Flowering Response of Pharbitis nil to Agents Affecting Cytoplasmic pH

Abstract

Permeant weak acids and auxins have been shown to reduce the cytosplasmic pH in several systems. Lactic, citric, formic, butyric, salicylic, parahydroxybenzoic, propionic acid, and sodium propionate inhibited the flowering response of Pharbitis nil seedlings when applied immediately before an inductive dark period. The acidic auxins IAA, indolebutyric, and a-naphtaleneacetic acid, as well as the nonacidic auxin a-naphtaleneaceteamid, also inhibited the flowering response. Inhibition was generally more pronounced with a 12-hour than with a 16-hour dark period. Salicylic acid and sodium propionate shifted the response curve of the dark period by about 2 hours. Salicyclic acid, sodium propionate, and indolebutyric acid were inhibitory when applied during the first few hours of the dark period. The permeant weak bases NH4CI, procaine, and trisodium citrate enhanced the flowering response. NH4CI reduced the length of the critical dark period. The inhibition of flowering by acids and auxins as well as the promotion of flowering by bases was obtained even when only the cotyledons had been treated. The inhibition of floral induction by auxins may not be dependent on their effect on the cytoplasmic pH.Pharbitis nil is a short-day plant that can be induced to flower by a single photoinductive dark period (21). Notwithstanding extensive research efforts during the past decades, the cellular events leading to floral induction are still largely unknown (2, 21). The metabolic activities of cellular and organellar compartments are known to be strongly influenced by pH (13,16,20). The intracellular pH is believed to be under tight control (13,16,20 (1,10,(16)(17)(18). Weak bases such as ammonium salts and procaine, on the other hand, raise the cytosolic pH (7,13,16,19).Auxins have been known for many years to inhibit photoperiodic floral induction in SD plants (2, 1 1). The mode of action of this inhibition is unknown (11). Application of exogenous auxins has been shown to decrease the cytosolic pH in several plant systems (3, 5-8). There is a possibility, therefore, that auxins influence floral induction through their effect on the pH of the cytoplasm. This hypothesis has also been tested in the present study. MATERIALS AND METHODS Seeds of Pharbitis nil RESULTSOrganic acids, auxins, and bases were applied to plants immediately before the start ofthe inductive dark period. The effect of the various agents was examined at 2 lengths of the dark period, 12 and 16 h.Lactic and citric acid were inhibitory at 20 mM in plants receiving a 12 h dark period, while there was no effect with a 16-h dark period (Fig. 1, A and B). With formic acid, sodium propionate (Fig. 1, C and D) and propionic acid (Table I) inhibition was obtained at higher concentrations. An inhibitory trend could be seen with formic acid and sodium propionate even with a 16-h dark period. A much stronger inhibition and at a lower concentration (5 mM) was obtained with salicyclic acids (Fig. 2)

The role of PnACO1 in light- and IAA-regulated flower inhibition in Pharbitis nil

“…In P. nil, the highest auxin effectiveness was observed following its application to the cotyledons directly before or during the first half of the inductive night (Amagasa and Suge 1987;Friedman et al 1990;Kulikowska-Gulewska et al 1995;Ogawa and Zeevaart 1967). In turn, the level of endogenous auxin in the cotyledons of P. nil seedlings before and during the first half of the inductive darkness remained low, only growing between hours 8 and 12 into the night (Bodson 1985).…”

“…A search for a substance responsible for flower induction caused by a relevant photoperiod allowed many chemical compounds to be identified, which have either a stimulating or inhibiting effect on the flowering of the model short-day plant (SDP) Pharbitis nil. The former group consists of gibberellins (Galoch et al 2002;King et al 1987;Wijayanti et al 1996), cytokinins (Friedman et al 1990;Galoch et al 1996;Halevy et al 1991) and prostaglandins (Groenewald and van der Westhuizen 2001). The latter group consists of auxins (Kulikowska-Gulewska et al 1995;Wijayanti et al 1997), ethylene (Amagasa and Suge 1987;Kęsy et al 2008), jasmonic acid (Maciejewska and Kopcewicz 2003), abscisic acid (Wijayanti et al 1997;Wilmowicz et al 2008) and brassinosteroids (Kęsy et al 2003).…”

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

“…Ethylene and auxins are among the compounds that show the strongest inhibitory effect on flowering in the model SDP Pharbitis nil. Ethylene only inhibits generative induction of P. nil completely when applied in the second half of 16 h inductive night (Suge, 1972;Friedman et al, 1990;Kulikowska-Gulewska et al, 1995;Kęsy et al, 2008;Wilmowicz et al, 2008). Auxin applied to cotyledons of P. nil seedlings just prior or during the first half of the inductive dark period has a similar effect (Ogawa and Zeevaart, 1967;Amagasa and Suge, 1987;KulikowskaGulewska et al, 1995).…”

“…Like auxins, ethylene is considered to be one of the most effective flower induction inhibitors in the model short-day plant P. nil (Suge, 1972;Friedman et al, 1990;Kulikowska-Gulewska et al, 1995;Kęsy et al, 2008). Since auxin's flower inhibition effect most probably results from increased ethylene production preceded by intensive transcriptional activity of ACC synthases Frankowski et al, 2009;Kęsy et al, 2010), we studied the effect of IAA on PnACO3 expression in cotyledons of seedlings cultivated under different photoperiods.…”

The florigen mystery

“…32 In teenstelling hiermee is bevind dat salisielsuur blomvorming by Pharbitis nil (KDP) rem. 34,37,45 Die salisielsuurremming van blomvorming by P. nil is 'n belangrike skakel in die moontlike verklaring van die proses (blomvorming) waarin prostaglandiene dit stimuleer.…”