Parthenocarpy in Cucumber: Mechanism of Action of Auxin Transport Inhibitors1

Abstract

Abstract A hypothesis is proposed and tested for the mechanism of action of parthenocarpy induction in cucumber (Cucumis sativus L. cv. ‘GY3’) by the potent inhibitors of auxin transport 3,3a-dihy dro-2-(p-methoxy phenyl)-8H-pyrazolo [5,1-a] isoindol-8-one (DPX1840), methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (morphactin), N-l-naphthylphthalamic acid (naptalam), and 2,3,5-triiodobenzoic acid (TIBA). The transport of NAA-l-14C in 5-mm peduncle sections was strongly polar in the basipetal direction (i.e., out of the ovary toward the stem) and was inhibited within 0.5 hr by each transport inhibitor when applied at 500 to 1000 mg/1 to intact plants. Ether extractions of ovary tissue from plants treated in a similar manner contained significantly greater auxin activity as determined by the Avena coleoptile straight growth bioassay. These results are compatible with the hypothesis that auxin transport inhibitors induce parthenocarpy in cucumber by rapidly blocking the natural outward flow of auxin from the ovary thereby resulting in an accumulation of auxin within the ovary sufficient to trigger parthenocarpy.