Activity of Pectin Esterase and Cellulase in the Abscission Zone of Citrus Leaf Explants

Abstract

Abstract. The activity of pectin esterase and cellulase in abscission of citrus explants was studied. No relation was established between pectin esterase and abscission, while cellulase activity was markedly increased before absoission and for a certain period after excision. IAA and cycloheximide delay abscission and cellulase activity, while ethylene and, to a lesser extent, GA. acoelerate them. Application of cycloheximide during the lag period and before cellulase activity can be measured, inhibits to a certain extent the formation of 'cellulase An escape from the inhibitory effect of cycloheximide is detected when inhibitor is supplied at the end of the -lag period. Osiborne (21) claimed that pectin esterase (PE) participates in the abscission process of bean leaves. In a later report Horton and Osborne (12) mention that cellulase is also active in the albscission zone of bean leaves. While studying the role of PE in the abscission zone of citrus explants we found that cellulase rather than PE is responsible for the separation process.Very recently, Abeles (5) published a parallel study, showing the role of cellulase in the abscission zone of bean, cotton, and coleus explants which were aged for 20 hr and then transferred into ethylene environment. He concludes that the mechanism of ethylene action during cell separation induces protein synthesis which is essential for cell separation by the production of essgential enzymes for the physiological processes of abscission. The present work was carried out independently although simultaneously with that of Abeles (5). The objective was to define the time relationship which exists between the ajbscission mechanism and cellulase activity in citrus leaves. Petioles of 10 explants were tied to a glass-slide and kept for the desired period in a humidified Petri dish, 9 cm in diameter, in the dark and at 250. At the end of each experiment the percent of abscission was determined by counting the distal sections which had already abscised and those which albscised due to a gentle touch administered by forceps (7).Pectin Esterase (PE) Assay. The method employed was that of Kertez (14) with the modification of Rouse and Atkins '(25). Two sections of 2 mm were cut from 20 explants, from each side of the abscission-layer over a 8 mm wide section from the proximal to the distal end (21). Twenty similar sections, representing the same portion with respect to the abscission line, were pooled, weighed, and homogenized in 20 ml of 0.2 N NaCl in a mortar. The homogenate was transferred into 50 ml of 1 % 1717 www.plantphysiol.org on May 12, 2018 -Published by Downloaded from

Caracterização físico-química e enzimática de uva 'Patricia' cultivada na região de Primavera do Leste - MT

“…A obtenção do extrato de poligalacturonase (PG) seguiu técnica descrita por Buecher & Furmanski (1978) e a determinação da atividade enzimática pelo método descrito por Markovic et al (1975). A determinação da atividade enzimática peroxidase (POD), seguiu as técnicas de Hultin et al (1966) e Ratner et al (1969), com modificações de Vilas-Boas (1995).…”

Suculência e solubilização de pectinas de maçãs 'Gala' submetidas a diferentes tempos de resfriamento e aplicação de 1-MCP

“…O conteúdo de pectina solúvel (mg de ácido galacturônico por 100 g de polpa) foi extraído segundo a técnica descrita por McCready e McComb (1952), sendo a determinação realizada colorimetricamente pela reação com carbazol, segundo Bitter e Muir (1962). A PME (U) foi determinada pela técnica empregada por Ratner et al (1969). A unidade de atividade enzimática da pectinametilesterase foi considerada como sendo a quantidade de enzima capaz de catalisar a desmetilação de pectina correspondente a um nmol de NaOH por minuto nas condições do ensaio.…”

Abscission of Citrus Leaf Explants

“…This retarding effect could be connected to the delayinf effect of auxin on the activity of hydrolytic enzymes in the AZ (17,22). The mechanism which causes auxin to lose its delaying ability, however, is still obscure.…”

“…The data presented in the following are based on kinetic studies of NAA conjugation at various stages of abscission of Citrus leaf explants, which are a sensitive and reliable system for physiological study of abscission, and conjugate NAA effectively. Their performances in abscission studies have been well characterized in this laboratory (1 1, 12, 18, 19 (12,17).…”

“…Experiments were repeated at least twice. Per cent of abscission was determined by counting the distal sections which had already abscised and those which abscised following a gentle touch (6,17).…”