Plant Physiol, July 2002, Vol. 129, pp. 1330-1340

Gibberellic Acid, Synthetic Auxins, and Ethylene Differentially Modulate -L-Arabinofuranosidase Activities in Antisense 1-Aminocyclopropane-1-Carboxylic Acid Synthase Tomato Pericarp Discs¹

Cátedra de Fruticultura, Departamento de Producción Vegetal, Facultad de Agronomía, Universidad de Buenos Aires, C 1417 DSE Buenos Aires, Argentina (G.O.S.); Department of Pomology, University of California, Davis, California 95616-8683 (L.C.G., J.M.L.); and Department of Chemistry, Western Washington University, Bellingham, Washington 98225-9150 (G.A.P.)

-L-Arabinofuranosidases (-Afs) are plant enzymes capable of releasing terminal arabinofuranosyl residues from cell wall matrix polymers, as well as from different glycoconjugates. Three different -Af isoforms were distinguished by size exclusion chromatography of protein extracts from control tomatoes (Lycopersicon esculentum) and an ethylene synthesis-suppressed (ESS) line expressing an antisense 1-aminocyclopropane-1-carboxylic synthase transgene. -Af I and II are active throughout fruit ontogeny. -Af I is the first Zn-dependent cell wall enzyme isolated from tomato pericarp tissues, thus suggesting the involvement of zinc in fruit cell wall metabolism. This isoform is inhibited by 1,10-phenanthroline, but remains stable in the presence of NaCl and sucrose. -Af II activity accounts for over 80% of the total -Af activity in 10-d-old fruit, but activity drops during ripening. In contrast, -Af III is ethylene dependent and specifically active during ripening. -Af I released monosaccharide arabinose from KOH-soluble polysaccharides from tomato cell walls, whereas -Af II and III acted on Na₂CO₃-soluble pectins. Different -Af isoform responses to gibberellic acid, synthetic auxins, and ethylene were followed by using a novel ESS mature-green tomato pericarp disc system. -Af I and II activity increased when gibberellic acid or 2,4-dichlorophenoxyacetic acid was applied, whereas ethylene treatment enhanced only -Af III activity. Results suggest that tomato -Afs are encoded by a gene family under differential hormonal controls, and probably have different in vivo functions. The ESS pericarp explant system allows comprehensive studies involving effects of physiological levels of different growth regulators on gene expression and enzyme activity with negligible wound-induced ethylene production.