Sugar Content and Uptake in the Strawberry Fruit

in Journal of the American Society for Horticultural Science
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  • 1 Department of Horticulture, Oregon State University, Corvallis, OR 97331

Abstract

Sucrose was not detected in developing fruit of ‘Brighton’ strawberry (Fragaria × ananassa Duch.) until 10 days after anthesis. Thereafter, its concentration increased rapidly but then declined as fruit became red ripe. The concentration of glucose and fructose were similar and higher than that of sucrose during early fruit growth and in ripe fruit. Uptake of 14C-sugars was followed in excised disks of cortical tissue from fruit 15–17 days old. The addition of CaCl2 was necessary to maintain tissue respiration. Sucrose uptake into tissue disks was nearly constant over 4 hr and had a pH optimum of 5.0. Kinetic analysis of sucrose uptake revealed both linear and saturable components. The kinetic characteristics of fructose uptake was similar to those for sucrose. Glucose, however, was taken up much more rapidly than either sucrose or fructose and only demonstrated saturation kinetics. The metabolic inhibitors NaCN (5 mM), dinitrophenol (DNP, 3 Mm) and carbonyl cyanide m-chlorophenyl hydrazone (CCCP, 100 μM) stimulated sucrose uptake 34%, 94%, and 54%, respectively. DNP eliminated the saturable component. Uptake of sucrose was inhibited by 36% with 10 μm DNP, 16% with 5 mM glucose, and 16% in a 100% N2 atmosphere. After incubation in 14C-sugars for 2 hr, about 90% of the label recovered from disks was in a neutral fraction. Half or more of this was in either glucose or fructose, depending upon the sugar fed. The distribution of 14C between glucose and fructose moieties of sucrose isolated from tissue fed (14C-fructosyl) sucrose indicated that a portion of the sucrose recovered underwent hydrolysis and randomization. Similar results were found with sucrose isolated from attached, whole fruit 8 hr after abraded leaves were fed labeled sugars. Results suggest that sucrose may be hydrolized prior to uptake into fruit tissue.

Contributor Notes

Present address: ARS/USDA, 2021 S. Peach Ave., Fresno, CA 93727.

Received for publication 14 May 1985. Oregon Agr. Expt. Sta. Tech. Paper no. 7528. From the PhD dissertation of the senior author. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.