Involvement of the IAA-Regulated ACC Oxidase Gene PnACO3 in Pharbitis Nil Flower Inhibition

The study examined the influence of light and auxin on the transcription level of PnACO3, a gene involved in ethylene production, in relation to the inhibitory effect of ethylene on flower induction in the short-day plant Pharbitis nil (=Ipomoea nil). Exogenous auxin was shown to increase the level of PnACO3 mRNA, with the effect depending on the experimental conditions. Light did not affect the level of PnACO3 mRNA. Applying auxin to seedling cotyledons at the beginning of inductive night boosted PnACO3 transcriptional activity even threefold during the next few hours, supporting our previous suggestion that the inhibitory effect of auxin on P. nil flowering results from its stimulatory effect on ethylene production.

Involvement of aba in flower induction of Pharbitis nil

<p>Flowering of plants is controlled by hormones among which both stimulators and inhibitors are present. The role of abscisic acid (ABA) in flower induction of the short day plant <em>Pharbitis nil</em> was shown in our experiments through exogenous applications and endogenous level determination of the hormone in cotyledons of seedlings grown under special light conditions.</p><p>The application of ABA to cotyledons or shoot apices during the first half of a 24-h long inductive night inhibits flowering. The same compound applied towards the end of or after a 14-h long subinductive night increases the number of flower buds produced by these plants.</p><p>Exposing <em>P. nil</em> seedlings at the beginning of a 24-h long inductive night to far red light (FR) decreases the level of endogenous abscisic acid in cotyledons and leads to flower inhibition. However, a pulse of red light (R) reversing the inhibitory effect of far red light on the flowering of <em>P. nil</em> increases the ABA content.</p><p>The results obtained confirm previous observations that ABA may play a dual and an important role in the regulation of floral bud formation in <em>P. nil</em>. The flowering occurs when the level of endogenous abscisic acid is low at the beginning and is high toward the end of the inductive night.</p>