Biochemical analysis of amylose-extender (ae) mutant of rice (Oryza sativa) revealed that the mutation in the gene for starch-branching enzyme IIb (BEIIb) specifically altered the structure of amylopectin in the endosperm by reducing short chains with degree of polymerization of 17 or less, with the greatest decrease in chains with degree of polymerization of 8 to 12. The extent of such change was correlated with the gelatinization properties of the starch granules, as determined in terms of solubility in urea solution. The ae mutation caused a dramatic reduction in the activity of BEIIb. The activity of soluble starch synthase I (SSI) in the ae mutant was significantly lower than in the wild type, suggesting that the mutation had a pleiotropic effect on the SSI activity. In contrast, the activities of BEI, BEIIa, ADP-Glc pyrophosphorylase, isoamylase, isoamylase, pullulanase, and Suc synthase were not affected by the mutation. Therefore, it is stressed that the function of BEIIb cannot be complemented by BEIIa and BEI. These results strongly suggest that BEIIb plays a specific role in the transfer of short chains, which might then be extended by SS to form the A and B 1 chains of amylopectin cluster in rice endosperm.Starch is composed of two types of molecule, namely amylose and amylopectin. Amylose is an essentially linear molecule composed of ␣(134)-linked glucosidic chains, whereas amylopectin is a highly branched glucan with ␣(136) glucosidic bonds that connect linear chains. The ␣-1,4 chains of amylopectin consist of A chains that carry no additional chains, B chains that carry A chains or other B chains, and a C chain that includes the reducing terminus (Peat et al., 1952). Hizukuri (1986) proposed a cluster model for amylopectin. In this model, A and B 1 chains form a single cluster, whereas B 2 and B 3 chains extend to two and three clusters, respectively. Hanashiro et al. (1996) proposed that, in amylopectin, chains of degree of polymerization (DP) Ϲ12, 13 Ϲ DP Ϲ 24, 25 Ϲ DP Ϲ 36, and DP м 37 correspond to A chains, B 1 chains, B 2 chains, and B 3 and longer chains, respectively.

Fig. 2 Effects of some oxidants of the C 2 H 4 -oxidant cell with graphite/ PTFE cathode on the Wacker oxidation. C 2 H 4 (39 kPa), H 2 O (13 kPa), anode ¡ aq. H 3 PO 4 in silica wool ¡ cathode, oxidants. Oxidants: NO 2 (5 kPa), NO (20 kPa), O 2 (50 kPa), NO (50 kPa) + O 2 (51 kPa), and NO (6 kPa) + O 2 (51 kPa). T = 353 K.

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Oxidations of C2H4 and C3H6 were performed using an false[normalalkene|normalPd black false(normalanodefalse)|H3PO4|normalgraphite false(normalcathodefalse)|NO+O2false] gas cell at 353 K. The cofeed of NO with O2 at the cathode dramatically enhanced the Wacker-type oxidations of the alkenes. The enhancement was ascribed to the acceleration in the rate of electrochemical oxidation of Pd(0) to Pd(II) due to the formation of NO2 at the cathode. The formation of NO2 increased the electromotive force of the cell and the polarization at the Pd anode. The graphite without precious metals was sufficient as the cathode for the reduction of NO2 into NO under the reaction conditions in this work. The NO cofed with O2 works as a mediator for the electrochemical reduction of O2. In the case of propene oxidation, acetone was the major product for the C3H6­false(NO+O2false) cell. The formation of acrolein, the major product for the C3H6­O2 cell, was decreased markedly when NO had been cofed with O2. These observations could be ascribed to the changes in the concentrations of Pd(0) and Pd(II) responsible for the π-allyl and Wacker type oxidations, respectively. © 2001 The Electrochemical Society. All right reserved.