Ethylene Formation in Sugar Beet Leaves

Abstract

Ethylene production by sugar beet (Beta vulgaris L.) leaf discs is inhibited by white (or red, >610 nm) light or by wounding. In contrast, in wounded leaf discs, ethylene production is stimulated by light. The effect of light on wounded leaf discs has been studied by using an in vitro system which mimics the loss of compartmentation in the wounded leaf.Chlorophyll-free extracts from sugar beet leaves stimulate the production of the superoxide free radical ion (as a prerequisite for ethylene formation) by Muminated chloroplast lamellae. The substance from the crude leaf extracts which is active in stimulating the production of the superoxide free radical ion has been identified as 3-hydroxytyramine (dopamine). Exogenous dopamine between 5 jLM and 100 FM stimulates ethylene formation by iluminated chloroplast lameflae from methional. It also stimulates the production of the superoxide free radical ion, the formation of which apparently involves both a lamellar phenoloxidase and photosynthetic electron transport as a 1-electron donor, and is cyanide-sensitive. Ethylene (1) seems to be responsible for the induction of the enzymes involved in the biosynthesis of several phenolic compounds, the reactions participating in the resistance to infections, fruit ripening, and the senescence of higher plants. Ethylene production, in turn, is initiated by physiological or artificially induced stress conditions. The biochemical mechanism of the induction of ethylene biosynthesis is unknown. However, the prerequisites for ethylene formation by higher plant tissue seem to be an oxygen-activating system together with an appropriate ethylene donor such as methionine, 2-keto-4-mercaptomethyl butyrate, methional (3-mercaptomethyl propanal), or linolenic acid (1,19,24,34). In the case of the model compounds 2-keto-4-mercaptomethyl butyrate or 3-mercaptomethyl propanal, the OH radical produced after monovalent oxygen reduction has been shown to be the oxidant (5, 10-12) yielding ethylene and other products (35).In the present communication, we wish to report on experiments concerning the induction of monovalent oxygen reduction (production of O2--) and ethylene formation in chloroplasts from sugar beet leaves, involving the function of endogenous 3-hydroxytyramine (dopamine) as the cofactor of monovalent oxygen reduction. (13). The activity units of superoxide dismutase were determined as described by McCord and Fridovich (23). Ethylene formation was monitored as previously described (10-12).3-Hydroxytyramine was isolated from sugar beet leaves according to the procedure of Gardner et al. (16). The aqueous phase from sugar beet leaves (see ref. 16) was evaporated to dryness and dissolved in methanol containing 0.25% concentrated HCI. The filtered solution was loaded onto a cellulose column (prepared by stirring 15 g cellulose [Avicel, Merck-Darmstadt] in a 150-ml butanone-2-formic acid-acetone-water mixture, 40:1:2:6, v/v). The column was washed with increasing amounts of the same solution. The fractions containing 3-hydroxyt...

Untargeted liquid chromatography coupled with mass spectrometry reveals metabolic changes in nitrogen-deficient Isatis indigotica Fortune

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Exogenous Dopamine Application Promotes Alkali Tolerance of Apple Seedlings

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Biochemical aspects of wound healing in yams (Dioscorea spp)

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