Unusual transfer cells in the epithelium of the nectaries ofAsclepias curassavica L.

Summary The secretory cells of the nectaries ofAsclepias curassavica form a glandular epithelium in the inner parts of the stigmatic chambers. They resemble transfer cells in having many infoldings of the plasmalemma. The wall protuberances, however, are poorly developed and often lacking. The plasmalemma is highly convoluted and forms, in places, external compound membranes where the extracytoplasmic space is collapsed completely. Active glands contain dilated cisternae of the ER and large vesicles which are mainly associated with the cis face of the dictyosomes. In addition, small vesicles are observed in high number. It is discussed whether the secretion is granulocrine or eccrine and whether the enlargement of the plasmalemma is the cause or the consequence of the high secretory activity. After the secretory phase the outer peripheral part of the cytoplasm disintegrates. The remaining part of the protoplast is covered by a new plasmalemma.     

On the fine structure of the liquid producing floral gland of the orchid, Coryanthes speciosa

The flowers of the "bucket–orchid", Coryanthes speciosa , have two finger–like glands on each side of the column. They secrete large amounts of an aqueous fluid which drips into a bucket–like part of the labellum, the epichile. The fluid contains low amounts of sugars (glucose, fructose, saccharose, mannose), of ions, of a polysaccharide mucilage and unknown substances which provide odour and taste. The fluid seems to be discharged from the epithelial cells of the gland. They contain many dictyosomes, a well developed ER, occurring mainly as smooth, tubular interconnected elements, and coated pits at the plasmalemma as well as coated vesicles at the cell periphery and around the dictyosomes. Especially in young glands, the coated pits are frequently associated with lumps of osmiophilic material at the outer surface of the plasmalemma which are. however, observed also independent of coaled pits. The cuticle consists of an outer, homogeneous layer and an irregular, inner one. The latter is interspersed with a network of fibrils which merge into a mucilage that fills a voluminous subcuticular space in active plants. It is assumed that water secretion is the consequence of mucilage discharge and that the cuticle functions as a filter. The ER seems to supply the dictyosomes with membrane material. It is possible that the coated pits recycle membranes; an exocytotic function, however, cannot be excluded.     

Fine structure of the wet,detached cell stigma of the orchid Dendrobium speciosum Sm.

Summary The stigmatic surface of the orchid Dendrobium speciosum is a cup containing detached cells suspended in a mainly carbohydrate mucilage. The fine structure of the detached cells and their organelles is indicative of secretory cells. The cells contain numerous mitochondria with well-developed cristae, dictyosomes containing extensive cisternae, an extensive network of rough and smooth endoplasmic reticulum and free polysomes throughout. There are many amyloplasts in the vicinity of the nucleus. Vesicles are seen arising from the dictyosomes and endoplasmic reticulum. The plasmalemma is undulating, and vesicles can be seen in its vicinity, giving the typical appearance of a granulocrine secretory system. Cetylpyridinium chloride (CPC) fixation to immobilise acidic carbohydrates detected a highly electron-opaque layer surrounding each cell and globules dispersed through the cell wall. The walls of the detached cells show irregular surface projections which are the remains of pitfields. Biochemical analysis showed that carbohydrates and arabinogalactan proteins are major components of the mucilage.     

Developmental and comparative ultrastructure of glandular hairs in the two Urticaceae. I. Urtica dioica

Secretion produced by glandular hairs is deposited mainly in the periplasmic space of the head cells. It stains intensely for both proteins and polysaccharides. The ultrastructure of meristematic, differentiating, mature and senescent head cells as well as the stalk and basal cells has been described in comparison to that in other cell types of the leaf. The specific features of the head cells are the proliferation of the granular endoplasmic reticulum as well as the multiplication of the dictyosomes and mitochondria during transition to the secretion stage. However, the frequency of dictyosomes varies among secreting hairs. The ER produces neither secretory nor transition vesicles and does not anastomose with the plasmalemma. In the absence of transition vesicles, the transport of secretory proteins and enzymes of polysaccharide synthesis from the ER to dictyosomes apparently includes the cytosolic step. Dictyosomes, though not appearing hypersecretory, produce two types of smooth secretory vesicles generated by the trans Golgi reticulum. The vectorial transfer of prosecretion and membranes across the dictyosome stack proceeds via the transport (shuttle) vesicles. It is, therefore, concluded that exocytosis of smooth secretory Golgi vesicles is the sole mechanism of release of both proteins and polysaccharides. Coated vesicles occasionally seen near the plasmalemma are likely to be involved in the endocytotic membrane retrieval. The secretion product disappears during senescence of the hairs and the secretory cells undergo vacuolation by means of local autophagy.     

Die Morphologie der Schleimsekretion im Fruchtknoten vonAptenia cordifolia

Zusammenfassung Der Fruchtknoten vonAptenia cordifolia enthÄlt wÄhrend der Samenentwicklung einen proteinreichen Polysaccharidschleim. Verschieden alte schleimproduzierende Placentarpapillen werden einer elektronenmikroskopischen Analyse unterzogen. Kurz vor dem Einsetzen der Schleimproduktion ist das rauhe ER noch spÄrlich entwickelt. Der Golgi-Apparat ist unauffÄllig und wenig aktiv. Zu Beginn der Schleimbildung sind als hauptsÄchliche Strukturkomponenten hypersekretorische Dictyosomen und ER-umschlossene Vakuolen (storage vesicles) zu beobachten. Es wird angenommen, da\ diese Komplexe aus rauhem ER und vermutlich mitèinander verschmolzenen Golgi-Vesikeln die charakteristischen Synthese-Einheiten für den Polysaccharid-Protein-Schleim darstellen, da sie nachweislich neben Polysacchariden auch Proteine enthalten. Membranfusionen zwischen Vesikeln und dem Plasmalemma deuten auf Exocytose-Prozesse unter Beteiligung des Golgi-Apparates hin. Daneben wird eine holocrine Ausscheidung des in den storage vesicles zunÄchst gespeicherten Polysaccharid-Protein-Schleimes bei Degeneration des Protoplasten vermutet.

---

Morphology of slime secretion in the seed vessels ofAptenia cordifolia

Summary During seed development the gynaeceum ofAptenia cordifolia produces a mucilage rich in carbohydrates and protein. The mucilage-producing placentary papillae are analyzed in different developmental stages by electron microscopy. Just before mucilage production is started, the rough ER occurs but sparsely. At that time the dictyosomes are inconspicuous and of low activity. When mucilage production commences, one can observe hypersecretory dictyosomes and ER-ensheathed vacuoles (storage vesicles) as the main structural components. It is suggested that the complexes of rough ER and probably fused Golgi vesicles are the synthetizing units of the carbohydrate protein mucilage, since in these complexes both components can be identified cytochemically. Fusion sites of plasmalemma and vesicles indicate processes of exocytosis-probably involving the Golgi apparatus. In addition, a holocrine excretion of the mucilage initially enclosed in the storage vesicles via degeneration of the protoplast is assumed.

     

DEVELOPMENT,STRUCTURE AND FUNCTION OF SECRETORY TRICHOMES IN PSYCHOTRIA BACTERIOPHILA (RUBIACEAE)

Mucilage-secreting dendroid trichomes develop from the adaxial epidermis of young stipules surrounding the shoot apex. Each trichome consists of a multicellular stalk from which radiate many branch cells. The trichome has no cuticle and the branch cell walls distally are loose cellulosic frameworks. Dictyosomes produce vesicles whose products are secreted through the plasma-lemma and cell wall. Enlarged portions of the ER are frequently associated with dictyosomes and may be part of the system for synthesis and transport of secretion products. Bacteria, which later occur in leaf nodules, are present in the mucilage surrounding trichomes and young leaves. The latter develop stomata through which the bacteria enter. As stipules and leaves grow out of the apical region, the secretory trichomes degenerate and are replaced by non-secretory ones.     

Defective Secretion of Mucilage is the Cellular Basis for Agravitropism in Primary Roots of Zea mays cv. Ageotropic

Root caps of primary, secondary, and seminal roots of Z. mayscv. Kys secrete large amounts of mucilage and are in close contactwith the root all along the root apex. These roots are stronglygraviresponsive. Secondary and seminal roots of Z. mays cv.Ageotropic are also strongly graviresponsive. Similarly, theircaps secrete mucilage and closely appress the root all alongthe root apex. However, primary roots of Z. mays cv. Ageotropicare non-responsive to gravity. Their caps secrete negligibleamounts of mucilage and contact the root only at the extremeapex of the root along the calyptrogen. These roots become graviresponsivewhen their tips are coated with mucilage or mucilage-like materials.Peripheral cells of root caps of roots of Z. mays cv. Kys containmany dictyosomes associated with vesicles that migrate to andfuse with the plasmalemma. Root-cap cells of secondary and seminal(i.e. graviresponsive) roots of Z. mays cv. Ageotropic are similarto those of primary roots of Z. mays cv. Kys. However, root-capcells of primary (i.e. non-graviresponsive) roots of Z. mayscv. Ageotropic have distended dictyosomal cisternae filled withan electron-dense, granular material. Large vesicles full ofthis material populate the cells and apparently do not fusewith the plasmalemma. Taken together, these results suggestthat non-graviresponsiveness of primary roots of Z. mays cv.Ageotropic results from the lack of apoplastic continuity betweenthe root and the periphery of the root cap. This is a resultof negligible secretion of mucilage by cells along the edgeof the root cap which, in turn, appears to be due to the malfunctioningof dictyosomes in these cells. Corn, dictyosomes, mucilage, root gravitropism, Zea mays cv. Ageotropic, Zea mays cv. Kys     

Reversible inhibition of secretion in root cap cells of cress after treatment with cytochalasin B: Support for the membrane flow concept

After treatment of cress roots with cytochalasin B (cytB) (25 μg/ml. 5.2 × 10^?5 M) for 4 h, marked structural changes are observed in the peripheral secretory calyptra cells. Deposits of slime outside the plasma membrane are smaller than in cells of untreated roots, whereas secretory vesicles accumulate within the treated cells. Dictyosomes are no longer present and the number of cisternae of rough endoplasmic reticulum surrounding the nucleus is increased at least three-fold. After an 8 h leaching of the drug, the structure of the secretory cells changes again. Accumulation of secretory vesicles no longer takes place, slime is deposited outside the plasma membrane and the number of ER cisternae surrounding the nucleus decreases. On the other hand, dictyosomes are now present. However, they are different from those in the hypertrophied stage of cells exhibiting high secretory activity, but are similar to those of an early developmental stage found at the beginning of the secretion process. This indicates that the dictyosomes are rebuilt during the leaching procedure. The results show that ER membranes accumulate near the nuclear envelope. They also indicate that bulk membrane material is transferred from the RER to the plasma membrane via dictyosome membranes and secretory vesicles, i.e. that membrane flow occurs in secretory cells of higher plants.     

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.     

Cytochalasin B,but not colchicine,inhibits migration of secretory vesicles in root tips of maize

Summary The effects of colchicine and cytochalasin B on the structure of dictyosomes of maize root tips were studied. Colchicine did not significantly affect dictyosome structure or change the distribution of dictyosome-derived secretory vesicles. Cytochalasin B did not significantly change dictyosome structure or intercisternal fibers, but did alter markedly the distribution of the secretory vesicles in both the epidermal and outer cap cells. With cytochalasin B, the vesicles accumulated in a region close to their site of formation and did not migrate to the cell surface. The results show that a cytochalasin B-sensitive subcellular component is involved in the vectorial movement of secretory vesicles from sites of formation at dictyosomes to sites of fusion at the cell surface.     

Ultrastructural observations of maize root tips following exposure to monensin

Summary Epidermal and outer rootcap cells of maize root tips were treated with the sodium selective ionophore, monensin, and the ultrastructural changes were studied. In the presence of 10^–5 to 10^–3 M monensin, dictyosomes became distorted, cisternae separated from the stack, and secretory vesicles were released. Released secretory vesicles disappeard from the cytoplasm suggesting that their transport to, and fusion with, the plasma membrane was unaffected. Monensin did not inhibit cytoplasmic streaming of the outer rootcap cells. No new secretory vesicles were formed on the remaining dictyosomes or dictyosome fragments. In contrast to results with animal cells, swelling of plant dictyosome cisternae was observed only after fixation in glutaraldehyde-osmium tetroxide and not after fixation in potassium permanganate. Other cell components were not altered structurally by monensin. The effects of monensin on the Golgi apparatus were reversible, and dictyosomes were either repaired or new dictyosomes were formed after the root tips were removed from the monensin.Dictyosomes in epidermal cells reacted in the same manner as those in the rootcap except that numerous secretory vesicles remained in the cytoplasm, mostly in association with dictyosome fragments. Some secretory vesicles increased in size but no evidence of vesicle-vesicle fusion was noted. Cell plate formation was partially inhibited or blocked by monensin.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of this product by the USDA.     

Post Golgi apparatus structures and membrane removal in plants

Summary In nongrowing secretory cells of plants, large quantities of membrane are transferred from the Golgi apparatus to the plasma membrane without a corresponding increase in cell surface area or accumulation of internal membranes. Movement and/or redistribution of membrane occurs also in trans Golgi apparatus cisternae which disappear after being sloughed from the dictyosome, and in secretory vesicles which lose much of their membrane in transit to the cell surface. These processes have been visualized in freeze-substituted corn rootcap cells and a structural basis for membrane loss during trafficking is seen. It involves three forms of coated membranes associated with the trans parts of the Golgi apparatus, with cisternae and secretory vesicles, and with plasma membranes. The coated regions of the plasma membrane were predominantly located at sites of recent fusion of secretory vesicles suggesting a vesicular mechanism of membrane removal. The two other forms of coated vesicles were associated with the trans cisternae, with secretory vesicles, and with a post Golgi apparatus tubular/vesicular network not unlike the TGN of animal cells. However, the trans Golgi network in plants, unlike that in animals, appears to derive directly from the trans cisternae and then vesiculate. The magnitude of the coated membrane-mediated contribution of the endocytic pathway to the formation of the TGN in rootcap cells is unknown. Continued formation of new Golgi apparatus cisternae would be required to maintain the relatively constant form of the Golgi apparatus and TGN, as is observed during periods of active secretion.     

An ultrastructural study of abscission zone cells with special reference to the mechanism of enzyme secretion

Summary The ultrastructural changes which occur during the foliar abscission ofImpatiens sultani Hook. andColeus blumei Benth. have been described. In both cases fracture of the separation zone results from a modification of the wall and cleavage along the line of the middle lamella. This process starts at the corners of the cells and in regions rich in plasmodesmata.During the period of wall breakdown, cellular integrity is maintained and the membrane degradation described by others was not observed. Plasmolysis studies confirmed that the separation zone cells retained their selective permeability characteristics until well after wall fracture. Quantitative data are presented to show that there is an increase in the frequency of rough endoplasmic reticulum, dictyosomes and dictyosome vesicles during the period when wall-hydrolyzing enzyme secretion is occurring. These changes are interpreted as reflecting an increase in demand for the secretory machinery of the endomembrane system. The possible involvement of plasmodesmata in this process is also discussed.     

Morphology and function of the Golgi apparatus

The polymorphism of the dictyosomes in the root meristeme ofFagopyrum is connected with their various functions in secretory processes and cell differentiation. The dictyosomes containing vesicular dilatations of the cisternae, which in this object occur more frequently than in others, probably participate in a similar way as the Golgi apparatus of the animal cell in the formation of lysozomes, in the formation of elements belonging to the group of dense bodies analogical lysozomes. These bodies are present in large numbers in the cytoplasm of cells, containing dictyosomes with vesicular dilatations. The other forms of the dictyosomes reveal indications of their participation in the production of the carbohydrate material of the cell walls, like most dictyosomes of other plant objects. However, no fusion of the Golgi vesicles with the plasmalemma was observed. According to their morphological appearance the typical forms of dictyosomes were classified on the basis of their relationship to secretory processes. Simultaneously the morphology and function of the Golgi apparatus was compared in the animal and plant cell. Several morphological varieties of the dictyosomes of plant cells, observed after the action of pathogenic factors and the effect of the fixation procedures, were also noticed in small quantities in the cells of the investigated objects.     

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     

Structural differentiation of membranes involved in the secretion of polysaccharide slime by root cap cells of cress (Lepidium sativum L.)

The peripheral secretion tissue of the root cap of Lepidium sativum L. was investigated by electronmicroscopy and freeze-fracturing in order to study structural changes of membranes involved in the secretion process of polysaccharide slime. Exocytosis of slime-transporting vesicles occurs chiefly in the distal region of the anticlinal cell walls. The protoplasmic fracture face (PF) of the plasmalemma of this region is characterized by a high number of homogenously distributed intramembranous particles (IMPs) interrupted by areas nearly free of IMPs. Near such areas slime-transporting vesicles are found to be underlying the plasma membrane. It can be concluded that areas poor in particles are prospective sites for membrane fusion. During the formation of slime-transporting vesicles, the number of IMPs undergoes a striking change in the PF of dictyosome membranes and their derivatives. It is high in dictyosome cisternae and remarkably lower in the budding region at the periphery of the cisternae. Slime-transporting vesicles are as poor in IMPs as the areas of the plasmalemma. Microvesicles rich in IMPs are observed in the surroundings of dictyosomes. The results indicate that in the plasmalemma and in membranes of the Golgi apparatus special classes of proteins — recognizable as IMPs — are displaced laterally into adjacent membrane regions. Since the exoplasmic fracture face (EF) of these membranes is principally poor in particles, it can be concluded that membrane fusion occurs in areas characterized by a high quantity of lipid molecules. It is obvious that the Golgi apparatus regulates the molecular composition of the plasma membrane by selection of specific membrane components. The drastic membrane transformation during the formation of slime-transporting vesicles in the Golgi apparatus causes the enrichment of dictyosome membranes by IMPs, whereas the plasma membrane probably is enriched by lipids. The structural differentiations in both the plasma membrane and in Golgi membranes are discussed in relation to membrane transformation, membrane flow, membrane fusion, and recycling of membrane constituents.Abbreviations PF protoplasmic fracture face - EF exoplasmic fracture face - IMP intramembranous particle     

Structure,differentiation, and multiplication of Golgi apparatus in fungal hyphae

Summary Golgi apparatus in subapical regions of hyphae consist of paranuclear dictyosomes with 4–5 cisternae each. Transverse and tangential sections provide ultrastructural evidence for a three-dimensional architectural model of the Golgi apparatus and a stepwise mechanism for dictyosome multiplication. The dictyosomes are polarized, with progressive morphological and developmental differentiation of cisternae from the cis to the trans pole. Small membrane blebs and transition vesicles provide developmental continuity between the nuclear envelope and the adjacent dictyosome cisterna at the cis face. Cisternae are formed as fenestrated plates with extended tubular peripheries. The morphology of each cisterna depends on its position in the stack, consistent with a developmental gradient of progressive maturation and turnover of cisternae. Mature cisternae at the trans face are dissociated to produce spheroid and tubular vesicles. Evidence in support of a schematic sequence for increasing the numbers of dictyosomes comes from images of distinctive and unusual forms of Golgi apparatus in hyphal regions where nuclei and dictyosomes multiply, as follows: (a) The area of the nuclear envelope exhibiting forming-face activity next to a dictyosome expands, which in turn increases the size of cisternae subsequently assembled at the cis face of the dictyosome. (b) As subsequent large cisternae are formed and mature as they pass through the dictyosome, an entire dictyosome about twice normal size is built up. The number of cisternae per stack remains the same because of continuing turnover and loss of cisternae at the trans face, (c) This enlarged dictyosome becomes separated into two by a small region of the nuclear envelope next to the cis face that acquires polyribosomes and no longer generates transition vesicles, (d) As a consequence, assembly of new dictyosomes is physically separated into two adjacent regions, (e) As.the enlarged cisternae are lost to vesiculation at the trans pole, they are replaced by two separate stacks of cisternae with typical normal diameters, (f) The net result is two adjacent dictyosomes where one existed previously. Dictyosome multiplication is thus accomplished as part of the normal developmental turnover of cisternae, without interrupting the functioning of the Golgi apparatus as it continues to produce new secretory vesicles from mature cisternae at the trans face. Coordination of Golgi apparatus multiplication with nuclear division ensures that each daughter nucleus receives a complement of paranuclear dictyosomes.     

高压冷冻及低温替代技术制备的拟南芥花蜜腺超微结构的研究

采用高压冷冻和低温替代技术对不同时期泌蜜前、泌蜜早期和泌蜜晚期的拟南齐(Arabidopsisthaliana L.)成熟花蜜腺的超微结构进行了研究。着重对小泡运输过程中是否与细胞质膜发生融合以及蜜腺组织中深色细胞与伴胞的区别等问题进行了讨论。拟南芥花中有一对较大的侧蜜腺以及2～4枚中蜜腺。中蜜腺位于2枚长雄蕊基部或它们之间,而侧蜜腺则位于两花瓣之间的短雄蕊附近。泌蜜前和泌蜜期,液泡的大小、高尔基体及内质网的数量、线粒体的分布以及质体内淀粉粒的大小都会发生一定的变化。当高尔基小泡从细胞内运输至细胞外时,并没有发生与细胞质膜融合的过程,与经典的“胞吐”假说不同。深色细胞在泌蜜期大量出现与筛分子旁的伴胞明显不同,前者与蜜腺顶端的气孔器相连,形成“通道”从而使蜜汁从蜜腺排出。     

Dictyosome polarity and membrane differentiation in outer cap cells of the maize root tip

Outer rootcap cells of maize produce large numbers of secretory vesicles that ultimately fuse with the plasma membrane to discharge their product from the cell. As a result of the fusion, these vesicles contribute large quantities of membrane to the cell surface. In the present study, this phenomenon has been investigated using sections stained with phosphotungstic acid at low pH (PACP), a procedure in plant cells that specifically stains the plasma membrane. In the maize root tip, the PACP also stains the membranes of the secretory vesicles derived from Golgi apparatus to about the same density that it stains the plasma membrane. Additionally, the membranes of the secretory vesicles acquire the staining characteristic while still attached to the Golgi apparatus. The staining progresses across the dictyosome from the forming to the maturing pole, thus confirming the marked polarity of these dictyosomes. Interestingly, the PACP staining of Golgi apparatus is confined to the membranes of the secretory vesicles. It is largely absent from the central plates or peripheral tubules and provides an unambiguous example of lateral differentiation of membranes orthogonal to the major polarity axis. In the cytoplasm we could find no vesicles other than secretory vesicles bearing polysaccharide that were PACP positive. Even the occasional coated vesicle seen in the vicinity of the Golgi apparatus did not stain. Thus, if exocytotic vesicles are present in the maize root cap cell, they are formed in a manner where the PACP-staining constituent is not retained by the internalized membrane. The findings confirm dictyosome polarity in the maize root cap, provide evidence for membrane differentiation both across and at right angles to the major polarity axis, and suggest that endocytotic vesicles, if present, exclude the PACP-staining component.     

Development of mucilage cells of Araucaria angustifolia (Araucariaceae)

The roles of mucilage cells were investigated through morphological and cytological analysis during leaf development in young Araucaria angustifolia plants. Differentiation began in leaf primordia in the shoot apex, when the young cells underwent a greater increase in volume in comparison with other mesophyll cells. The mucilage polysaccharides were synthesized by dictyosomes, from where they were taken by large vesicles and released into a cavity formed by detachment of the tonoplast, which was separated from the cytoplasm. At the end of differentiation, the cell was completely filled with mucilage, a gel consisting of a denser reticular structure surrounding less dense regions. The nucleus and cytoplasm were degenerated in mature cells. The A. angustifolia mucilage cells presented some cytological resemblances to the mucilage cells of members of some dicotyledonous families; however, differences in the dictyosomes and the secretion route were observed. Translocation and water storage of solutes was suggested by the use of the hydroxy pyrenetrisulfonic acid tri-sodium salt apoplastic tracer. The tonoplast detachment, dechromatinization, nuclear condensation, and general degeneration of the membrane systems observed during maturity indicated a programmed cell death process, one not yet described for angiosperm mucilage cells.