鸟类不看日历，却能赶在春昼变长时准时启动繁殖——鹌鹑的身体如何把“白昼变长”翻译成性腺发育的命令？
Birds consult no calendar, yet they launch breeding right as spring days lengthen — how does a quail's body translate 'longer daylight' into the command for gonadal growth?
感光并不只靠眼睛，光信息还能直抵下丘脑深部的脑内光感受器。一次长日照后数小时内，垂体结节部便分泌促甲状腺激素，使基底下丘脑的DIO2上调、DIO3下调，把局部甲状腺素T4转成高活性T3；T3继而激活下丘脑—垂体—性腺轴，推动性腺复苏。这条级联就是鸟类丈量日长的分子季节钟。
Light sensing is not confined to the eyes: photons also reach deep-brain photoreceptors near the hypothalamus. Within hours of a single long day, the pituitary pars tuberalis secretes thyroid-stimulating hormone, raising DIO2 and lowering DIO3 in the mediobasal hypothalamus, which converts local thyroxine (T4) into potent triiodothyronine (T3). T3 then activates the hypothalamic–pituitary–gonadal axis and revives the gonads — a molecular seasonal clock that measures day length.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 来源待核验 · Source pending review
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出处备注：著录含书名，但缺版次 / 出版社 / 年份中的一部分，需编辑补全后才能做独立比对。
Nakao 等：《光诱导的T4向T3激素转换调控鸟类性腺的光周期反应》，Nature，2008
Nakao et al., 'Light-induced hormone conversion of T4 to T3 regulates photoperiodic response of gonads in birds', Nature, 2008
#光周期 #季节生物学 #甲状腺激素
为什么许多植物只在特定日长下开花？请以拟南芥为例，说明叶片如何测量光周期并把“开花信号”送到茎顶端。
Why do many plants flower only under a specific day length? Using Arabidopsis as an example, describe how the leaf measures photoperiod and sends the flowering signal to the shoot apex.
叶片的光受体与内生昼夜钟共同测量夜长：长日照下黄昏仍有光照，使CO蛋白稳定累积，进而驱动叶片中FT基因转录；FT蛋白即“成花素”，经韧皮部长途运输到茎顶端分生组织，与FD协作开启花的发育程序，诱发花芽分化。短日植物逻辑相反：长日照反而促使其开花抑制物积累。该机制让繁殖对准气候适宜的季节。
Photoreceptors and the internal clock in the leaf gauge night length. Under long days, light still falling at dusk stabilizes the CONSTANS protein, which turns on FT transcription in leaves. The FT protein—florigen—travels through the phloem to the shoot apical meristem, partners with FD, and launches the floral developmental program. Short-day plants invert this logic: long days favor accumulation of their flowering inhibitors. Day-length measurement thereby times reproduction to favorable seasons.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-02
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Corbesier 等：《FT蛋白的移动促进拟南芥成花诱导中的长距离信号传递》，Science，2007
Corbesier et al., 'FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis', Science, 2007
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1126/science.1141752：FT Protein Movement
#光周期 #开花调控 #成花素
在短日照植物（如苍耳）的长夜中间闪一次红光会阻止其开花，紧接着再照一次远红光又能让开花恢复。这揭示了植物怎样感知季节？
In short-day plants such as cocklebur, a flash of red light in the middle of a long night blocks flowering, yet a following far-red flash restores it. What does this reveal about how plants sense the season?
短日植物真正测量的是连续黑暗的时长。叶片中的光敏色素经红光照射转为生理活跃的Pfr型，午夜的红光闪光使Pfr回升，相当于把一个长夜切成两个短夜，成花诱导被中断；随后的远红光把色素推回Pr型，效应随之逆转。这种红-远红可逆性证明感受昼夜的是光敏色素，且开花由夜长而非昼长决定。
Short-day plants measure the length of uninterrupted darkness. Leaf phytochrome shifts into its active Pfr form under red light; a midnight red flash resets Pfr, effectively splitting the long night into two short ones and interrupting the flowering signal. A subsequent far-red flash pushes the pigment back to the Pr form and reverses the effect. This red/far-red reversibility identifies phytochrome as the sensor and shows that flowering depends on night length, not daylight hours.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-02
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Borthwick、Hendricks 与 Parker：《控制成花诱导的反应》，PNAS，1952
Borthwick, Hendricks & Parker, 'The reaction controlling floral initiation', PNAS 38:929-934 (1952)
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1073/pnas.38.11.929：The Reaction Controll
#光周期 #临界夜长 #光敏色素