark period, compared to the end of either period, with an average of 21.3% improvement in survival. Thus, freezing survival was related to the photoperiod, but cycled from low, to high, to low within each 12-hour light period and within each 12-hour dark period, indicating ultradian cyclic variation of freezing tolerance. Quantitative real-time PCR analysis of expression levels of CBF genes 14 and 15 indicated that expression of these two genes also varied cyclically, but essentially 180° out of phase with each other. Proton nuclear magnetic resonance analysis (1H-NMR) showed that the chemical composition of the wheat plants' cellular fluid varied diurnally, with consistent separation of the light and dark phases of growth. A compound identified as glutamine was consistently found in greater concentration in a strongly freezing-tolerant wheat line, compared to moderately and poorly freezing-tolerant lines. The glutamine also varied in ultradian fashion in the freezing-tolerant wheat line, consistent with the ultradian variation in freezing tolerance, but did not vary in the less-tolerant lines. These results suggest at least two distinct signaling pathways, one conditioning freezing tolerance in the light, and one conditioning freezing tolerance in the dark; both are at least partially under the control of the CBF regulon.
冬小麦（Triticum aestivum L.）植株通过冷驯化获得抗冻能力是一种复杂的性状，它对许多环境线索做出反应，包括日照长度和温度。抗冻能力的很大一部分取决于 C 重复结合因子（CBF）基因调控因子。我们研究了在恒定低温和 12 小时光周期下生长的植物中，12 个冬小麦品系的抗冻能力是否在白天和夜间发生变化。与光照期结束时相比，当暴露于亚冷冻温度开始于光照期的中点或黑暗期的中点时，抗冻能力显著更高（P<0.0001），平均存活率提高了 21.3%。因此，抗冻存活率与光周期有关，但在每个 12 小时的光照期和每个 12 小时的黑暗期内，从低到高再到低循环，表明抗冻能力存在超日周期的周期性变化。对 CBF 基因 14 和 15 的表达水平进行定量实时 PCR 分析表明，这两个基因的表达也呈周期性变化，但基本上彼此相差 180°。质子核磁共振分析（1H-NMR）表明，小麦植株细胞液的化学成分随昼夜变化而变化，生长的光照期和黑暗期始终分离。与中度和低度抗冻性的品系相比，在一个具有强抗冻性的小麦品系中，一种鉴定为谷氨酰胺的化合物始终以更高的浓度存在。在抗冻性较强的小麦品系中，谷氨酰胺也呈超日周期变化，与抗冻性的超日周期变化一致，但在抗冻性较弱的品系中没有变化。这些结果表明，至少有两种不同的信号通路，一种在光照下调节抗冻性，一种在黑暗中调节抗冻性；这两种通路至少部分受 CBF 调控因子的控制。
