Patterns of Ethylene and Carbon Dioxide Evolution during Cotton Explant Abscission

Abstract

The relationship between abscission and the evolution of ethylene and CO2 was examined in explants and explant segments of cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-1) under both static and flow system conditions, and in the presence and absence of mercuric perchlorate. Explant excision was immediately followed by increased ethylene evolution (wound ethylene); senescence was also accompanied by increased ethylene evolution (senescence ethylene Cotton plants have provided the materials for extensive abscission research, and ETH2 has been implicated in the regulation of this abscission many times over (1,8,9,19,21,24,26 In a flow system specifically designed for this work, the patterns of ETH and CO2 evolution accompanying abscission in control explants were established and then compared with those patterns in explants treated with IAA and ABA. Abscission of hormone-treated and untreated explants was compared in the presence and absence of MP. Patterns of ETH and CO2 evolution were also studied in segments of cotton explants and in individual explants. MATERIALS AND METHODSGeneral Explant Techniques. All experiments were performed with excised cotyledonary nodes of 14-day-old cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-1) or with further subdivisions of this explant. Subdivision of a standard explant consisted of excising the petiole stumps and dividing them each into two segments 2 to 2.5 mm in length. The proximal segments contained the abscission zones with their surrounding tissues and were called abscission zone segments. The distal segments and the axes were referred to, respectively, as petiole stump segments and axial segments. On subdivision, each standard explant yielded two abscission zone segments, two petiole stump segments, and one axial segment. The standard growth regime and cotton explant procedures were followed with minor modifications (7,12,28). Briefly, the explants were supported in an upright position by a shallow layer (5 mm) of 1.5% agar covering the base of the explant chamber, approximately 10 g of pressure was applied to the petioles in testing for abscission, and abscised petioles were not removed from the explant chambers until all gas production data had been obtained. Agar droplets were omitted on all stem and petiole stumps unless otherwise indicated.Flow System, Chromatography, and Sampling. Most experiments were conducted in a flow system. Rates of ETH and CO2 evolution were determined from chromatographic analysis of gas samples withdrawn from the explant chambers (22,23). Instantaneous rates of gas evolution were calculated using the appropriate formula (22), and total amounts produced were estimated by cutting and weighing Xerox copies of the individual rate versus time graphs.The atmosphere of the flow system was Purafil-filtered ETHfree air. The flow system was similar to that described by Claypool and Keefer (14) for respiration studies.

Changes of Respiration Rate, Ethylene Evolution, and Abscisic Acid Content in Developing Inflorescence and Young Fruit of Olive (Olea europaea L. cv. Konservolia)

“…The increased respiration rate from 4 days before FB is probably related to the increased ethylene production during FB and flower abscission. Similar results have been found in cotton explant abscission (Marynick 1977) and coleus explants (Reid 1985). However, the increased rates of respiration during the 2nd week AFB may be partially a result of the early fruit development.…”

Early gene expression events in the laminar abscission zone of abscission-promoted citrus leaves after a cycle of water stress/rehydration: involvement of CitbHLH1

“…However, although physiological roles remain to be determined, increases in peroxidase activity in the AZ during the onset of abscission are well documented ( Hinman and Lang, 1965 ; Gahagan et al , 1968 ; Henry, 1975 ; McManus, 1994 ). Oxidative reactions are thought to be essential for abscission ( Marynick, 1977 ) and antioxidant treatments are able to reduce significantly abscission rates under certain conditions ( Michaeli et al , 1999 ). In addition, peroxidases may be involved in the coordination of gene expression in response to pathogens ( Sexton and Roberts, 1982 ).…”

Ethylene-induced differential gene expression during abscission of citrus leaves

“…Increases in peroxidase activity in the abscission zone during the onset of abscission are well documented ( Hinman and Lang, 1965 ; Gahagan et al , 1968 ; Henry, 1975 ) although their roles in the process of abscission are still unclear. Marynick (1977) concluded that oxidative respiration is essential to trigger abscission, while Michaeli et al (1999) demonstrated that whole plant antioxidant treatments significantly reduced low temperature-induced leaf abscission in Ixora coccinea . On the other hand, Sexton and Roberts (1982) , proposed that peroxidases may be involved in the co-ordination of gene expression in response to pathogens.…”