Cellular and Molecular Evidence for a New Class of Plant Growth Regulators: Extracellular Nucleotide

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Cellular and Molecular Evidence for a New Class
of Plant Growth Regulators Extracellular
Nucleotides

• Discovery Lab Lecture, Jan. 25, 2006

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Extracellular ATP (eATP) is a signaling agent in
animals

• eATP and eADP signals are mediated through
• purinoceptors (P2 receptors).
• Two main classes of receptors P2X (ion-
• channel-linked) and P2Y
  (G-protein-linked)
• Activities mediated by purinoceptors include
• respiratory burst in neutrophils,
• inflammatory response and apoptosis.

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Extracellular Nucleotides Also Regulate Responses
in Plants

• They induce increases in Ca2cyt in both roots
  (Demidchik et al., 2003) and shoots (Jeter et
  al., 2004).
• They and the apyrase enzymes that control their
  concentration mediate growth changes in
  Arabidopsis.
• They substitute for wound stimulus in inducing
  superoxide production and increased expression of
  the genes in wound-signaling pathways.

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ATP-induced increase in Ca2cyt Measured in
Apoaequorin Transgenic Arabidopsis Plants
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ATP-induced increase in Ca2cytExcised Roots
Respond to Extracellular ATP
Taken from Demidchik et al., Plant Physiol. 133
456 (2003)
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Touch and Stress Stimuli Release ATP from Cells
Jeter et al. (2004) Plant Cell
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Extracellular nucleotides induce dose-dependent
growth changes
Effect of nucleotides on pollen tube growth
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Key missing data (01/25/07)

• Identification of purinoceptors in plants
• Quantify dynamic changes in eATP induced by
  various stimuli
• Clarify signaling steps that connect ?eATP to
  growth changes

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General Structure of Plant Roots
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Arabidopsis Roots, Root Hairs
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critique of 2004 data

• Major discovery, previously unreported
• Dosage effects seen down to 50 mM eATP applied
• Only inhibition observed
• All data were averages of final lengths of root
  hairs in a zone after several days continuous
  growth in eATP. So, no individual growth rates
  recorded.
• Dosages needed for inhibition may have been
  biased by receptor de-sensitization

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Schedule today

• 330 - 345 Lecture on use of ImageJ to measure
  growth
• 345 - 445 Plant seeds for next weeks
  experiment.
• 445 - 600 Split into two groups to
• (1) Learn how to observe and take pictures of
  growing root hairs
• (2) Take pictures of growing root hairs at two
  different time points.