Peroxidases in Tobacco Abscission Zone Tissue

Abstract

Ethylene-induced abscission in flower pedicels of Nicotiana tabacum L. cv. Little Turkish causes a progressive increase in peroxidase activity during the first 4 hours of a 5-hour time course ethylene treatment period, with decrease in peroxidase activity occurring between 4 hours and 5 hours, when the supernatant extracts of abscission zone segments are tested spectrophotometrically for peroxidase activity, using guaiacol and hydrogen peroxide. Nonethylene-treated tissue has a much lower level of peroxidase activity over the same time course period. In ethylene-treated tissue the decline in break-strength correlates with the beginning of increase in peroxidase activity (3 hours). When the abscission zone area of the pedicel is further divided into proximal, abscission zone, and distal portions, respectively, the ethylene-treated tissue has the highest peroxidase activity in the abscission zone portion, with the maximum peak occurring at 4 hours and decreasing between 4 hours and 5 hours. Acrylamide gel electrophoresis of enzyme breis from ethylene-treated aand nonethylene-treated plants reveals that no new peroxidase isozymes are formed in response to ethylene, indicating an increase in the amount of one or in both of the two already existing isozyme banding patterns. The measurement of protein in the proximal, abscission zone, and distal segments, over a 5-hour ethylene treatment period, indicates that it is being translocated in a distal to proximal direction in the abscission zone pedicel. The possible participatory role for peroxidase in ethylene-induced tobacco flower pedicel abscission are discussed.Ethylene can stimulate peroxidase activity in petiole, stem, and leaf blade tissue of cotton plants (6, 12); in the pulvinus and separation layer of bean explants (3,14); in etiolated peas (1); and in sweet potato root discs (3). It has been suggested that the distribution of peroxidase activity and IAA oxidase content can be correlated with the processes of natural abscission (10,11,13,17 (Fig. 1).Groups of 10 segments (each segment 6 mm in length) from the flower pedicels were used for the spectrophotometric assay to determine peroxidase activity. A separate group of 10 segments was collected, and the 6-mm portion of the flower pedicel was further divided into distal (2 mm), abscission zone (2 mm), and proximal (2 mm) segments. Peroxidase activity in enzyme breis prepared from tissue segments was determined where the tissue had been previously exposed to ethylene for periods up to 5 hr.After excision from the flower pedicel the tissue segments (6-and 2-mm sections) were weighed and immediately put into prechilled mortars at 4 C. The tissue samples were ground with a mortar and pestle at 4 C for 5 min in 4 ml of 0.01 M phosphate buffer, pH 6.0. The tissue homogenates were centrifuged for 10 min at 4 C at 2.000g to remove cellular debris.The supernatant fraction was used for the peroxidase assays (15).Spectrophotometric determinations were measured at a wavelength of 460 nm, using a Beckman model DU s...

Regulation of pollination‐induced ethylene and its role in petal abscission of Pelargonium×hortorum

“…The cycloheximide was applied to the cut pedicel, where one would expect transpiration to favor its movement to the petals, and thus across the abscission zone, to a greater extent than to the upper portions of the pistil. The fact that cycloheximide completely blocked pollination-induced (the present work) and ethylene-induced (Evensen et al 1993) abscission of geranium petals suggests that protein synthesis is required for petal abscission, as indicated by previous research on leaves and flowers (Abeles et al 1971, Henry et al 1974, Ten Cate et al 1975.…”

Expression profiling of tomato pre-abscission pedicels provides insights into abscission zone properties including competence to respond to abscission signals

“…Expansin is a cell wall remodeling protein and reportedly regulates abscission of leaflets in elderberry ( Sambucus nigra ) and pedicels in Arabidopsis [25,26]. Gene expression or enzyme activity of peroxidases is detected during abscission in tobacco ( Nicotiana tabacum ) flower pedicels and citrus leaves [29,54]. Although the expression of the genes for PG, expansin and peroxidase were expressed preferentially in AZs, the expression levels of the genes at the pre-abscission stage was much lower than after the onset of abscission (Figure  2B) [25,27].…”

Genome-wide digital transcript analysis of putative fruitlet abscission related genes regulated by ethephon in litchi

“…Previously, some reports supported a link between ROS and abscission. In tobacco, Henry et al ( 1974 ) found that POD activity was increased during the ethylene-induced pedicel abscission. In tomato, delayed abscission of flowers and fruits was related to the increase of ROS-scavenging enzymes (Djanaguiraman et al, 2004 ).…”