A chitinase activity was detected in fractions of xylem sap collected from
the cut surface of cucumber stems. A 28-kDa acidic protein was purified fro
m the active fractions and its N-terminal amino acid sequence was found to
be identical to that of a chitinase gene. Cucumber roots produce and secret
e an acidic chitinase, one of the PR proteins, into xylem sap and deliver i
t to aboveground organs.