第二节 光周期现象

1、第二节 光周期现象 photoperiodism,Flower clock Swedish botanist Carl von Linn observed that flowers open and close at certain times of day. In 1745 he proposed a flower clock to complement the then used sundials. It would indicate the time with an accuracy of half an hour, even when sky is overcast. This dia

2、l was painted by Ursula Schleicher-Benz in 1948.,光周期（photoperiod）,光周期现象 Photoperiodism,MELATONIN: A POTENTIAL NIGHT-SIGNAL,5-methoxy N-acetyltryptamine,Tuberization,Bolting,Flowering,植物对光周期的反应,GarnerandAllard (1920),MARYLAND MAMMOTH locus is a recessive gene in N. tabacum that confers short-day beha

3、vior (Allard, 1919; Lang, 1948).,In 1920, Wightman Wells Garner and Henry Ardell Allard were working at the USDA, in Beltsville on tobacco Nicotiana, which normally flowers in the summer. They also noticed that soy beans sown at different times in the greenhouse all flowered at the same time, regard

4、less of the date of sowing. Attempting to breed tobacco, they were working with a mutant named Maryland Mammoth, which did not flower in the summer, but did flower in the winter. Plants grew to 12 or 15 feet in height before the plants flowered. One of their goals was to pollinate the normal tobacco

5、 using pollen from the Maryland Mammoth, but the time interval of flowering between each plant was too long to allow pollination. They therefore set out to attempt to force the Maryland Mammoth to flower during the summer at the same time as the normal tobacco. Maryland Mammoth tobacco requires a da

6、ylength of 12 hour or less in order to flower. The latitude of the U.S.D.A. in Maryland is approximately 40o N. Tobacco seeds are normally sown in the greenhouse in Feb and March, and the seedlings are planted out in the field during April and May, when the temperature is milder. When planted in the

7、 field the daylength is approximately 14 hr. This increases to 15 hr and then on June 21, the daylengths begin to decrease during the summer and fall, finally reaching a 12 hr daylength by September 21, when flowering is initiated. Following floral initiation, a number of weeks are necessary for flo

8、ral development to occur. After keeping the plants in a greenhouse, and adjusting temperatures unsuccessfully, they formed a hypothesis that stated that it was the length of day which controlled flowering. It was difficult to understand that flowering was actually promoted by giving less light, a co

9、ndition which in general prevented flowering. They built a light-tight tent around the Maryland Mammoth, which they put up each day at 5:00 pm and took down at 9:00 am each morning, giving only an 8-hour daylength. It workedand the Maryland Mammoth tobacco was forced into flowering. This work laid t

10、he foundation of an enormous amount of research dealing with the Photoperiodic Responses of Plants. Thousands of papers have been published dealing with Photoperiodism. But in all, we have no sweeping generalities. Each species, and even varieties, seems to have its own features of response.,长日植物（lo

11、ng-day plant，LDP）,指在24小时昼夜周期中，日照长度必须长于一定时数，才能成花的植物。 延长光照可促进和提早开花；相反，如延长黑暗则推迟开花或不能成花。 属于长日植物的有：小麦、大麦、黑麦、油菜、菠菜、萝卜、白菜、甘蓝、芹菜、甜菜、胡萝卜、金光菊、山茶、杜鹃、桂花、天仙子等。 如典型的长日植物天仙子必须满足一定天数的8.511.5小时日照才能开花，如果日照长度短于8.5或11.5小时就不能开花。,Spinach long day plant MC,Long Day Plants,Spinach,Lettuce,Long Day Plants,指在24小时昼夜周期中，日照长度短于

12、一定时数才能成花的植物。 对这些植物适当延长黑暗或缩短光照可促进和提早开花，如延长日照则推迟开花或不能成花。 属于短日植物的有：水稻、大豆、高梁、苍耳、紫苏、大麻、黄麻、草莓、烟草、菊花、秋海棠、腊梅、日本牵牛等。 如菊花须满足少于10小时的日照才能开花。,短日植物（short-day plant，SDP）,Short Day Chrysanthemum MC 菊花,Poinsettia short day MC 一品红,Short Day Plants,日中性植物（day-neutral plant，缩写为DNP）这类植物的成花对日照长度不敏感，在任何长度的日照下均能开花。如黄瓜、茄子、番茄

13、、辣椒、菜豆、棉花、君子兰、向日葵、蒲公英等。,Day Neutral Buckwheat MC 普通荞麦,Day Neutral Plants,中日照植物（intermediate-daylength plant）只有在某一定中等长度的日照条件下才能开花，而在较长或较短日照下均保持营养生长状态的植物，如甘蔗要求11.512.5小时日照。 长短日植物（long-short day plant）这类植物要求先长日后短日的双重日照条件，如大叶落地生根、芦荟、夜香树等。 短长日植物（short-long day plant）这类植物要求先短日后长日的双重日照条件，如风铃草、鸭茅、瓦松、白三叶草等。

14、两极光周期植物（amphophotoperiodism plant）与中日照植物相反，这类植物在中等日照条件下保持营养生长状态，而在较长或较短日照下才开花，如狗尾草等。,几个问题,临界日长要求的相对性和绝对性 长日植物与短日植物的相对性 临界日长与植物品种、温度等的关系 光期与暗期的作用,Cocklebur（苍耳）, Xanthium strumarium 典型的短日植物,Hamner and Bonner in the late 1920s,光周期现象的机理,光周期的感受部位 光周期诱导与开花素（florigen） 光周期诱导与光敏素 光周期诱导与生物钟 光周期诱导的分子机制,M. Kh.

15、Chailakyan,光周期的感受部位,开花素 Florigen,Perilla 紫苏，SDP,Four Examples from the Crassulaceae in Which Flowering Is Induced in a Noninduced Scion by Transmission of Florigen from a Florally Induced Stock. In each case, the stock (below the graft union) is the donor, and the scion (above the graft union) is th

16、e receptor. Arrows point toward the graft unions. In each case, the appropriate photoperiodic conditions were used to induce flowering of the donor plant, whereas the receptor was in a noninductive photoperiod. None of the control grafts with noninduced donors caused flowering in the receptors (data

17、 not shown). (A) The SDP Kalanchoe blossfeldiana as donor for the LDP Sedum spectabile as receptor (Zeevaart, 1958). (B) The LDP S. spectabile as donor for the SLDP Echeveria harmsii (my unpublished data). (C) The LSDP Bryophyllum crenatum as donor for the LDP S. spectabile (my unpublished data). (D

18、) The LSDP B. daigremontianum as donor for the SLDP E. harmsii (Zeevaart, 1982).,Graft-transmission of SFT (SINGLE-FLOWER TRUSS) signal from tomato to promote flowering in Maryland Mammoth tobacco (Lifschitzet al. 2006). (a) A Maryland Mammoth plant grown under long (18-h light/6-h dark) days, which

19、 did not flower. (b) Early flowering in long-daygrown Maryland Mammoth plants expressing the 35S:SFT transgene. (c) Tomato 35S:SFT donor scions grafted onto leaf petioles (boxed) of a Maryland Mammoth receiver induced flowering in the tobacco receiver (arrow) grown under long-day conditions. The pho

20、tographswere reproduced from (Lifschitz et al. 2006).,Phytochrome is the primary photoreceptor in photoperiodism,Blue-light receptors also regulate flowering,cry2 mutants flower much later than wild type during long but not short days,光周期诱导与生物钟,The Hourglass Model,Models for the mechanism of photope

21、riodic timing. The coincidence model 耦合模型,(A) In the external coincidence model, responses may be triggered when light coincides with a photoinducible phase. This photoinducible phase may be determined by the diurnal pattern of expression of a regulatory molecule, represented by the solid wavy line.

22、 Expression of this molecule is expected to be restricted to the dark period under short days, but to coincide with light under long-day conditions (arrows). (B) In the internal coincidence model, the effect of photoperiod is to alter the phase angle between two endogenous rhythms (represented by th

23、e solid and dotted lines). Oscillations in the levels of two regulatory molecules that require each other for activity may allow a response when brought into coincidence, under long-day conditions, for example. White and black boxes at the top of the diagrams represent periods of light and darkness,

24、 respectively.,MODEL FOR A FEEDBACK LOOP INVOLVING LHY, CCA1, AND TOC1,3) LHY, CCA1 repress expression of TOC1, their positive regulator,1) PHY and CRY as photoreceptors,2) LHY, CCA1 and TOC1 negative feedback loop,4) Generation of circadian rhythms, including that of CO for flowering time,6) ZLP an

25、d GI also act on light input,41,Molecular interactions that shape the plant circadian oscillator,LHCB and other morning genes ,CONSTANS (CO) stimulates FLOWERING,CONSTANS (CO) = zinc finger transcription factor = promotes flowering under LD = stimulates expression of FT (FLOWERING LOCUS T),35S:GFP:C

26、O,CONSTANS mRNA and protein,EOD End -Of-Day,To flower or not to flower. The interplay of photoreceptors and the circadian clock in the regulation of CO expression. CO mRNA levels (wavy magenta lines) are regulated by the circadian clock, which is entrained through the action (green arrow) of phytoch

27、rome and cryptochrome (Cry) photoreceptors. The peak circadian rhythm of CO mRNA expression (dashed magenta curve) runs from the late afternoon to the early morning. CO protein levels (depicted by the number of blue spheres) are determined not only by CO mRNA expression, but also by protein degradat

28、ion in the proteasome (yellow). CO degradation is promoted by phyB, but is inhibited by Cry and phyA during the day. During the night, the amount of CO mRNA remains high, but little CO protein accumulates because of CO proteolysis. During long days, phyA and Cry help to maintain the higher CO protei

29、n levels that promote flowering. (Arrows indicate stimulatory actions; lines with bar-head represent inhibitory actions; dashed lines suggest the involvement of additional proteins.),VOL 309 SEPTEMBER 2005,Leaf-specific heat shock activation of gene expression. GUS staining in whole plants (A to C)

30、and shoot apex (D to F) of Hsp:GUS plants grown under short-day conditions.,Integration of signals to generate a flower. Appropriate day length allows the accumulation of the transcription factor CO that controls expression of FT in the leaf. (Inset) FT transcript moves through the phloem to the sho

31、ot apex where the FT protein is produced and interacts with the transcription factor FD. The complex then activates key genes such as AP1 to start flower development. LEAFY (LFY) is a transcription factor required for AP1 expression in wild-type plants. LFY expression is up-regulated by FT in the sh

32、oot apex.,A current model of the action of the FT florigen. (A) Vegetative phase. In the absence of proper light signals or at very young seedling stage,FTexpression is absent. TFL1 protein is translated in the inner cells and becomes evenly distributed across the SAM (shown as blue shading). TFL1 p

33、rotein interacts with a bZIP transcription factor FD and prevents FD from activating target genes for flowering. (B) Floral transition. Transcription ofFTis induced in the phloem companion cells in the leaf (shown as pink lines around phloem represented by a white line) in response to light signals

34、via action of CO protein. FT protein is translated and is transported to the shoot apex where it interacts with a bZIP transcription factor FD by competing against TFL1 protein (shown as blue shading). The FTFD complex becomes localized in the nucleus and activates transcription of target genes such

35、 as a floral meristem identity gene,AP1(shown as yellow shading).AP1, in turn, specified the floral fate of nascent lateral meristems to initiate floral morphogenesis. FT protein does not promote its own transcription (a gray broken arrow with an X on it) but may actin transto facilitate its movemen

36、t (a black broken arrow with a question mark). See text for details.,Hd3a protein, which is the flowering hormone of the rice plant, is produced in the fibrovascular bundle of the leaves and then transported to the meristem at the tip of the stem, where it causes flowers to form. (NARA Institute of

37、Science and Technology),A physiological model of photoperiodic time measurement,The coincidence model,A conserved flowering-time pathway in rice and Arabidopsis confers the opposite effect to day length,The Coincidence Model of Photoperiodism,Hd1 = Heading-date1, rice ortholog of CO Hd3a = Heading-date 3a, rice ortholog of FT,H d1 Represser activity,Comparison of the function of orthologs CO and Hd1, FT and Hd3a,Kobayashi and Weigel 2007 Genes Dev 21: 2371-2384,A model for the p