Histochemical study of detailed laticifer structure and rubber biosynthesis-related protein localization in <Emphasis Type="Italic">Hevea brasiliensis</Emphasis> using spectral confocal laser scanning microscopy

In Hevea brasiliensis, laticifers produce and accumulate rubber particles. Despite observation using histochemical methods, development stage structure and structures with ceasing functions have rarely been described. Spectral confocal laser scanning microscopy with Nile red staining simplifies laticifer structure observation in tangential sections while enhancing the resolution. Laticifer and ray images were extracted from unmixed images and used to monitor changes during growth. A laticifer network structure developed from increased anastomoses between adjoining laticifers outside of the conducting phloem, but because of increased radial division and growth of rays, the network structure ruptured and disintegrated. We also investigated immunohistochemical localization of two rubber particle-associated proteins in the laticifers: small rubber particle protein (SRPP) and rubber elongation factor (REF). Mature bark test results show that SRPP is localized only in the laticifer layers in the conducting phloem; REF is localized in all laticifer layers. Because SRPP plays a positive role in rubber biosynthesis, results show that the rubber biosynthesis capability of laticifers is concentrated where rays and the sieve tube actively transport metabolites.     

Intra and Inter-Cellular Changes in Constitution during the Development of Laticiferous System in Garlic Scape

Systematic investigations, mainly based on electron microscopy, have been conducted on constitutional changes in the laticifer and its adjoining parenchyma during the development of laticiferous system in garlic scape. The laticiferous system of the scape consists of several layers of articulated unbranched latieifers. About half of them are situated 2–3 cell layers below the epidermis, and the rest scattered throughout the cortex (Fig. 23). Latieifer differentiation starts with a thinning out and vacuolation of the dense protoplasm in the latieifer initials (Fig.2), which is followed by gradual degeneration of nuclei, plastids, endoplasmic reticulum, and dictyosomes; and by a sharp diminution of free ribosomes (Figs.3, 4). Remanent and defective forms of some organelles can still be found in the laticifer at the later stage. In spite of these drawbacks, the differentiating laticifer appears to function actively. Its protoplasm is delimited by a distinct plasmalemma (Figs. 3, 4). Its wall is interspersed with pits inclose spacings, to which most plasmodesmata are confined (Figs. 8, 24). The cell interior is packed with vesicles and mitoehondria (Figs. 4, 11, 15). Structurally, the laticifer seems well adapted to material exchange with the adjoining parenchyma. During the sprouting stage of the scape, the laticifer initials enlarge itself or fuse with each other by lateral wall dissolution to extend the diameter; at the same time, the laticifer elongates at an increasingly rapid rate. As a final result, the laticifer can attain 30–50 times the length and 2–3 times. the diameter of the adjoining parenchyma. The electron-dense material which protrudes into the laticifer initial from the parenchyma may be of lysosomal nature and probably concerned with wall dissolution and intracellular lytic processes in latieifer formation (Figs. 5, 7, 10). An excised garlic scape is employed in the observation of mature laticifers, which is always full of sap and is quite turgid. Once the scape is cut open, sap exudes almost exclusively from the cut end of the laticifers at the periphery, which lasts only some seconds. However, if the scape is left aside for a few days, exudation will again take place at the fresh cut end. Unlike the milky juice of many latex plants, the sap exuded from the garlic scape is watery and slightly turbid. The organic solute content is mainly made up of simple sugar and amino acids. It also contains a small amount of proteins and even protoplasmic fragments. Besides, it is worthy to note that decrease in organic solutes in the exudation is closely connected with the degree of exhaustion of cell contents from the withering scape, which is, as has already been shownm the sole agent of supplying materials required for the formation of apical cloves. All the above facts seem to indicate that there exists a loading and unloading process in the latieifer. Our electron micrographs (Figs. 16, 22) give evidence that vesicular transport through plasmodesmata in the pit field is capable of performing such a process: from the parenchyma to the laticifer in loading and from the latter to the former in unloading. The possible role of the laticifers in garlie scape could be a temporary storage of cell contents released successively from the deteriorating parenchyma. The sap content in the laticifer is in full turgidity as a result of loading, and can be readily drawn by unloading if so required. Transcellular cytosis is a term tentatively given by us to designate intercellular transport of sap, solutes, and macromolecular particles in small vesicles, which are formed and packed in one celt, traverse through plasmodesmata and merge into the other; whereas endo and exoeytosis refer to vesicular transport in a single cell only and to its moving in and out of the cell primarily through the plasma membrane, which also takes active part in the formation and dissolution of the vesicle and in the enclosure and release of its content. Transcellular cytosis was first observed by us in the withering parenchyma of an excised garlic scape; and, in the present case, between the latieifer and parenehyma, both being active functionally. As compared with the early notion that intercellular material transport is primarily carried out by secretion and reabsorption of highly degraded products through plasmalemma, transcellular eytosis appears to be a far more efficient means of translocating prefabricated assortment and well packed cargo from one cell into the other.     

Cytochemical localization of pectinase activity in laticifers ofNerium oleander L.

Summary A method is described for the cytochemical localization of pectinase activity at the ultrastructural level. The procedure involves the use of Benedict's reagent to form an electron-dense copper precipitate when reacted with reducing sugars liberated from exogenously supplied pectin. Using this technique, pectinase activity was examined in the nonarticulated, branched laticifers ofNerium oleander. Electron opaque crystalline deposits indicating the presence of pectolytic enzymes were identified in laticifer central vacuoles. Smaller amounts of reaction product were distributed along the middle lamella between laticifers and adjacent cells. This report represents the first direct evidence for the involvement of pectinase in intrusive growth of nonarticulated laticifers.     

Accumulation of non-utilizable starch in laticifers of Euphorbia heterophylla and E. myrsinites

Starch biosynthesis and degradation was studied in seedlings and mature plants of Euphorbia heterophylla L. and E. myrsinites L. Mature embryos, which lack starch grains in the non-articulated laticifers, develop into seedlings that accumulate starch rapidly when grown either in the light or the dark. Starch accumulation in laticifers of dark-grown seedlings was ca. 47 and 43% of total starch in light-grown controls in E. heterophylla and E. myrsinites, respectively. In light-grown seedlings, starch was present in laticifers as well as parenchyma of stems and leaves, whereas in dark-grown seedlings starch synthesis was almost exclusively limited to laticifers. In 7-month-old plants placed into total darkness, the starch in chyma was depleted within 6 d, whereas starch in laticifers was not mobilized. The starch content of latex in plants during development of floral primordia, flowering, and subsequent fruit formation remained rather constant. The results indicate that laticifers in seedlings divert embryonal storage reserves to synthesize starch even under stress conditions (darkness) in contrast to other cells, and that starch accumulated in laticifers does not serve as a metabolic reserve. The laticifer in Euphorbia functions in the accumulation and storage of secondary metabolites yet retains the capacity to produce, but not utilize starch, a primary metabolite.     

Localization of cell wall polysaccharides in nonarticulated laticifers ofAsclepias speciosa Torr.

Summary Asclepias speciosa Torr, has latex-containing cells known as nonarticulated laticifers. In stem sections of this species, we have analyzed the cell walls of nonarticulated laticifers and surrounding cells with various stains, lectins, and monoclonal antibodies. These analyses revealed that laticifer walls are rich in (1→4) β-D-glucans and pectin polymers. Immunolocalization of pectic epitopes with the antihomogalacturonan antibodies JIM5 and JIM7 produced distinct labeling patterns. JIM7 labeled all cells including laticifers, while JIM5 only labeled mature epidermal cells and xylem elements. Two antibodies, LM5 and LM6, which recognize rhamnogalacturonan I epitopes distinctly labeled laticifer walls. LM6, which binds to a (l→5) α-arabinan epitope, labeled laticifer walls more intensely than walls of other cells. LM5, which recognizes a (1→4) β-D-galac-tan epitope, did not label laticifer segments at the shoot apex but labeled more mature portions of laticifers. Also the LM5 antibody did not label cells at the shoot apical meristem, but as cells grew and matured the LM5 epitope was expressed in all cells. LM2, a monoclonal antibody that binds to β-D-glucuronic acid residues in arabinogalactan proteins, did not label laticifers but specifically labeled sieve tubes. Sieve tubes were also specifically labeled byRicinus communis agglutinin, a lectin that binds to terminal β-D-galactosyl residues. Taken together, the analyses conducted showed that laticifer walls have distinctive cytochemical properties and that these properties change along the length of laticifers. In addition, this study revealed differences in the expression of pectin and arabinogalactan protein epitopes during shoot development or among different cell types.     

Fine structure,distribution and frequency of plasmodesmata and pits in the cortex ofLaminaria hyperborea andL. saccharina

Prior to a long-distance transport of photoassimilate in the sieve elements ofLaminaria, a parenchyma transport across the cortex must occur. It is suggested that this transport is a symplastic one. The structural basis for this statement, continuous cytoplasmic interconnections of cells along the transport pathway, is demonstrated here forL. hyperborea andL. saccharina. The distribution, size, and frequency of pit fields in cell walls of all planes were determined. The data suggest that the conductivity for assimilate transport in the cortex is highest in the long axis of the thallus, not radially across the cortex. The fine structure, arrangement and number of plasmodesmata in pit fields were studied. The estimated flux rates and the anatomical findings clearly point to a symplastic parechyma transport of photoassimilate in the cortex ofLaminaria.     

Plasmodesmatal distribution and frequency in vascular bundles and contiguous tissues of the leaf ofThemeda triandra

Small and intermediate vascular bundles and contiguous tissues of the leaf blade ofThemeda triandra var.imberbis (Retz.) A. Camus were examined with transmission and scanning electron microscopes to determine the distribution and frequency of plasmodesmata between various cell types. Plasmodesmata are most abundant at the mesophyll/bundle-sheath cell and bundle-sheath/vascular parenchyma cell interfaces, and their numbers decrease with increasing proximity to both thick- and thin-walled sieve tubes. Among cells of the vascular bundles, the greatest frequency of plasmodesmata occurs between vascular parenchyma cells, followed by that of plasmodesmata between vascular parenchyma cells and companion cells, and then by the pore-plasmodesmata connections between companion cells and thin-walled sieve tubes (sieve tube-companion cell complexes). The sieve tube-companion cell complexes of theT. triandra leaf are not isolated symplastically from the rest of the leaf and, in this respect, differ from their counterparts in theZea mays leaf. However, the thick-walled sieve tubes, like their counterparts inZea mays, lack companion cells and are symplastically connected with vascular parenchyma cells that about the xylem.Abbreviations SEM scanning electron microscope - TEM transmission electron microscope     

Occurrence of plasmodesmata between differentiating vessels and other xylem cells inSorbus torminalis L. Crantz and their fate during xylem maturation

Summary The development of pit-pairs between differentiating xylem cells has been examined by transmission electron microscopy in young shoots ofSorbus torminalis. In some vessel-to-tracheid pits, as well as in previously studied intertracheid pits, a thickening of the pit membrane containing branched plasmodesmata was observed. A secondary wall-like cap was deposited over the thickening prior to cytoplasmic autolysis; some plasmodesmata, parallel to the plane of section, appeared to perforate the cap. At the end of the cell maturation stage, the central part of the primary wall thickening was hydrolysed, while the cap, including plasmodesmata remnants, appeared unaltered. In half-bordered pit-pairs between a parenchyma cell and a vessel or a tracheid, similar structures could be observed beside the conducting elements. When the vessel or tracheid matured, sealing of the pit membrane plasmodesmata resulted from the formation of a protective layer on the parenchyma-side rather than from the deposition of a cap on the conducting cell-side. These observations provide the first information on the presence of symplasmic connections in pits between differentiating vessels and neighbouring xylem cells. InS. torminalis, xylem differentiation is probably highly coordinated within a symplasmic domain; the persistence of such connections may account for the lack of specialization ofSorbus wood.     

Histochemical study of trans-polyisoprene accumulation by spectral confocal laser scanning microscopy and a specific dye showing fluorescence solvatochromism in the rubber-producing plant, Eucommia ulmoides Oliver

A microscopic technique combining spectral confocal laser scanning microscopy with a lipophilic fluorescent dye, Nile red, which can emit trans-polyisoprene specific fluorescence, was developed, and unmixed images of synthesized trans-polyisoprene in situ in Eucommia ulmoides were successfully obtained. The images showed that trans-polyisoprene was initially synthesized as granules in non-articulated laticifers that changed shape to fibers during laticifer maturation. Non-articulated laticifers are developed from single laticiferous cells, which are differentiated from surrounding parenchyma cells in the cambium. Therefore, these observations suggested that trans-polyisoprene biosynthesis first started in laticifer cells as granules and then the granules accumulated and fused in the inner space of the laticifers over time. Finally, laticifers were filled with the synthesized trans-polyisoprene, which formed a fibrous structure fitting the laticifers shape. Both trans- and cis-polyisoprene are among the most important polymers naturally produced by plants, and this microscopic technique combined with histological study should provide useful information in the fields of plant histology, bioindustry and phytochemistry.     

An impregnated suberized wall layer in laticifers of theConvolvulaceae,and its resemblance to that in walls of oil cells

Summary The cell wall in laticifers of theConvolvulaceae, Calystegia silvatica, C. soldanella, C. tuguriorum, Convolvulus cneorum, C. verecundus, C. sabaticus subsp.mauritanicus, andIpomoea indica, contains an impregnated layer that surrounds the cells. The impregnated layer lies inside the primary wall of the laticifer, separated from the protoplast by a third (tertiary) layer of variable thickness. Histochemical and cytochemical staining give a positive reaction for suberin. The layer is often differentiated into dark and translucent regions, the latter frequently being composed of lamellae. The ultrastructure of this layer and its position within the cell wall of the laticifer is comparable to the condition found in oil cells where the walls contain a suberized layer. A suberized layer within the wall is unique for a laticifer system.     

夹竹桃科2种引种植物分泌结构的解剖学研究

为了解夹竹桃科(Apocynaceae)植物乳汁管的发生发育,对爱之蔓(Ceropegia woodii)和百万心(Dischidia ruscifolia)营养器官中的分泌结构进行了显微观察。结果表明,爱之蔓和百万心营养器官中均有无节分枝乳汁管的分布,茎皮层中的乳汁管大部分具有明显的分枝,叶中乳汁管具明显分枝,分布与走向多与叶脉维管组织平行。另外,爱之蔓营养器官中的分泌结构除乳汁管外,还有分泌腔。这为夹竹桃科植物的系统分类研究提供了解剖学依据。     

LEAF OF SPINACIA OLERACEA (SPINACH): ULTRASTRUCTURE,AND PLASMODESMATAL DISTRIBUTION AND FREQUENCY,IN RELATION TO SIEVE-TUBE LOADING

Minor veins and contiguous tissues of the Spinacia oleracea leaf were analyzed by electron microscopy to determine the characteristics of the component cells and the structure, distribution, and frequency of plasmodesmata between the various cell types of the leaf. Mesophyll and bundle-sheath cells contain components typical of photosynthetic cells although the latter cell type contains smaller chloroplasts and fewer mitochondria and microbodies than the mesophyll cells. In addition, the mesophyll cells contain numerous invaginations of the plasmalemma bordering the chloroplasts and evaginations of the outer membrane of the opposing chloroplast envelope. In places, these membranes appear continuous with each other. The minor veins consist of tracheary elements, xylem parenchyma cells, sieve-tube members, companion and phloem parenchyma cells, and other cells simply designated vascular parenchyma cells. The companion and phloem parenchyma cells are typically larger than the sieve-tube members with the companion cells containing a much denser cytoplasm that the phloem parenchyma. Cytoplasmic connections occur along all possible routes from the mesophyll to the sieve-tube members and consist of either simple or branched plasmodesmata between parenchymatic elements or pore-plasmodesmata between the sieve-tube members and parenchyma cells. The highest frequency of plasmodesmata occurs between the sieve-tube members and companion cells, although the value is essentially the same as between the various parenchymatic elements of the phloem. Compared to several previously studied species, the frequency of plasmodesmata between cell types of the spinach leaf is low. These results are discussed in relation to apoplastic vs. symplastic solute transport and sieve-tube loading in this species.     

ORIGIN AND EARLY DEVELOPMENT OF NONARTICULATED LATICIFERS IN EMBRYOS OF EUPHORBIA MARGINATA

In E. marginata 12 nonarticulated laticifer initials arise in the cotyledonary node of the young embryo during the early heart stage. The initials arise progressively in the developing embryo, the first laticifers differentiating simultaneously with or shortly before the elements of the pro-cambium. The laticifers occupy a position lateral to the six procambial strands which are formed in the embryo. Upon subsequent growth each laticifer becomes vacuolated and nuclear division unaccompanied by cytokinesis results in the formation of a coenocytic protoplast. The enlarging laticifer produces several branches, one growing into the cotyledon, another growing down along the hypocotyl penetrating toward the root meristem, and one or several growing along intercellular spaces of adjacent cells. No fusion of these branches with one another or adjoining parenchyma cells was observed.     

Minor vein structure and sugar transport in Arabidopsis thaliana

Leaf and minor vein structure were studied in Arabidopsis thaliana (L.) Heynh. to gain insight into the mechanism(s) of phloem loading. Vein density (length of veins per unit leaf area) is extremely low. Almost all veins are intimately associated with the mesophyll and are probably involved in loading. In transverse sections of veins there are, on average, two companion cells for each sieve element. Phloem parenchyma cells appear to be specialized for delivery of photoassimilate from the bundle sheath to sieve element-companion cell complexes: they make numerous contacts with the bundle sheath and with companion cells and they have transfer cell wall ingrowths where they are in contact with sieve elements. Plasmodesmatal frequencies are high at interfaces involving phloem parenchyma cells. The plasmodesmata between phloem parenchyma cells and companion cells are structurally distinct in that there are several branches on the phloem parenchyma cell side of the wall and only one branch on the companion cell side. Most of the translocated sugar in A. thaliana is sucrose, but raffinose is also transported. Based on structural evidence, the most likely route of sucrose transport is from bundle sheath to phloem parenchyma cells through plasmodesmata, followed by efflux into the apoplasm across wall ingrowths and carrier-mediated uptake into the sieve element-companion cell complex. Received: 5 October 1999 / Accepted: 20 November 1999     

灵武长枣果实维管束韧皮部及周围细胞的超微结构特征

为了探讨灵武长枣果实光合同化物韧皮部卸载和运输的途径,该研究采用透射电镜技术,对不同发育时期灵武长枣果实维管束韧皮部及其周围薄壁细胞的超微结构特征进行了分析.结果表明:筛管/伴胞复合体及其周围韧皮薄壁细胞间在果实膨大前期富含胞间连丝,而韧皮薄壁细胞与周围库细胞以及相邻库细胞间几乎不存在胞间连丝,形成共质体隔离;筛管/伴...     

宁夏枸杞果实韧皮部及其周围细胞超微结构研究

应用透射电镜技术研究了宁夏枸杞果实韧皮部细胞的超微结构变化。结果表明:(1)随着枸杞果实的发育成熟,果实维管组织中的韧皮部筛分子筛域逐渐变宽,筛孔大而多,通过筛孔的物质运输十分活跃;筛分子和伴胞间有胞间连丝联系,伴胞属传递细胞类型,与其相邻韧皮薄壁细胞和果肉薄壁细胞连接处的细胞界面发生质膜内突,整个筛分子/伴胞复合体与韧皮薄壁细胞之间形成共质体隔离,韧皮部糖分的卸载方式主要以质外体途径进行。(2)韧皮薄壁细胞间的胞间连丝较多,而韧皮薄壁细胞与果肉薄壁细胞的胞间连丝相对较少,但果肉薄壁细胞间几乎无胞间连丝;果肉薄壁细胞之间胞间隙较大,细胞壁和质膜内突间形成较大的质外体空间,为质外体的糖分运输创造了条件。(3)筛管、伴胞、韧皮薄壁细胞和果肉薄壁细胞中丰富的囊泡以及活跃的囊泡运输现象,暗示囊泡也参与了果实糖分的运输过程。研究推测,枸杞果实韧皮部同化物的卸载方式以及卸载后的同化物运输主要以质外体途径为主。     

Fine structure and development of laticifers inGnetum gnemon L.

Summary Articulated laticifers are a regular component of stem cortex and pith ofGnetum gnemon L. Differentiation of laticifers starts very early and is completed within the very first centimeters adjacent to the apical meristem.Ultrastructurally, young laticifers ofGnetum can be distinguished from surrounding cells by the presence of characteristic cytoplasmic inclusions, called spherule complexes and composed of 40–70 nm light spherules and up to 0.5 by 1.0 m large particles. While there is no record on their first beginnings, a connection between rER and the large particles can be demonstrated during many steps of laticifer differentiation which includes an increase in spherule complex areas. On account of positive Sudan staining and responses to EM fixations and in comparison to other laticifers it is concluded that the spherule complexes are terpenoid-containing. A transition from spherules to larger particles (orvice versa) is discussed, but could not be documented.Relative to the formation of the spherule complexes the other changes during laticifer maturation are inferior. The vacuolar system, in close connection to an extensive ER system, does largely expand and finally takes over the almost entire cell lumina. Nuclei do persist for an extended period, even after breakdown of the end walls and during disorganization of the cytoplasm. Plastids in all stages of laticifer ontogeny are very rarely encountered.Supplemented part of an investigation presented in 1976 by S. H. to the Fakultät für Biologie der Universität Heidelberg in partial fulfilment of the requirements for the degree of a Diplom-Biologe.     

Immunolocalization of beta-D-glucans,pectins, and arabinogalactan-proteins during intrusive growth and elongation of nonarticulated laticifers in Asclepias speciosa Torr

Nonarticulated laticifers are latex-containing cells that elongate indefinitely and grow intrusively between the walls of meristematic cells. To identify biochemical mechanisms involved in the growth of nonarticulated laticifers, we have analyzed the distribution of various polysaccharides and proteoglycans in walls of meristematic cells in contact with laticifers, nonadjacent to laticifers, and in laticifer walls. In the shoot apex of Asclepias speciosa, the levels of callose and a (1-->4)-beta-galactan epitope are lower in meristematic walls in contact with laticifers than in nonadjacent walls. In contrast, we did not detect a decline in xyloglucan, homogalacturonan, and arabinogalactan-protein epitopes upon contact of meristematic cells with laticifers. Laticifer elongation is also associated with the development of a homogalacturonan-rich middle lamella between laticifers and their neighboring cells. Furthermore, laticifers lay down walls that differ from those of their surrounding cells. This is particularly evident for epitopes in rhamnogalacturonan I. A (1-->5)-alpha-arabinan epitope in this pectin is more abundant in laticifers than meristematic cells, while the opposite is observed for a (1-->4)-beta-galactan epitope. Also, different cell wall components exhibit distinct distribution patterns within laticifer walls. The (1-->5)-alpha-arabinan epitope is distributed throughout the laticifer walls while certain homogalacturonan and arabinogalactan-protein epitopes are preferentially located in particular regions of laticifer walls. Taken together, our results indicate that laticifer penetration causes changes in the walls of meristematic cells and that there are differences in wall composition within laticifer walls and between laticifers and their surrounding cells.     

文冠果果实韧皮部及其周围薄壁细胞的超微结构观察及功能分析

该研究应用透射电镜技术,对生长发育过程中的文冠果果实的韧皮部及其周围薄壁细胞的超微结构进行了观察,以探讨文冠果果实同化物韧皮部卸载的细胞学路径及其机理。结果显示:(1)文冠果果实发育过程中,筛分子细胞胞腔较空,几乎没有细胞器,但有类似于囊泡的丝状不定型物存在;伴胞胞质浓密且细胞器丰富,液泡化程度不一,大多数存在多个小液泡;薄壁细胞具有中央大液泡,发育中期富含线粒体、高尔基体、内质网等细胞器,并存在囊泡运输现象,发育后期细胞器发生降解,说明随着果实生长发育,果实内物质代谢和转运活跃程度逐渐下降。(2)果实发育过程中筛分子和伴胞之间始终有胞间连丝,薄壁细胞之间也一直存在大量的胞间连丝,而筛分子-伴胞复合体与薄壁细胞之间只有在果实发育前期和后期存在一定数量的胞间连丝,发育中期却几乎没有胞间连丝。研究结果表明,文冠果果实发育过程中同化物韧皮部卸载路径可能发生了共质体途径-质外体途径-共质体途径的转变。     

MITOSIS IN THE NON-ARTICULATED LATICIFER OF EUPHORBIA MARGINATA

The multinucleate condition in the non-articulated laticifers of embryos of Euphorbia marginata arises as a result of mitosis. Successive stages of mitosis in the nuclei of the laticifer appear in the form of a wave. No sequence of mitotic stages has been noticed in the neighboring longitudinal tiers of cells. This difference in the mitotic pattern in the laticifer and other parenchymatous cells of the embryo suggests that the synthesis of factor(s) responsible for triggering mitosis occurs within the laticifer and does not diffuse to the surrounding cells. The mitotic waves originate distally from the meristems, either in the cotyledonary or hypocotyl portion of the laticifer, and move uni- or bidirectionally along its longitudinal axis. The mitotic stimulus does not start simultaneously in all the laticifers. The variable velocity of the mitotic substance results in aphasic mitotic waves in laticifers of the same embryo. Mitotic aberrations have not been observed in the dividing nuclei of the laticifer. A chromosome estimation made from a polar view of metaphase does not suggest polyploidization in the observed laticifers.