Enhancement of the inhibitory activity for greening in xylem sap of squashroot with waterlogging

Squash plants are used as rootstock for cucumber plants to prevent soil-bor ne disease. The chlorophyll content in the cotyledons of cucumber was obser ved in the present study to decrease in response to grafting onto squash ro otstock. The decrease in chlorophyll content was enhanced by the waterloggi ng of squash root. To prove the hypothesis that root-derived chemical signa ls are involved in the shoot behavior of waterlogged plants, the xylem sap collected from waterlogged squash root was analyzed for activity related to the greening of etiolated cucumber cotyledon. When the fractions of xylem sap separated on a Sephadex G-25 column were subjected to the greening assa y, a much stronger inhibition of greening was observed in the xylem sap obt ained from waterlogged squash plants than in that from control plants at th e position corresponding to an apparent molecular mass of 1 400. These resu lts suggest that a novel higher molecular mass chemical signal in xylem sap might mediate between shoots and roots in waterlogged plants. (C) 2001 Edi tions scientifiques et medicales Elsevier SAS.