Formerly of the Rubber Research Institute of Malaysia.
Yale J Biol Med. 2019 Jun 27;92(2):213-223. eCollection 2019 Jun.
The widely held explanation for photoperiod-controlled flowering in long-day plants is largely embodied in the External Coincidence Hypothesis which posits that flowering is induced when activity of a rhythmic gene that regulates it (a putative "flowering gene") occurs in the presence of light. Nevertheless, re-examination of the flowering data from non 24-hour cycles of Roden suggests that External Coincidence is not tenable if the circadian rhythm of the "flowering gene" were entrained to sunrise as commonly accepted. On the other hand, the hypothesis is supported if circadian cycling of the gene conforms to a solar rhythm, and its entrainment is to midnight on the solar clock. Data available point to flowering being induced by the gene which peaks in its expression between 16 to 19 h after midnight. In the normal 24 h cycle, that would be between 4 p.m. and 7 p.m., regardless of the photoperiod. Such timing of the "flowering gene" expression allows for variable coincidence between gene activity and light, depending on the photoperiod and cycle period. A correlation is found between earliness of flowering and the degree of coincidence of "flowering gene" expression with light (r = 0.88, p<0.01).
长日照植物的光周期控制开花的广泛解释主要体现在外部巧合假说中，该假说假设当调节它的节律基因（假定的“开花基因”）的活性在光存在下发生时，就会诱导开花。然而，对 Roden 的非 24 小时周期的开花数据的重新检查表明，如果如普遍接受的那样将“开花基因”的昼夜节律与日出同步，那么外部巧合就不可行。另一方面，如果基因的昼夜循环符合太阳节律，并且其同步是在太阳钟的午夜，那么该假说就得到支持。现有的数据表明，开花是由在午夜后 16 到 19 小时之间表达峰值的基因诱导的。在正常的 24 小时周期中，无论光周期如何，这都在下午 4 点到 7 点之间。这种“开花基因”表达的时间安排允许根据光周期和周期长度在基因活性和光之间进行可变的巧合。开花的早期与“开花基因”表达与光的巧合程度之间存在相关性（r = 0.88，p<0.01）。
