REGULATION OF BUD REST IN TUBERS OF POTATO SOLANUM TUBEROSUM L.: I. EFFECT OF GROWTH SUBSTANCES ON EXCISED POTATO BUDS

Excised plugs containing buds from potato tubers were treatedwith 5-µliter droplets of a number of growth-regulatingsubstances. Gibberellin A₃ stimulated sprouting over a widerange of concentrations. Gibberellins A₃, A₄, A₅, and A₇ stimulatedsprouting, and A₆, A₈, and A₉ either had no effect or slightlyinhibited. Extracts of gibberellinlike substances from potatopeelings promoted sprouting. NAA and IAA both promoted sproutingslightly at low concentrations (4 x 10^–8M) but inhibitedsprouting at 4 x 10^–5M. Leaching of plugs resulted indelayed sprouting, and gibberellin restored total sproutingpotential. Plug size influenced rate of sprouting: small plugs(8 mm in diameter) sprouted faster than large (23 mm) plugs,and gibberellin stimulated sprouting slightly faster in thelarger than in the 8 mm plugs. None of the presumed componentsof ß, including cinnamic, chlorogenic, and caffeicacids, and coumarin, convincingly inhibited sprouting; in fact,they stimulated sprouting at almost all concentrations tested.5- Fluorouracil (5-FU) inhibited sprouting only slightly; andgibberellin completely or partially promoted sprouting in plugspreviously treated with 5-FU. Failure of 5-FU to inhibit sproutingwas considered to be the result of slow penetration of the inhibitorinto the potato bud. The potato "eye" bioassay is deficient in certain aspects, especiallyin view of the inconsistent rates of sprouting between experimentsand of nonspecificity. The results of this study, however, donot obviate the use of potato buds as a bioassay for inhibitorsof sprouting. ¹This research was supported in part by United States PublicHealth Service Grant EF-61. ²Present address: Department of Botany, Hebrew University, Jerusalem,Israel. ³Present address: U.S.D.A.-A.R.S., Department of Agronomy, Universityof California, Davis, California, U.S.A.