Expression of ascorbic acid oxidase in zucchini squash (Cucurbita pepo L.)

• Published in: Plant physiology (Bethesda) Vol. 96; no. 1; pp. 159 - 165
• Main Authors: Lin, L.S. (Washington State University, St. Louis, MO), Varner, J.E
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.05.1991
• Subjects: 551000 - Physiological Systems; ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; ASCORBIC ACID; BASIC BIOLOGICAL SCIENCES; Biological and medical sciences; BIOLOGICAL FUNCTIONS; BIOLOGICAL LOCALIZATION; Calcium; CELL CONSTITUENTS; Cell growth; CELL WALL; Cell walls; CONTENIDO PROTEICO; CRECIMIENTO; CROISSANCE; CUCURBITA PEPO; ENZYME ACTIVITY; ENZYMES; ETAPAS DE DESARROLLO DE LA PLANTA; FOOD; Fruits; Fundamental and applied biological sciences. Psychology; Gels; GROWTH; MESSENGER-RNA; Metabolism; NUCLEIC ACIDS; ORGANIC COMPOUNDS; Oxalates; Oxidases; OXIDOREDUCTASES; OXIDORREDUCTASAS; OXYDOREDUCTASE; PLANT GROWTH; Plant physiology and development; PLANTS; PROTEINAS; PROTEINE; PROTEINS; RNA; Squashes; STADE DE DEVELOPPEMENT VEGETAL; TECHNIQUE ANALYTIQUE; TECNICAS ANALITICAS; TENEUR EN PROTEINES; VEGETABLES; VITAMINS; Radiolabelling; RNA; Enzyme; Growth; Cucurbitaceae; Cucurbita pepo; Gene expression; Enzymatic activity; Dicotyledones; Angiospermae; Ascorbate oxidase; Spermatophyta; Fodder crop
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.96.1.159

The expression of ascorbic acid oxidase was studied in zucchini squash (Cucurbita pepo L.), one of the most abundant natural sources of the enzyme. In the developing fruit, specific activity of ascorbic acid oxidase was highest between 4 and 6 days after anthesis. Protein and mRNA levels followed the same trend as enzyme activity. Highest growth rate of the fruit occurred before 6 days after anthesis. Within a given fruit, ascorbic acid oxidase activity and mRNA level were highest in the epidermis, and lowest in the central placental region. In leaf tissue, ascorbic acid oxidase activity was higher in young leaves, and very low in old leaves. Within a given leaf, enzyme activity was highest in the fast-growing region (approximately the lower third of the blade), and lowest in the slow-growing region (near leaf apex). High expression of ascorbic acid oxidase at a stage when rapid growth is occurring (in both fruits and leaves), and localization of the enzyme in the fruit epidermis, where cells are under greatest tension during rapid growth in girth, suggest that ascorbic acid oxidase might be involved in reorganization of the cell wall to allow for expansion. Based on the known chemistry of dehydroascorbic acid, the end product of the ascorbic acid oxidase-catalyzed reaction, we have proposed several hypotheses to explain how dehydroascorbic acid might cause cell wall "loosening."