LEAF HISTOGENESIS IN LACTUCA SATIVA WITH EMPHASIS UPON LATICIFER ONTOGENY

The leaf primordia of Lactuca sativa ‘Meikoningen’ develop from a subapical initial in the second layer of the tunica on the side of a fiat shoot apex. Subsequent growth of the subsurface lamina is initiated by submarginal initials which divide anticlinally to produce an adaxial layer and ***a biseriate abaxiallayer, and periclinally to produce a middle layer from which procambium differentiates. The protoderm is derived from the first tunica layer by continuous anticlinal divisions. The activity of the subapical and submarginal initials is completed when the leaf is 0.3 mm in length and 4.0 mm in width, respectively. Continued growth of the leaf to 130-150 mm results from intercalary cell division and enlargement. The mature venation is visibly delineated when the leaf is 25-30 mm in length. Laticifer and phloem cells are initiated by the same mother cells in the ***procambium. The former become non-septate laticifers by resorption of cross walls. They mature concurrently with the phloem and before the xylem.     

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.     

Development of laticifer cells in callus cultures of Calotropis procera (Ait.) R. Br.

Tissue cultures were established from stem explants of Calotropis procera, a hydrocarbon yielding desert shrub on Murashige and Skoog's medium supplemented with 1.5 mg. 1^–01 2,4-D + 0.5 mg.1^–1 kinetin and polyvinylpyrrolidone. Laticifer cells were not present in young callus but were observed after 4 weeks of callus growth when examined histochemically. These young laticifers were detected in the 5th week of culture and were distinguished from surrounding cells by the presence of characteristic cytoplasm and thin walls. A group of cells with extensive branching was developed after 8 weeks of growth of the callus cultures. These cells were thick walled and contained latex particles in coagulated masses. Positive Liebermann-Burchard test proved the presence of terpenoids in these laticifers.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - KIN Kinetin - PVP Polyvinylpyrrolidone - HHS Heidenhain's Haematoxylin and safranin     

LATICIFER ULTRASTRUCTURE AND DIFFERENTIATION IN SEEDLINGS OF PAPAVER BRACTEATUM LINDL., POPULATION ARYA II (PAPAVERACEAE)

Laticifers of Papaver bracteatum Lindl., population Arya II, seedlings were examined by electron microscopy. Laticifers were first differentiated in procambium of the radicle associated with phloem about 72 hr after seeds were sown. Proliferation of membrane-bound vesicles of apparent endoplasmic reticulum origin distinguished laticifers from adjacent cells. Vesicles developed electron-dense caps from the internal condensation of small particles. Laticifer initials possessed the usual complement of organelles that became obscured in mature cells by the large, closely packed vesicles. Plastids contained an electron-dense, membrane-bound inclusion, but never developed lamellae or starch grains. Articulation and anastomoses between laticifer elements resulted from gradual removal of wall materials by both cells on opposite sides of the common walls at a perforation site. Differentiation of the laticifer initials and the micromorphology of the protoplast of P. bracteatum is similar to that reported for P. somniferum.     

STRUCTURE AND ONTOGENY OF LATICIFERS IN CICHORIUM INTYBUS (COMPOSITAE)

The branched anastomosed laticifer system in the primary body of Cichorium intybus L. originates in embryos from files of laticiferous members at the boundary between phloic procambium and ground meristem. Upon seed germination, laticiferous members develop perforations in the end walls which become entirely resorbed. Perforations also develop in the longitudinal walls of contiguous laticiferous members and from lateral connections between developing laticifer branches. Additional laticiferous members originate as procambium differentiation proceeds, and their differentiation follows a continuous acropetal sequence in leaf primordia of the plumule. In roots, laticifers closely associated with sieve tubes in the secondary phloem originate from derivatives of fusiform initials in the vascular cambium. These laticifers develop wall perforations and in a mature condition resemble laticifers in the primary body. As the girth of the root increases, laticifers toward the periphery, unlike associated sieve tubes, resist crushing and obliteration. Laticifers vary in width from about 4 to 22 μm; the widest ones occur in involucral bracts and the narrowest ones in florets. There was no evidence that intrusive growth occurs during development of the laticifer system, although such growth may occur during development of occasional branches which extend through ground tissue independent of phloem and terminate in contact with the epidermis. Presence of amorphous callose deposits is related to aging of laticifers and mechanical injury.     

Die Milch macht's – auch bei Pflanzen. Milchröhren und Milchsaft

Laticifers and latex Many different plants have laticifers and produce latex. Latex flows out when the plant is injured and coagulates quickly thus protecting the wound. It is a mixture of vacuoles and cytoplasm and contains various secondary plant products, especially polyterpenes (usually in the form of latex particles) and often toxins. The diversity of the latex corresponds with the diversity of laticifers. Nonarticulated laticifers are long, single cells, articulated ones are derived from cell fusions. Both kinds of laticifers may be branched. Reputed/ill‐reputed is the latex of Papaver somniferum, the source of opium. Technically very important has become the rubber of Hevea brasiliensis, after vulcanization of polyterpenes had been invented.     

Characterization of Stelar Initiation in Shoot Apices of Ferns

Procambium is commonly recognized as a vascular meristem inshoot apices of vascular plants. Prestelar tissue comprisingprovascular tissue (PVT) and pith mother cells (PMCs) immediatelysubjacent to the single cell layer of promeristem has been consideredto represent the initial stage of stelar differentiation precedingprocambium and rib meristem in ferns. In addition to characterizationof PVT and PMCs on the basis of cell morphology, cytologicalfeatures and developmental continuity with procambium and ribmeristem, four lines of evidence from studies of shoot apicesof Matteuccia struthiopteris and Osmunda cinnamomea supportthis interpretation of initial differentiation. (1) Differentialstaining by safranin-fast green and crystal violet-erythrosinshows that PVT and PMCs differ in colour reactions from promeristemand resemble procambium and pith meristem, respectively. (2)Comparative ultrastructural study reveals qualitative differencesin the cell membrane system, nuclei, cytoplasm, vacuoles andplastids between promeristem and PVT but similarity of PVT toprocambium. (3) Large droplets of tannins occur in promeristembut not in PVT, PMCs and procambium. (4) Cytochemical studyof the shoot apex of Osmunda shows that carboxylesterase activityis strongly demonstrated in PVT and procambial cells but notin promeristem cells and PMCs. These observations further substantiatethe interpretation that PVT represents initial vascular differentiationand PMCs reflect a commitment to pith development.Copyright1995, 1999 Academic Press Initial vascular differentiation, provascular tissue, differential staining, ultrastructure, tannins, carboxylesterase, shoot apex, Matteuccia struthiopteris, Osmunda cinnamomea     

Differentiation of Non-articulated Laticifers in Poinsettia (Euphorbia pulcherrima Willd.)

Differentiation of non-articulated laticifers in poinsettia(Euphorbia pulcherrima Willd.) was studied ultra-structurally.Growing laticifers show: (1) a multinucleate apical region containingabundant ribosomes but few other differentiated organelles and(2) a sub-apical zone where the cytoplasm is dominated by vacuolesof diverse morphology with latex particles. These particlesappear first within narrow tubular vacuoles developed especiallyin the peripheral cytoplasm. During vacuolation of the laticifer,portions of cytoplasm, including some of the nuclei, becomeisolated by the enlarging and fusing vacuoles; eventually thesebecome lysed, except the latex particles which remain in thecentral vacuole. During differentiation of a laticifer branch,the cytoplasm contains the usual organelles, including a fewmicrobodies and coated vesicles. The plastids that lie withinthe peripheral cytoplasm differentiate into amyloplasts witha single elongated starch grain. Towards the end of differentiationthe cytoplasm becomes restricted to a thin parietal layer, withthe remaining organelles reduced or degenerate, surroundinga central vacuole filled with latex particles. Euphorbia pulcherrima Willd, poinsettia, ultrastructure, differentiation, laticifers     

The Latex of Hevea brasiliensis Contains High Levels of Both Chitinases and Chitinases/Lysozymes

The latex of the commercial rubber tree, Hevea brasiliensis, was fractionated by ultracentrifugation as described by G. F. J. Moir ([1959] Nature 184: 1626-1628) into a top layer of rubber particles, a cleared cytoplasm, and a pellet that contains primarily specialized vacuoles known as lutoids. The proteins in each fraction were resolved by two-dimensional gel electrophoresis. Both the pellet fraction and cleared cytoplasm contained large amounts of relatively few proteins, suggesting that laticifers serve a very specialized function in the plant. More than 75% of the total soluble protein in latex was found in the pellet fraction. Twenty-five percent of the protein in the pellet was identified as chitinases/lysozymes, which are capable of degrading the chitin component of fungal cell walls and the peptidoglycan component of bacterial cell walls. Both the chitinase and lysozyme activities were localized exclusively in the pellet or lutoid fraction. The chitinases/lysozymes were resolved into acidic and basic classes of proteins and further purified. An acidic protein (molecular mass 25.5 kD) represented 20% of the chitinase activity in latex; this protein lacked the low level of lysozyme activity that is associated with many plant chitinases. Six basic proteins, having both chitinase and lysozyme activities in various ratios and molecular mass of 27.5 or 26 kD, were resolved. Two of the basic proteins had very high lysozyme specific activities which were comparable to the specific activities reported for animal lysozymes. Like animal lysozymes, but unlike previously characterized plant chitinases/lysozymes, these basic chitinases/lysozymes were also capable of completely lysing or clearing suspensions of bacterial cell walls. These results suggest that laticifers may serve a defensive role in the plant.     

CHARACTERIZATION OF STARCH GRAINS IN THE NONARTICULATED LATICIFER OF EUPHORBIA PULCHERRIMA (POINSETTIA)

Starch grain morphology in laticifer amyloplasts of Euphorbia pulcherrima Willd. (poinsettia) was examined for evidence of starch metabolism in vegetative and flowering plants. Laticifer starch grains in vegetative plants were rod shaped with lengths ranging from 3 to 60 μm. Average grain size was significantly larger in stems than leaves, and in older than younger tissues. Starch grain length frequency was unimodal and approximated a normal probability distribution in stems, but was skewed positively toward smaller grains in leaves. Frequency distributions were shifted toward larger grains in older tissues. Under short-day photoperiod (flowering) conditions, round starch grains formed in latex of stems, and the average length of rod-shaped grains decreased in latex of stems and leaves. Round grains did not occur in laticifers of leaves or bracts. Round starch grains often occurred in aggregates of two or more subunits. Changes in size and shape of latex starch grains indicate that amyloplasts in fully differentiated laticifers metabolize starch. Identification of metabolically active amyloplasts in differentiated laticifers suggests that the function of these organelles may involve starch mobilization under certain physiological conditions.     

ONTOGENY AND CYTOCHEMISTRY OF ALKALOIDAL VESICLES IN LATICIFERS OF PAPAVER SOMNIFERUM L. (PAPAVERACEAE)

Development of alkaloidal vesicles in laticifers of opium poppy, Papaver somniferum L., was investigated at the ultrastructural level. Laticifer initials possessed abundant endoplasmic reticulum throughout their dense cytoplasm. During differentiation the endoplasmic reticulum organized into long, folded sheets that were parallel to the longitudinal walls along the periphery of the cell. Vesicles appeared to be derived from dilation of endoplasmic reticulum. This relationship was confirmed through cytochemical data obtained with zinc iodide-osmium tetroxide and osmium tetroxide impregnation. Alkaloidal vesicles had electron-dense regions or caps that occurred early in laticifer differentiation, but these caps became less conspicuous in mature cells. Caps appeared to be derived from small particles which condensed along the inner surface of the vesicle membrane and subsequently accumulated at one or two positions along the membrane of the vesicle.     

Cellulase in latex and its possible significance in cell differentiation

Summary Cellulase was found to be present in the latex of species with articulated laticifers but it could not be detected in the latex of species with nonarticulated laticifers. It is suggested that cellulase is involved in the removal of end walls during the differentiation of articulated laticifers.     

Ultrastructure and development of nonarticulated laticifers in seedlings ofEuphorbia maculata L.

The ultrastructure of nonarticulated laticifers in the seedlings ofEuphorbia maculata was studied at various developmental stages. The apical regions of the seedling laticifers growing intrusively contained large nuclei with mainly euchromatin and dense cytoplasm possessing various and many organelles such as rich ribosomes, several small vacuoles, giant mitochondria with dense matrices, rough endoplasmic reticulum, dictyosomes, and proplastids. This result suggested that the apical regions of laticifers were metabolically very active. Laticifers in seedlings at the first-leaf developmental stage did not contain latex particle. In seedlings at second-leaf growth stage, the laticifer cells contained numerous and elongated small vacuoles. These vacuoles appeared to arise by dilation of the endoplasmic reticulum and frequently possessed osmiophilic or electron-dense latex particles. The small vacuoles fused with the large vacuole occupying the central portion of the subapical region of laticifers, and then the latex particles were released into the large central vacuole. The latex particles varied in size and were lightly or darkly stained. Proplastids with a dense matrix and a few osmiophilic plastoglobuli were filled with an elongated starch grain and thus were transformed into amyloplasts. Latex particles were initially produced in the laticifers after seedlings had developed their second young leaves. In seedlings at forth-leaf stage, latex particles with an alveolated rim were found in the laticifers.     

Vascular Differentiation in the Shoot Apex of Matteuccia struthiopteris

Initial vascular differentiation is generally considered tooccur in procambium. In ferns, however, a provascular tissueimmediately subjacent to the promeristem has been suggestedas an initial stage within which the procambium is subsequentlyformed. In contrast to this interpretation, a zonation conceptapplied in ferns recognizes a promeristem consisting of severallayers of cells in which no differentiation takes place. Thisstudy demonstrates that the shoot apex of Matteuccia struthiopterishas one cell layer of promeristem. Immediately subjacent tothe promeristem is the provascular tissue surrounding a centralgroup of pith mother cells. The developmental continuity betweenthe provascular tissue and the mature vascular tissue, and betweenthe pith mother cells and the pith, through transitional stages,indicates that the initial differentiation of vascular tissueand pith takes place in this prestelar tissue. The continuityof vascular differentiation in the area confronting young leavesor incipient leaf positions is interrupted by the formationof leaf gap initials. Developing leaves thus begin to exertinfluence on the vascular system at the prestelar stage. Smallprotoxylem elements with helical cell wall thickening, and distinctiveprotophloem elements are present in the leaf traces, but endabruptly near the junction regions of leaf traces to the meristele.Copyright1994, 1999 Academic Press Initial vascular differentiation, provascular tissue, pith mother cells, shoot apex, Matteuccia struthiopteris     

EMBRYOGENY AND HISTOGENESIS IN NERIUM OLEANDER II. ORIGIN AND DEVELOPMENT OF THE NON-ARTICULATED LATICIFER

Mahlberg , P. G. (U. Pittsburgh, Pittsburgh, Pa.) Embryogeny and histogenesis in Nerium oleander. II. Origin and development of the non-articulated Iaticifer. Amer. Jour. Bot. 48(1): 90–99. Illus. 1961.—Laticifer initials, collectively considered as a laticifer system, are differentiated in the globular embryo from meristematic cells which occupy a position within the potential procambial tissue. A total of usually 28 initials, in Nerium oleander, arise as an irregular ring of cells directly below the embryonic shoot apex, during initiation of the cotyledonary primordia. No anastomoses occur between laticifer initials. During subsequent development of the embryo, the laticifer initials grow in a bi-directional manner and penetrate into the root, cotyledons and toward the shoot apex. Upon enlargement the initials bifurcate repeatedly, many branches penetrate into the cotyledons, others grow into the cortex of the hypocotyl or penetrate between cells of the procambium. Repeated nuclear divisions within each initial result in the formation of a multinucleated protoplast in this cell type. The tips of laticifers occupy intercellular spaces during their growth; they do not penetrate into or through adjacent cells. A plexus of laticifer branches is formed within the cotyledonary node of the mature embryo. No new initials are formed during subsequent growth of the plant, rather certain branches from the cotyledonary nodal plexus penetrate into the enlarging shoot system. The nature of their growth habit and branching suggests that the tips of laticifer initials exhibit an intrusive form of growth.     

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.     

Laticifers: An historical perspective

This review describes the development of the laticifer concept, with emphasis upon the nonarticulated type, from early observations of plant exudates and “juices” to the presentation of laticifers by Esau (1953). Classical writers and herbalists described practical applications of these substances. With the advent of the microscope early investigators believed that these substances occurred in structures present in most, if not all, plants and, wrongly, equated these structures to the circulatory system in animals. Introduction of the term, latex, into botany derived from its early use as a term for a blood component by physicians, and not for analogy to milk. However, the origin of the terms, laticifer and laticiferous, remains uncertain. Initial studies of laticifers were marked by the controversy of whether they represented intercellular spaces or elongated cells. Confirmation of their cellular character led to the designation of nonarticulated and articulated laticifers. Nonarticulated laticifers were shown to arise during early embryogeny in some plants. The ontogenetic origin of the articulated laticifer was unclear to early workers, but new laticifers were detected to be formed by cambium activity. Nonarticulated laticifers were described to develop by intrusive growth whereby tips of the cell penetrated between adjacent cells. The coenocytic condition of the nonarticulated laticifer resulted from nuclear divisions along the cell positioned in the growth region of the shoot and the subsequent distribution of the daughter nuclei along the length of the cell.     

白鲜根的发育解剖学研究

应用半薄切片、常规石蜡切片并结合离析法,对药用植物白鲜(Dictamnus dasycarpus Turcz.)根的发生发育过程进行了研究。结果表明:白鲜根的发生发育过程包括4个阶段,即原分生组织阶段、初生分生组织阶段、初生结构阶段以及次生结构阶段。原分生组织位于根冠内侧及初生分生组织之间,衍生细胞分化为初生分生组织。初生分生组织由原表皮、基本分生组织以及中柱原组成。原表皮分化为表皮,基本分生组织分化为皮层,中柱原分化为维管柱,共同组成根的初生结构;在初生结构中,部分表皮细胞外壁向外延伸形成根毛,皮层中分布有油细胞,内皮层有凯氏带,初生木质部为二原型或偶见三原型,外始式;根初生结构有髓或无。次生结构来源于原形成层起源的维管形成层的活动以及中柱鞘起源的木栓形成层的活动;白鲜次生韧皮部宽广,其中多年生根中可占根横切面积的85%,另外除基本组成分子外,还分布有油细胞;周皮发达,木栓层厚;初生皮层、次生木质部和次生韧皮部薄壁细胞中常充满丰富的淀粉粒。