真珠形成機構の生鉱物学的研究

和田, 浩爾

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真珠形成機構の生鉱物学的研究

https://fra.repo.nii.ac.jp/records/2009010

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紀要論文 / Departmental Bulletin Paper(1)

公開日

2024-06-27

タイトル

真珠形成機構の生鉱物学的研究

言語

タイトル

Biomineralogical studies on the mechanism of pearl formation.

言語

jpn

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http://purl.org/coar/resource_type/c_6501

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departmental bulletin paper

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metadata only access

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http://purl.org/coar/access_right/c_14cb

著者

和田, 浩爾

抄録

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Abstract

内容記述

第１章　真珠の鉱物成分（要約）

1) 各種アコヤガイ真珠を示差熱分析及びX線回折によって調べた。
2) 軟体動物鉱物化組織中の炭酸石灰の多型について補足論議をおこなった。

言語

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第２章　真珠の建築学的構造（要約）

1) 真珠の基本的な建築学的構造，結晶質構造，成層変化及び層状構造変化を調べ，この面から真珠形成機構を追究した。
2) 真珠の基本的な建築構造はそれに相当する貝殻質層のそれと全く同様であるが，構成鉱物成分が真珠形成の中心に対して同中心ないし放射状繊維構造を示す点を異にする。ただし殻皮層真珠は貝殻殻皮層にくらべて複雑な成層を示す。
3) 真珠を構成している鉱物成分は規則的な配向を示しながら成長しており，特に真珠の真珠層においては aragonite 微結晶のb軸及びc軸が貝殻のそれと同様に，層の水平及び垂直な成長方向にほぼ並行に配列した二重繊維構造をもっていると考えられる。
4) 真珠の結晶質構造を貝殻のそれと比較検討すると，真珠袋上皮細胞はその水平方向の拡がりに一定の伸びないし方向性を持っていると考えられる。
5) 成層変化は真珠形成初期にかなりしばしば観察されるが，移植片が外套膜部分における本来の分泌機能を獲得した後には，特殊な場合を除いてその出現率は非常に小さい。
6) 真珠形成過程に種々の層状構造や外形の歪形を生ずる。
7) イケチョウガイ真珠には建築構造上では真珠層と類似している炭酸石灰以外の鉱物成分からなる特殊なものがある。

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第３章　真珠の鉱物化について（要約）

1) 真珠の鉱物化機構の特徴を解明するために，外套膜の移植にともなう真珠袋の形成，外套膜の区域による分泌機能の特殊性，貝殻物質の沈着現象及び結晶成長等を調べた。
2) 真珠袋上皮には一定方向の拡がりがあり，この拡がりは移植片上皮細胞の移動した方向に相当するものと考えられる。こうした力学的な力が organic growth をしていると考えられる。その結果として真珠の結晶質構造にみられる二重繊維構造を生ずる。
3) 真珠の鉱物化にあたって conchiolin と鉱物結晶は epitaxial growth をしていると考えられる。
4) 個々の結晶成長は無生物界のそれと類似しており，その集合状態は樹枝状生長及びラセン転位成長理論の導入によって説明が可能である。ただ母液が生物の複雑な物質代謝によって作りだされる点で異なる。
5) 貝殻物質のあらい層状構造は上皮組織の周期的石灰分泌活動の高低によって準備され，有機相と鉱物相の交代形成および単位鉱物薄板の厚さの均一化は母液中の organic matrix と CaCO3 の結晶の（001）面あるいは conchiolin 膜への吸着力の平衡関係によるものと考えられる。
6) 真珠の鉱物化は貝殻のそれと原則的に全く同一機構によると考えられる。
7) 外套膜での区域による分泌機能の特殊性は移植後もよく保持されている。
8) 移植片上皮は真珠袋を作り母床組織と組織学的な有機的結合を営んでいるから，被移植生物の生理活動の高低によって分泌活動に変動を生じ，結晶成長に差を生ずる。その結果真珠層の形成量及び層状構造に変化がおこる。
9) 原因が何であるにせよ貝が衰弱すると一般に真珠物質の形成量の減退及び層状構造の乱れを生じ，真珠の品質に悪影響を及ぼす。
10) 真珠の巻きはまず形成初期の沈着層の種類で差を生じ，次に養成中の真珠層形成速度によって更に差を生ずる。真珠層の形成速度はアコヤガイでは単位時間に作られる鉱物板の数によって第一義的に決定され，イケチョウガイでは単位時間に成長する一枚の鉱物薄板の厚さで決定されている。
11) 石灰代謝活動と黄色色素代謝活動との間には正の相関があるとは考えられない。

言語

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第４章　真珠の構造と色沢（要約）

1) アコヤガイ及びイケチョウガイ養殖真珠の色沢と構造の関係を調べ，真珠色沢の特徴を究明した。
2) 真珠色（実体色）を着色機構の主因から大別すると
　a) 真珠層自体の多重層薄膜類似の構造による光の干渉及び拡散。
　b) 真珠層以外の介在異質物の光の選択吸収。
　c) 真珠層中に含有する黄色色素の光の選択吸収。
となる。この内 (a) は単独で真珠色となるが，他の二者はこれらの物質の吸光が加味された消色混色として真珠色に反映する。
3) 真珠の色彩は形成初期に異質物が生成するかどうかによって第１次分化がおこり，その後の真珠質分泌活動の変化や黄色色素代謝の有無によって第２次分化がおこる。
4) 真珠層の結晶粒相互間の集合，配列，大きさ，形及び層板の重畳様式は真珠の光沢感，透明度，平滑度及び柔硬感に関係しており，真珠においては光沢は単に表面構造のみの属性ではない。
5) 介在異質物が真珠色の着色機構の主因になる場合は，異質物の種類及び真珠層の性質によって異なるが，限定された条件のもとにおいて真珠色となり得る。
6) 巻き量と色沢との間には極く薄巻のものを除けば正の相関はない。

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第５章　加工処理の真珠品質への影響（要約）

加工珠を観察し，加工上の注意及び真珠組織の損傷度合の検査方法を検討した。

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第６章　人工真珠の構造（要約）

人工真珠の構造を観察し，養殖真珠と構造及び光学性について比較した。

言語

抄録

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The author studied on the mechanism of pearl formation by biological and physical techniques from the biomineralogical viewpoint as have already been reported in his preceding paper entitled "Crystal growth of molluscan shells".

Pearls are a complex system consisting of the alternate accumulation of mineral and organic substances as in the case of calcareous shells of molluscs. Carbonate minerals in natural and cultured pearls of Pinctada martensii (Dunker) show aragonite type in the nacre and calcite type in the prismatic substance. Consequently, mineral constituent of pearls depends on shell substances occurred in the processes of pearl formation. For example, pearls with only a nacreous layer are composed of fully aragonite. Same mineral constituent was seen in the natural and cultured pearls. But, in the present investigation, calcium peroxide was detected in the pearls, which was called "kotsu-dama", created in Hyriopsis schlegeli (v. Martens) with X-ray analysis. The author yet has no papers on calcium peroxide in molluscan mineralized tissues, so a detailed report will be given elswhere.

Schmidt (1923) observed the crystalline element in various pearls collected from Mytilus edulis and Meleagrina margartifera under crossed nicols and stated that thin slices of the pearls were the analogous appearance to spherulite of minerals in a polarized light but the structure and the mechanism of their formation were very different between each other. Wada (1961) has pointed out that the tension and elongation of the shell-forming tissue govern directly or indirectly orientation of inorganic crystals during the mineralization of molluscan shells, and the definite current would be occurred in the mother fluid surrounding a shell surface by such powers. The natural and cultured pearls of P. martensii and H. schlegeli are divided into following four kinds in their architecture:
(1) The nacreous layer pearls showing the concentrical laminary structure of mineral laminae and conchiolin membrane piled up alternately around the center of a pearl. As the crystalline texture of the nacre of these shells shows, the nacre of the pearls have the double fibrous structure of aragonite microcrystals, their orthorhombic b and c axes being nearly parallel to the dominant directions of growth which are horizontal and vertical to the pearl surface respectively. The orientation of their b and c axes is indicated schematically in Figs. 2-9 and -28. Accordingly, under conoscope, thin slices parallel to a pearl surface give the directions image of biaxial crystals (Fig. 2-8), and the extionction as a spherulite is revealed in vertical thin slices cut through the center of a pearl under crossed nicols (Fig. 2 - 10).
(2) The prismatic layer pearls, each prism of which elongating radially towards the surface of a pearl from its center, and polygonal prismatic structures being more dominant than laminary ones in a vertical section under optical microscope. The c axis of calcite microcrystals in the pearls arranges nearly parallel to a morphorogical long axis of prisms. The architecture of prismatic layer of the pearl does not differ from that of the shell except radial aggregation of prisms found in a pearl.
(3) Periostracal pearl of P. martensii has, for the most part, not only organic substances but also some mineral matters which are deposited at random. Organic substances constructing the pearls do not always coincide with the periostracum of the shell, but very often contain many dead wandering cells. Of course, the periostracal layer secreted from pearl-sac epithelium shows roughly laminar structures.
(4) The hypostracal pearl is produced by the characteristic pearl-sac happened within an adductor muscle, and is mostly composed of the nacre and the hypostracum alternately piled up. The hypostracal layer in pearls shows the prismatic structure just like the prismatic layer of ones (Fig. 2-7), but its mineral is of aragonite. Moreover, thin slice of the layer showed a brilliant appearance under optical microscope, and its laminary structure is rather indistinct under an electron microscope in comparison with other pearls (Plate VI-21). The author had no pearl with a hypostracal layer produced by any pearl-sac derived from a mantle piece which was grafted in the gonad of P. martensii, and could not find a pearl with only a prismatic layer of H. schlegeli given in this work.

Homoplastic and heteroplastic transplantations were done to elucidate following three points:
(1) The relations of mineralization of pearls between grafts from various areas of a mantle and different parts of a soft body into which these grafts were inserted. (2) The effects of the movement of epithelial cells in a graft upon the definite arrangement of shell substances in the pearl and shell formation.
(3) Polymorphism of calcium carbonate in the processes of mineralization of molluscan shells and pearls. Homoplastic transplantation was carried out with P. martensii. A mantle piece grafted in the gonad or the adductor muscle was developed into pearl-sac in 10 days after operation in summer (water temperature; 25-28C), and deposits also scattered on pearl nucleus by that time. Although deposits were varied with the features of the epithelium of a pearl-sac during pearl formation, the differentiation of secreting function and feature of most pearl-sac epithelium seems to be already decided by the graft irrespective of the grafted parts. For example, pearl-sac epithelium originated from a piece of the mantle edge is dominant to produce periostracal substance at an early stage of pearl formation and thereafter prismatic layer. Moreover, pearl-sac epithelium derived from a piece of the middle part and cavity of the mantle secrets nacreous substances, though the other shell substances are formed at an early stage (Plate IV-14). Histological difference between the gonad and the adductor muscle probably has no effect upon polymorphism of calcium carbonate in molluscan shells and pearls, but seems to have some effects on the architecture of pearls. In heteroplastic transplantation, P. martensii was employed as the host, and Clamys nobilis (Reeve) and Ostrea gigas Thunberg, having shell valves consisting of only calcite, were chosen as the donor. All species belong to the order Anisomiaria. The manner and pace of the movement of the epithelial cells in the mantle pieces cut off from the latter two species were similar to those observed in the homoplastic transplantation for several days after the operation, but the graft began to be absorbed before long and completely disappeared until two months after the operation. Deposits contained mineral matter appeared between coverslip and graft during the process of the spread of epithelial cells (Figs. 3-12 and -14), though the mineral could not be determined in this experiment.

For the observation on relations between deposits and living epithelial cells, a mantle piece was sandwiched between two pieces of coverslip, about 2x 3mm in size, and was inserted into the adductor muscle of another pearl oyster. Epithelial cells in a graft began to wander along the fiber axis of muscular cells and spread in an unknown definite direction few days after the transplantation (Figs. 3-6 and -7). Positive organic substance in metachromasia reaction was revealed about 4 days after the operation and small sphelurite of calcium carbonate came to grow here and there. The sphelurite grew up larger, very often increasing in size larger than epithelial cells existed there, although the single crystal was of course very small. The arrangement of deposits appeared never to occur at random (Figs. 3-7 and -8b). That is, it seems that the fixation of calcium and the orientation of mineral crystals were governed directly or indirectly by the elongation of epithelial cells, the morecular structure of organic matrix and the presence of mucopolysaccharide, as had been assumed in molluscan shells (Wada, 1961). The author could actually observe bead-like fibrous structure of conchiolin in a definite direction on the (001) plane of aragonite crystals (Plate III-10). It had already been described that the orientation of the crystallographical axes of microcrystals in pearls was related closely with the growth directions of the nacre. These results suggest that the tension or the elongation of the epithelium in a definite direction is present in a pearl-sac as in a mantle.

The growth and aggregation of mineral crystals in pearls were not, as a rule, different from those in shells, but were remarkably varied according to the seasonal changes in the physiological activity of an animal. Besides, the secreting activity of a pearl-sac is affected by the abnormal conditions of environments and animals, showing considerable individual variations. Mineral crystals on a pearl surface are eroded sometimes. The superficial and laminary structures of pearls are decided by the shape, particle size and aggregation of crystals, and are concerned in the reflection of a light. Although many workers have reported that the frequency of yellowish pearls is varied with the culture depth and the culture farms, and that the thickness of yellowish pearls increases larger than that of other colored pearls in a same culture period, the occurrence of the yellow pigment in pearls seems to have no correlation with the speed of calcium metabolism. In P. martensii, the thickness of an elemental mineral lamina in pearls does not correlate with the speed of calcium carbonate deposition, whereas the thicker is the elemental mineral one in pearls, the more increases the speed of calcium carbonate deposition in H. schlegeli. The growth rate of a prismatic layer in Pinctada pearls is about two times of that of a nacreous one.

Raman (1935) examined the iridescet shells and discussed the iridescence exhibited by the light reflected between mineral lamellae and on the surface of them. The relations between the color and the thickness of an elemental mineral lamina in Pinctada pearls were reported by Omori (1948), Uchida et al. (1947) and other workers. According to Watabe's (1955) and Wada's (1961) reports, the luster of pearls was close with their superficial structure. The present observations were also indicated that the luster of pearls was mainly attributed to the superficial texture of the nacre and to the laminary structure in the subsurface of pearls. The granular structure and the disorder of mineral laminae occurred during the accumulation of the lamina seem to give the nacres the translucency exhibited by pearls and sometimes reveal the characteristic iridescence out of the layer. The optical effects exhibited by the nacre are somewhat different from the colored reflections by films, and the reflection curves of pearls tend to be level in spectrophotometric reflectance. The color of such pearls may probably be explained by the diffusion and the reflection of light between mineral laminae, and is related closely with their luster. While colorings of yellow and blue pearls of P. martensii are respectively due to the yellow pigment occurred in the nacre and the other shell substances, prismatic and periostracal substances, formed during pearl formation (refer to Figs. 4-7 and -11). The iridescence and the body-color of pearls exhibited by the structural elements of the nacre move about in the locus as shown in Fig. 4-12, and the colors of pearls which are attributed to the yellow pigment and the other shell substances deviate from this locus and spread over in the area which is lined obliquely (Fig. 4-12).

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書誌情報

ja : 国立真珠研究所報告
en : Bulletin of the National Pearl Research Laboratory

巻 8, p. 948-1059, ページ数 112, 発行日 1962-09-30

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国立真珠研究所

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National Pearl Research Laboratory

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AN00091717

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真珠形成機構の生鉱物学的研究

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