REGULATION OF BUD REST IN TUBERS OF POTATO <italic>SOLANUM TUBEROSUM L.</italic>: I. EFFECT OF GROWTH SUBSTANCES ON EXCISED POTATO BUDS<xref ref-type="fn" rid="fn1"><sup>1</sup></xref>

Excised plugs containing buds from potato tubers were treated with 5-μliter droplets of a number of growth-regulating substances. Gibberellin A3 stimulated sprouting over a wide range of concentrations. Gibberellins A3, A4, A5, and A7 stimulated sprouting, and A6, A8, and A9 either had no effect or slightly inhibited. Extracts of gibberellinlike substances from potato peelings promoted sprouting. NAA and IAA both promoted sprouting slightly at low concentrations (4 × 10−8M) but inhibited sprouting at 4 × 10−5M. Leaching of plugs resulted in delayed sprouting, and gibberellin restored total sprouting potential. 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 the larger than in the 8 mm plugs. None of the presumed components of β, including cinnamic, chlorogenic, and caffeic acids, and coumarin, convincingly inhibited sprouting; in fact, they stimulated sprouting at almost all concentrations tested. 5- Fluorouracil (5-FU) inhibited sprouting only slightly; and gibberellin completely or partially promoted sprouting in plugs previously treated with 5-FU. Failure of 5-FU to inhibit sprouting was considered to be the result of slow penetration of the inhibitor into the potato bud. The potato “eye” bioassay is deficient in certain aspects, especially in view of the inconsistent rates of sprouting between experiments and of nonspecificity. The results of this study, however, do not obviate the use of potato buds as a bioassay for inhibitors of sprouting.