No abstract

No abstract

No abstract

No abstract

Abstract. In a close parallel to the developmental pattern of a-amylase activity, a rapid increase of maltase activity occurred in the endosperm tissue of g:rminating rice seeds after about 4 days of the seed imbibition. The overall pattern -of the 2 hydrolytic enzyme activities strongly suggest that amylolytic breakdown is the major metabolic route of starch utilization in the germinating rice seeds. Results of the chemical analyses of sugar constituents as well as the measurements of sucrose synthetase aotivity show that the scutelluim is the site of sucrose synthesis in the germinating rice seeds. It is thus supported that glucose derived from the reserve starch in endosperm is transported to scutellum, where it is converted to sucrose. Sucrose is further mobilized to the growing tissues, shoots and roots.In a previous paper of this series (10) Materials and MethodsRice Seed Germiiinationt. Throughout the study, the same procedure of so-wing rice seeds (Oryza sativa L. var. Fujiminori) and growing in the dark chamber as reported previously were used (10).Enzymne Assay. Maltase was assayed by the following procedure. Endosperm tissues of 40 rice seeds devoid of roots, roots and scutella ((approximately 1.3 g fresh wt) were ground with 4 ml of 0.01 M tris-HCl buffer (pH 7.5) in a chilled mortar and the whole homogenate centrifuged at 4°. An aliquot (1.5 ml) of the supernatant fraction w-as applied onto a column of Sephadex G-25, whiclh was equilibrated by 0.01 M tris-HCl buffer (pH /7.5). and the eluate (4.5 ml) was used as the enzyme source. The reaction mixture contained (in 1imoles) Na-acetate buffer (pH 4.5), 2.5; malitose, 0.25; and enzyme preparation, 20,l,, in a total volume of 30 gl. The reaction (350 for 60 min) was stopped by adding 0.5 ml of 0.1 N NaOH. The amount of glucose formiied wvas analyzed by determininig the increa,se of the reducing sugar content utsing the Somogyi-Nelson method (11). It w\vas confirmed that crystalline bacterial a-amylase (Nagase Sangyo Company Ltd., Osaka) did not h-drolyze the maltose rmolecule.In the analysis of sucrose synthetase, 100 scutella of germinating rice seeds were honmogenized in a chilled small--size glass homogenizer using 0.8 ml of 0.01 M tris-HCl buffer (pH 7.5). The whole lhomogenate was centrifuged and a 0.5 ml aliquot of the supernatant fraction was passed tlhrough a column of Sephadex G-25 which was equilibrated by 0.01 M tris-HCl buffer (pH 7.5). The eluate (2.5 nml) 765www.plantphysiol.org on May 12, 2018 -Published by Downloaded from

No abstract

No abstract

No abstract