Ultrastructural studies on the secretory cavities ofCitrus deliciosa ten. II. Development of the essential oil-accumulating central space of the gland and process of active secretion

Summary Oil glands ofCitrus deliciosa are multicellular secretory structures, globular to oval in shape, in the centre of which an essential oil-accumulating space is formed. Opening of this space begins from a single cell. It undergoes lysis which later extends to the neighbouring gland cells.Secretory material in form of droplets is produced in plastids, from where it is transported to the parietal cytoplasm of the secretory cells via numerous ER-elements. After fusion of the ER-membranes with the plasmalemma, the exudate reaches the apoplast, through which it is driven to the central cavity of the gland.Peripheral cells of the secretory complex are modified into a protective sheath with thick walls and large vacuoles, while their plastids are differentiated from leucoplasts into typical amyloplasts.     

花椒果实分泌囊超微结构的研究

利用电子显微镜对花椒果实分泌囊的超微结构进行研究,表明分泌囊上皮细胞和鞘细胞的最显著特征是具许多含嗜锇物质的质体。这些质体内膜结构不发达,周围分布大量内质网槽库、含油滴的液泡和环状油滴。在此基础上,对质体的功能以及精油合成、贮存和转运的可能场所和途径进行了讨论。     

Ultrastructure and histochemistry of secretory ducts in Artemisia campestris ssp. maritima (Compositae)

The histochemical characterization of the oleoresin produced by secretory ducts of Artemkiu campestris ssp. maritima revealed the presence of terpenoids (essential oils, resiniferous acids and probably steroids), alkaloids and fatty acids, eventually polyacetylenes.
The ultrastructural study of A. campestris ducts enabled us to consider that the secretory activity begins very early during the duct development. The oleoresin deposited in the duct cavity is produced by epithelial and sub-epithelial cells that contain, at the secretory phase, a great amount of smooth endoplasmic reticulum (SER) surrounding plastids with few thylakoids. These organelles may play an important role in the oleoresin production, the SER probably being responsible for some steps in the biosynthesis of oleoresin components and for the transport of the secreted material towards the plasmalemma. Endoplasmic reticulum and mitochondria probably have a role in the synthesis of steroids.
After secretion, the duct glandular cells degenerate progressively. The extrusion process of secretion may be considered mero-holocrine.     

Studies on the Relation Between the Ultrastructure of Secretory Cells and Their Synthesis and Secretion of Lacquer in Laticiferous Canals of Rhus verniciflus

Secretory cells of laticiferous canals contain many plastids and endoplasmic reticulum (ER) in Rhus verniciflua. The electron microscopy suggests that osmiophiiic Lacquer component is mainly synthesized in the plastids and ER. They may be eliminated from the protoplasts to the space between the plasmalemma and the cell wall in three ways: (1) by ER elements, (2) by vesicles approaching the plasmalemma and fusing their membrances with the latter, and (3) by their becoming surrounded by plasmalemma invaginations, and then they traverse the wall through the channels of plasmodesmata which became disconnected during the schizogenous development of the canals and percolate through the wall that faded into an even looser mesh of fibrillar material toward the canal lumen. More or less, nucleus, mitochondria, Golgi bodies and ground cytoplasm also take part in the above-mentioned process.     

漆树乳汁道分泌细胞的超微结构及其与生漆产生和分泌关系的研究

漆树(Rhus verniciflua)乳汁道分泌细胞含有丰富的质体、内质网和嗜锇物质。电子显微镜的现察结果表明,嗜锇的生漆成分合成的可能场所是质体和内质网,并且通过内质网分子和小泡群与质膜相互接触并融合以及质膜内褶包被等三种形式释放到质膜和细胞壁之间的间隙中;再经过细胞壁中乳汁道腔形成时断裂了的胞间连丝通道和扩散渗透两条途径,越过细胞壁分泌到乳汁道腔中。细胞核、线粒体、高尔基体以及细胞质基质或多或少也参与了上述过程。     

Aspects of sieve element ultrastructure in Primula obconica

Summary At maturity, the enucleate sieve element of Primula obconica is lined with a parietal layer of cytoplasm consisting of plasmalemma, one or more cisterna-like layers of endoplasmic reticulum, numerous mitochondria and plastids, and a membrane which apparently separates these cytoplasmic components from a large central cavity. The central cavity contains numerous longitudinally oriented slime tubules. We believe these tubules normally form strands which run the length of the cell and traverse consecutive cells through the sieve-plate pores. Developmental aspects are discussed.This research has been supported by NSF Grant GB 3193.     

花椒果实分泌囊发育过程的超微结构研究

电镜观察结果表明,花椒(Zanthoxylum bungeanum Maxim.)果实分泌囊是由裂生方式形成,由鞘细胞、上皮细胞和油腔构成。对分泌囊的原始细胞、油腔发生和扩大以及发育成熟3个时期的超微结构研究表明,其精油是在分泌囊油腔发生时开始积累,以油滴形态存在于上皮细胞的质体内及其周围的细胞质中。根据各细胞器的变化规律分析,质体是精油合成的主要场所,内质网参与精油的合成和转运,线粒体为上述活动提供能量。上皮细胞内积累的精油可能通过两种途径排出细胞,分泌至油腔内贮存。鞘细胞内也积累精油,其主要合成场所也与质体有关,以后转运至上皮细胞内。成熟分泌囊的质体由于功能改变,其内出现蛋白质结晶和淀粉粒。     

Ultrastructure and Development of Oil Idioblasts in Annona muricata L.

The ultrastructure and development of oil idioblasts in theshoot apex and leaves in Annona muricata L. are described, andthree arbitrary developmental stages are distinguished: cellsin which no additional cell wall layers have been depositedagainst the initial primary cell wall, possessing an electron-translucentcytoplasm and distinct plastids which lack thylakoids (stage1); cells in which a suberized layer has been deposited againstthe primary wall (stage 2, the cytoplasm resembles that of thepreceding stage), and cells in which an additional inner walllayer has been deposited against the suberized layer, whichincreases in thickness with development (stage 3). In this stagean oil cavity is formed, surrounded by the plasmalemma, andattached to a bell-like protrusion of the inner wall layer,the cupule. A complex membranous structure occurs next to thecupule. Smooth tubular endoplasmic reticulum (ER), appearingas linearly arranged tubules, and groups of crystalline bodieswith an almost hexagonal outline are present. The final stagewas further subdivided into three subgroups (a, b, c) basedon the extent of the oil cavity, its contents, and the compositionof the cytoplasm, and increasing thickness of the inner walllayer. The oil is probably synthesized in the plastids, releasedinto the cytoplasm, and then passed through the plasmalemmasurrounding the oil cavity. Oil idioblasts, Annona muricata L., suberized layer, inner wall layer, oil cavity, cupule, smooth tubular ER, crystalline bodies     

杭白芷根的分泌道超微结构与其挥发油分泌的关系

利用光镜及透射电子显微镜技术研究了杭白芷根中分泌道结构及其挥发油的分泌,并重点探讨分泌道中挥发油的分泌过程。结果显示:(1)杭白芷的分泌道是由上皮细胞围绕着的伸长的胞间隙,腔道内贮存着挥发油。(2)分泌道细胞的质体、细胞基质以及线粒体参与挥发油或其前体物质的合成。(3)在分泌道发育的后期,大量小泡与分泌细胞的液泡膜和细胞质膜融合,将其内的物质释放进入空腔。研究认为,杭白芷分泌道中挥发油主要合成部位为质体及细胞基质,之后以扩散渗透或通过膜质小泡与液泡及质膜融合这两种方式分泌到空腔内,丰富的线粒体可能为这一系列过程提供能量。     

FINE STRUCTURE OF EPITHELIAL CANAL CELLS IN PETIOLES OF XANTHIUM PENSYLVANICUM

Secretory canals, lined with an epithelium, occur in many families, e.g., Umbelliferae, Compositae. These canals are said to extend continuously through the root and shoot systems and are known, in some cases, to secrete resins, essential oils, etc. In Xanthium the canals arise schizogenously from cells derived from canal initials. Subsequent divisions lead to a ring of 7–12 epithelial cells surrounding a central cavity. During maturation the epithelium becomes crushed and obliterated. Canals were examined in petioles of Xanthium pensyhanicum (Cocklebur) grown under long day illumination to maintain vegetative growth. The fine structure of the canal and its epithelium was studied by electron microscopy of thin sections cut transverse to the principal axis of petioles from leaves in an early stage of development. The canal proper is delimited by walls of epithelial cells which protrude into a scallop shaped cavity. In comparison to the surrounding parenchyma, the epithelial cells are smaller, cytoplasmically more dense, and less vacuolate. The epithelium contains pleomorphic starch-free plastids with planar thylakoids frequently stacked into grana; thus, the plastids are presumed photosynthetically active. Mitochondria are abundant and often dense. The cytoplasm is rich in free polysomes, and smooth endoplasmic reticulum predominates over the rough form. Spheroidal granules averaging about 530 nm in diameter are numerous in the epithelium and appear at lower concentration in neighboring cells. Many features of fine structure of the epithelial cells suggest that a high metabolic activity is present in this tissue during this early stage of development. A possible function of the canals is defense against insect predation and animal grazing.     

木立芦荟叶内芦荟素的超微细胞化学研究

使用醋酸铅溶液对木立芦荟叶的药用成分芦荟素进行细胞化学定位,在透射电镜下探讨芦荟素产生、转运和贮藏的过程。结果表明:芦荟素由同化薄壁组织产生,质体的类囊体为其合成部位。通过质体膜形成的小泡转移到周围的内质网,以后内质网小泡与质膜融合:或质体小泡直接与质膜融合。通过胞吐作用将芦荟素释放到质膜外,经质外体途径到达维管束的鞘细胞。在鞘细胞中, 芦荟素经内质网小泡转移至内切向壁,由胞间连丝运输到芦荟素细胞的细胞质,最终贮藏在芦荟素细胞的液泡中。     

薄荷头状腺毛分泌过程的超微结构研究

电镜观察表明,刚形成的薄荷头状腺毛的头部细胞,细胞核较大细胞质浓,有一些小液泡,质体和线粒体最显著,分泌前期,内质网及高尔基体数量明显     

Development and ultrastructure of the primary phloem in the shoot of Ephedra viridis (Ephedraceae)

Sieve cell differentiation in the primary phloem of Ephedra viridis is first indicated by an increase in thickness of the wall, which begins in the corners of the cell, and next by the proliferation of smooth tubular endoplasmic reticulum (ER). As differentiation proceeds, cisternae of rough ER form stacks along the wall, losing their ribosomes in the process. Concomitantly, all of the mitochondria, plastids, and ER become parietal in distribution, and the vacuoles collapse. Nuclear degeneration is pycnotic and accompanied by the formation of tubular invaginations of the nuclear envelope into the peripheral chromatin. At maturity, an anastomosing network of smooth ER borders the plasmalemma, interconnecting aggregates of smooth tubular ER located primarily opposite the sieve areas. In addition to ER, the mature sieve cell contains mitochondria, plastids, and remnants of the degenerate nucleus, all of which are parietal in distribution. P-protein is lacking at all stages of sieve cell development. Sieve pore and compound median cavity development is similar to that reported for the sieve cells of conifers. Albuminous cells are associated with the sieve cells of the metaphloem throughout the shoot but with sieve cells of the protophloem only in the node. Among their cytoplasmic components are broad bundles of microfilaments spatially associated with a complex system of rough and smooth ER.     

Ultrastructural studies on the process of aloin production and accumulation in Aloe arborescens (Asphodelaceae) leaves

Aloin, a kind of anthraquinone, is a chemical component in Aloe leaves used in medicine. The processes of aloin production, transport and storage were studied with a transmission electron microscope using the lead acetate precipitate method for ultracytochemical localization of aloin in the leaf of Aloe arborescens Mill. Results showed that aloin was produced in the plastids of the assimilating tissue, transported through the plastid membrane to the surrounding endoplasmic reticulum and enveloped in the vesicles by the endoplasmic reticulum elements. The vesicles approached, and later fused with, the plasmalemma, released their contents into the apoplast through exocytosis and finally, reached the vascular bundle sheath by apoplastic translocation. Aloin was transported to the internal tangential wall of the vascular bundle sheath cell through endoplasmic reticulum vesicles, and reached the cytoplasm of the aloin cell by means of plasmodesmata. Finally, aloin was stored in the vacuole of the cell in which it was produced.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 241–247.     

Seasonal changes in the ultrastructure of the vascular cambium of Robinia pseudoacacia

 The ultrastructure of the vascular cambium of Robinia pseudoacacia L. was examined in trunk tissues collected over a 2 ¹/₂ year period. During dormancy, fusiform cells are densely cytoplasmic with many small vacuoles and centrally located nuclei. Mitochondria are round to oval in sectional view. The plastids are variable in shape, have few internal membranes, and generally lack starch grains. The plasmalemma is smooth in outline. Proteinaceous material occurs in the vacuoles and many lipid droplets are scattered throughout the ground substance. Smooth tubular ER, often highly dilated, predominates, but short segments of rough ER are also present. Abundant free ribosomes are evenly distributed throughout the ground substance and the dictyosomes are inactive. Microtubules are parietal and have various orientations. During reactivation, the plasmalemma becomes irregular in outline and begins to form invaginations. Concurrently, the proteinaceous material disappears, the vacuoles begin to fuse, polysomes appear, and the dictyosomes begin to produce vesicles. During the period of cambial activity, fusiform cells are highly vacuolate, and the nuclei are centrally located. The mitochondria are round, oval, or elongate. Now the plastids contain phytoferritin, starch grains, or both. Many large invaginations of the plasmalemma intrude into the vacuole, pushing the tonoplast inward and pinching off into the vacuole, which lacks proteinaceous material. Lipid droplets are scarce. Most ER is rough, and ribosomes are generally aggregated as polysomes. Dictyosomes are actively producing vesicles. During the transition to dormancy, the fusiform cells gradually assume the appearance typical of the dormant cambium.     

STRUCTURE AND DEVELOPMENT OF THE SIEVE ELEMENTS IN PSILOTUM NUDUM

Shoot tissue of Psilotum nudum (L.) Griseb. was fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. Young sieve elements can be distinguished from contiguous parenchyma cells by their distinctive plastids, the presence of refractive spherules, and the overall dense appearance of their protoplast. The refractive spherules apparently originate in the intracisternal spaces of the endoplasmic reticulum (ER). With increasing age the sieve-element wall undergoes a marked increase in thickness. Concomitantly, a marked increase occurs in the production of dictyosome vesicles, many of which can be seen in varying degrees of fusion with the plasmalemma. Other fibril- and vesicle-containing vacuoles also are found in the cytoplasm. In many instances the delimiting membrane of these vacuoles was continuous with the plasmalemma. Vesicles and fibrillar materials similar to those of the vacuoles were found in the younger portions of the wall. At maturity the plasmalemma-lined sieve element contains a parietal network of ER, plastids, mitochondria, and remnants of nuclei. The protoplasts of contiguous sieve elements are connected by solitary pores on lateral walls and pores aggregated into sieve areas on end walls. All pores are lined by the plasmalemma and filled with numerous ER membranes which arise selectively at developing pore sites, independently of the ER elsewhere in the cell. P-protein and callose are lacking at all stages of development.     

Sieve Element of Impatiens Sultanii: 2. Developmental Aspects

The sieve elements arise from vacuolate cells, and enlargementof one or more slime bodies increases the volume of cytoplasmrelative to that of the vacuole. The slime finally dispersesthroughout the region once occupied by the vacuole. A new term,mictoplasm, is proposed for the resulting mixture of non-membranouscytoplasmic material, including slime, with the contents ofthe vacuole. The nucleus disappears during development, butbefore losing its chromaticity, it apparently releases one ormore nucleoli into the cytoplasm. The extruded nucleoli areprominent during development but usually disappear with thetonoplast, nucleus, and dictyosomes as the cell matures. Atmaturity, small vesicles, plastids containing spherical starchgrains, and sparsely distributed mitochondria deficient in tubulesare attached to the plasmalemma. The sieve-plate connectingstrand develops in a pore site bearing a pair of callose plateletsand penetrated in the centre by a plasmodesms. The callose cylinderwhich surrounds the mature connecting strand is followed sothat the shape of a connecting strand in cross section is stellate.Mictoplasm and the plasmalemma are continuous from one cellto the next through the sieve-plate connecting strands.     

Fine Structure of Tapetal Cells and Ubisch Bodies in the Anther of Ophiopogon japonicus

The development of the tapetum in Ophiopogon ]aponicus is of secretory type Tapetum develops at their peak during the microspore mother cell stage. There are abundant organelles, consisting of a lot of mitochondria, dictyosomes and plastids, especially endoplasmic reticulum. Pro-Ubisch bodies e. merge as early as at the stage of microspore mother cell. At tetrad stage, a large number of pro-Ubisch bodies accumulate between inner tangential face of the plasmalemma and the cell wall. At the early microspore stage, pro-Ubisch bodies are distributed in the small embayments of the plasmalemma. As the sporopollenin begins to deposit on them, proubisch bodies develop into Ubisch bodies which consist of two types: single and aggregated. Tapetal cells degenerate completely when pollen grains reach maturity.     

油菜花蜜腺发育过程的超微结构变化与泌蜜机理的研究

油菜花蜜腺由２枚侧蜜腺和２枝中蜜腺组成,其基本结构类似。在蜜腺发育过程中,产蜜组织细胞内的内质网、高尔基体、质体和线粒体以及液泡都发生有规律变化。泌蜜前,细胞器的数量增加。其中,质体内积累淀粉,此过程与蜜腺内初皮部的分化并和线粒体的增加相关。泌蜜时,内质网数量增多,并产生小泡．小泡向质膜移动。泌蜜后,细胞液泡化,细胞器数量减少,细胞萎缩。根据观察结果分析,其原蜜汁来源于韧皮部,转运至产蜜组织细胞的质体、内质网和高尔基体内加工成蜜汁,最后通过胞吐和渗透相结合的方式泌出。     

Ultrastructure of dormant buds of Salix sp. in early winter

In the apex of dormant buds of Salk a histological zonation comparable to that found in growing buds was observed. However, significant changes in relative volumes of cell components between dormant and growing buds were noted; the dormant buds had a lower volume density of vacuoles and higher relative volumes of mitochondria, plastids, lipid bodies, and starch grains than the growing buds. In the leaf primordia the relative volume of nuclei decreased with age, while the relative volume of plastids and mitochondria increased. The large central vacuole found in cells of e.g. the pro-cambium and rib meristem in growing buds is split into many smaller ones during the winter. A high content of tannin and calcium oxalate crystals was noted in dormant buds. They also accumulate lipids and starch. Phytoferritin may appear in plastids. Stacked ER and concentric sheaths of ER around lipid bodies appear, probably as a consequence of either anaerobic conditions or water stress. Several indications of metabolic activities in the seemingly dormant buds were found; plasmatubules at the plasmalemma particularly in the procambium, sheaths of smooth ER around the plastids, electron opaque globules (probably calcium-binding sites), and vacuoles that seemed to be autophagic.