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