Phloem Lecture 1

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What gets transported from leaf to root through the phloem?
- sucrose
- amino acids
- some ions
What are the structural components of phloem transport?
- conducting cells:
- - sieve elements
- - sieve cells (gymnosperms)
- - sieve tube cells (angiosperms)
- companion cells
- parenchyma
- fibers
- laticifers
*sieve elements
- living cells highly specialized for translocation
- lose their nucleus and vacuole
- retain modified mitochondria, plastids, and smooth endoplasmic reticulum
sieve areas
- parts of the cell wall with pores
- lateral transport
sieve plates
- found at the end walls of sieve tube cells
- have larger pores
*companion cells
- adjacent to sieve cells
- connected through plasmodesmata
- densely cytoplasmic and have numerous mitochondria
- take over metabolic functions of sieve tube
- 3 types:
- companion cell
- intermediary cell
- transfer cell
*transfer cells
- has finger like wall in growths - increase the surface area
- specialized for taking up solutes
intermediary cells

use symplastic transfer of solutes
evidence for the sieve tube as the transporting cell
- 1) application of radioactive label:
- ¹⁴CO2 supplied to leaf
- ¹⁶C- sucrose supplied to leaf
- 2) localization of radioactive label in transport cells - autoradiography
autoradiography
- 1) rapidly freeze
- 2) freeze-dried
- 3) embedded in resin
- 4) sliced into thin sections
- 5) coated photographically
- 6) expose
- 7) silver grains appear (saw in sieve tube)
P-protein
- phloem protein
- forms a gel
- puncture repair substance
wounding response
- P-protein blocks sieve plate pores
- callose forms (callase enzyme)

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cornpops

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Phloem Lecture 1

Description

plant physiology and biochemistry exam 6

Updated

2011-12-02T03:36:58Z

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