A cell wall bound adenosine nucleosidase is involved in the salvage of extracellular ATP in Solanum tuberosum.
Extracellular ATP (eATP) has recently been demonstrated to play a crucial role in plant
development and growth. To investigate the fate of eATP within the apoplast, we used intact
potato (Solanum tuberosum) tuber slices as experimental system enabling access to the
apoplast without interference of cytosolic contaminations. (i) Incubation of intact tuber slices
with ATP led to the formation of ADP, AMP, adenosine, adenine and ribose, indicating
operation of apyrase, 5’-nucleotidase and nucleosidase. (ii) Measurement of apyrase, 5’-
nucleotidase and nucleosidase activities in fractionated tuber tissue confirmed apoplastic
localization for apyrase and phosphatase in potato and led to the identification of a novel cellwall
bound adenosine nucleosidase activity. (iii) When intact tuber slices were incubated with
saturating concentrations of adenosine, the conversion of adenosine into adenine was much
higher than adenosine import into the cell suggesting a potential bypass of adenosine import.
Consistent with this, import of radio-labeled adenine into tuber slices was inhibited when
ATP, ADP or AMP were added to the slices. (iv) In wild type plants, apyrase and adenosine
nucleosidase activities were found to be co-regulated, indicating functional linkage of these
enzymes in a shared pathway. (v) Moreover, adenosine nucleosidase activity was reduced in
transgenic lines with strongly reduced apoplastic apyrase activity. When taken together,
these results suggest that a complete ATP-salvage pathway is present in the apoplast of
Riewe, D.; Grosman, L.; Fernie, A.R.; Zauber, H.; Wucke, C.; Geigenberger, P. 2008. A cell wall bound adenosine nucleosidase is involved in the salvage of extracellular ATP in Solanum tuberosum. Plant and Cell Physiology 49, 1572-1579.