Microtubular configurations during the cellularization of coenocytic endosperm in Ranunculus sceleratus L.

Summary Endosperm cellularization in Ranunculus sceleratus was studied in terms of the initiation of cell-wall formation in the coenocytic endosperm. The first endosperm cell walls were in an anticlinal position relative to the cell wall of the embryo sac and originated from the cell plates and not from wall ingrowths from the embryo-sac wall itself. Alveolar endosperm was formed 3 days after pollination. Microtubules were associated with the freely growing wall ends of the anticlinal walls and were observed in various orientations that generally ranged from angles of 45 ° to 90 ° to the plane of the wall. They were absent in the regions where vesicles had already fused. These microtubules may function in maintaining the growth and the direction of growth of the anticlinal wall until cellularization is completed. At the site where three neighbouring alveoli share their freely growing wall ends, remarkable configurations of microtubules were observed: in each alveolus, microtubules ran predominantly parallel to the bisector of the angle formed by the common walls. These microtubules may form a physically stable framework and maintain the direction of growth of the wall edges. It is concluded that the growing edge of the anticlinal endosperm wall and its associated microtubules are a special continuum of the original phragmoplast that gave rise to the anticlinal wall.     

Zostera capensis setchell: III. Some aspects of wall ingrowth development in leaf blade epidermal cells

Summary The development of wall ingrowths in leaf blade epidermal cells of the marine angiospermZostera capensis was studied by electron microscopy. Prior to the appearance of ingrowths long profiles of endoplasmic reticulum cisternae become arranged peripherally closely following the contours of the walls. The plasmalemma assumes a wavy appearance and in regions where wall ingrowths first start forming (i.e., along the radial, inner tangential and transverse walls) the plasmalemma becomes separated from the walls by an undulating extracytoplasmic space. Small, irregular projections of secondary wall material make their appearance here. Paramural bodies, dictyosomes, endoplasmic reticulum (ER) and possibly also microtubules seem to be closely associated with the initiation and subsequent development of wall projections. As the cells mature, new ingrowths arise in a centrifugal direction along the radial and transverse walls. When wall ingrowths reach a certain stage of their development, mitochondria become strongly polarized towards them and become closely associated with the plasmalemma which ensheaths the ingrowths. There is often also a close association between ER cisternae and the involuted plasmalemma of the wall projections. Initially ingrowths are slender, curved structures, but become more complex as the cells mature. Ingrowths are most extensively developed along the inner tangential and transverse walls. As epidermal cells age there is a loss of wall material from the ingrowths. The probable significance of the formation of wall ingrowths in the epidermal cells is also discussed.     

Effects of anoxia on pollen tube growth and tube wall formation of Impatiens glandulifera

Summary When pollen of Impatiens glandulifera was cultured in aerated liquid medium for 1 h, 70% of the pollen grains germinated; these attained an average tube length of 1 mm. Subsequently, these aerobic growth conditions were changed to anaerobic by substituting a nitrogen inlet for the air inlet. As a result, the pollen tubes stopped elongating and burst. The ultrastructural changes which occurred upon inducing anoxia were studied with samples taken at 0 s, 45 s, and 4 min after changing the gas. Anoxia caused rapid and considerable changes in the ultrastructure of the dictyosome vesicles involved in cell wall formation. There was an increase in the osmiophyly of the vesicle content, and the presence of fibrillar material became apparent. Simultaneously, the fusion behavior of the dictyosome vesicles changed. Instead of the normal fusion of the dictyosome vesicles with the plasma membrane, there was a premature fusion of the vesicles with each other inside the cytoplasm that resulted in the formation of aggregates. Furthermore, the cell wall precursors that were excreted were not incorporated in their usual configuration into the growing cell wall. Instead of a smooth inner cell wall surface, irregular thickenings were formed.     

薏苡胚乳细胞化的超微结构观察

采用透射电镜对薏苡早期的胚乳细胞化进行了研究,在胚乳游离核时期,胚乳游离核及细胞质绕中央细胞分布,游离核间没有发现胚囊壁内突、成膜体等结构。胚乳细胞化过程中初始垂周壁形成过程如下：（１）胚乳细胞质中出现液泡,使细胞质和核向中央液泡推进：（２）一对相邻细胞核间液泡成对存在,且呈垂周分布,而且两液泡间的细胞质很狭窄;（３）在这狭窄的细胞质中出现成行排列的小泡;（４）小泡融合形成细胞板,细胞板悬于两液泡     

Distortion of plant cell plate formation by the intracellular-calcium antagonist TMB-8

Summary Caulonema tip cells ofFunaria deposit new oblique cross walls of specific morphology and placement by a highly defined reorientation mechanism. In the presence of the purported intracellular Ca²⁺ antagonist 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), these cross walls form in the proper place but exhibit a distorted morphology. Video microscopy indicates that the deformation takes place during the reorientation of the cell plate from a perpendicular to an oblique configuration. Electron micrographs of TMB-8 treated cells indicate a stabilization of phragmoplast microtubules and a greater amount of vesicles and membrane in the developing cell plate. TMB-8 treated cells also show intense chlortetracycline fluorescence from mitochondria, vesicles and endoplasmic reticulum as compared to untreated cells indicating that TMB-8 is blocking release of Ca²⁺ from intracellular stores. It is concluded that this may cause distortation of cross walls as they form by delaying vesicle fusion, stabilizing microtubules, and increasing the amount of new wall material in the developing cell plate.Abbreviations CTC chlortetracycline - OsFeCN osmium ferricyanide method - TMB-8 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate     

Cell division in leaves ofNicotiana

Summary Young leaves ofNicotiana tabacum were fixed in glutaraldehyde-formaldehyde followed by osmium tetroxide. The fine structure of dividing cells was studied. Before prophase a band of microtubules was observed between the nucleus and the cell wall at a position judged as the future plane of division. The microtubules in the band are 4–6 units deep and relatively closely packed, giving sections of the band a characteristic appearance. Micro-tubules of the mitotic spindle, the phragmoplast, and the preprophase band are morphologically similar. Some of the microtubules of the mitotic spindle and the phragmoplast have an undulate appearance. It is suggested that the undulate microtubules may have been fixed at a time when microwaves were traveling along them. The cell plate is formed by a fusion of small smooth surfaced vesicles and small coated vesicles. Fusion of small vesicles results first in larger vesicles and then in a meshwork of new cell-wall material surrounded by new regions of plasma membrane. Most of the vesicles are derived from dictyosomes and may be produced before and during prophase as well as during later stages of division. The ER may also contribute some vesicles to the cell plate.     

SECRETIONS FROM THE PISTIL OF LILIUM LONGIFLORUM

The pistil of Lilium longiflorum secretes two forms of exudate, one from the stigma surface and the other from the canal cavity. Electrophoretic studies of these exudates have revealed quantitative and qualitative differences in protein profiles. The exudatic components which are transferred to the cell wall by endoplasmic reticulum and Golgi vesicles, are stored within the cell wall of the secretive tissues and secreted from the cell walls directly. The cell wall structure of these secretive tissues differs. The canal cell wall has thick characteristic ingrowths that are supplied mainly from Golgi vesicles, while the papilla cell wall of the stigma is thinner, lacks ingrowths, and is supplied from ER vesicles.     

Metabolism of P-particles (polysaccharide particles) in mature pollen grains ofEryngium campestre L. (Apiaceae)

Summary The metabolism of P-particles (polysaccharide particles) was investigated in mature pollen grains ofEryngium campestre L. Numerous P-particles, originating from dictyosome activity, are found to be accumulated near the apertures, followed by mitochondria. A single layer of ER profiles seems to prevent the fusion of the P-particles with the intine. Instead of this, they fuse with each other forming nonmembrane-bounded polysaccharide-aggregates, which subsequently change their granulated structure to an amorphous. Mitochondria together with small vesicles are involved in the conversion-process. The so formed wall precursors pass through the ER and fuse into the intine.     

The endomembrane system and mechanism of membrane flow in the green alga,Gloeomonas kupfferi (Volvocales,Chlorophyta) I. An ultrastructural analysis

Summary The endomembrane system of the chlamydomonad flagellate,Gloeomonas kupfferi (Chlorophyta), is complex. It consists of a proliferating ER network, a perinuclear complex of 14–18 dictyosomes and 8–12 vacuoles and an anterior contractile vacuole complex. The ER network extends from the nuclear envelope outwards, ensheafhs a dictyosome, extends out through a lobe of the chloroplast and terminates in the thin zone of peripheral cytoplasm between the chloroplast and plasmamembrane. The individual dictyosome is polar with distinct cis- and trans-faces. The cis-face is closely associated with transition vesicles emerging from the adjacent ER. Large vesicles emerge from peripheral swellings of terminal cisternae. The dictyosome-associated ER is connected to the peripheral vacuolar system. During cell division and cytokinesis, changes in the endomembrane system occur. Dictyosomes divide and quickly separate to form perinuclear complexes around the daughter nuclei. Each dictyosome undergoes morphological changes during this wall precursor-producing stage. ER lines the furrow zone and is closely associated with phycoplast microtubules. A discussion of the endomembrane system in membrane flow mechanics is provided.Abbreviations ER endoplasmic reticulum - OsFeCN Osmium ferricyanide     

ULTRASTRUCTURE OF SPERMATIUM LIBERATION IN THE MARINE RED ALGA PTILOTA DENSA1

The differentiation of male gametes of the marine red alga Ptilota densa was studied by electron microscopy. Mature primary spermatangia are enveloped by a single cell wall and possess a clearly polar subcellular organization. The nucleus is situated apical to large, striated, fibrous vacuoles which are apparently formed by the repeated fusion of dictyosome vesicles. The transformation and liberation of spermatia from spermatangia involve both the secretion of the fibrous vacuoles at the base of the cell and the subsequent rupturing of the spermatangial cell wall. Liberated spermatia are coated with a thin mucilage layer and contain numerous small vesicles and several mitochondria and dictyosomes. The nucleus is cup-shaped and generally lacks a limiting envelope. These findings are discussed in relation to other light and electron microscopic studies of differentiating spermatangia in red algae.     

CELL DIVISION AND FILAMENT FORMATION IN THE DESMID BAMBUSINA BREBISSONII (CHLOROPHYTA)1

Cell division and semicell expansion in the filamentous desmid Bambusina brebissonii Kütz. were investigated using transmission and scanning electron microscopy. Interphase cells are typical of desmids, containing a full complement of organelles and a cell wall penetrated by complex pores, but the cells lack a well-defined median constriction. Cell division involves an open spindle and the centripetal growth of a primary septum formed by the fusion of small, dark-staining vesicles probably derived from dictyosomes. Telophase nuclei are separated by a system of interzonal microtubules and numerous large, lighter-staining vesicles also derived from the dictyosomes. Following cell division, an elaborate replicate cross wall is formed which consists of both primary and secondary wall layers. During semicell expansion, a portion of the primary wall splits apart as the new semicells evaginate and expand to their full size. The primary wall stops splitting at a thick ring of secondary wall material leaving the cells united by the remaining common layer of primary wall. When semicell expansion is completed, the primary wall is not shed from the lateral walls of the new semicells, and pores through both primary and secondary wall layers begin to produce sheath material. However, pores in the end walls of cells do not function unless the filament is broken. The intact primary wall between cells and the absence of sheath production between cells comprise the mechanism serving to hold the cells of Bambusina brebissonii together in long filaments.     

Early Endosperm Development in Ovules of Soybean, Glycine max (L) Merr. (Fabaceae)

Endosperm development was studied in normally setting flowersand pods of soybean from anthesis to a pod length of 10–20mm. The free-nuclear stage following double fertilization istypified by loss of starch and increasing vacuolation. The cytoplasmprovides evidence of extensive metabolic activity. Wall ingrowths,already present at the micropylar end of the embryo sac wallprior to fertilization, develop along the lateral wall of thecentral cell as well as at the chalazal endosperm haustorium.Endosperm cellularization begins when the embryo has developeda distinct globular embryo proper and suspensor. Cellularizationstarts at the micropylar end of the embryo sac as a series ofantidinal walls projecting into the endosperm cytoplasm fromthe wall of the central cell. The free, growing ends of thesewalls are associated with vesicles, microtubules, and endoplasrnicreticulum. Pendinal walls that complete the compartmentalizalionof portions of the endosperm cytoplasm are initiated as cellplates formed during continued mitosis of the endosperm nuclei.Endosperm cell walls are traversed by plasmodesmata. This studywill provide a basis for comparison with endosperin from soybeanflowers programmed to abscise. Glycine max, soybean, endosperm, ovules     

Induction of wall ingrowths of transfer cells occurs rapidly and depends upon gene expression in cotyledons of developing Vicia faba seeds

Summary. Abaxial epidermal cells of developing faba bean (Vicia faba) cotyledons are modified to a transfer cell morphology and function. In contrast, the adaxial epidermal cells do not form transfer cells but can be induced to do so when excised cotyledons are cultured on an agar medium. The first fenestrated layer of wall ingrowths is apparent within 24 h of cotyledon exposure to culture medium. The time course of wall ingrowth formation was examined further. By 2 h following cotyledon excision, a 350 nm thick wall was deposited evenly over the outer periclinal walls of adaxial epidermal cells and densities of cytoplasmic vesicles increased. After 3 h in culture, 10% of epidermal cells contained small projections of wall material on their outer periclinal walls. Thereafter, this percentage rose sharply and reached a maximum of 90% by 15 h. Continuous culture of cotyledons on a medium containing 6-methyl purine (an inhibitor of RNA synthesis) completely blocked wall ingrowth formation. In contrast, if exposure to 6-methyl purine was delayed for 1 h at the start of the culture period, the adaxial epidermal cells were found to contain small wall ingrowths. Treating cotyledons for 1 h with 6-methyl purine at 15 h following cotyledon excision halted further wall ingrowth development. We conclude that transfer cell induction is rapid and that signalling and early events leading to wall ingrowth formation depend upon gene expression. In addition, these gene products have a high turnover rate. Correspondence and reprints: School of Environmental and Life Sciences, Biology Building, University of Newcastle, Callaghan, NSW 2308, Australia.     

Cytochalasin-D causes abnormal wall-ingrowths and organelle-crowding in legume root hairs

Root hair cytoplasmic microtubules and filamentous actin are known to maintain the location of the nucleus in relation to the hair tip. After cytochalasin-D treatment, fragments of F-actin were found to be closely associated with the nucleus and plastids, and with accumulations of mitochondria, dictyosomes and vesicles. Abnormal wal ingrowths found after cytochalasin-D treatment did not occur when microtubules were depolymerised by the herbicide cremart, or when treated with both drugs. These ingrowths may occur as the cessation of streaming (by the action of cytochalasin-D) causes cell wall precursors to be unloaded next to the nearest (cortical) microtubules. Thus, when microtubules are depolymerised, vesicles are unable to unload the precursors. The significance of these results is discussed in the context of infection in theRhizobium/legume symbiosis.     

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。     

Ultrastructural characteristics of « Diplotaxis erucoides (L.) DC. » suspensor

Abstract

The development and general morphology of Diplotaxis erucoides (L.) DC. suspensor is of the « Onagrad Type », « Alyssum Variation ». Maximum growth of the suspensor occurs from the globular to the early heart stage of embryo development. The suspensor starts then to degenerate disintegrating shortly after the torpedo stage of the embryo.

The wall ingrowths of the long, tapering, basal cell are especially abundant at the cell's micropilar pole which is closely surrounded by well developed wall ingrowths formed by the endosperm. Wall ingrowths and plasmodesmata are present on the suspensor cells cross walls with the exception of the cell closest to the embryo. No such structures in fact are present on the walls separating this last cell both from the embryo and from the rest of the suspensor. Wall ingrowths are generally associated with numerous, large, mitochondria.

The morphological data seem to indicate that absorption and transport of nutrients from the surrounding tissues is a main function of the suspensor. The possibility of an elaborative and secretory function of this structure is discussed.     

Callose deposition and breakdown, followed by phytomelan synthesis in the seed coat ofGasteria verrucosa (Mill.) H. Duval

Summary In the seed coat ofGasteria verrucosa the deposition of phytomelan takes place during seed development in three stages. Phytomelan is a black cell wall material which is chemically very inert. First the radial walls and part of the transverse cell wall of the outer epidermis of the outer integument become thickened by exocytosis of dictyosome vesicles. Callose is deposited at the tangential plasma membrane against those walls. After the callose deposition about two thirds of the original cell volume is filled with callose. During the second stage the callose is broken down, probably into glucose monomers or small polymers. At the same time cellulose is deposited at the outer tangential plasma membrane, forming a wall between the dissolving callose and the plasma membrane. In the third phase small granules appear in the solution of dissolved callose. which grow out and finally fuse to form a block of phytomelan, consisting of spherical 15-nm units. Remarkable is the function of the callose: it determines the size of the phytomelan block, and it probably functions as carbohydrate source for the phytomelan synthesis and/or for the cellulose inner layer. In this study transmission electron microscopy and cryo scanning electron microscopy are used to study the three developmental stages of the formation of the phytomelan layer.     

Ultrastructural research on cell wall regeneration by cultured pollen protoplasts of Lilium longiflorum

Summary Protoplasts from pollen grains of Lilium longiflorum regenerate amorphous cellulosic cell walls in culture, during which some precursors of cellulose are polymerized, thus producing progressively harder cellulosic cell walls as the period of culture continues. It is presumed that the components of the cell wall regenerated during 1 week in culture differ from those of the intine of the pollen grain wall. The regenerated cell wall is formed by means of large smooth vesicles; in addition, numerous coated vesicles and pits aid in wall regeneration. The pollen tube that germinates from the 8-day-old cultured protoplast has numerous Golgi bodies and many vesicles which build the pollen tube wall. The tube wall has two layers just like a normal pollen tube wall.     

Polarized microtubule deposition coincides with wall ingrowth formation in transfer cells ofVicia faba L. cotyledons

Summary The epidermal transfer cells in developingVicia faba L. cotyledons are highly polarized. Extensive wall ingrowths occur on their outer periclinal walls and extend part way down both anticlinal walls. This ingrowth development serves to increase the surface area of the plasma membrane and thus maximize porter-dependent uptake of sugars from the seed apoplasm. In contrast, the inner periclinal walls of these transfer cells do not form wall ingrowths. We have commenced a study of the mechanisms responsible for establishing this polarity by first analysing the microtubule (MT) cytoskeleton in developing transfer cells. Thin sections of fixed cotyledons embedded in methacrylate resin were processed for immunofluorescence microscopy using monoclonal anti--tubulin and counterstained with Calcofluor White to visualize wall ingrowths. In epidermal cells of young cotyledons where wall ingrowths were yet to develop, MT labelling was detected around all cortical regions of the cell. However, in cells where wall ingrowths were clearly established, MT labelling was detected almost exclusively in cortical regions adjacent to the wall ingrowths. Little, if any, MT labelling was detected on the anticlinal or inner periclinal walls of these cells. This distribution of MTs was most prominent in cells with well developed wall ingrowths. In these cells, a subpopulation of MTs were also detected emanating from the subcortex and extending towards the wall ingrowth region. The possible role of MT distribution in establishing transfer cell polarity and wall ingrowth formation is discussed.Abbreviations MT microtubule     

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。