Proplastid

Japanese: proplastid

…A general term for chloroplasts contained in green plant cells and related organelles characterized by containing pigments. They are found in undifferentiated plant cells such as meristematic tissues, but are absent in animal cells and fungi, and are organelles that develop from proplastids, which are rod-shaped or oblong bodies measuring 1 to 3 μm in size and lack chlorophyll. Their shape, internal structure, and function vary significantly depending on the species, and in addition to chloroplasts that are photosynthetic organelles, there are leucoplasts that lack chlorophyll, etioplasts in etiolated plants, amyloplasts that contain large storage starch, colored plastids found in yellow and orange cells, protenoplasts that contain protein crystals, and oleoplasts that contain large oil droplets and lipid granules. …

From [Chloroplasts]

...The thylakoid membrane is made up mainly of lipids and proteins, and is characterized by a high content of glycolipids and a high content of unsaturated fatty acids (82%) in the fatty acids that make up the lipids, especially linoleic acid.
[Formation and Degeneration]
In higher plants, undifferentiated small (0.5-1.0 μm) plastids (proplastids) that will develop into chloroplasts in the future are observed in undifferentiated cells such as the growing point of the stem (Figure 6). Proplastids are said to develop from plastid initials smaller than 0.5 μm in size, and at the proplastid stage, they have a small number of vesicle structures formed by invagination of the inner membrane of the envelope and an undifferentiated inner membrane called primary thylakoid.

*Some of the terminology explanations that mention "proplastid" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…緑色植物の細胞に含まれる葉緑体と，その類縁で色素を含むことで特徴づけられる細胞小器官の総称。動物細胞･菌類に欠けているが，分裂組織など未分化な植物細胞にみられ，大きさ1～3μmの桿（かん）状または長楕円体のクロロフィルをもたない原色素体proplastidから発達する細胞小器官である。その形状，内部構造，機能などは，種類によって著しく異なり，光合成器官になっている葉緑体のほか，クロロフィルを欠く白色体，黄化植物のエチオプラスト，大きな貯蔵デンプンをもつアミロプラスト，黄色や橙色細胞にみられる有色色素体，タンパク質の結晶を含むプロテノプラスト，大きな油滴や脂質顆粒（かりゆう）をもつオレオプラストなどがある。…

【葉緑体】より

…チラコイド膜はおもに脂質とタンパク質で作られており，糖脂質が多いこと，脂質を構成する脂肪酸の組成では不飽和脂肪酸が多く82％に達すること，とくにリノレン酸が多いことが特徴である。
［形成と退化］
　高等植物において，茎の生長点など未分化な細胞の中には，将来葉緑体に発達する未分化な小さな(0.5～1.0μm)色素体(前色素体proplastid)が観察される(図6)。前色素体は0.5μmより小さいプラスチド始原体plastid initialから発達したものといわれ，前色素体の段階になると包膜の内膜の陥入により生じた少量の小胞構造vesicleや未分化な内膜primary thylakoidをもっている。…

※「proplastid」について言及している用語解説の一部を掲載しています。

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