(03!31!2008)Phloem Lecture Yu
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Transcript of (03!31!2008)Phloem Lecture Yu
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Translocation in the Phloem
Plant PhysiologyTaiz & Zeiger Chapter 10
Tien-Shin YuInstitute of Plant & Microbial Biology
Plant PhysiologyMarch 31, 2008
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Phloem:
•Nature of conduit•Substance being transported•Mechanism of phloem translocation•Direction: source to sink•An information superhighway
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Plant Vasculature: Xylem and Phloem
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Arrangement of Plant Vascular Tissue
Phloem
Xylem
RootShoot
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SeiveSeiveelementelement
SeiveSeiveplateplate
Phloem Phloem Parenchyma Parenchyma
cellcell
CompanionCompanioncellcell
The Compositions of Phloem
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Architecture of Sieve Element-Companion Cell (SE-CC) Complex
Protection:1.P-protein2.Callose
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Angiosperms CC-SE Complex
Sievepore
Sievepore
SE
SECC
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Gymnosperms CC-SE Complex
No P-proteins
Pores appear blocked
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P-proteins
PP1: phloem protein that forms filamentsPP2: phloem lectin associated with filaments
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Types of Companion Cells: Apoplastic Loading
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Types of Companion Cells: Symplastic Loading
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Types of Companion Cells: Symplastic Loading
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Connection of CC-SE by Specialized Plasmodesmata
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Network of the phloem
SE
Stain withAniline blue(callose)
SE
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Phloem:
•Nature of conduit•Substance being transported•Mechanism of phloem translocation•Direction: source to sink•An information superhighway
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• Sugar, Ions, Hormone• Proteins, Peptides• RNA
Molecules in the PhloemAphid styletCucurbit phloem exudate
Rate: 10 mL/hr Rate: 100 nL/hr
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Xylem: water, minerals, andhormones (cytokinin)
Phloem: photosynthate (sugars),ions,hormones (IAA, GA),amino acids, peptides, proteins, and RNA.
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Sugars in Phloem Sap
Most abundantin the phloem
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Nitrogenous Compounds in Phloem Sap
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Protein Composition in Phloem Sap
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mRNA and small RNA in Phloem Sap
At least 2,500 mRNA have been identified from phloem sap
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Phloem:
•Nature of conduit•Substance being transported•Mechanism of phloem translocation•Direction: source to sink•An information superhighway
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Bulk Flow Hypothesis
Flow rate:1 m/hr
Ernst Münch1930
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Loading into SE: Apoplastic and Symplastic Pathways
Sucrosetransporter
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Apoplasmic Step Model
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Symplasmic – Polymer-trap Model
BS-IM PD size exclusion limit of 0.8 kDa
IC-SE PD size exclusion limit of 25 kDa
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Apex
Phloem
Phloem Unloading
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Phloem Unloading from SE
More common
In DevelopingSeed
Type I
Type II
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Phloem:
•Nature of conduit•Substance being transported•Mechanism of phloem translocation•Direction: source to sink•An information superhighway
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Direction & rate of phloem translocation is controlled by local
Sink Strength
Phloem translocationis a Non-Circulatory
vascular system
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Phloem Translocation Regulates by Proximity
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Leaf Blade Sink-Source Transition from Tip to Base
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Major Vein: Unloading; Minor Vein: Loading
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Allocation and Partition
Allocation: The regulation of Sugar distributes into various metabolic pathway
Partitioning: Differential distribution of sugar within the plant
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Phloem:
•Nature of conduit•Substance being transported•Mechanism of phloem translocation•Direction: source to sink•An information superhighway
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Signal Molecules in the Phloem
•Hormones: Auxin, GA•Chemical: JA in pathogen defense•Sugars•Protein•mRNA•etc
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Protein Composition in Phloem Sap
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Source Leaf Sink Leaf
GFP Protein Unloading in the sink leaf
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mRNA and small RNA in Phloem Sap
At least 2,000 different RNA identified from phloem sap
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Florigen is a Phloem Mobile Macromolecule!!
Graft union
Non-inducedplant
Floral induction Non induction
PCO-GUS PFT-GUS
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Thank you