Phloem Lecture 3

pressure flow hypothesis for transport through the sieve tube
- 100 cm/hr is too fast for diffusion
- driving force for bulk flow is the hydrostatic pressure gradient
- gradient maintained by phloem loading at the source and phloem unloading at the sink
- sieve plates create a resistance
evidence for pressure flow hypothesis
- demonstration of adequate pressure gradients
- demonstration of open sieve plate pores - rapid freezing and fixation
- demonstration of bulk flow particle movement - viruses
- mathematical modeling supports bulk flow through the sieve tube
phloem unloading
- sieve tube unloading
- short distance transport
- storage and metabolism in receiver cell
symplastic unloading
- young leaves
- sugar beet
- tobacco
- primary root tips
apoplastic unloading
- in developing leaves of monocots - few plasmodesmata
- cell wall invertase
- sucrose -> gluctose + fructose
- sugar-H+ symporter
active membrane transport into receiver cells
- sucrose-proton antiporter - sugar is transported to the vacuoles
- vacuolar H+ ATPase pumps protons into vacuole

Author

cornpops

120227

Card Set

Phloem Lecture 3

Description

plant physiology and biochemistry exam 6

Updated

2011-12-02T06:25:28Z