THERMO-INHIBITION OF SEED GERMINATION AND PRE-GERMINATION SEED VERNALIZATION IN WINTER ANNUAL WEEDS

1.种子萌发的热抑制当种子感觉到温度过高而不能萌发时，它们促进阿坝的合成，维持较高的阿坝含量，从而阻止种子萌发。当温度过高时，种子对阿坝的敏感性增强，阿坝的合成仍保持在较高水平，但对GA_1的含量无明显影响。因此，为了降低内源阿坝含量，使种子萌发免于严重的热抑制，必须将外源GA对阿坝合成的抑制与阿坝催化剂的增强结合起来。这种由阿坝介导的温度感觉机制将在控制冬季一年生杂草的生活史中发挥决定性作用。2.发芽前种子春化兼性冬季一年生植物的种子在秋季和春季都发芽。冬性一年生植物小飞蓬（Conyza canadensis）的土埋种子在冬季低温条件下，春季萌发种子的植株表现出早花性状。这种现象被定义为发芽前种子春化（PGSV）。在103种冬性一年生植物中，有21种表现出种子萌发前春化的特性，未发现低温诱导种子二次休眠的现象。我们的结论是，发芽前的种子春化作用是一个关键的生态因子调节生活史的兼性冬季一年生植物，导致早期开花的春天发芽的植物。使用消减筛选，30个基因被分离出的冷种子的加拿大柑橘。

1.Thermo-inhibition of seed germinationWhen the seeds sense that the temperature is too high to germinate, they enhance ABA biosynthesis and maintain high ABA contents to prevent their germination. If the temperature is much higher, the seeds increase their sensitivities to ABA, maintaining the enhanced ABA biosynthesis, but not affecting the bioactive GA_1 contents. Therefore, for reducing the endogenous ABA contents sufficiently to rescue seed germination from the severe thermoinhibition, the inhibition of ABA synthesis must be combined with the enhancement of ABA catabolism by exogenous GA. This temperature-sensory mechanism mediated by ABA will play a decisive role in the control of life cycles in winter annual weeds.2.Pre-germination seed vernalizationSeeds of facultative winter annuals germinate both in autumn and spring. When soil-buried seeds of a winter annual, Conyza canadensis, had been exposed to low temperatures in winter, plants from spring-germinating seeds showed early flowering traits. This phenomenon was defined as pre-germination seed vernalization (PGSV). Out of 103 winter annuals, 21 species expressed the characteristic of pre-germination seed vernalization, showing no induction of secondary seed dormancy by the chilling. We conclude that pre-germination seed vernalization is a key ecological factor regulating life cycle of facultative winter annuals, resulting in early flowering of the spring-germinated plants. Using subtractive screenings, thirty genes were isolated from the chilled seeds of C.canadensis.