External Periclinal Wall Research Articles

Microtubules and lithocyst morphogenesis in Pilea cadierei

Lithocysts in Pilea cadierei are initiated by differential divisions, the plane of which is predicted by typical preprophase microtubule bands. They soon become polarized and undergo a unique differentiation. The external periclinal wall thickens considerably in the absence of microtubules. In incipient lithocysts, a periclinal band of microtubules lines the external ends of the anticlinal walls. A distinct local thickening, possessing periclinal cellulose microfibrils, underlies the microtubule band. The cystolith stalk originates as a cylindrical wall ingrowth of a limited central region of the external periclinal wall. This grows inwards in the absence of microtubules in a preformed cytoplasmic diaphragm, approaching the internal periclinal wall. Stalk formation as well as the external periclinal wall thickening are not affected by colchicine and isopropyl n(3-chlorophenyl) carbamate. A cystolith body is formed within a cytoplasmic diaphragm in which most of the lithocyst organelles are located; this body is rich in cellulose microfibrils and is formed by the deposition of large amounts of wall material at the free end of the stalk, at right angles to its axis. This morphogenetic shift is preceded by the formation of a system of microtubules that converge in cortical sites close to the stalk. They proliferate and form an axial sheath around the cystolith body. The cellulose microfibrils are aligned in a parallel fashion with microtubules. Microtubule destruction by colchicine results in malformation of both the lithocyst and the cystolith body. Aberrant cystolith bodies are also formed in the presence of isopropyl n(3-chlorophenyl) carbamate, which seems to interfere with microtubule formation. These observations suggest that the lithocyst – cystolith body morphogenesis is controlled by microtubules.

Microtubule organization during development of stomatal complexes inLolium rigidum

Microtubule (MT) arrays in stomatal complexes ofLolium have been studied using cryosectioning and immunofluorescence microscopy. This in situ analysis reveals that the arrangement of MTs in pairs of guard cells (GCs) or subsidiary cells (SCs) within a complex is very similar, indicating that MT deployment is closely coordinated during development. In premitotic guard mother cells (GMCs), MTs of the transverse interphase MT band (IMB) are reorganized into a longitudinal array via a transitory array in which the MTs appear to radiate from the cell edges towards the centre of the walls. Following the longitudinal division of GMCs, cortical MTs are reinstated in the GCs at the edge of the periclinal and ventral walls. The MTs become organized into arrays which radiate across the periclinal walls, initially from along the length of the ventral wall and later only from the pore site. As the GCs elongate, the organization of MTs and the patterns of wall expansion differ on the internal and external periclinal walls. A final reorientation of MTs from transverse to longitudinal is associated with the elongation and constriction of GCs to produce mature complexes. During cytokinesis in the subsidiary mother cells (SMCs), MTs appear around the reforming nucleus in the daughter epidermal cells but appear in the cortex of the SC once division is complete. Our results are thus consistent with the idea that interphase MTs are nucleated in the cell cortex in all cells of the stomatal complex but not in adjacent epidermal cells.

Anatomia foliar de Eugenia sulcata Spring ex Mart. (Myrtaceae)

A lâmina foliar de Eugenia sulcata Spring ex Mart, é analisada, ressaltando-se aspectos de suas epidermes, à luz da microscopia óptica e da microscopia eletrônica de transmissão e de varredura. As paredes anticlinais destas células são sinuosas e as periclinais externas têm espessura não uniforme, em decorrência de projeções internas destas paredes. Ao microscópio eletrônico de transmissão tais paredes apresentam-se constituidas por 3 camadas distintas. O microscópio eletrônico de varredura mostra completa ausência de estriações na superfície externa da epiderme abaxial. Os estômatos são classificados como anomoestaurocíticos quanto ao numero e arranjo das células subsidiárias e considerados graminóides em função do espessamento desigual das células estomáticas. A lâmina foliar tem estrutura dorsiventral, ocorrendo no mesofilo bolsas secretoras em posição subepidérmica.

Ultrastructure and Analytical Microscopy of Silicon in the Leaf Cuticle of Ficus lyrata Warb.

Leaves of Ficus lyrata contain large deposits of silicon (Si) in the adaxial and abaxial cuticles. Si was also found in the external and internal periclinal and anticlinal walls of epidermal and subepidermal cells. The Si in the cuticle filled large interstices that were sometimes confluent with each other and with the underlying cell wall material. Si deposits were more abundant in the adaxial than in the abaxial surface. Samples prepared without heavy metal stains showed that Si deposits have high intrinsic electron density. Sections incubted in 5% HFI had Substantially less Si than adjacent serial, nontreated sections. The Accumulation of the Si in the cuticle of F. lyrata is consistent with the proposed mechanism of apoplastic movement of monosilicic acid in the transpiration stream.

Studies on the formation of 'floating' guard cell mother cells in Anemia.

The protodermal cells producing the 'floating' guard cell mother cells (GMCs) in three Anemia species undergo an extraordinary polarization and an unexpected shaping. During interphase an intercellular space is initiated at the internal proximal end of the cell, while the polar region bulges outwards. At this stage a microtubule girdle traverses the cortical cytoplasm underneath the rims of the external periclinal wall curvature. In addition, another system of microtubules converges on a cortical site adjoining the wall delimiting the intercellular space and, or, the neighbouring region of the internal periclinal wall (internal polar cortical site, IPCS). Vacuoles are found in all regions of the cell except for that between the centrally located nucleus and the intercellular space. As the cell approaches mitosis, the growing vacuolar system retreats from the cytoplasmic region below the external periclinal wall curvature. In most cells the polarized cytoplasm forms an inclined truncated cone, the bases of which abut on the external periclinal wall curvature and the wall lining the IPCS. The organization of the cortical microtubule cytoskeleton does not change significantly during preprophase-prophase. A preprophase microtubule band (PMB) is localized in the cortex lining the rims of the external periclinal wall curvature, while some microtubules traverse the IPCS and the cytoplasm adjacent to the neighbouring wall regions. The mitotic spindle axis is diagonal, while the cell plate separating the GMCs exhibits an unusual mode of growth. It gradually encircles the proximal daughter nucleus, becoming funnel-shaped. One of its periclinal edges fuses with the external periclinal wall area lined by the PMB cortical zone and the other with the internal periclinal wall area adjoining the IPCS. The latter region seems to behave like the PMB cortical zone. The results show that the morphogenetic mechanism underlying the formation of the conical GMCs includes a series of highly integrated processes, initiated or carried out during cell polarization.

Studies on the development of the air pores and air chambers of Marchanda paleacea. II. Ultrastructure of the initial aperture formation with particular reference to cortical microtubule organizing centres

The initiation of the intercellular spaces (ISs) of the initial apertures (IAs) follows the formation of surface cavities (SCs). The latter represent slight deepenings in the external periclinal walls of particular superficial thallus cells at the regions where their anticlinal walls meet one another. This event keeps pace with the deposition of wall pads at the wall junctions below the SC. Afterwards, the thickened wall areas are detached and thus the IS is initiated. By an inward development the IS reaches the subprotodermal layer. This is carried out by the coordination of three gradual processes: the inward spreading of the local wall thickening and the following detachment and expansion of the thickened regions. The findings favour the conclusion that the opening of the IS is the outcome of a highly controlled morphogenetic process. The interphase IA cells possess a well-organized cortical microtubule (MT) cytoskeleton, particularly at the area where the IS opens. In these regions, sets of anticlinal and periclinal MTs appear. During the SC stage the anticlinal MTs dominate, while during IS formation, the periclinal ones are most abundant. The above MTs, as well as other ones entering deeper in the cytoplasm, initially converge on the cortical cytoplasm adjacent to the SC and later on the region surrounding the lower part of the growing IS, where vesicles and endoplasmic reticulum are gathered. The observations suggest the continuous function of cortical MT organizing centres in the cytoplasm and (or) the adjoining plasmalemma, initially underneath the SC and later below the lower part of the growing IS, where local wall thickenings are deposited.

A cytological study of the oat coleoptile

A study has been made of the cytoplasmic organization of epidermal and sub- epidermal parenchyma of oat coleoptiles both before and after the onset of extension growth. In the youngest cells studied (coleoptiles 0.5 mm long) the epidermal parenchyma was characterized by large stellate vacuoles and by the secretion of vesicles through the plasmalemma into the external periclinal cell wall. Vesicular secretion was not observed in the anticlinal walls or into the walls of subepidermal parenchyma. The subepidermal parenchyma was characterized by the presence of numerous thick-walled vacuolar structures and plastids rich in starch. In the extension phase (coleoptiles > 10 mm long) vesicular secretion was not observed, starch was absent from the plastids, and the cells contained large vacuoles with only a thin peripheral zone of cytoplasm. During the later stages of this phase the plasmalemma appeared to consist of two darkly stained membranes separated by a light zone, or of elaborations of this structure, e.g. dark, light, dark, light, dark. By contrast, in the pre-extension phase the plasmalemma appeared as a single membrane. The implications of these observations are discussed in relation to the process of wall formation.