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.     

Ultrastructure of transfer cells in spontaneous nodules of alfalfa (Medicago sativa)

Summary Spontaneous nodules were formed on the primary roots of alfalfa plants in the absence ofRhizobium. Histologically, these white single-to-multilobed structures showed nodule meristems, cortex, endodermis, central zone, and vascular strands. Nodules were devoid of bacteria and infection threads. Instead, the larger cells were completely filled with many starch grains while smaller cells had very few or none. Xylem parenchyma and phloem companion cells exhibited long, filiform and branched wall ingrowths. The characteristic features of both types of transfer cells were polarity of wall ingrowths, high cytoplasmic density, numerous mitochondria, abundant ribosomes, well-developed nucleus and nucleolus, and vesicles originated from rough endoplasmic reticulum. These results were compared with normal nodules induced byRhizobium. Our results suggest that xylem parenchyma and phloem companion transfer cells are active and probably involved in the short distance transport of solutes in and out of spontaneous nodules. Since younger nodules showed short, papillate, and unbranched wall ingrowths, and older tissue showed elongated, filiform and branched wall ingrowths, the development of wall ingrowths seemed to be gradual rather then abrupt. The occurrence of both type-A and -B wall ingrowths suggests that phloem companion transfer cells may be active in loading and unloading of sieve elements. Since there were no symbiotic bacteria and thus no fixed nitrogen, it is tempting to speculate that xylem parenchyma transfer cells may be re-transporting accumulated carbon from starch grains to the rest of the plant body by loading xylem vessels. Fusion of ER-originated vesicles with wall ingrowth membrane indicated the involvement of ER in the membrane formation for elongating wall ingrowths. Since transfer cells were a characteristic feature of both spontaneous andRhizobium-induced nodules, their occurrence and development is controlled by the genetic make-up of alfalfa plant and not by a physiological source or sink emanating from symbiotic bacteria.Abbreviations ATP adenosine triphosphate - ATPase adenosine triphosphatase - EH emergent root hair - EM electron microscope - Nar nodulation in the absence of Rhizobium - RT root tip - RER rough endoplasmic reticulum - YEMG yeast extract mannitol-gluconate     

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.     

GIGANTEA is a component of a regulatory pathway determining wall ingrowth deposition in phloem parenchyma transfer cells of Arabidopsis thaliana

Transfer cells are specialised transport cells containing invaginated wall ingrowths that generate an amplified plasma membrane surface area with high densities of transporter proteins. They trans‐differentiate from differentiated cells at sites at which enhanced rates of nutrient transport occur across apo/symplasmic boundaries. Despite their physiological importance, little is known of the molecular mechanisms regulating construction of their intricate wall ingrowths. We investigated the genetic control of wall ingrowth formation in phloem parenchyma transfer cells of leaf minor veins in Arabidopsis thaliana. Wall ingrowth development in these cells is substantially enhanced upon exposing plants to high‐light or cold treatments. A hierarchical bioinformatic analysis of public microarray datasets derived from the leaves of plants subjected to these treatments identified GIGANTEA (GI) as one of 46 genes that are commonly up‐regulated twofold or more under both high‐light and cold conditions. Histological analysis of the GI mutants gi‐2 and gi‐3 showed that the amount of phloem parenchyma containing wall ingrowths was reduced 15‐fold compared with wild‐type. Discrete papillate wall ingrowths were formed in gi‐2 plants but failed to develop into branched networks. Wall ingrowth development in gi‐2 was not rescued by exposing these plants to high‐light or cold conditions. In contrast, over‐expression of GI in the gi‐2 background restored wall ingrowth deposition to wild‐type levels. These results indicate that GI regulates the ongoing development of wall ingrowth networks at a point downstream of inputs from environmental signals.     

THE OCCURRENCE AND PHYLOGENETIC SIGNIFICANCE OF PUTATIVE PLACENTAL TRANSFER CELLS IN THE GREEN ALGA COLEOCHAETE

Following fertilization, zygotes of the green alga Coleochaete orbicularis, which are retained on the haploid thallus, first enlarge, then become covered with a layer of vegetative cells. Light microscopy and high-voltage electron microscopy revealed the presence of localized wall ingrowths in vegetative cells adjacent to zygotes. These covering cells resemble the gametophytic placental transfer cells of embryophytes in their morphology, location, and time of development. If Coleochaete cells with wall protuberances function as do placental transfer cells of embryophytes, their presence is evidence that photosynthates may be transported between haploid thallus cells and zygotes. Thus, a nutritional relationship between different phases of the life cycle, similar to that which occurs in embryophytes, may also have evolved in green algae. This first report of putative placental transfer cells in a green alga supports Bower's (1908) ideas concerning the origin of land plant sporophytes and alternation of generations. The presence or absence of cells with wall ingrowths in several species of Coleochaete was correlated with estimates of zygote-plant area ratios.     

Pure culture and reconstitution of the Anthoceros-Nostoc symbiotic association

The partners of the symbiotic association between Anthoceros punctatus L. and Nostoc spp. have been cultured separately in a pure state. The symbiotic association was reconstituted following dual culture in liquid Anthoceros growth medium with a variety of axenic Nostoc isolates and mutant strains. The heterocyst frequency of competent Nostoc strains increased four- to fivefold when in symbiotic association relative to free-living N₂-grown cultures. Dinitrogen fixation by symbiotic Nostoc supported the growth of Anthoceros tissue, although this growth was nitrogen-limited relative to that supported by exogenous ammonium. When the association was reconstituted in the presence of two or three wild-type and mutant Nostoc strains some of these strains were found to compete in infection of Anthoceros tissue and a fraction of the symbiotic Nostoc colonies contained more than one strain. Exogenous ammonium did not affect infection, but repressed development of the symbiotic Nostoc colonies in Anthoceros tissue, and symbiotic Nostoc in N₂-grown Anthoceros tissue appeared to regress from the symbiotic state in the presence of exogenous ammonium. The results show that the Anthoceros-Nostoc symbiotic association is amenable to specific experimental manipulations; their implications are discussed with respect to infection of Anthoceros tissue and control of the development of symbiotic Nostoc.     

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.     

Organization of the nif genes in cyanobacteria in symbiotic association with Azolla and Anthoceros

The sizes of endonuclease digestion fragments of DNA from cyanobacteria in symbiotic association with Azolla caroliniana or Anthoceros punctatus, or in free-living culture, were compared by Southern hybridization using cloned nitrogenase (nif) genes from Anabaena sp. PCC 7120 as probes. The restriction fragment pattern produced by cyanobacteria isolated from A. caroliniana by culture through symbiotic association with Anthoceros differed from that of the major symbiotic cyanobacterium freshly separated from A. caroliniana. The results indicate that minor cyanobacterial symbionts occur in association with Azolla and that the dominant symbiont was not cultured in the free-living state. Both the absence of hybridization to an xisA gene probe and the mapping of restriction fragments indicated a contiguous nifHDK organization in all cells of the symbiont in association with Azolla. On the other hand, in the cultured isolate from Azolla and in Nostoc sp. 7801, the nifD and nifK genes are nominally separated by an interval of unknown length, compatible with the interruption of the nifHDK operon by a DNA element as observed in Anabaena sp. PCC 7120. In the above cultured strains, restriction fragments consistent with a contiguous nifHDK operon were also present at varying hybridization intensities, especially in Nostoc sp. 7801 grown in association with Anthoceros, presumably due to gene rearrangement in a fraction of the cells.Non-standard abbreviations bp base pairs - kb kilobase pairs - kd kilodaltons     

LEAF PARENCHYMA WITH TRANSFER CELL-LIKE CHARACTERISTICS IN THE MOSS,POLYTRICHUM COMMUNE HEDW

Mature leaves of Polytrichum commune Hedw. were examined in regard to structural features and possible solute transport mechanisms. The leaf bundle is organized into several parenchyma layers which are termed passage cells, deuters, and socci. The deuters (leptoids of some authors) are large-diametered parenchymatic elements which exhibit papillate wall ingrowths characteristic of transfer cells. The deuter cytoplasm is typical of transfer cells, including a large number of mitochondria, numerous polysomes, and a peripheral network of ER associated with the wall ingrowths. Deuters show little ultrastructural similarity to leptoids (sieve elements of bryophytes) of the stem. Socci parenchyma and passage cells have a distinct inner wall layer which is convoluted in places, and therefore, these cells as well as the deuters might be involved in intensive short-distance fluxes of solutes. A possible translocation mechanism involving an active, carrier-mediated loading of leaf parenchyma is discussed in relation to these structural features.     

Glomus claroideum forms an arbuscular mycorrhiza-like symbiosis with the hornwort Anthoceros punctatus

Glomus claroideum (Schenck & Smith emend. Walker & Vestberg) were investigated for ability to form arbuscular mycorrhiza-like symbioses with the hornwort Anthoceros punctatus (L.). Spores were transferred to a cellulose acetate filter on water agar and a small portion of an Anthoceros thallus was placed directly upon the spores. Light-microscope observations 20 days after inoculation revealed branched hyphae growing within the thallus. After 45 days, arbuscules and vesicles were studied by light- and electron-microscopy. After 60 days in water agar culture, the colonised Anthoceros thalli were transferred to a low-nutrient medium agar. Hyphae spread in the agar and newly formed spores were observed 5 weeks after the transfer. After 4 months, about 1000 spores were formed in each Petri dish. This is the first report of an experimentally established arbuscular mycorrhiza-like symbiosis between an identified fungus belonging to the Glomales and a bryophyte. Accepted: 11 January 2000     

The intermediary cell: Minor-vein anatomy and raffinose oligosaccharide synthesis in the Scrophulariaceae

Minor-vein anatomy, sugar content, sugar synthesis, and translocation were studied in mature leaves of nine members of the Scrophulariaceae to determine if there is a correlation between companion-cell type and class of sugar translocated. Three types of companion cell were found: intermediary cells with extensive plasmodesmatal connections to the bundle sheath; transfer cells with wall ingrowths and few plasmodesmata; and ordinary companion cells with few plasmodesmata and no wall ingrowths. Alonsoa warscewiczii Regal., Verbascum chaixi Vill., and Mimulus cardinalis Dougl. ex. Benth. have intermediary cells and ordinary companion cells in the minor veins. These plants synthesize large amounts of raffinose and stachyose as well as sucrose. Nemesia strumosa Benth., and Rhodochiton atrosanguineum Zucc. have both intermediary cells and transfer cells and make proportionately less raffinose oligosaccharide than the species above. In N. strumosa, a single sieve element may abut both an intermediary cell and a transfer cell. The minor veins of Asarina scandens (Cav.) Penn. have transfer cells and what appear to be modified intermediary cells that have fewer plasmodesmata than other species, and occasional wall ingrowths. Asarina scandens synthesizes little raffinose or stachyose. Cymbalaria muralis P. Gaertn et al. and Linaria maroccana Hook.f. have only transfer cells and Digitalis grandiflora Mill. has only ordinary companion cells; these species make a trace of galactinol and raffinose, but no stachyose. Translocation experiments indicate that there is long-distance movement of raffinose oligosaccharide in these plants, even when it is synthesized in very small quantities in the leaves. We conclude that intermediary cells are as distinct a cell type as the transfer cell. In contrast to transfer cells, which are specialized for uptake of solute from the apoplast, intermediary cells are specialized for symplastic transfer of photoassimilate from the mesophyll and for synthesis of raffinose oligosaccharide. This supports our contention that raffinose oligosaccharide synthesis and symplastic phloem loading are mechanistically linked (Turgeon and Gowan 1990, Plant Physiol. 94, 1244–1249). Minor-vein anatomy and sugar synthesis may be useful characters in determining the phylogenetic relationships of plants in this family.We thank Andrea Wolfe and Wayne Elisens for helpful discussions on the taxonomy of the Scrophulariaceae. This research was supported by National Science Foundation grant DCB-9104159, U.S. Department of Agriculture Competetive Grant 92-37306-7819, and Hatch funds.     

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.     

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     

Absorptive cells in protoxylem: Association between mitochondria and the plasmalemma

Summary In parenchyma cells grouped around the stem protoxylem in Pinus pinea characteristic wall ingrowths occur. The numerous mitochondria of such cells are very closely associated with the plasmalemma bounding the ingrowths. A functional relationship between this association and salt absorption from the xylem transpiration stream is suggested.     

Amplification of inter-symbiont surface by root epidermal transfer cells in thePisonia mycorrhiza

Summary Cells of the root epidermis ofPisonia grandis R. Br. at the interface with the mycorrhizal fungus are modified as transfer cells. The length of wall profile in transverse section is increased 1.7-fold by the wall ingrowths, on average, over the outer tangential wall and the outer third of the radial walls; this corresponds to a 1.3—fold increase in wall profile length over the whole cell. These increases in length of wall profile approximate—slightly underestimating-the amplification of surface area of the epidermal cells that results from the ingrowths. The surface area between the symbionts in thePisonia mycorrhiza is less amplified than in classical ectomycorrhizas with a Hartig net: this may be functionally adequate because of the extremely high nutrient status of theP. grandis habitat.     

Transfer cells and flange cells in sinkers of the mistletoePhoradendron macrophyllum (Viscaceae), and their novel combination

Summary The unusual thick-walled cells in contact with host and parasite vessels, first noted by Calvin 1967 in sinkers (structures composed of tracheary elements and parenchyma that originate from parasite bark strands that grow centripetally to the host vascular cambium and become embedded by successive development of xylem) of the mistletoePhoradendron macrophyllum (Englem.) Cockerell, have been investigated by modern methods of microscopy. The wall is thickest in cells abutting large-diameter host vessels, less so against smaller host vessels and those abutting sinker vessels. Transmission electron microscopy reveals the wall to be complex, consisting of a basement primary wall, upon which two developments of secondary-wall material occur. These are represented by lignified thickenings, in the form of flanges, and a labyrinth of wall ingrowths characteristic of a transfer cell. The wall ingrowths occur mostly in the primary-wall regions between the flanges, but when in contact with a large host vessel the ingrowths also differentiate on top of the flanges. Cells with such a transfer cell labyrinth have not been previously reported in the endophytic system of a mistletoe. The cells are confined to the xylary portion of the primary haustorium and sinkers. InP. macrophyllum, however, the cells differ from ordinary transfer cells in that they have differentiated as part of a flange parenchyma cell. This arrangement represents a novel anatomical situation. The name flange-walled transfer cell is used for these cells. The xylem of primary haustorium and sinkers also contain numerous ordinary flange cells. In both flange-walled transfer cells and ordinary flange cells the flanges are lignified and form a reticulate pattern of thickenings, separated by rounded areas of primary pit fields. The extent of development of the flange wall can vary in different parts of a sinker. At the host interface, the existence of a flange-walled transfer cell in direct contact with a vessel reflects a site associated with high loading into the parasite. Similarly, a labyrinth against a sinker vessel indicates a site of unloading from surrounding sinker tissue into the vessel for subsequent longdistance transport within the parasite.Dedicated to the memory of Dr. Katherine Esau (1898–1997)     

ULTRASTRUCTURE OF THE TRANSFER TISSUES DURING VIVIPAROUS SEEDLING DEVELOPMENT IN RHIZOPHORA MANGLE (RHIZOPHORACEAE)

All water and nutrients required for the growth of the huge viviparous seedlings of Rhizophora mangle must be transported from the inner surface of the integument (maternal tissue), across a layer of persistent endosperm cells (seedling tissue), and to the surface of the cylindrical cotyledonary body. We describe the ultrastructure of these tissues at two functionally different stages of embryo and seedling development (i.e., 2–3 wk and 2–3 mo postgermination, respectively). Integumentary cells adjacent to the endosperm have unique plastids and divide more frequently than cells further away from the endosperm/integument interface. Later, fibrillar inclusions develop in vacuoles of the integument cells. The outermost layer of endosperm cells differentiates into transfer cells with wall ingrowths on the external walls, and the remainder of the endosperm degenerates during the embryo to seedling transition. The wall ingrowths gradually occlude the lumena of the transfer cells, a process which is complete long before the seedling abscises; therefore, the seedling may be photosynthetically independent throughout most of its development. The outer surface of the seedling cotyledonary body is minimally papillate and exhibits several ultrastructural specializations: centripetal degeneration of external walls which are bounded by electron-dense deposits; numerous mitochondria; and plastids of unusual structure with many plastoglobuli, and which contain unique yellow pigments having absorption spectra characteristic of carotenoids. HPLC residence times of these pigments are unlike those of β-carotene or other common carotenoids. Transfer tissues of Rhizophora may have functions not found in other plants, such as salt exclusion and facilitating viviparous germination, but the ultrastuctural correlates of these functions remain uncertain.     

Some aspects of organization and histochemistry of the embryo sac ofScilla sibirica sato

Summary The present investigation deals with some of the organizational and histochemical aspects of the embryo sac ofScilla sibirica. Both the synergids and egg cell are invested by PAS-positive complete walls. The filiform apparatus comprises an elaborate system of fibrillar projections, showing extensive ramifications. The micropylar region of the embryo sac wall from where the filiform apparatus originates is composed of three distinct layers. On a histochemical basis it may be surmised that, unlike the egg cell, the synergids are metabolically very active. Two kinds of wall ingrowths (i) massive and highly branched very much akin to the filiform apparatus, and (ii) small tuberculate wall projections, are unique to the antipodal cells of S.sibirica. Small tuberculate projections have also been observed along the wall of the central cell adjacent to the nutrient-rich nucellar cells. The antipodals and the central cell show the presence of starch grains and abundant total proteins. All the cell types in the embryo sac ofS. sibirica are structurally so organized as to meet the requirements of its nutrition during pre- and postfertilization development. The presence of abundant PAS-positive granular substance in the cells of nucellar epidermis probably establishes a gradient which assists in the pollen tube growth.     

Cytochemical localization of adenosine triphosphatase in the phloem of Pisum sativum and its relation to the function of transfer cells

The cytochemical localization of ATPase in differentiating and mature phloem cells of Pisum sativum L. has been studied using a lead precipitation technique. Phloem transfer cells at early stages of differentiation exhibit strong enzyme activity in the endoplasmic reticulum (ER) and some reaction product is deposited on the vacuolar and plasma membranes. As the phloem transfer cells mature and develop their characteristic wall structures, strong enzyme activity can be observed in association with the plasma membranes and nuclear envelopes. Mature phloem transfer cells with elaborate cell-wall ingrowths show ATPase activity evenly distributed on plasma-membrane surfaces. Differentiating sieve elements show little or no enzyme activity. When sieve elements are fully mature they have reaction product in the parietal and stacked cisternae of the ER. There is no ATPase activity associated with P-protein at any stage of sieve-element differentiation or with the sieve-element plasma membranes. It is suggested that the intensive ATPase activity on the plasma membranes of the transfer cells is evidence for a transport system involved in the active movement of photosynthetic products through these cells.Key to labeling in the figures ER endoplasmic reticulum - P parenchyma cell - PP P-protein - SE sieve element - SPP sieve-plate pore - TC transfer cell     

Transfer Cells in Suspensur and Endosperm during Early Embryogeny of Vigna sinensis

During early embryogeny, structural differentiation of the suspensor and endosperm can be observed with the formation of cells with wall ingrowths. In the early proembryo stage, wall ingrowths are seen only on the boundary walls of the embryo sac around the proembryo and at the chalazal end. Later, ingrowths appear in the outer walls of the basal suspensor cells and some wall ingrowths also begin to develop in the outer walls of cellular endospermic cells adjacent to the nucellar cap and the inner integumentary tissues. The suspensor appears to remain active throughout the differentiation stages. Two regions can be clearly distinguished in the suspensor: a basal region and a neck region. Wall ingrowths appear to form only in the cells of the basal region. During the development of the cellular endospermic sheath, its cell number and size both increase slightly. Later, these cells rapidly become separated from each other. Those endospermic cells that abut directly onto the integumentary tissues also develop wall ingrowths. In the region of the fluid endosperm, wall ingrowths are especially abundant in the boundary walls on the ventral side of the embryo sac. The possible pathway of nutrient flow to the developing embryo is discussed.