第七章植物的生殖生理

terminal flower 1 (tfl1):
Convert the inflorescence meristem to the flower meristem.
leafy (lfy): produce more
inflorescences, delayed flowering
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tfl1
• [FUNCTION] Controls inflorescence meristem identity and is required for maintenance of a indeterminate inflorescence. Prevents the expression of 'APETALA1' and 'LEAFY'. Also plays a role in the regulation of the time of flowering in the long-day flowering pathway. May form complexes with phosphorylated ligands by interfering with kinases and their effectors] Expressed below the apical dome of inflorescence and coflorescence meristems, and in inflorescence stem. Weakly expressed in vegetative phase from day 2 or day 3. Increased expression after commitment to flowering from day 7 on.
Florigen
Florigen
?
Florigen
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•
Recent studies in Arabidopsis and rice have made a strong case that florigen, or at least acomponent of the floral stimulus, is the floral integrator FT. • The FT gene is expressed in leaves, and the protein travels to the meristem where it interacts with another integrator, FD, to initiate the floral transition • FT-like genes ( FD, FVE, FCA, FY, and FPA) are ubiquitous in plants and have been found to regulate flowering in a variety of species including wheat and poplar
Plant Reproduction
Zichao Mao
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Life cycle of plant
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பைடு நூலகம்
Plant Reproduction
• Transition to reproduction • Flower organ development • Gametogenesis and fertilization
LEAFY;
• LFY, FUNCTIONS IN: chromatin DNA binding, transcription factor activity, sequence-specific DNA binding; INVOLVED IN: flower development, maintenance of inflorescence meristem identity, response to gibberellin stimulus, gibberellic acid mediated signaling; LOCATED IN: nucleus; • EXPRESSED IN: shoot apex, leaf whorl, embryo, flower, seed; EXPRESSED DURING: 7 growth stages;
vegetative or reproductive growth?
• the flowering signal is generated in the leaf
SAM
• the signal goes one way: from the leaf to the apex
• Grafting transmittable
affecting formation of inflorescence and floral meristems
Flower (from Floral meristem)
Inflorescence (from Inflorescence meristem)
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Mutations in floral identity genes
Photoperiodism: ability of an organism to measure the proportion of daylight during a 24-hour period
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Photoperiod
Varies according to the latitude and seasonal changes.
Garner and Allard (1920’s) Soybeans (Glycine max) planted over a three-month period all flowered about the same time
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Many more experiments were followed:
Floral meristem
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Flowering-time genes
affecting the transition of vegetative growth to reproductive growth
WT
emf1
emf2
embryonic flower
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Floral identity genes
Factors regulating the transition to reproduction
Vegetative meristem
EMF LFY Inflorescence meristem Floral meristem
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TF1
The discovery of photoperiodism
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Plants that respond to lengthening days and flower in the spring or early summer are known as long-day (LD) plants. Short-day (SD) plants flower in the late summer or autumn in response to shortening days and lengthening nights
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Exp. 1: The leaf or apex of Perilla（紫苏 ） (a short day plant) was exposed to different daylength.
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Exp. 2: Grafting experiment with Perilla
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The flowering signal: florigen
• Short interruption of dark period,
even by a pulse of light as short as 1 minute delays flowering.
• The relative length of dark is not the determining factor.
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Similar results were obtained with other SD plants. For LD plants A longer dark period inhibits flowering. Light break induces flowering.
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What tissues/organs perceive photoperiod?
2. Convert inflorescence meristem to floral meristem (terminal, flowers)
SC: stem cell P: organ primordia Se: sepal
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Factors regulating the transitions
• Eliminate a variety of environmental conditions: Nutrition, temperature, and light intensity • Relative length of day and night decides the flowering time
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Critical daylength
Critical Daylength (CD)
Xanthium(苍耳）: a short day plant, flowers when CD is LESS than 15.5 hours.
Hyoscyamus(茛菪 ): a long day plant, flowers when CD is MORE than 11 hours.
Vegetative meristem
•
• • • •
Inflorescence meristem