We analysed the positions of four silkworms’ spinnerets over their cocoon construction in order to clarify the relationship between silkworm spinneret positions and the movement of cocoons in the reeling bath. From the distribution of the spinneret positions for four Bombyx mori silkworms with three different races, N140×C140, N124×C124 and Okusa×Kojiki, the difference in spinning behaviour between the races is considered to directly affect the unevenness of a cocoon shell in thickness. The results also suggest that peanut-shaped cocoons such as Okusa×Kojiki are thinner in the middle than ellipsoid-shaped cocoons such as those of N140×C140 and N124×C124. It further showed that the unevenness may be related to its shape. Estimated rotational angles of a cocoon in the reeling bath showed that its angle approximately followed a Gamma probability distribution. The probability of a cocoon rotating more than a specified angle was significantly smaller for one of the two Okusa × Kojiki silkworms than for the three other silkworms. The similar gentle movement in the reeling bath for the Okusa × Kojiki silkworm was also indicated by the analysis of sample spherical variance. In contrast, there was no difference between the two Okusa×Kojiki silkworms and the N140×C140 and N124×C124 silkworms, in the direction of the rotating cocoons.

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A novel prenylated flavanone was isolated from ethyl acetate extracts of the hard-wood cutting root of Kinuyutaka, a cultivar of Morus alba. The structure, 7, 2', 4', 6'-tetrahydoroxy-6-geranylflavanone, was revealed by spectral analyses. This prenylated flavanone exhibited cytotoxic activity against rat hepatoma (dRLh84) cells with an IC₅₀ of 52.8μg/ml.

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The male gametogenesis is a complex process that is influenced by various components. In some Bombyx mori strains, the remarkabley reduced meiotic recombination rates had been observed when they were calculated based on the frequency of crossing over between two marker genes, Striped (p^S) and Yellow blood (Y). We have employed a differential display analysis of testis transcripts and isolated two clones that were down regulated in the r20 strain, wherein low recombination is maintained. The RT-PCR analysis revealed that the expression of relevant genes was not restricted in the testis. Also the developmental profiles of the expression of these genes in the testis were examined; one of the transcripts, termed BmPI-T1, was expressed during the larval and pupal stage, but disappeared at the adult stage. The other transcript, termed BmLSP-T, was strongly expressed on day 3 to 5 of the fifth instar. The BmPI-T1 and BmLSP-T mRNAs contained open reading frames of 1086 and 801 nucleotides in length, encoding 362 and 267 amino acid residues, respectively. The former resembles the membrane transport facilitator superfamily and the latter is akin to the 30kDa proteins. The current proteins are novel candidates that may be involved in metabolic events during the male gametegenesis.

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Xanthine dehydrogenase (XDH) catalyzes oxidation of hypoxanthine and xanthine to uric acid, which makes silkworm larval skin opaque. The silkworm, Bombyx mori, has two XDH isozymes (XDHα and XDHβ) and two XDH genes (BmXDH1 and BmXDH2). The BmXDH1 gene has been shown to be identical to the oq gene, whose mutation inactivates XDHα and makes larval skin translucent. Thus, BmXDH1 is the XDHα gene, and BmXDH2 is hypothesized to encode XDHβ. In order to test the hypothesis, XDH isozymes were analyzed by Western blotting with antibodies against BmXDH1 and BmXDH2. Both antibodies immunoreacted with bands of expected sizes in normal silkworms but BmXDH1 was not detected in the oq mutant. Since the mutant expresses BmXDH1 (oq) mRNA, this result suggests that BmXDH1 translation is suppressed in the mutant, which has an 8-bp deletion in the BmXDH1 (oq) gene resulting in a premature stop codon. BmXDH2 protein was detected both in oq/oq and +/+ fat body. Western blotting with anti-BmXDH2 antibody also showed that XDHβ is BmXDH2 because they have same electrophoretic mobility on native PAGE.

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A mutant with a black body in the larval stage was discovered in a hybrid race (Kinshyu×Shyouwa) of the silkworm. Genetic analysis indicated that this character was controlled by one dominant gene, which was allelic to U gene, located at position 40.5 on the 14th linkage group. This new mutation was named “Dark-black ursa”, with the gene symbol U^D. Heterozygous larvae (U^D/+) had black marking, except for a white longitudinal line on the dorsal side of the abdomen that was narrower in width than that of U larvae. Homozygous larvae (U^D/U^D) were much darker than heterozygous larvae (U^D/+) in each pigmented region. The ventral integument and intersegmental membranes of the abdomen were also black. In addition to these characteristics, ecdysis at the fourth molting was apt to be difficult for the U^D/U^D larvae. The U^D/U^D moths of both sexes were fertile, but copulation was difficult in the male moths.

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The morphological characteristics of leaves of ‘Ryoumenguwa’, a dorsoventral mutant of mulberry (Morus alba L.) which often has more than two blades or a cup-shaped blade on one petiole, were investigated for 4 years in an attempt to evaluate the regularity of leaf mutation expression and to elucidate the mechanism of leaf morphogenesis. The leaves were classified into single-flat-blade type, cup-shaped-blade type and multi-blade types, according to the leaf shape and the number of blades in the leaf. The leaf shape of the single-flat-blade type was the same as that of the wild type ‘Ichibei’, while those of the cup-shaped-blade type and the multi-blade types could only be seen in the mutant ‘Ryoumenguwa’. The multi-blade types included single-flat-blade plus additional blade(s) types and cup-shaped-blade plus additional blade(s) types. The leaves with a single-flat-blade plus one additional blade formed the most dominant leaf type, accounting for 45.6% of the leaves in four years, distributing more at the middle part than the other parts in the shoots. The leaves with a cup-shaped-blade plus one additional blade formed the second dominant leaf type. Some distinctive characters were observed in the vein structure. One of these was the vein-fused character where veins of different blades fused together in their dorsal sides. 41.9% of the total leaves had vein-fused characters. The other special character was protuberance which was contained at 3.3% of the leaves. Histological observation demonstrated that the adaxial-abaxial axis of typical ‘Ryoumenguwa’ mutant leaf had a (ventral-dorsal)-(dorsal-ventral) polarity in most cases, and appeared to be a new type of the leaf dorsoventral mutant.

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