Galactosidases in tomato fruit ontogeny: decreased galactosidase activities in antisense ACC synthase fruit during ripening and reversal with exogenous ethylene

Abstract

α- and β-galactosidase (α- and β-Gal) activities, firmness and pigment content were analysed in tomato (Lycopersicon esculentum Mill.) pericarp during fruit growth and ripening, comparing normal fruit with transgenic fruit containing an ACC-synthase antisense transgene. Normal and transgenic immature green fruit had similar temporal patterns of total α- and β-Gal activity. Immature 21-day-old fruit displayed 93% and 134% higher α- and β-Gal activity on a per gram fresh weight basis, respectively, than mature-green fruit. During ripening, normal fruit presented increasing levels of α- and β-Gal activity towards the red-ripe stage. β-Gal II was detected in mature-green tomatoes; it rose rapidly and reached maximum values at the red-ripe stage. In contrast, α- and β-Gal activity in antisense fruit decreased after reaching the breaker stage, and a low continuous level of activity was apparent between 54 and 108 days after anthesis. 48- to 108-day-old transgenic fruit showed constant basal levels of β-Gal II. There were no significant differences in enzyme activity between antisense attached and detached fruit. An exogenous ethylene treatment performed in transgenic tomatoes brought about a promotive effect on total α- and β-Gal activity in general and on β-Gal II in particular, thus suggesting a role for ethylene in de novo synthesis or activation of these enzymes. Softening, chlorophyll breakdown and lycopene biosynthesis were impaired in the antisense fruits, but the impairment was only complete for lycopene synthesis and all were reversed by applied ethylene. These results can be associated with the signal transduction pathways proposed to be operational during tomato ripening.

Postharvest softening of apple (Malus domestica) fruit: A review

“…1; Johnston et al 2001aJohnston et al , 2002a. This softening curve is not unique to apple, and is similar to that from fruits of several melon cultivars (Aggelis et al 1997), tomatoes (Sozzi et al 1998), and early harvested kiwifruit (MacRae et al 1989). However, apples only soften by 25-50% to a final firmness of 35-50 N, whereas melons, tomatoes, and kiwifruit soften by 75-100% during ripening to a final firmness of 0-10 N (Bourne 1979;Johnston et al 2001a).…”

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

“…5), reportedly in close correlation with the decrease in fruit firmness of cv VF36 (Sozzi et al, 1998). The highest ␣-Af III activity-as well as maximum softening-is found in red-ripe fruit (56 DAA).…”

“…A multigenic ␤-galactosidase (␤-Gal) gene family has recently been identified (Smith and Gross, 2000); three different gene products were purified and characterized for the first time two decades ago (Pressey, 1983). One of them, designated ␤-Gal II, is specifically active during ripening and is probably involved in fruit softening (Pressey, 1983;Carey et al, 1995;Smith et al, 1998;Sozzi et al, 1998). However, little is known about other major glycosidase classes, including the arabinofuranosidases.…”

“…Inhibition of the expression of ACC synthase, achieved in transgenic tomato plants (Oeller et al, 1991), is particularly useful in assessing whether ethylene enhances or triggers the gene expression or the activity of potential cell wall-modifying enzymes (Sitrit and Bennett, 1998;Sozzi et al, 1998) without applying inhibitors of ethylene synthesis or action. Herein, we demonstrate the utility of a pericarp disc system from ESS fruit for testing fruit tissue responsiveness to physiological levels of several biological regulators, including ethylene.…”

β-Galactosidase and α-L-Arabinofuranosidase Activities and Gene Expression in European and Chinese Pear Fruit During Ripening

“…β-Galactosidase and α-L-arabinofuranosidase extraction and assay Extraction of β-Gal and α-Af was done according to the method described by Sozzi et al (1998) with slight modifications. Two grams of frozen fruit samples was ground to a fine powder with a pestle and mortar in the presence of liquid nitrogen and transferred to tubes containing three volumes of cold 0.1 M sodium acetate/ acetic acid buffer (pH 5.0) containing 1.4 M NaCl, 1 mM ZnCl 2 , 5 mM 2-mercaptoethanol, and 1.5% (w/v) polyvinylpolypyrrolidone.…”