Pretreatment of detached carnation petals (Dianhius caryophyUs cvWhite Sim) for 24 hours with 0

Spiegelstein, H, and Mayak, S. 1985, The site of 1-amitiocy-cIopropane-1-carbosylic acid syntbesis in senescing carnation petals, -Physiol, Plant. 65;[196][197][198][199][200][201][202] To study the cause of the uneven production of ethyiene by upper and basal portions of detached petals of carnation (Dianthus caryophyllus L, cv. White Sim), the petals were divided and exposed to ethylene (30 (il 1^' for 16 h). The treatment induced rapid wilting and autocatalytic ethylene production in the basai portion similar to that induced in entire petals. In contrast to the response in entire petals and the basal portions, the upper portions responded to ethylene by delayed wilting and much lower ethylene production, Aminocyclopropane carboxylic acid (ACC)-synthase activity in the basal portion of the petals was 38 to 400 times that in the upper portion. In yntreated detached petal pieces from senescing carnation flowers, etbylene production by tbe upper portion declined after 6 h while the basal portion was still producing ethylene at a steady rate 18 h later. Application of ACC to the upper portion of senescing petals increased their ethylene production, a-Aminooxyacetic acid (0,5 mM), reduced tbe ethylene production of the senescing basai portion more than that of the upper portion. Endogenous ACC eontent in basal portions of senescing carnation petals was 3 to 4 times higher than in the upper parts. When detached senescing petals were divided immediately after detaching, the endogenous ACC ieveis in upper portions remained steady or declined during 24 h after division, while in the basal portions the ACC level rose steadily as in the intact petals. There was no change in the conjugated ACC in either portioti after 24 b, Benzyladenine (BA) applied as a pretreatment to entire preclimacteric petals greatly reduced the development of ACCsynthase activity of the basal portion, but had little effect on tbe activity in the upper portioti of the petal. In both portions, however, BA effectively reduced the conversion of ACC to ethylene.Additional key words -Aminooxyacetie acid, benzyladenine, conjugated ACC, Dianthus caryophyllus, ethyiene forming enzyme, flower senescence, Y. Mor, A. H. Halevy (reprint requests), H. Spiegelstein .and S. Mayak,

Tentative identification using HPLC and RIA techniques indicated the presence of zeatin-0-glucoside, zeatin, ribosylzeatin, dihydrozeatin, iso-pentenyladenine and isopentenyladenosine in the petals of carnation flowers. Dihydrozeatin is apparently responsible for most of the biological activity.Within the petals most activity was detected in the basal parts which also senesced much slower than the upper parts of the petals. Treatment with AOA extended petal longevity and reduced ethylene production. This was associated with higher cytokinin-like activity in the basal parts of the petals.These higher levels of cytokinins were not observed in the petals of ACC treated flowers or in the detached control flowers. It is suggested that cytokinin transport and/or metabolism may play an important role in regulating ethylene production in cut carnations.

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)

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