Involvement of Ethylene in Responses of Etiolated Bean Hypocotyl Hook to Coumarin

Abstract

Coumarin, at concentrations between 1.0 and 0.1 mM, inhibited red light-induced opening of the etiolated bean hypocotyl hook. In addition, anthocyanin synthesis and geotropic bending were inhibited. Coumarin stimulated ethylene synthesis, and ethylene was shown to mediate the inhibitory actions of coumarin. This conclusion was supported by: (a) the parallel concentration dependence and time sequence of hook closing and ethylene synthesis, (b) the restriction of the bulk of coumarin-induced ethylene production to the curved portion of the hook where opening is expressed, (c) the ability of both coumarin and ethylene to reclose partially opened hooks, and (d) the In the course of a study of bean and cotton seedling development (28), we observed that coumarin is a striking inhibitor of hypocotyl hook opening. Auxin is known to have a similar inhibitory effect on hook opening (17), a property which it shares with ethylene (12, 15). Further, endogenous ethylene has been shown to regulate the hook opening process (12,13,15).An explanation of the growth-inhibiting effect of exogenous auxin has developed from the demonstration that auxins stimulate synthesis of ethylene (23, 24 cotyl, some of which appear to be mediated by ethylene produced in response to the inhibitor. MATERIALS AND METHODSThe culture of etiolated bean (Phaseolus vulgaris L., cv. Black Valentine) seedlings and handling of excised hypocotyl parts were described in detail previously (28) and will only be reviewed briefly. Seeds were germinated in the dark, and after 5 days hypocotyl parts were excised under a green safe light. Hooks were excised and placed at random into Petri dishes or Erlenmeyer flasks containing two pieces of Whatman No. 3 filter paper and 10 ml of liquid. In specific experiments the crooked portion of the hook was excised at a point opposite the apical end of the hook to yield a straight section of hypocotyl 20 mm in length. Ten hooks or hypocotyl sections were used per flask or dish representing one replication.Coumarin was supplied in aqueous solutions, and controls received distilled water. Coumarin (K&K Laboratories, Inc., lot 39220L) was purified by recrystallizing it twice from an aqueous ethanol solution. The recrystallized material had a sharp melting point at 69 to 70 C and was used in all experiments subsequent to the initial test (Fig. 1). Exposure to red light (28) or darkness occurred after the tissue pieces were in the various solutions. The number of replications, concentrations of coumarin and duration of red light exposure, where applicable, are given in the various legends.Hook angles were measured 22 to 24 hr after excision as previously described (17,28). Fresh weights were obtained after other determinations. In some tests anthocyanin pigments were extracted with 3 volumes of 0.1 N HCI. The extract was brought to 12 ml/g fresh weight with 0.1 N HCI, and the relative pigment content was measured at 520 nm with a Beckman DB spectrophotometer.When ethylene was to be measured, tissues were placed in 500-ml ...

Ethylene Control of Anthocyanin Synthesis in Sorghum

“…As reported for other plants (8,9), data presented in this paper demonstrated that ethylene could act as an inhibitor of light-stimulated anthocyanin synthesis in sorghum. The active ethylene concentrations were similar to those reported for other plant processes regulated by ethylene (10).…”

“…Early observations by Kropfitsch (8) on Vicia faba indicated that ethylene inhibited anthocyanin synthesis in the nectaries but had no effect on anthocyanin development in the stem. Other reports have indicated that ethylene inhibits anthocyanin formation in bean seedlings (9) and that ethylene promotes anthocyanin synthesis in cranberry fruit (2). It was the purpose of this paper to determine the role of ethylene in light-induced anthocyanin synthesis in sorghum tissue.…”

Auxin Transport: A New Synthetic Inhibitor

“…The first is the ability of DPX1840 to induce complete hook opening in Phaseoliis vulgaris L. and Pisuin sativumn L. seedlings in the dark where they would not normally open. Ethylene which is naturallv produced in the hook appears to play a regulatory role in maintaining the hook in a closed or reflexed position (22,23,38). The ability of DPX1840 to completely negate this effect of ethylene suggests that ethylene-mediated hook closure is dependent on a functional auxin transport system.…”

Localization and Pattern of Graviresponse across the Pulvinus of Barley Hordeum vulgare

“…Rather, it alters the expression of the perceived stimulus, either at the level of transduction or response. For example, coumarin may simply enhance ethylene production, as has been observed in bean stem tissue (20). The local increase in cell expansion in the radial direction, then, may be indicative of the local ethylene level.…”