THE MECHANISM OF LIFE CYCLE REGULATION IN WINTER ANNUAL PLANTS VIA TEMPERATURE RESPONSEVENSS OF SEEDS

冬季一年生植物已经适应了它们的生活周期，以适应季节变化的温度。为了了解它们是如何进化生活史的，我们研究了控制萌发时间的生态生理机制，并提出了如下模型：冬季一年生植物作为土壤埋藏的种子在夏季逃逸生长。种子的萌发在夏季受到抑制，因为萌发的最高温度略低于土壤中的最低温度。种子在秋季萌发，此时萌发温度范围与土壤中的温度范围重叠。也就是说，埋藏的种子通过感知高温来检测合适的发芽时间，当种子感觉到温度过高而无法萌发时，它们会促进ABA的生物合成，并保持较高的ABA水平，以阻止其萌发。内源GA水平较低，但对ABA降解有积极作用。通过抑制ABA的合成，克服了这种情况，即在较低的过适温度下热抑制。温度越高，种子对ABA的敏感性越高，对ABA的合成也越敏感，但对GA水平的影响不大。因此，为了恢复种子在超适温度下的萌发，抑制ABA的合成和促进ABA的降解是必要的。

Winter annual plants have adapted their life cycles to seasonally changing temperature. To know how they have evolved the life cycles we investigated the eco-physiological mechanisms controlling the germination timing, and proposed a model as follows.Winter annuals escape their growth in summer as soil-buried seeds. Germination of the seeds is inhibited during summer because the maximum temperatures for germination were just below the minimum temperatures in the soil. The seeds germinate in autumn when the temperature range for germination and those in the soil overlap. That is, the buried seeds detect appropriate germination timing by sensing the high temperatures.When seeds sense the temperature is too high to germinate, they enhance ABA biosynthesis and maintain a high ABA level to prevent their germination. Endogenous GA level is low, but it will play a positive role on ABA degradation. This situation, thermo-inhibition at the lower supraoptimal temperature, is overcome by inhibition of ABA synthesis. If the temperature is much higher, the seeds raise their sensitivities to ABA in addition to the enhanced ABA synthesis, but not affect the GA level. Therefore, for restoring the seed germination at the supraoptimal temperature, a combined action of the inhibition of ABA synthesis and the enhancement of ABA degradation is necessary.