Anatomy and Ultrastructure of Galls Induced by Neuroterus quercusbaccarum (Hymenoptera: Cynipidae) on Oak Leaves (Quercus robur)

The structure and ultrastructure of two developmental stages of the spangle gall induced by Neuroterus quercusbaccarum (Hymenoptera, Cynipidae) were investigated using light microscopy (LM), fluorescence microscopy (FM), and transmission (TEM) and scanning (SEM) electron microscopy. The general design of the gall structure was typical of Cynipidae, but some structural features distinguished the spangle gall. Previously undescribed, characteristic multicellular epidermal protuberances with large openings were observed in autumn on the surface of galls. These may facilitate the gas exchange between the atmosphere and the inside of the gall, thus assisting larval respiration. The larval chamber is surrounded by both a sclerenchymatous capsule and numerous cells containing calcium oxalate crystals that may both serve as protective barriers. In young galls, the nutritive tissue is a wall-less protoplasmic mass, potentially easily accessible to young larvae with delicate mandibles. Cell walls only develop at a later stage. The nutritive tissue was found to be rich in proteins and lipids, but starch grains were not observed. Cellular topology suggests that spangle galls grow by anticlinal division of marginal epidermal cells and periclinal division of subepidermal cells. Cellular proliferation (hyperplasia) also occurs in the leaf tissue near the connection with the gall peduncle, which eventually lignifies.

Three-dimensional quantitative analysis of the Arabidopsis quiescent centre

Quiescent centre (QC) cells represent an integral part of the root stem cell niche. They typically display a low division frequency that has been reported to be controlled by hormone signaling and different regulators, including the ETHYLENE RESPONSE FACTOR 115 (ERF115) transcription factor and D-type cyclins. Here, we applied a three-dimensional (3D) imaging to visualize the Arabidopsis QC cell number, volume and division patterns, including visualization of anticlinal divisions that cannot be deduced from longitudinal 2D imaging. We found that 5-day-old seedlings possess on average eight QC cells which are organized in a monolayered disc. In a period of 7 d, half of the QC cells undergo anticlinal division in a largely invariant space. Ectopic expression of ERF115 and CYCLIN D1;1 (CYCD1;1) promote both anticlinal and periclinal QC cell divisions, the latter resulting in a dual-layered QC zone holding up to 2-fold more QC cells compared with the wild type. In contrast, application of cytokinin or ethylene results in an increase in the number of periclinal, but a decrease in anticlinal QC divisions, suggesting that they control the orientation of QC cell division. Our data illustrate the power of 3D visualization in revealing unexpected QC characteristics.

The parenchymo-vascular cambium and its derivative tissues in stems and roots of Bougainvillaea glabra Choisy (Nyctaginaceae)

In the shoots and roots of <i>Bougainmllaea</i>, the parenchymo-vascular cambium produces thinwalled secondary parenchyma to one side and the secondary vascular bundles embedded in the "conjunctive tissue" to the other. Periclinal division of a single cambial cell in one radial row brings about periclinal divisions of the adjacent cells of the neighbouring rows. Anticlinal division of a single cambial cell at one level, on the other hand, causes anticlinal. divisions of the adjacent cells of the overlying and underlying tiers.

Cambial Development and Tracheid Length of Dwarf Pines (Pinus Densiflora and P. Thunbergii)

From a comparison of cambial cells and their derivatives between naturally occurring dwarf trees and normal ones, it was concluded that tracheids in the annual rings of dwarf trees are shorter, narrower and fewer than those of normal trees. The frequency of anticlinal division and loss of cambial initials is low during differentiation of xylem cells from cambial initials in dwarf pines. The length and intrusive growth of fusiform initials are slightly less than those of normal trees. Thus, it is concluded that the shortening of tracheids in dwarf trees is due to the fact that cambial initials are themselves shortened and that intrusive growth during differentiation of xylem mother cells has occurred.

Division and differentiation during normal and liguleless-1 maize leaf development

The maize leaf is composed of a blade and a sheath, which are separated at the ligular region by a ligule and an auricle. Mutants homozygous for the recessive liguleless-1 (lg1) allele exhibit loss of normal ligule and auricle. The cellular events associated with development of these structures in both normal and liguleless plants are investigated with respect to the timing of cell division and differentiation. A new method is used to assess orientation of anticlinal division planes during development and to determine a division index based on recent epidermal cross-wall deposition. A normal leaf follows three stages of development: first is a preligule stage, in which the primordium is undifferentiated and dividing throughout its length. This stage ends when a row of cells in the preligule region divides more rapidly in both transverse and longitudinal anticlinal planes. During the second stage, ligule and auricle form, blade grows more rapidly than sheath, divisions in the blade become exclusively transverse in orientation, and differentiation begins. The third stage is marked by rapid increase in sheath length. The leaf does not have a distinct basal meristem. Instead, cell divisions are gradually restricted to the base of the leaf with localized sites of increased division at the preligule region. Divisions are not localized to the base of the sheath until near the end of development. The liguleless-1 homozygote shows no alteration in this overall pattern of growth, but does show distinct alteration in the anticlinal division pattern in the preligule region. Two abnormal patterns are observed: either the increase in division rate at the preligule site is absent or it exhibits loss of all longitudinal divisions so that only transverse (or cell-file producing) divisions are present. This pattern is particularly apparent in developing adult leaves on older lg1 plants, in which sporadic ligule vestiges form. From these and results previously published (Becraft et al. (1990) Devl Biol. 14), we conclude that the information carried by the Lg1+ gene product acts earlier in development than formation of the ligule proper. We hypothesize that Lg1+ may be effective at the stage when the blade-sheath boundary is first determined.

Vascular cambium and wood development in Carboniferous plants. III. Arthropitys (Equisetales; Calamitaceae)

Vascular cambium activity was examined in Arthropitys communis (Binney) Hirmer et Knoell, and A. deltoides Cichan et Taylor, anatomically preserved calamite stems from the Pennsylvanian of Kentucky. Developmental characteristics of the meristem were inferred from changes in the size and number of tracheids and ray cells determined from serial tangential sections of the secondary xylem. In A. communis, circumferential enlargement of the cambium seems to have been accommodated primarily by the enlargement of fusiform initials. Qualitative and quantitative evidence is also presented indicating that “marginal” interfascicular ray initials were converted to fusiform initials during the early stages of cambial activity. In A. deltoides, circumferential enlargement of the meristem was accommodated by the enlargement of fusiform initials and by an increase in size and number of interfascicular ray initials. Multiplicative division of the fascicular ray initials appears to have been an important feature of cambial activity in both species. There is no qualitative or quantitative evidence that the number of fusiform initials in either species was augmented by anticlinal division as in extant seed plants.

Glandular trichomes on the inflorescence of Chrysanthemum morifolium cv. Dramatic (Compositae). I. Development and morphology

Floral apices of Chrysanthemum morifolium cv. Dramatic form glandular trichomes on the receptacle in interfloret positions and on the corolla tube above the constriction subtended by the ovary. The glandular trichomes in both positions are initiated by the enlargement of single epidermal cells followed by a single anticlinal division and a series of periclinal divisions resulting in a 10-celled biseriate structure. Receptacular trichomes develop while florets are being initiated on the flanks of the floral apex and by the time petal primordia are initiated these trichomes are mature. Glandular trichomes on the corolla tube are initiated on peripheral florets while florets are still being initiated in a centripetal direction. Each glandular trichome has a cuticular covering beneath which secreted materials accumulate, thereby distending the cuticle. A large pore eventually forms in the cuticle and presumably allows the escape of secreted substances.

Glandular trichomes on the inflorescence of Chrysanthemum morifolium cv. Dramatic (Compositae). II. Ultrastructure and histochemistry

Glandular trichomes on the inflorescence of Chrysanthemum morifolium cv. Dramatic are initiated from a single epidermal cell outgrowth and develop through an anticlinal division and a series of periclinal divisions to form a biseriate multicellular structure. Cells of the young trichome contain a large nucleus with prominent nucleoli and few small cellular organelles. Prior to the secretory stage, numerous ribosomes, polyribosomes, and dictyosomes are present in a dense cytoplasm but most of the dictyosomes are lost as secretion commences. Plastids in the stalk cells senesce but in a different manner than those in the upper tiers of secretory cells. Lipoidal substances form in the degenerating plastids. Cell wall ingrowths and the deposition of a flocculent material in the primary cell wall characterize secretory hairs. In very old hairs cellular lysis takes place with mitochondria being the last cellular organelle to remain intact. The secreted material, which collects in a subcuticular space, appears to be a terpenoid. The function of this material is not known.

A survey of cell length and frequency of multiplicative divisions in the cambium of conifers

Study of many species of conifers has revealed certain trends with respect to cell length and rate of anticlinal division in the multiplication of fusiform initials in the cambium. In the stem, rate of anticlinal division tends to be high when annual rings are narrow, and to stabilize at a relatively low level when rings exceed 2 mm in width. Cell length at division is usually greatest when rings are about 1 mm wide, and decreases with both widening and narrowing of the rings from the optimal width. Significant differences occur between species in both rate of anticlinal division and cell length. In general, rate of anticlinal division and cell length are inversely related, but in some species there is wide deviation from the common trend.

Variations in cell length and frequency of anticlinal division in the vascular cambium throughout a white spruce tree

In the early growth of the stem, branches, and roots, the vascular elements are relatively short and the frequency of anticlinal division involved in cambial cell multiplication is high. As growth sheaths are added in the stem, length of cell increases and rate of multiplicative division declines. A similar trend occurs upward through the lower quarter to half the height of the stem. In the root system, the later growth of vertical roots is characterized by shortness of cell and high frequency of anticlinal division, and conversely, that of horizontal roots by great length of cell and low rate of anticlinal division. Although a general negative relationship exists between rate of anticlinal division and cell length throughout much of the tree, these features sometimes vary independently, and length of cell seems to be more closely related to amount of yearly radial accretion. Through the middle to late growth of the stem a negative relationship obtains between length of cell and width of annual ring, cell length maximating at a ring width of 1–2 mm. At this stage, frequency of division may fluctuate only narrowly over a considerable range of ring width. A continued decline in ring width to less than 0.5 mm, such as may occur on senescence, is accompanied by decreased cell length and accelerated anticlinal division. Length of the cell plate in anticlinal division, relative to that of the dividing cell, is greater in the early growth of the stem and branches and throughout horizontal roots than elsewhere in the tree. Most of the anticlinal divisions are pseudotransverse. The proportion of lateral divisions ranges from about 1% in the late growth of stems to 11% in horizontal roots.