PEROXIDASES IN TOBACCO ABSCISSION ZONE TISSUE .6. ULTRASTRUCTURAL LOCALIZATION IN PLASMODESMATA DURING ETHYLENE-INDUCED ABSCISSION

It has been suggested that peroxidases can mediate the oxidation or decarboxy-lation of indol-3yl-acetic acid (IAA) in vitro (Beaudreau and Yasanobu 1966, Galston, Bonner and Baker 1953, McCune 1961, Morita, Kameda and Mizano 1962), thus controlling growth caused by the reduction of IAA in the tissue (van Overbeek 1935). The incidence of peroxidase activity in plant tissues appears to be ubiqui-tous; therefore, it is possible that this enzyme may be involved in cell wall exten-sibility (Ridge and Osborne 1970), ethylene biosynthesis (Mapson and Wardale 1972) and disease resistance (Kosuge 1969, Seevers, Daly and Catedral 1971). With respect to bean leaf abscission, several reports have thoroughly described the gross anatomy (Brown and Addicott 1950, Scott, Miller, Webster and Leopold 1967, Osborne 1968, Webster 1968, 1970, Webster and Leopold 1972, Webster and Chiu 1975). In tobacco flower pedicel abscission zone tissue, there have been several studies on both naturally occurring (Jensen and Valdovinos 1967, 1968, Valdovinos and Jensen 1968) and ethylene-induced (Valdovinos, Jensen and Sicko 1971, Henry, Valdovinos and Jensen 1971, Jensen and Valdovinos 1972, Valdovinos, Jensen and Sicko 1972, Henry and Jensen 1973, Henry, Valdovinos and Jensen 1974, Henry 1974, 1975a, 1975b, 1977) abscission. The use of diaminobenzidine (DAB) in fine-structural cytochemistry was initially introduced by Graham and Karnovsky (1966), when they reported on the fine structural localization of horesradish peroxidase activity. Diaminobenzidine (DAB) has since been used to ultrastructurally identify peroxidase activity in leaf peroxisomes (Israel and Steward 1967), chloroplast thylakoids (Nir and Seligman 1970, Henry, Valdovinos and Jensen 1971, Henry and Jensen 1973, Henry 1975a, 1975b), kidney peroxisomes (Beard and Novikoff 1969, Fahimi 1969) and to characterize cytochrome c oxidase activity in mitochondria (Seligman, Karnovsky, Wasserkrug and Hanker 1968). There are other reports on the use of DAB to indicate enzymatic activity in plant tissues (Frederick and Newcomb 1969, Vigil, 1969, 1970, Henry, Valdovinos and Jensen 1971, Henry and Jensen 1973, Henry 1975a, 1975b). The inclusion of potassium cyanide, a generalized inhibitor of heme-containing enzymes, such as peroxidase, in the DAB incubation medium, results in a reduced degree of staining (Vigil 1969, 1970, Hepler, Rice and Terranova 1972). It has been reported that aminotriazole, a specific inhibitor of catalase activity, does not obviate peroxidase staining of DAB-incubated tissue in biochemical assays (Margoliash and Novogrodsky 1958, Margoliash, Novogrodsky and Schejter 1960), in animals (Fahimi 1968, 1969, 1970) and in plants (Frederick and Newcomb 1969, Vigil 1969, 1970, Hepler, Rice and Terranova 1972). Ethylene-treated tobacco flower pedicel abscission zone tissue, in biochemical assays, shows a significant increase in endogenous peroxidase between 3 hr and 5 hr in exposure (Henry, Valsovinos and Jensen 1971, Henry, Valdovinos and Jensen 1974). Also, it has recently been reported that both peroxidase and RNase activities of older (7 week) tobacco callus tissue were substantially higher than in younger (4 week) tissue, suggesting that rising levels of these enzymes may be concerned with plant tissue senescence (Vetter 1973). Earlier studies revealed that ethylene-treated tobacco flower pedicels show a 30-fold increase in the proliferation of rough endoplasmic reticula (RER) between 2 hr and 5 hr of ethylene exposure (Valdovinos, Jensen and Sicko 1971). Also, ultrastructural studies indicated the localization of peroxidase in the rough endoplasmic reticula of ethylene-treated pedicels (Henry 1975b). Accordingly, an investigation was undertaken to ascertain if ethylene treatment had any effect on plasmodesmata in tobacco abscission zone flower pedicel tissue. © 1979, Japan Mendel Society, International Society of Cytology. All rights reserved.