Effects of 9,10-ketol-octadecadienoic acid (KODA) application on single and marginal short-day induction of flowering in Pharbitis nil cv. Violet

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Seedlings of the Japanese morning glory (Pharbitis nil, formerly Ipomoea nil) cv. Violet are induced to flower by a single short day treatment, and endogenous levels of 9,10-ketol-octadecadienoic acid (KODA) in cotyledons were found to correlate with this mode of short-day induction. When 100 µM KODA solution was sprayed on 7-day-old seedlings before and after a marginal short-day induction, the seedlings bore approximately 4 flower buds, a one-bud increase compared with control seedlings. In treated seedlings, the second node most commonly bore the first flower bud, one node lower than in the control seedlings. We then used RT-PCR to determine expression levels of 10 genes related to photoperiodic induction of flowering. In the cotyledons, no differences were observed in expression of any genes, including P. nil FLOWERING TIME LOCUS T (PnFT1 and PnFT2), between the KODA-treated and the control seedlings. In the apical buds, P. nil APETALA1 (PnAP1) was expressed earlier in the KODA-treated seedlings than in the control seedlings. A decrease in the expression of P. nil TERMINAL FLOWER1b (PnTFL1b) was also observed in the KODA-treated seedlings. These results suggest that KODA acts as a weak enhancer of flower bud formation.