References

226 S.J. Roux, C. Song, C. Jeter
(Arteca and Arteca 1999; Reymond et al. 2000), mechanical stimuli known
to induce animal cells to release ATP into the ECM (Sauer et al. 2000), so the
authors tested whether these mechanical stresses could induce the same
tissues that respond to externally applied nucleotides to release ATP.
As assayed by the sensitive luciferin–luciferase method, stress stimuli
do indeed induce measurable ATP release from young seedlings (Jeter et
al. 2004; Fig. 15.2). The touch stimulus was applied by gently shaking the
seedlings, and the hypertonic stress was applied by briefly submerging the
seedlings in 300 mM NaCl. Seedlings recovered from the stresses applied
and appeared normal within 24 h, indicating that it was unlikely the released
ATP came from damaged cells.
Pathogen attack is another form of stress, and plants typically respond to
this stress by the release of oligogalacturonides (OGA) in their ECM. This
OGAservesasasignalingmoleculetoinducedefenseresponsesthrough
a transduction pathway that includes increase in [Ca 2+ ]cyt as an early step.
Since ATP release from damaged cells would be another likely event induced
by pathogen attack, could ATP and OGA function together to elicit wound
responses?
Jeter et al. (2004) investigated this point and found that OGA and ATPγS
mutually enhanced each other’s effects on the ∆[Ca 2+ ]cyt.ADPβSwithOGA
similarly increased [Ca 2+ ]cyt together, whereas AMPS had a significant
inhibitory effect. These results suggested that nucleotide derivatives could
function together with OGA to modulate plant responses to wounding or
herbivory, but they raise the question of the relationship between ATP and
OGA signaling pathways.
Cessna and Low (2001) concluded that OGA induces increased [Ca 2+ ]cyt
by Ca 2+ release from internal stores, whereas the results of both Demid-
Fig.15.2. Various stress stimuli induce ATP release from Arabidopsis seedlings. The relative
ATP level in the medium surrounding the seedlings was measured using the luciferin–
luciferase assay (Taken from Jeter et al. 2004, with permission)