Amylopectin is the principal component of starch. The amylose extender (ae) gene encodes the starch-branching enzyme IIb, which is critical in determining the fine structure of endosperm starch. To determine the relationship between the fine structure of amylopectin and its physical properties, rice mutant lines defective in the ae function with altered fine structure of amylopectin and in combination with the waxy (wx) background were selected for comparative studies with primary wild-type and ae starches. The ae mutant endosperms accumulated a high amylose content starch with long amylopectin chains. The ae and wx ae starches showed no significant difference in the unit chain-length distribution of amylopectin and starch granule morphology. The wx ae starch displayed a higher pasting temperature and higher peak viscosity. The gelatinization peak temperatures of the wx, ae, and wx ae starches were 2.2, 13.1, and 17.1 degrees C higher, respectively, than that of the wild-type starch, and the wx ae starch showed a retrogradation peak with a shorter cooling period than that of ae starch. The raw ae and wx ae starches were almost indigestible by alpha-amylase in vitro. Rats fed the wx ae starch showed slowly increasing blood glucose at a lower level than the rats fed the wx or wild-type starch. These results indicate that the primary structure of the rice wx ae amylopectin with enriched long chains changes the granular structure of the starch, including its crystal structure, and results in resistance to in vitro or in vivo degradation.

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This study was carried out to examine the underlying mechanism for the high susceptibility of bovine aged oocytes to activation stimulus. The oocytes were matured for 21, 27, 33, and 39 h and were then parthenogenetically activated with different concentrations of cycloheximide (CHX); their activation rates were then assessed. Additionally, the p34 cdc2 kinase activities in oocytes matured for different time periods were determined. The activation rates of oocytes treated with CHX increased with oocyte aging. In oocytes cultured for as long as 39 h in maturation medium, the treatment led to maximal activation rate of oocytes even in those with the lowest concentration of CHX. The p34 cdc2 kinase activity in oocytes decreased progressively with prolonged incubation time and the activity of the oocytes cultured for 39 h was approximately 40% of that of oocytes cultured for 21 h. In conclusion, the sensitivity of bovine oocytes to activation stimulus increases during in vitro aging; also, the time dependent decline in the capacity of oocytes to synthesize the regulatory protein required for maintaining MII stage may contribute to a high susceptibility of aged oocytes to protein synthesis inhibitor (activation stimulus). Key words: Bovine oocyte, Aged oocyte, Cycloheximide, MPF, ActivationIn a study to explore the influence of interactions between aged gametes on fertilization and early development, Smith and Lodge [1] found that pronuclear development of long-term aged ova was higher than that of short-term aged ova when fertilized by all groups of aged sperm. This showed that the aging of matured oocytes primed their intrinsic ability to undergo pronuclear formation. In nuclear transferred embryos reconstructed with aged oocytes as recipient cytoplasm, it has been reported that not only pronuclear formation and 2-cell progression but also blastocyst formation were improved [2-4]. Additionally, higher fertilization and pronuclear formation rates were noted in aged oocytes which were used for intracytoplasmic sperm injection [5,6]. These results suggest the possibility that aging of oocytes may result in increasing sensitivity to various activation stimulus treatments.Meiotic arrest of mammalian oocytes is known to be maintained by persistently high activity of maturation promoting factor (MPF). The sustained high MPF activity is maintained by cytostatic factor (CSF) activity [7]. The key component of CSF, Mos, may regulate MAPK which is activated by the MAP kinase cascade [8,9]. Inactivation of these kinases (MPF, MAPKs, and Mos) is caused by fertilization or other parthenogenetic stimuli through the oscillations of intracellular Ca 2+ , leading to release from MII arrest and pronuclear formation [10,11]. Accordingly, it is thought that much readier occurrences of activation in aged oocytes are dependent on the decline in the activities of enzymes, including MPF, MAPK, and Mos. However, the relationship between the activation of aged oocytes and the changes in their enzyme activities remains to be fully e...

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