title: Squash xylem sap has activities that inhibit proliferation and promote the elongation of tobacco BY-2 cell protoplasts.
abstract: To elucidate the physiological functions of the substances in xylem sap, we analyzed the biological activities of xylem sap from squash (Cucurbita maxima Duch.) root using tobacco BY-2 (Nicotiana tabacum L. cv. Bright Yellow 2) cell protoplasts. When BY-2 cell protoplasts were cultivated with the total substance of squash xylem sap, the protoplasts elongated remarkably, and cell division was inhibited. Although trans-zeatin riboside (ZR), the most abundant cytokinin in squash xylem sap, had a concentration-dependent effect similar to that of total squash xylem sap, ZR concentrations several orders of magnitude greater than those found endogenously in squash xylem sap (i.e. 2 x 10(-8) M) were required to affect the growth of BY-2 cell protoplasts. The ability to stimulate cell elongation and inhibit cell division in BY-2 cell protoplasts was observed for the ethyl acetate phase fraction (pH 2) of squash xylem sap and an acetonitrile-eluate fraction from reverse-phase chromatography. The xylem sap also showed inhibitory activity for auxin-induced elongation of excised cucumber hypocotyls. These results suggest that an organic substance other than ZR is produced in the root and transported to above-ground organs through the xylem via the transpiration stream, where it is involved in regulating cell proliferation and elongation in the shoot, possibly as an auxin antagonist.
authors.affiliation: Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kuroha
authors.forename: Masato
authors.initials: M
authors.lastname: Sakurai
authors.forename: Shinobu
authors.initials: S
authors.lastname: Satoh
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D018929:Cell Culture Techniques; D002455:Cell Division / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D048430:Cell Shape; D002478:Cells, Cultured; D005591:Chemical Fractionation; D028464:Cucurbita / Q000378:metabolism*; D018546:Hypocotyl / Q000378:metabolism; D007541:Isopentenyladenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D018517:Plant Roots / Q000378:metabolism; D011523:Protoplasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014026:Nicotiana / Q000166:cytology*
chemical_list: D007541:Isopentenyladenosine; C009699:zeatin riboside; D000241:Adenosine