传递细胞——物质短途运输中起作用的特化细胞

传递细胞广泛存在于植物界的各种群。传递细胞的分化主要与器官的发育程度以及转运物质的供应有关。当植物某个部位所需的运输速率远高于溶质正常跨膜运输速率时,在此部位就可能有传递细胞。传递细胞最基本的特征是细胞壁向内突起生长（壁内突）并与质膜共同形成壁膜器。壁内突从形态上可划分为2种类型：网状内突和肋状内突。大多数传递细胞壁内突的发育在沿着溶质流动的方向表现出极性。传递细胞的胞质一般比周围薄壁组织细胞浓,胞内富含线粒体和内膜分泌系统细胞器如内质网、高尔基体、小囊泡等。传递细胞在物质的短途运输中起作用。玉米胚乳传递细胞可能还具有防御病原微生物进入胚乳和胚的功能。本文就传递细胞的种类和特性、结构和功能、形成机制和诱导因素,以及基因表达调控等方面的研究进展做介绍。     

毛竹茎秆纤维发育过程的超微结构观察

利用透射和扫描电镜观察了毛竹（Phyllostachys edulis (Carr.) H. De Lehaie）茎秆纤维发育过程中的超微结构变化。在纤维细胞初生壁形成期,细胞质中线粒体、内质网、高尔基体等细胞器数量有明显的增加,出现大量的由内质网与高尔基体分泌形成的运输小泡,周质微管平行分布于质膜内侧,出现环状片层结构,并在细胞壁与质膜之间出现壁旁体结构。随着次生壁的逐渐形成,细胞质中细胞器逐渐地解体并出现多泡小体;纤维细胞核出现染色质凝聚并边缘化,但在8 年生的纤维中可以持续存在;在纤维次生壁形成的整个阶段都存在与周围细胞相联系的胞间连丝和运输小泡;次生壁 在前4 年加厚明显,以后加厚程度减缓,但可以持续很长一段时间,并随着加厚出现宽窄交替的多层结构。结果表明,线粒体、内质网、高尔基体和壁旁体等细胞器与周质微管一起参与了初生壁和次生壁早期的形成;纤维细胞次生壁的形成过程就是一个漫长的程序性细胞死亡（PCD）,而PCD 的产物与胞间连丝一起参与了次生壁的形成与加厚;染色质凝聚并边缘化的细胞核与胞间连丝的持续存在,证明毛竹茎秆纤维细胞是一种典型的长寿细胞。     

毛竹茎秆纤维发育过程的超微结构观察

利用透射和扫描电镜观察了毛竹(Phyllostachys edulis(Carr.)H.De Lehaie)茎秆纤维发育过程中的超微结构变化.在纤维细胞初生壁形成期,细胞质中线粒体、内质网、高尔基体等细胞器数量有明显的增加,出现大量的由内质网与高尔基体分泌形成的运输小泡,周质微管平行分布于质膜内侧,出现环状片层结构,并在细胞壁与质膜之间出现壁旁体结构.随着次生壁的逐渐形成,细胞质中细胞器逐渐地解体并出现多泡小体;纤维细胞核出现染色质凝聚并边缘化,但在8年生的纤维中可以持续存在;在纤维次生壁形成的整个阶段都存在与周围细胞相联系的胞间连丝和运输小泡;次生壁在前4年加厚明显,以后加厚程度减缓,但可以持续很长一段时间,并随着加厚出现宽窄交替的多层结构.结果表明,线粒体、内质网、高尔基体和壁旁体等细胞器与周质微管一起参与了初生壁和次生壁早期的形成;纤维细胞次生壁的形成过程就是一个漫长的程序性细胞死亡(PCD),而PCD的产物与胞间连丝一起参与了次生壁的形成与加厚;染色质凝聚并边缘化的细胞核与胞间连丝的持续存在,证明毛竹茎秆纤维细胞是一种典型的长寿细胞.     

被子植物生殖器官中的传递细胞

传递细胞（ｔｒａｎｓｆｅｒｃｅｌｌ）是一类特殊的薄壁细胞,其特征是细胞壁向内突起生长,形成壁内突的结构,质膜紧贴细胞壁生长,从而使质膜的表面积大大增加,扩大了原生质体表面积与体积之比,有利于细胞吸收和分泌某些物质,在细胞物质的短途运输中起重要作用。超微结构研究表明,传递细胞的细胞核较大,细胞质浓,并富含线粒体、高尔基体等细胞器。传递细胞在被子植物生殖器官中普遍存在,对于这些器官完成其功能起到重要作用。下面简单介绍生殖器官各结构中存在的传递细胞及其功能。１　花柱的通道细胞开放型花柱具有花柱道,花柱…     

白刺胚乳早期发育的超微结构研究

白刺(Nitraria sibirica)胚乳发育经历游离核阶段、细胞化阶段和被吸收解体阶段。游离核胚乳沿胚囊壁均匀排列为一层,胞质浓厚,其中有丰富的质体、线粒体、高尔基体、内质网和各种小泡等细胞器。珠孔区域的胚囊壁具发达的分枝状壁内突,而周缘区域的胚囊壁具间隔的钉状内突,内突周围的细胞质中具多数线粒体和小泡。胚乳细胞化时,初始垂周壁源于核有丝分裂产生的细胞板。在细胞板两端开始壁的游离生长,一端与胚囊壁相连接,另一端向心自由延伸。壁的游离生长依赖于小泡的融合。早期胚乳细胞具大液泡,具核或无核,细胞质中有大量的线粒体,质体缺乏,其壁仍由多层膜结构组成。     

浙贝母鳞片细胞在寒冷条件下超微结构的变化

利用电镜手段观察了浙贝母鳞片细胞在寒冷条件下超微结构的变化。细胞中最明显的变化是出现了大量脂滴和淀粉粒壳的结构由清晰到模糊。一些高尔基体结构不清晰,内质网泡化。细胞中壁旁体较多,细胞核、细胞壁和胞间连丝正常。有时可见线粒体溢裂现象。以上现象表明为适应寒冷条件,细胞进行了内在代谢机制的调整。     

牡丹苗端由营养生长转向生殖生长过程中超微结构研究

电镜观察了营养生长和生殖生长两个发育埋藏的牡丹（Ｐａｅｎｉａ ｓｕｆｆｒｕｔｉｃｏｓａ．）苗端。结果如下：（１）营养生长期,原套和原体的细胞壁厚薄不均,多有胞间连丝分布。两者细胞核内均在较多异染色质。细胞质内含许多质体、嗜锇细胞主少量的线粒体,内质网和高尔基体。质体无片层结构,部分质体有淀粉粒和脂滴。原体细胞的液泡化过程比原套细胞略高。原体下方扁平细胞的大部分空间被大量的淀粉质体和液泡占据,淀粉粒     

花生胚乳细胞化的超微结构观察

花生（ＡｒａｃｈｉｓｈｙｐｏｇｅａｅＬ．）心形胚期的胚乳游离核多瓣裂,或具长尾状结构。胚乳细胞质内有大量线粒体、质体、高尔基体、小泡及少量内质网。中央细胞壁有壁内突。球胚及心形胚期常见胚乳瘤。心形胚晚期,胚乳开始细胞化,胚乳细胞壁形成有３种方式,分别存在于不同的胚珠中：（１）从胚囊壁产生自由生长壁形成初始垂周壁,具有明显的电子密度深的中层,其生长主要靠末端的高尔基体小泡及内质网囊泡的融合。两相邻的自由生长壁末端或其分枝末端相连形成胚乳细胞。（２）核有丝分裂后产生细胞板,细胞板向外扩展并可分枝。间期的非姊妹核间也观察到形成了细胞板。小泡与微管参与细胞板的扩展,高尔基体和内质网是小泡的主要来源。细胞板的扩展末端相互连接,形成胚乳细胞的前身。小泡继续加入细胞板的组成,以后形成胚乳细胞壁。（３）胚乳细胞质中,出现一些比较大的不规则形的片段性泡状结构,它们可能来源于高尔基体小泡,这些片段性泡状结构随机相连形成细胞壁,未见微管参与。胚乳细胞外切向壁及经向壁上有壁内突。     

大葱卵器及受精后助细胞的超微结构

章丘大葱（Ａllium fistulosum L.cv.Zhangqiu)的卵器由１个卵细胞及２个助细胞组成,观察到不少卵器没有卵细胞,只有２个助细胞。卵细胞的核及大部分细胞质位于细胞的合点端,１个大液泡占据了细胞其他部位。卵细胞含有很多的核糖体及多聚核糖体、嵴明显的线粒体、粗面内质网、高尔基体具小泡,卵细胞似是一个活跃的细胞。细胞外被细胞壁,其合点端及侧方与助细胞共同壁不连续,助细胞有一较大的核,位于细胞膨大的部位,众多的小液泡遍布细胞中。核糖体及聚合核糖体、线粒体,粗面内质网及风心圆环状粗面内质丰富,高尔基体及小泡常见,反映了其活跃的代谢作用。助细胞合点端及侧方与卵细胞、中央细胞的共同壁不连续,与卵细胞共同壁含胞间连丝,壁不连续处,有不状多层膜结构伸入卵细胞质,显示助细胞可能对卵细胞提供营养,伟粉后,一个助细胞退化,宿存助细胞至随胚胚期尚存在,它经历了一个缓慢的退化过程,出现质壁分离,细胞质变稀,液泡扩大,细胞器逐渐减少,在椭形胚期,宿存助细胞核内的染色质及核仁消失,有细胞质侵入核内,因宿存助细胞壁变厚,细胞质出现现脂滴,宿存助细胞可能仍有合成功能,宿存助细胞壁出现若干无壁部位,细胞内的营养物质可能通过无壁部位向胚乳转运,供游离核胚乳及胚乳细胞化初期的发育。     

玉米胚乳传递细胞的结构观察研究

以玉米品种'登海11号'为材料,分别于授粉后8、10、15和20 d采集颖果,取所需部位并采用树脂包埋的方法及半薄和超薄切片技术,对玉米胚乳传递细胞进行了显微和超微结构观察.结果显示:(1)胚乳传递细胞的壁内突从外层向内层依次递减,溶质浓度逐步降低,形成了明显的溶质浓度梯度,有利于溶质的运输;(2)中层胚乳传递细胞和内层胚乳传递细胞的邻壁上存在胞间连丝或一些孔径较大的胞壁孔道,从而使溶质更快的进入内层胚乳传递细胞;(3)在壁内突周围存在许多线粒体.研究表明,玉米胚乳传递细胞的结构适合溶质运输.     

Ultrastructure of Transfer Cells in Endosperm of Coix lacryma-jobi

Special attention was paid to the ultrastructure of transfer cells (TCs) in different locations of basal endosperm in Coix lacryma-jobi at 10 and 25 days after pollination. At 10 days after pollination. TCs of the outermost layer had long wall ingrowths (WIs) whereas those of the second layer possessed fewer and shorter Wis. In both layers TCs had a lobed nucleus, abundant mitochondria, rough endoplasmic reticulum (RER), ribosomes, and a certain number of dictyosomes and vesicles which contained dense substance connected with plasma membrane of WIs. Mitochondria were located near or between WIs. The distribution of organelles in TCs of the second layer was similar to that of the outermost layer. Mitochondria had well defined cristae and dictyosomes and RER seemed more numerous than in TCs of the outermost layer. At 25 days after pollination, TCs of the outermost and the second layer were almost filled with Wis but the organelles were recognizable. TCs of the fourth layer had branched and network-like WIs, many mitochondria, starch grain within plastids and lipids locating near WIs and in the interstices of WIs. Dictyosomes were frequently found but less RER fragments were seen. TCs of the fifth layer with short WIs contained large starch grains and small protein bodies. Plasmodesmata were not observed in the walls of TCs of the outermost and second layer at both 10 and 25 days after pollination but were found in the walls of TCs of the fourth and upper layers and also in the network-like WIs at 25 days after pollination. The roles of the organelles and functions of TCs of different layers were discussed.     

COTTON EMBRYOGENESIS: THE EARLY DEVELOPMENT OF THE FREE NUCLEAR ENDOSPERM

An electron microscope study was made of the central cell and the development of the free nuclear endosperm surrounding the zygote and synergids during the first three days after pollination. The cytoplasm of the central cell, concentrated around the partially-fused polar nuclei, contains many ribosomes, mitochondria and large, dense, starch-containing plastids, some dictyosomes and lipid bodies, and long, single cisternae of rough endoplasmic reticulum (RER) that frequently terminate in whorls. Dense, core-containing microbodies are closely associated with the RER. After fertilization the cytoplasm of the 2-and 4-nucleate endosperm shows an increase in number of dictyosomes, and in amount of RER which becomes stacked in arrays of parallel cisternae. Cup-shaped plastids are associated with many long, helical polysomes. Perinuclear aggregates of dense, granular material also appear after fertilization. Granular aggregates and helical polysomes disappear after the first few divisions of the primary endosperm nucleus. During the second and third days of development there is an increase in dictyosome number and RER proliferation, and endosperm nuclei become deeply lobed. Concurrently, there is a sharp decline in the starch and lipid reserves of the central cell and elaborate transfer walls are formed at the micropylar end of the embryo sac and on the outer surface of the degenerating synergid. The transfer walls contain groups of small, membrane-bound vesicles, and are associated with large numbers of mitochondria and with the smooth endoplasmic reticulum.     

STRATIFICATION AND SUBSEQUENT BEHAVIOR OF PLANT CELL ORGANELLES

Living excised roots of pea were centrifuged at 20,000 g for 24 hours, and the behavior of organelles was followed by electron microscopy at various intervals after centrifugation. With these forces, organelles are not perceptibly or irreversibly damaged, nor is the viability of the whole root destroyed. Organelles stratify generally in the order of lipid (centripetal pole), vacuoles, smooth endoplasmic reticulum and dictyosomes, proplastids (without starch), mitochondria, rough endoplasmic reticulum, proplastids with starch. The nucleus distends from the vacuolar region to the extreme centrifugal pole of the cell, while the chromatin and nucleolus seek the centrifugal pole of the nucleus. During the redistribution of organelles the rough endoplasmic reticulum is among the first to reorient, and possible explanations for this are discussed. Mitochondria can be stretched elastically many times their original length, but proplastids seem fairly rigid. Small vacuoles, forced together during centrifugation, apparently may fuse to form a large unit. Lipid droplets, on the other hand, tend to remain separate. Dictyosomes and smooth endoplasmic reticulum layer in the same region of the centrifuged cell, indicating a density similarity between these two organelles.     

Electron microscopic study of spermiogenesis in the free-living marine nematode <Emphasis Type="Italic">Leptosomatides marinae</Emphasis> Platonova 1976 (Enoplida: Leptosomatidae)

The ultrastructure of spermatocytes, spermatids and spermatozoa of the free-living marine nematode Leptosomatides marinae was studied by transmission electron microscopy. In early spermatids, the number of mitochondria, cisterns of the rough endoplasmic reticulum (RER) and dictyosomes increased; the number of membranous organelles (MOs) was insignificant. Later, dictyosomes and MOs filled the cytoplasm. The cytoplasm became distinctly segregated in late spermatids and the MOs concentrated around the nucleus; the mitochondria and organelles of synthesis settled on the cell periphery. Later, a densely packed conglomerate was formed from the central nucleus and a mass of MOs surrounded by an extensive zone of the cytoplasm containing mitochondria and organelles of synthesis. Early spermatozoa had an elongated nucleus surrounded by a layer of cytoplasm containing mitochondria, polarized MOs and bundles of filamentous material, which can be interpreted as fibrous bodies (FBs). The formed spermatozoa had elongated nuclei surrounded by a transparent halo; the cell periphery was a dense matrix, in which MOs and sparse mitochondria were submerged; no FBs were revealed in that phase. In general, the spermatozoa of L. marinae have the main attributes common to the Enoplida spermatozoa, availability of nuclear environment and development of the specific organelles, MOs and FBs, which are not united in complexes.     

An ultrastructural study of early endosperm development and synergid changes in unfertilized cotton ovules

Excised, unfertilized cotton (Gossypium hirsutum L.) ovules were cultured for 1–5 days postanthesis and embryo-sac development was studied with the electron microscope. In some ovules the two polar nuclei fuse and the diploid endosperm nucleus goes through a limited number of free nuclear divisions after 2–3 days in culture. Each nucleus has two nucleoli, in contrast to nuclei of fertilized triploid endosperm which have three nucleoli. Precocious cell walls form between the endosperm nuclei on the 3rd day in culture. The morphology of the plastids, mitochondria, rough endoplasmic reticulum (RER), dictyosomes and microbodies, and the amount of starch and lipid in the diploid cellular endosperm are similar to those of the central cell. A few large helical polysomes appear close to plastids and mitochondria. After 2 days in culture, one of the two synergids in the unfertilized cultured ovules shows degenerative changes which in fertilized ovules are associated with the presence of the pollen tube, i.e., increase in electron density, collapse of vacuoles, irregular darkening and thickening of mitochondrial and plastid membranes, disappearance of the plasmalemma and the membranes of the plasmalemma and the membranes of the RER. The second synergid remains unchanged in appearance. The egg cell does not shrink or divide or show structural changes characteristic of the cotton zygote. Embryo-sac development is arrested on the 4th and 5th days in culture. The nucellus continues growth and at 14 days crushes the degenerate embryo sac.     

薏苡胚乳发育及营养物质积累的研究

薏苡 ( Coix lacryma- jobi)授粉后 2 d,游离核胚乳已转变为细胞胚乳。授粉后 3d,中央细胞被胚乳细胞充满。起初 ,全部胚乳细胞均进行分裂 ,一定时期后 ,细胞分裂主要发生在胚乳周边区。授粉后 1 0 d,表皮停止平周分裂变为糊粉层 ,内方的数层形成层状细胞行平周分裂直到颖果接近成熟。胚乳内部生长则依赖于细胞体积扩大。胚乳基部 (颖果基部的胚乳 )形成了数层传递细胞。授粉后 9d,淀粉积累。授粉后 1 0 d,糊粉层及其内方数层细胞产生了脂体 ,后者的脂体以后又消失。授粉后 1 3、1 5 d,糊粉层细胞的液泡积累蛋白质。授粉后 2 0 d,液泡变为糊粉粒。授粉后 1 5 d淀粉胚乳细胞产生蛋白质体 ,营养物质积累持续到颖果成熟。还观察了胚和胚乳发育的对应关系。     

ULTRASTRUCTURE OF TETRASPOROGENESIS IN THE PARASITIC RED ALGA LEVRINGIELLA GARDNERI (SETCHELL) KYLIN12

Ultrastructural studies on tetraspore formation in Levringiella gardneri revealed that 3 stages may be recognized during their formation. The youngest stage consists of a uninucleate tetraspore mother cell with synaptonemal complexes present during early prophase of meiosis I. Mitochondria are aggregated around the nucleus, dictyosome activity is low, and chloroplasts occur in the peripheral cytoplasm. A 4-nucleate tetraspore mother cell is formed prior to tetrahedral cell cleavage, and an increase in the number of chloroplasts and mitochondria occurs. Small straight-profiled dictyosomes secrete vesicles into larger fibrous vesicles or contribute material to the developing tetraspore wall. During the second stage of tetraspore formation, striated vesicles form within endoplasmic reticulum, semicircular profiled dictyosomes secrete vesicles for fibrous vesicles or wall material, and starch formation increases. The final stage is characterized by the disappearance of striated vesicles, presence of straight, large dictyosomes which secrete cored vesicles, and an abundance of starch grains. Cleavage is usually complete at this stage and the tetraspore wall consists of a narrow outer layer of fibrillar material and an inner, electron transparent layer. These spores are surrounded by a tetrasporangial wall which was the original wall surrounding the tetraspore mother cell.     

大葱小孢子母细胞至二胞早期花粉发育的超微结构观察

用电镜观察了章丘大葱 (AlliumfistulosumL .)从小孢子母细胞至二胞早期花粉发育的超微结构。终变期的花粉母细胞 ,胼胝壁外方的相邻初生壁间及胞间隙内 ,存在胞间物质 ,四分体期 ,此物质尚部分存在。小孢子母细胞减数分裂前 ,细胞质内含有脂滴 ,小孢子有丝分裂以后 ,脂滴增多增大。小孢子分裂后期 ,质体已积累淀粉粒 1至多个。二胞早期花粉之营养细胞质内 ,有些含淀粉质体亦含脂滴。各发育期 ,核糖体及多聚合糖体丰富 ,并有很多的粗面内质网、高尔基体及小泡、线粒体 ,显示蛋白质、糖类及其它物质合成及运输作用的活跃。小孢子缺中央大液泡。有丝分裂后期 ,细胞器集中于未来的营养细胞极。小孢子胞质分裂期 ,有些内质网贴近或与花粉质膜相连 ,它们或有可能互相融合 ,扩大质膜面积而适应花粉的生长。还讨论了不同时期高尔基体小泡的作用。     

The sporophyte-gametophyte junction in the moss Acaulon muticum (Pottiaceae): EARLY STAGES OF DEVELOPMENT

The sporophyte-gametophyte junction in Acaulon muticum is composed of the sporophyte foot, the surrounding gametophyte vaginula, and an intervening placental space. At an early stage of development the foot has a large basal cell, characterized by extensive wall ingrowths beginning at the lowermost tip of the basal cell and extending along its tangential walls. Sporophyte cells in contact with the basal cell develop ingrowths on their outer tangential walls and on radial walls in contact with the basal cell. All sporophyte cells at this stage are characterized by numerous mitochondria, strands of endoplasmic reticulum, and dictyosomes, particularly in the cytoplasm adjacent to areas of extensive wall development. Plastids typically contain abundant starch reserves. As development proceeds, wall ingrowths become more extensive on all walls in the sporophyte foot but are never found on the upper wall of the basal cell in contact with the remainder of the sporophyte. Plastids in the foot contain fewer starch reserves later in development. Wall ingrowths are not visible in the cells of the gametophyte vaginula until well after extensive development has occurred in the sporophyte foot. Stacks or layers of endoplasmic reticulum are characteristic of the cells of the gametophyte vaginula, along with numerous mitochondria, dictyosomes, and well-developed plastids. Starch reserves typically are less abundant in cells of the gametophyte. The early development of extensive wall elaborations in the cells of the sporophyte foot, and particularly in the basal cell, may favor the rapid movement of water and nutrients from the gametophyte into the sporophyte at a time when rapid development in this minute, ephemeral moss is critical.     

Studies on Endosperm Development and Deposition of Storage Reserves in Coix lacryma-jobi

The transition from free nuclear to cellular endosperm of Coix lacryma-jobi was eompleted 2 days after pollination. By 3 days after pollination the central cell was filled with endosperm cells. At first all cells of endosperm underwent division, later cell division was limited mainly in the peripheral region. 10 days after pollination the epidermal layer ceased its periclinal division and became the aleurone layer. Cell division persisted in the subepidermal 'cambium-like layers until the caryopsis nearly matured. Ceils of the inner region of endosperm became enlarged. Several layers of transfer cells were formed at the basal part of the endosperm. Starch grains appeared in endosperm cells on the 9th day after pollination. 10 days after pollination, lipid bodies occurred in the aleurone layer and the underlying layers. 13 and 15 days after pollination, the small vacuoles of aleurone cells contained protein and 20 days after pollenation they became aleurone grains. By 15 days after pollination pro tein bodies were formed in starch endosperm. Storage reserve deposition continued until the grain ripened. A correlation between endosperm and emoryo development was also observed.