• Journal of Life Science
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• v.31 no.8
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• pp.778-785
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• 2021

The germination of cucumber seeds begins with the degradation of reserved oil to fatty acids within the lipid body, which are then further metabolized to acyl-CoA. The acyl-CoA moves from the lipid body to the glyoxysome following β-oxidation for the production of acetyl-CoA. As an initial carbon source supplier, acetyl-CoA is an essential molecule in the glyoxylate cycle within the glyoxysome, which produces the metabolic intermediates of citrate and malate, among others. The glyoxylate cycle is a necessary metabolic pathway for oil seed plant germination because it produces the metabolic intermediates for the tricarboxylic acid (TCA) cycle and for gluconeogenesis, such as the oxaloacetate, which moves to the cytosol for the initiation of gluconeogenesis by phophoenolpyruvate carboxykinase (PEPCK). Following reserved oil mobilization, the production and transport of various metabolic intermediates are involved in the coordinated operation and activation of multiple metabolic pathways to supply directly usable carbohydrate in the form of glucose. Furthermore, corresponding gene expression regulation compatibly transforms the microbody to glyoxysome, which contains the organelle-specific malate synthase (MS) and isocitrate lyase (ICL) enzymes during oil seed germination. Together with glyoxylate cycle, carnitine, which mediates the supplementary route of the acetyl-CoA transport mechanism via the mitochondrial BOU (A BOUT DE SOUFFLE) system, possibly plays a secondary role in lipid metabolism for enhanced plant development.

• Journal of Life Science
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• v.33 no.8
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• pp.651-662
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• 2023

Peroxisomes, known as microbodies, are a class of morphologically similar subcellular organelles commonly found in most eukaryotic cells. They are 0.2~1.8 ㎛ in diameter and are bound by a single membrane. The matrix is usually finely granular, but occasionally crystalline or fibrillary inclusions are observed. They characteristically contain hydrogen peroxide (H₂O₂) generating oxidases and contain the enzyme catalase, thus confining the metabolism of the poisonous H₂O₂ within these organelles. Therefore, the eukaryotic organelles are greatly dynamic both in morphology and metabolism. Plant peroxisomes, in particular, are associated with numerous metabolic processes, including β-oxidation, the glyoxylate cycle and photorespiration. Furthermore, plant peroxisomes are involved in development, along with responses to stresses such as the synthesis of important phytohormones of auxins, salicylic acid and jasmonic acids. In the past few decades substantial progress has been made in the study of peroxisome biogenesis in eukaryotic organisms, mainly in animals and yeasts. Advancement of sophisticated techniques in molecular biology and widening of the range of genomic applications have led to the identification of most peroxisomal genes and proteins (peroxins, PEXs). Furthermore, recent applications of proteome study have produced fundamental information on biogenesis in plant peroxisomes, together with improving our understanding of peroxisomal protein targeting, regulation, and degradation. Nonetheless, despite this progress in peroxisome development, much remains to be explained about how peroxisomes originate from the endoplasmic reticulum (ER), then assemble and divide. Peroxisomes perform dynamic roles in many phases of plant development, and in this review, we focus on the latest progress in furthering our understanding of plant peroxisome functions, biogenesis, and dynamics.

• Applied Microscopy
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• v.9 no.1
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• pp.57-69
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• 1979

The ultrastructural changes of embryo and endosperm cells were observed during the green fruit with embryo about $250{\mu}$ long to germination. 1. In the embryo cells of green fruit with embryo about $250{\mu}$ long, mitochondrial cristae and plastid are undifferentiated and dictyosome are occasionally observed. There are electron-opaque globoids in the vacuole and a lot of spherosomes in the outer layer of smooth endoplasmic reticulum. Endosperm is filled with spherosomes and electron-opaque protein bodies surrounded by spherosomes, and due to these, other organelle are not observed. 2. In the embryo cells of seeds with red seed coat, mitochondrial cristae are well developed, electron-opaque globoids increased, and vacuoles are enlarged. In the endosperm, however, spherosomes increased, protein bodies are enlarged, and electron-opaque globoidal crystals are dispersed within them. 3. In the procambium and epicotyl cells of dehiscent seed, Golgi vacuoles and vesicles are well developed, and mitochondrial cristae are also well differentiated. Spherosomes are numerously present and radicle cells, peripheral cells of hypocotyl, and vacuoles of cotyledon are well differentiated. Endosperm is filled with spherosomes containing electron-opaque granules and protein bodies are surrounded by a single membrane. There are acid phosphatase around globoids and spherosomes. 4. At the time of seeding, spherosomes markedly increased in the outer layer of cotyledon and protein bodies are also observed. Cell organelles are differentiated and plastids containing starch are also present. 5. In the outer $2{\sim}3$ layers of cotyledons, radicle cells, and peripheral cells of hypocotyl during post-seeding to germination, spherosomes and plastids with starch increased, and mitochondria and microbodies are also found around the nucleus of embryo cells. With approaching, the germination stage, in the endosperm contacting with embryo, vacuoles are well differentiated but spherosomes decreased. There increased electron-opaque materials within vacuoles. In other endosperm, with the decrease of spherosome, mitochondria increased and electro n-opaque globular bodies are formed and gradually increased. The outer layer of protein bodies are reduced while electron-transparent portions are enlarged and fused together to occupy the outer layer where small particles are formed. 6. In the endosperm of germination stage, spherosomes decreased while protein bodies, are fused together to form 2 or 3 within a cell.