2. the most commonly translocated sugar

4. Radioactive tracer / NMR The mass transfer rate of phloem: 1 to 15 g / h cm 2 The movement velocity xylem 30 to 150 cm / h (0.25 mm/ s) 4 mm/s (14.4 m/h) Rates of movement

5. Pressure–flow model  The mechanism of translocation in the phloem Phloem loading Phloem unloading  pressure gradient between source and sink  the resistance of sieve plates, maintain pressure gradient  mass flow not osmosis, no membrane

6. Sieve plate pores are open channels  confocal laser scanning microscopy Earlier electron micrography Rapid freezing/fixation EM Confocal filter

7. double stain: red/green arrowhead : plastids arrow(  ): protein (L: sieve plate pores)  : protein body SE: sieve element SP: sieve plate CC: company cell A living, functional sieve elements membrane / translocation No bidirection transport in single sieve element

8. The energy requirement for phloem transport is small rapidly chilling a short segment of the petiole of a source leaf  Short-term respiration rate and ATP metabolism , but … p. 233R: a metabolic inhibitor (cyanide) treatment, an extreme condition  inhibit translocation observed by EM (1977), but confocal

9. The predictions of the pressure-flow model have been confirmed  Sieve plate pores are open channels. P-protein: along the periphery of the sieve tube elements, or it is evenly distributed throughout the lumen of the cell, but, previously….  Translocation rate is insensitive to the energy supply of the path tissues. in herbaceous plants  Bidirectional transport cannot be seen in single sieve elements.  Pressure gradients are sufficient to drive a mass flow of solution 0.41 MPa between sink and source 0.12 to 0.46 MPa is required for translocation by pressure flow

10. Significant questions about the pressure-flow model still exist — What’s the mechanism of phloem transport in gymnosperms? — Osmoregulatory flow: osmotically generated mass flow (06)? — small herbaceous vs. large tree plants more different species  Artificial sieve tubes as tools for studying phloem function (O-13) Created an artificial phloem microlithographically on microchips. Artificial sieve elements of 9-15  m diameter containing unique protein bodies were produced which formed continuous tubes but included constrictions resembling sieve plates. Using fluorescent dyes and confocal laser-scanning microscopy to trace the flow of artificial sieve tube under high [Ca 2+ ] condition.