• KOREAN JOURNAL OF CROP SCIENCE
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• v.20
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• pp.1-26
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• 1975

In order to provide basic information for the application of tissue culture to a rice breeding program. experiments were carried out on the callus formation from seedings and anthers and organ differentiation from the callus of rice varieties and their hybrids. It appeared that in general the callus tissue was more easily induced in japonicas than in indicas with significant varietal differences. A highly significant positive correlation (r=0.896$^{**}$) was obtained between the fresh weight of callus induced in NAA medium and in 2, 4-D medium in the same variety. Callus formed on the medium with 2, 4-D was more friable than that formed on the medium with NAA. The callus formation from seedlings was better than from anthers in upland rice varieties. The easiness of the callus formation appeared to be a dominant character in crosses of rice varieties. Varietal difference was also noticed in the organ differentiation from the callus and the root differentiation seemed to be easier than the shoot differentiation. Most of the plants derived from the cal1us were albinos and the frequency of occurrence of albinos was greater in callus of seedlings than in that of anthers. Greater amount of callus tissue was formed from anthers of $F_1$ plants than anyone of their parents in remote-crosses but it was clear in close-crosses. A highly significant positive correlation (r=0.504$^{**}$) was found between the callus formation from seedlings and from anthers.

• Korean Journal of Ichthyology
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• v.21 no.3
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• pp.141-148
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• 2009

Sex differentiation and gonad development were investigated in a marine medaka species, Oryzias dancena (Beloniformes; Teleostei). The average time to hatch was 11 days post-fertilization (dpf) at $25^{\circ}C$. Primordial germ cell (PGC) was first observed at 5 dpf and migrated to presumptive gonadal area between the gut and pronephric duct at 9 dpf. Male and female gonads were morphologically differentiated at 12 days post-hatching (dph). Early oocytes at perinucleolus stage as well as the formation of spermatid and efferent duct were observed at 28 dph. At 6 weeks of age, the ovary exhibited yolk granulation in many oocytes, while testis possessed a considerable number of spermatogonia and spermatids. The first ovulation was observed in 9-week-old females, and at the same age, males contained fully-matured spermatozoa. Data obtained in this study indicate that the gonad differentiation of O. dancena is the typical type of differentiated gonochorism.

• Korean Journal of Microbiology
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• v.28 no.1
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• pp.1-5
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• 1990

The coding sequence of hepatitis B viral core antigen (HBcAg) (subtype adr) contains two in-phase initiation codons, one for precore and the other for core antigen gene. To study the expression of core antigen and the role of precore region, the coding sequence of HBcAg with or without precore (pre-C) region were subcloned into yeast expression vector containing phosphoglycerate kinase (PGK) promoter. To study the role of upstream region in the expression of the core antigen, a series of 5' deletion mutants were also subcloned into the vector. After transformation into various host strains, the expression of HBcAg were analysed by radio-immunoassat. Under optimal condition of core antigen gene expression in yeast, the highest amount of antigen was detected in the cell line SHY4 containing pGKHBc plasmid composed of the yeast PGK gene promoter, terminator and C-gene. Regardless of the presence of precore region, core antigen was not detected in the medium but in cell extract. These results suggest that precore region cannot affect the secretion of core antigen in Saccharomyces cerevisiae.

• Journal of Aquaculture
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• v.13 no.3
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• pp.215-222
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• 2000

The primordial germ cell of the sweet fish was recognized from the 2-day old fry (tl : 0.66 cm), when it began to protrude into peritoneal cavity between meaonephric duct and gut. The primordial gonad, with the formation of genital ridge, developed on the 30-day old fry. Ovarian differentiation was identified by the presence of ovarian cavity and meiotic oocytes from the 90-day old fry (tl : 3.42 cm). Testicular differentiation was identified by the presence of spermatogonial cells with efferent duct from the 100-day old fry (11 : 4.50 cm). Hence the sweet fish belongs to the differentiated type of gonochoristic teleost.

• Journal of the Korea Computer Industry Society
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• v.2 no.10
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• pp.1339-1348
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• 2001

This study is directed to compare the payment systems between conventional and internet, under international commerce. A stable and secure payment system is necessary for the progress of e-business through the internet. There are three typical methods of payment system in conventional transactions; the letter of credit(L/C) basis, the collection basis and the remittance basis. The exporter prefers L/C basis because of authentic payment, financial convenience and reduced risk Buyers and sellers who have enjoyed long creditable relationships use carefully the collection basis. The remittance basis is adequate for small amount payment for sample. In this paper, the merits and demerits of electronic payment system are compared to the conventional payment one. Internet payment system has an advantage of speed-up in payment against the conventional, but has a limited usage in the area of consumer based(B to C) transaction. The conventional payment system has been becoming overwhelm electronic payment one in the business to business(B to B) area.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.1
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• pp.132-138
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• 1997

In order to obtain the basic information for seedling production of surf clam, Spisula sachalinensis, annual reproductive cycle was investigated from March 1994 to May 1995. S. sachalinensis was dioecious. The gonads are located between the digestive diverticula and muscle tissue of the foot. The condition factor was reached its maximum (0.19) in June, and then decreased to 0.16 in July. In November, the value was the lowest and then increased slowly. The age and minimum size for sexual maturation were 2 years old and about 50 mm in shell length, respectively. However, less than $10\%$ of sexually undifferentiated individuals were larger than 80 mm in shell length. On the other hand, the size of mature oocytes was ranged to $50\~60{\mu}m$ in diameter and testis-ova was observed in testis of the mature stage. Annual reproductive cycle could be classified into five successive stages : multiplicative (October to January), growing (February to April), mature (April to June), spawning (June and July) and degenerative and resting (August and September) stages.

• Korean Journal of Ichthyology
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• v.13 no.4
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• pp.248-253
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• 2001

An histological study was conducted to determine the initial treatment time and treatment duration in the use of sex-reversal hormones in relation to gonadal development and sexual differentiation in the bagrid catfish, Leiocassis ussuriensis. The primordial germ cell, which could be recognized from one-day-old fry, began to protrude into the peritoneal cavity between the mesonephric duct and the gut. The primordial gonad with a genital ridge was developed at 5~10 days after hatching. Sex differentiation of the ovary was identified by the ovarian cavity and meiotic oocytes from 20-day-old larvae. Testicular differentiation was also identified by spermatogonial cells from 20-day-old larvae. It may therefore be concluded that this species belongs to the differentiated type of gonochoristic teleost.

• Development and Reproduction
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• v.2 no.1
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• pp.69-74
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• 1998

The early gonadal development and sexual differentiation of Rhynchocypris oxycephalus are described from the stage of hatching to 150 days after hatching. During this peroid, the average length of the body grew from 0.64 cm to 5.96 cm. the primordial germ cells (PGCs), which could be recognized at the time of hatching, began to protrude into peritoneal cavity at a standard total length of 1.91 cm. At a standard total length of 2.29cm, initial ovarian differentiation wasidentified by the transformation of PGCs to meiotic oocytes. Finally, at the standard total length of 5.96 cm, the female gonads gradually developed towards migratory nucleus oocytes, characterisiing the maturation. Oocytes proliferated rapidly after sex differentiation while the testis entered a period of quiescence, as they continued to multiply but did not undergo growth until the standard total length of 4.00 cm. At a standard total length of 4.00 cm, spermatocytes arrested in thephase of interkinesis, Sertoli-like cells and sperm duct formation, with signs of meiotic activity, were observed. Therefore it may be concluded that R. oxycephalus belongs to the differentiated type of gonochoristic teleosts.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.3
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• pp.184-191
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• 2000

Gametogenesis and the reproductive cycle of the marsh clam, Corbicula leana(Prime} were investigated monthly Hyongsan estuary, Korea from January to December 1998 by histological observation. C. leana had separate sexes, and oviparous. The gonads were located between the sub-region of mid-intestinal gland in visceral cavity and reticular cennective tissue. The ovary and testis were composed of a number of ovarian and testicular tubules, respectively, Mature oocytes were characterized by germinal vesicles with nucleoli and their sizes ranged $70\;to\;80{\mu}m$ in diameter. A number of mesenchymal tissues and pigment granular cells were distributed in the growing oocytes and spermatocytes during early developmental stages. With the further development of gonad, these tissuse and cells gradually disappeared. The monthly changes in the fatness index were closely related to reproductive cycle. Minimun size for sexual maturity was reached over 10.0 mm in shell length. The reproductive cycle could be classified into 6 stages : multiplicative (March to April): early growing and growing (May to June), mature (July to August), spent (September), degenerative (October) and recovery (November to February).

• Proceedings of the Korean Society of Developmental Biology Conference
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• 2001.08a
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• pp.36-37
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• 2001

큰가리비는 자웅이체이다. 난환형성과정은 난모세포의 발달정도에 다라 다르게 나타나고 있다. 난자형성과정은 난원세포기, 전난황형성난모세포기, 초기난황형성난모세포기, 후기난황형성난모세포기, 성숙난모세포기의 연속적인 5단계의 과정으로 나눌 수 있었다. 전난황형성기 난모세포질 내에서는 핵주변 구역에 골지장치와 수많은 공포들 및 미토콘드리아들이 출현하고 있는데 이들은 차후, 지방적 형성에 관여한다. 난황형성전기난모세포(previtellogenic oocyte)에서는 지방적 및 지질과립들이 핵막 근처에서 출현하여 피질층쪽으로 분산되는 반면, 같은 발달 단계의 난모세포질의 피질구역에서는 피질과립들(단백질성 난황과립)이 처음으로 생성되어 난황막 근처의 피질층에서 핵주변 구역쪽으로 분산.분포된다. 난황형성후기 난모세포에서는 세포질 내의 골지장치, 공포, 미토콘드리아, 그리고 조면소포체들이 자율합성에 의해 난황과립 형성에 관여하고 있다. 반면 외인성 물질들인 지질형태의 과립들, 다량의 글리코겐 입자들이 생식상피 내에서 출현하고 있는데. 이들 물질이 생식상피에서 난황막 구조물인 미세융모를 통해 난황형성 후기 난모세포의 날질 내로 통과해 들어가는 현상이 관찰되었다. 이와같은 현상은 난황형성이 일어날 때에 heterosynthesis가 일어나고 있음을 시사한다. 완숙난모세포의 난경은 약 50~60$\mu\textrm{m}$이다. 정자형성과정은 정원세포기, 제1차정모세포기, 제2차정모세포기, 정세포기, 정자기의 연속적인 5단계로 나눌수 있었다. 정셍포기에서 정자로 변태되는 과정 중에 침체의 분화과정이 있는데 이에는 1. Golgi phase, 2. Cap phase 3. acrosome phase, 4. maturation phase의 단계를 거쳐 첨체가 완성된다. 정자는 원시적 형태를 이루고 있으며 4개의 미토콘드리아가 부핵을 형성하고 있다. 완숙정자 두부의 길이는 대략 $3 \mu$m 이며, 미부의 길이는 약 $30 \mu$m정도이다. 정자 미부편모의 axoneme은 중앙의 2개의 미세소관(microtubule)과 주변에 위치한 9개의 2중 미세소구관(microtublue)으로 이루어져 있다.