Journal of Plant Physiology 169 (2012) 1425–1429 Contents lists available at SciVerse ScienceDirect Journal of Plant Physiology jou rn al h o mepage: www.elsevier.de/jplph Short communication Endogenous ethylene does not regulate opening of unstressed Iris flowers but strongly inhibits it in water-stressed flowers Fisun G. C ¸ elikel 1 , Wouter G. van Doorn ∗ Wageningen University and Research Centre, Agrotechnology and Food Sciences Group (AFSG), P.O. Box 17, 6700 AA Wageningen, The Netherlands a r t i c l e i n f o Article history: Received 20 April 2012 Received in revised form 30 May 2012 Accepted 30 May 2012 Keywords: Elongation growth Ethylene Flower opening Inhibitors Iris Ovary growth Pedicel growth Water stress a b s t r a c t The floral buds of Iris flowers (Iris x hollandica) are enclosed by two sheath leaves. Flower opening depends on lifting the flower up to a position whereby the tepals can move laterally. This upward movement is carried out by elongation of the subtending pedicel and ovary. In the pedicels and ovaries of unstressed control flowers, the concentration of ACC (1-aminocyclopropane-1-carboxylic acid) and the rate of ethy- lene production increased during d 0–1 of flower opening, and then decreased. Exposure to ≥200 nL L -1 ethylene for 24 h at 20 ◦ C inhibited elongation of the pedicel + ovary, and inhibited flower opening. How- ever, pulsing of unstressed flowers with solutions containing inhibitors of ethylene synthesis (AOA, AVG), or an inhibitor of ethylene action (STS), did not affect pedicel + ovary elongation or flower opening. When the flowers were dehydrated for 2 d at 20 ◦ C and 60% RH, they did not open when subsequently placed in water, and showed inhibited elongation in the pedicel + ovary. This dehydration treatment resulted in elevated pedicel + ovary ACC levels and in increased ethylene production. Treatment with STS prevented the increase in ACC levels and ethylene production, overcame the effect of dehydration on elongation of the pedicel + ovary, and resulted in full flower opening. It is concluded that flower opening in unstressed Iris flowers is not regulated by endogenous ethylene. An increase in endogenous ethylene above nor- mal levels during stress, by contrast, strongly inhibited flower opening, due to its inhibitory effect on elongation of the pedicel + ovary. © 2012 Elsevier GmbH. All rights reserved. Introduction Flower opening usually depends on growth processes, and therefore might depend on growth regulators. Treatment with a cytokinin, for example, promoted opening in Iris flowers (Macnish et al., 2010). Opening of Ipomoea (previously called Pharbitis) flow- ers was greatly promoted by abscisic acid (ABA), whilst it was completely suppressed by auxin (indoleacetic acid; Kaihara and Takimoto, 1983). In Ipomoea flowers the rate of ethylene production increased prior to flower opening. The increased opening after ABA treatment was associated with an increase in ethylene production and the effect of ABA was eliminated by inhibitors of ethylene synthesis. Furthermore, treatment with 1-aminocyclopropane-1-carboxylic acid (ACC), the direct precursor of ethylene, stimulated opening as Abbreviations: AOA, aminooxyacetic acid; AVG, aminoethoxyvinylglycine; HQC, hydroxyquinoline citrate; STS, silver thiosulphate. ∗ Corresponding author. Present address: Mann Laboratory, Department of Plant Sciences, University of California, Davis, CA 95616, USA. Tel.: +1 530 867 3684; fax: +1 530 752 4554. E-mail address: wgvandoorn@ucdavis.edu (W.G. van Doorn). 1 Present address: Ondokuz Mayis University, Faculty of Agriculture, Department of Horticulture, 55139 Kurupelit, Samsun, Turkey. much as ABA did (Koning, 1986). These data suggest that ethylene is required for flower opening in Ipomoea. Cut flowering Iris stems comprise about 4–5 leaves. The upper- most two leaves tightly enclose the floral bud. Flower opening depends on lifting the flower base to a position with regard to the sheath leaves that allows the lateral opening movement of the outer tepals and the petaloid stamens. This lifting is due to elongation of the pedicel and ovary, which connect the flower base with the uppermost node on the stem (Mayak and Halevy, 1971; Reid and Evans, 1986; Macnish et al., 2010). We investigated the role of ethylene in bud opening of Iris flow- ers, both in flowers that had not been dehydrated and in flowers subjected to water stress. It was hypothesized that (a) normal open- ing requires ethylene and (b) that water stress inhibits opening by increasing the rate of ethylene production to supra-optimal lev- els. These hypotheses were investigated by measuring ACC and ethylene concentrations, and using treatments that inhibit ethylene synthesis or ethylene action. Materials and methods Plant material Iris flowers (Iris x hollandica Tub., cv. Blue Magic) were cut at the root–shoot junction and placed in water. Cutting took place 0176-1617/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.jplph.2012.05.012