The Relationship of the Peroxidative Indoleacetic Acid Oxidase System to in Vivo Ethylene Synthesis in Cotton

Abstract

Since peroxidase and manganese have been implicated in both auxin destruction and ethylene production, the effect of auxins and high tissue levels of manganese on the peroxidative indoleacetic acid oxidase system and the internal level of ethylene was determined in cotton (Gossypium hirsutum L.cv. Watson GL-7). The highest level of manganese tested produced manganese toxicity symptoms, including necrotic lesions, accompanied by an increase in internal ethylene levels at about 15 days after treatment initiation. Statistically significant increases in indoleacetic acid oxidase and peroxidase activity were first observed 2 days later and were paralleled by tissue manganese levels above 7.4 milligrams per gram dry weight and internal ethylene levels of 0.77 microliters per liter air. Eight hours after application of 2,4-dichlorophenoxyacetic acid or indoleacetic acid, the internal levels of ethylene were increased to above 6.6 microliters per liter air in cotton plants, and levels of this magnitude were maintained for a 72-hour period of observation. Modification of peroxidase and indoleacetic acid oxidase activity in auxintreated plants definitely occurred well after the elevation of internal ethylene levels. While ethylene levels and indoleacetic acid oxidase activity were increased by both experimental approaches, the earlier appearance of increased ethylene indicates that the peroxidative indoleacetic acid oxidase system in cotton is not involved in ethylene synthesis or that this enzyme is not the rate-limiting factor when ethylene synthesis is increased. Ethylene, as well as auxin destruction, may be involved in some of the long term plant responses to toxic levels of manganese. The findings also suggest that auxin-induced ethylene may play a role in the elevation of peroxidase and indoleacetic acid oxidase activity eventually seen in extracts of plants treated with auxins. The data support the assumption that the enzymatic portion of the indoleacetic acid oxidase system in cotton is a peroxidase. Thimann's observation, sufficient evidence has been accumulated to define the major substance responsible for auxin activity as indole-3-acetic acid and to attribute the destruction of IAA within the plant, primarily, to a peroxidase-based enzyme system generally known as IAA-oxidase (11,15,20,28,34,37). By virtue of its role in limiting the supply of IAA within the plant, the IAA-oxidase system has been recognized as a plant growth regulatory mechanism.The potential role of the IAA-oxidase system as a plant growth regulatory mechanism assumed new dimensions with Yang's (39) discovery that an enzyme system strikingly similar to the peroxidative IAA-oxidase system is capable of synthesizing the plant hormone ethylene. If this ethylene-synthesizing system functions in vivo, the growth regulatory activities of the peroxidative IAA-oxidase system may encompass those areas in which ethylene is involved as well as the growth phenomena associated with IAA. This additional regulatory role for peroxidases is supported...

Changes in enzyme activities in abscission zone and berry drop of ‘Kyoho’ grapes under high O2 or CO2 atmospheric storage

“…Compared with control air, the activity of POD increased sharply in 80% O 2 , whereas the increase was suppressed in 40% O 2 +30% CO 2 , which may be due to the fact that oxygen radical scavenging occurs at elevated O 2 levels, and is hampered by increased CO 2 (Hoogerwerf, Kets, & Dijksterhuis, 2002). However, the extent of berry drop was not statistically different between 80% O 2 and 40% O 2 +30% CO 2 , which suggested that POD may have an indirect effect on abscission through the control of IAA levels (Fowler & Morgan, 1972).…”

“…Peroxidase (POD), which is not involved in cell-wall degradation, has also been found in the AZ of many plants (Wittenbach & Bukovac, 1975;Mcmanus, 1994). It is involved in the oxidation of indoleacetic acid (IAA) (Fowler & Morgan, 1972), an auxin long implicated in the abscission process.…”

Peroxidase Activity in the Abscission Zone of Bean Leaves during Abscission

“…In debladed plants, the Peroxidase has been implicated in a number of diverse phenomena observed in plants (29,31,34,35) including the synthesis of ethylene (21,38). Similarly, conflicting reports (10,18) indicate that ethylene synthesis is not regulated by peroxidase. The localized increase in protein and RNA synthesis necessary for separation to occur in the abscission zone of Phaseolus vulgaris is increased by ethylene (2) and has been associated with an increase in cellulase activity (1,15,26).…”

Les peroxydases végétales de classe III

“…Un site de fixation de I' AlA a d'ailleurs ete mis en evidence en comparant Ia structure de ces proteines avec celle d'autres proteines fixant I' AlA (Savitsky eta!., 1999). In vivo, cette oxydation pourrait etre modulee par Ia presence d'antioxydants tels que des flavono"ides (Mathesius,200 I (Fowler, 1971 ), car elles sont capables in vitro de synthetiser ! 'ethylene a partir de son precurseur, l'acide 1-amino-cyclopropane-1-carboxylique (Penel et a/., 1990) A !…”