Ion Channels in the Plasma Membrane of Pollen Tube

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Ion Channels in the Plasma Membrane of Pollen Tube

• Presented by Xia Fan

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Introduction

• What Are Ion Channels
• They are pore-forming proteins that help
  establish the small voltage gradient that exists
  across the membrane of all living cells, by
  controlling the flow of ions.
• Archetypal channel pore is just one or two atoms
  wide at its narrowest point. It conducts a
  specific species of ion and conveys them through
  the membrane single file--nearly as fast as the
  ions move through free fluid. In some ion
  channels, access to the pore is governed by a
  "gate," which may be opened or closed by chemical
  or electrical signals, or mechanical force,
  depending on the variety of channel.

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• Different Types of Ion Channels
• Voltage-gated channels open or close, depending
  on the transmembrane potential.
• Stretch-activated channels open their pores in
  response to mechanical deformation of the plasma
  membrane. Though little is known about these
  channels, they may be linked to molecules in the
  cytoskeleton, which may open them by transmitting
  physical forces of stretch or pressure to the
  channels, causing them to undergo a
  conformational change. The channels may also be
  pulled open due to tension on the membrane itself
  . Opening the channels allows ions to which they
  are permeable to flow down their electrochemical
  gradients into or out of the cell, causing a
  change in membrane potential.

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Identification and Characterization of SA Ion
Channels in Pollen Protoplasts

• Result
• SA Ca2 channels are identified in pollen grain
  and tube tip protoplasts, with similar but not
  identical properties. These channels were
  localized to a small region of the grain
  protoplasts associated with the site of tube
  germination.
• SA K and spontaneous K channel are identified
  in pollen grain and they are distributed over the
  entire grain surface, but neither was present at
  the germination site or at the tip.
• Neither SA channel was detected in the grain
  protoplasts unless the grains were left in
  germination medium for at least 1 h.

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Spontaneous K Channels in Grain Protoplasts