Bud and crown architecture of white spruce and black spruce

Needle primordia in buds and branch lengths were assessed in the crown of a plantation-grown white spruce tree. There was a gradation in needle primordia in buds in branches within the crown. The largest number of primordia was in the terminal bud of the leading main stem shoot, with the number in first-order whorl lateral shoot terminal buds decreasing from whorl 1 to whorl 4, below which buds contained a similar small number of primordia (about one-third as many as in the terminal shoot). Previous year's shoot elongation followed a similar pattern (i.e., elongation of whorl branches was greater closer to the top of the tree and elongation in the fourth through ninth whorls was about one-third that of the main stem leader). Higher order branches within whorls had within-branch gradation in shoot elongation and number of needle primordia, with older branches having as few as 16–30 primordia in buds and 3–4 cm elongation for high-order branches on older main stem whorls. There were strong correlations between the number of primordia in branch terminal buds and branch length/diameter and bud length/diameter/volume. In both black spruce and white spruce, there were strong correlations of number of needle primordia in main stem leader terminal buds with number of needle primordia in terminal buds of first and second whorl leaders.     

A model for the morphogenesis of strip reduction patterns in phototrophic euglenids: evidence for heterochrony in pellicle evolution

We propose a general developmental model that explains the evolutionary origin, diversification, and inheritance of pellicle strip patterns in phototrophic euglenids. Dividing cells of Euglena gracilis, E. viridis, and Phacus similis were observed with scanning electron microscopy in order to study the morphogenesis of posterior whorls of strip reduction. We found evidence that constant whorl numbers are maintained through cell division because of organized strip growth before and during cytokinesis. Alternating nascent strips form a new whorl of strip reduction at each of the anterior and posterior ends of daughter cells. Strips that terminated to form posterior whorls in the mother cell change in length during the development of daughter cells. In the mother cells of E. gracilis, the strips forming whorls I and II grow to become whorls II and III, respectively, in the daughter cells; the strips forming whorl III in the mother cell lengthen and meet with other strips already present at the posterior tip of daughter cells. This process of whorl morphogenesis during asexual reproduction is consistent with known variation in pellicle strip patterns and suggests that heterochrony played a major role in the ultrastructural evolution of phototrophic euglenids.     

Bud set in<Emphasis Type="Italic"> Abies nordmanniana</Emphasis> Spach. influenced by bud and branch manipulations

Buds and branches were experimentally removed in spring from 3-year-old seedlings of Abies nordmanniana to stimulate growth allocation to the leader. Great allocation changes were observed the same year, not only to the leader but also to bud formation. Subapical buds, 'whorl buds', increased in average number from 4.5 up to 5.0, their diameter increased up to 36%, and the number of new lateral buds increased up to approximately 300%. Treatments involving the subapical ("whorl") buds had stronger effects than those involving other lateral buds and branches. The observations raise some questions as to the possible self-organizing mechanisms of a Massart architectural type tree and are discussed in relation to functionality and application for forestry.     

The Effect of Bud Position on Branch Growth and Bud Abscission in Quercus petraea (Matt.) Liebl.

The time at which a bud began to expand was related to its positionnot only on an individual shoot but also within the crown. Thedistribution of buds and branches on the shoot was uneven; theshoot tip, where they were densely clustered, was termed the‘whorl; and the remainder of the shoot, where they werewidely spaced, the ‘interwhorl’ stem. In spring,the terminal bud started expanding before the ‘whorl’buds which preceded the ‘interwhorl’ stem buds;completion of the flush of growth, determined by the end ofleaf expansion, occurred in the reverse order, ‘interwhorl’> ‘whorl’ > terminal. Similarly bud expansionstarted at the top of the crown and progressed downwards, andthe first shoots to complete their flush were at the bottomof the crown. Approximately 60% of the buds on each shoot beganexpanding in spring but only about half of these formed branches.Bud abscission began in May and by Sep. 45% of buds originallypresent had abscised. Most of-the buds that did not abscisewere the small buds at the base of the shoot that were not originallyassociated with a leaf. Approximately 42% of ‘whorl’buds and 28% of MnterwhorP stem buds formed branches. ‘Whorl’branches were approx. 60% longer that ‘interwhorl’stem branches; buds on the lower surface of the shoot producedlonger branches than those on the upper surface. The implicationsof the results for the development of crown form and selectionof superior oak are discussed. Quercus petraea, oak, buds, branches, crown form     

Apical control of branch movements in white pine: biological aspects

Two-year-old branches on control trees (Pinus strobus L.) were compared through a season with branches on trees stem-girdled just above, or below, the branch whorl. All branches first sagged down for 20 days and then moved up for 40 days. Then, control branches reversed and moved back down while branches in both girdle treatments continued to move up. Movement reversal correlated with cessation of both elongation and diameter growth in control branches. Diameter growth continued in branches of girdled trees. Control branches continued to stiffen even after diameter growth stopped. Differences in movements due to girdling are from compression wood formed after cessation of branch elongation. Apical control stops cambial activity and compression wood formation in branches after branch elongation ceases, allowing photosynthate produced in the branch to move to the stem. Control branches bend down from increasing self-weight after cambial activity ceases.     

Alpha-COPI coatomer protein is required for rough endoplasmic reticulum whorl formation in mosquito midgut epithelial cells

Background

One of the early events in midgut epithelial cells of Aedes aegypti mosquitoes is the dynamic reorganization of rough endoplasmic reticulum (RER) whorl structures coincident with the onset of blood meal digestion. Based on our previous studies showing that feeding on an amino acid meal induces TOR signaling in Ae. aegypti, we used proteomics and RNAi to functionally identify midgut epithelial cell proteins that contribute to RER whorl formation.

Methodology/Principal Findings

Adult female Ae. aegypti mosquitoes were maintained on sugar alone (unfed), or fed an amino acid meal, and then midgut epithelial cells were analyzed by electron microscopy and protein biochemistry. The size and number of RER whorls in midgut epithelial cells were found to decrease significantly after feeding, and several KDEL-containing proteins were shown to have altered expression levels. LC-MS/MS mass spectrometry was used to analyze midgut microsomal proteins isolated from unfed and amino acid fed mosquitoes, and of the 127 proteins identified, 8 were chosen as candidate whorl forming proteins. Three candidate proteins were COPI coatomer subunits (alpha, beta, beta''), all of which appeared to be present at higher levels in microsomal fractions from unfed mosquitoes. Using RNAi to knockdown alpha-COPI expression, electron microscopy revealed that both the size and number of RER whorls were dramatically reduced in unfed mosquitoes, and moreover, that extended regions of swollen RER were prevalent in fed mosquitoes. Lastly, while a deficiency in alpha-COPI had no effect on early trypsin protein synthesis or secretion 3 hr post blood meal (PBM), expression of late phase proteases at 24 hr PBM was completely blocked.

Conclusions

alpha-COPI was found to be required for the formation of RER whorls in midgut epithelial cells of unfed Aa. aegypti mosquitoes, as well as for the expression of late phase midgut proteases.     

Crown architecture and dynamics in Abies procera as influenced by cutting for greenery

Greenery production from 13 to 17 years old Abies procera was studied in three localities differing in soil and tree provenance. Two alternative clipping strategies for greenery were applied during 8 years. Subsequently, destructive crown analyses were carried out on the trees sampled from these and traditionally cut plots. Regeneration occurred from stubs or bases of cut primary branches. In cases when stubs were removed, proliferation took place around the scar; these branches compensated in numbers but not in biomass for the absence of stub branches. More severe cutting regimes resulted in an overall biomass reduction, most notably with shorter and lighter whorl branches. Interwhorl branches and branches issued from the base of primary branches were able to extend progressively in response to severe cutting. Base branches were apparently recruited along most of the trunk, the latency of growth points thus being up to at least 10 years. Competition among interwhorl branches, as well as more complicated interactions between whorl branches and secondary branches arising from their base, are indicated by the data. Reiteration directly from the stem could not be provoked and the results suggest that optimum greenery yield depends on careful stub management.     

Whorl Formation in Polysphondylium violaceum: Relevance to Organization by Cyclic AMP

Whorl formation in Polysphondylium is a simple and good system for the study of pattern formation. The first step of whorl formation is characterized by separation of the rear cell mass from an advancing primary mass during culmination. Using the iontophoresis method, it has been shown that after the establishment of multicellular organization cells respond chemotactically to 3',5' -cyclic adenosine monophosphate (cAMP), but not to glorin, the chemoattaractant at the aggregating stage. P. violaceum cell masses were also found to secrete actively cAMP. Therefore, morphogenetic movement of P. violaceum cells after aggregation could be controlled mainly by the cAMP signalling system. Vital staining of cells with neutral red (NR) revealed that there are anterior-like cells stained well with NR in the posterior region of a migrating P. violaceum slug, and that the staining pattern changes markedly during whorl formation. Just before separation of the whorl mass, the anterior-like cells altered their distribution, and eventually were arranged as an equatorial band on the surface of the presumptive whorl mass, which probably would turn to organizing tip cells of the secondary masses left on the primary stalk. Thus whorl formation may be caused by separation of the strongest cAMP-source into two regions; the primary (anterior) and secondary (posterior) tips.     

Cell patterning in branched and unbranched fruiting bodies of the cellular slime mold Polysphondylium pallidum

Cell patterning, the percentage of spores and stalk cells, was measured in branched and unbranched asexual fruiting bodies of Polysphondylium pallidum. Unlike D. discoideum, where small and large fruiting bodies are more stalky than average-sized fruiting bodies, the overall cell patterning was the same in branched and unbranched fruiting bodies of all sizes in P. pallidum. Light greatly increased the numbers of fruiting bodies in P. pallidum per unit area (or decreased aggregation territory size) so that most fruiting bodies formed in the light were small and unbranched. By contrast, light had little effect on the cell patterning of P. pallidum, although there was a slight increase in the percentage of stalk cells in the light compared to the dark. This indicates that the mechanisms governing light sensitivity of aggregation territory size and cell patterning have different components in P. pallidum. The accuracy of cell patterning of individual branches of branched fruiting bodies was so imprecise as to leave doubt that patterning is occurring at the branch level. Individual whorls of branched fruiting bodies had a greater percentage spores (90%) than whole fruiting bodies (78%) and the cell patterning was relatively imprecise. Only in whole fruiting bodies was the spore:stalk ratio highly correlated. These findings are consistent with cell pattern determination operating at the whole aggregate level, rather than at the individual whorl or branch level in P. pallidum.     

Ultrastructure within the Lateral Plexus of the Limulus Eye

The ultrastructure of the lateral plexus in the compound eye of Limulus is investigated by serial section technique. "Cores" of tissue containing the axons, lateral plexus, and neuropile associated with one sensory ommatidium show the following features: (a) collateral branches from retinular cells do not contribute to the lateral plexus proper, but do form retinular neuropile by contacting collaterals of a self-contained cluster of retinular axons; (b) collateral branches from eccentric cell axons always branch repeatedly upon leaving the parent axon, and compose the bulk of the lateral plexus; (c) the most distal collateral branches from an eccentric cell axon appear to form neuropile and synaptic contacts with each other, whereas more proximal branches form synaptic contacts with collaterals from eccentric cell axons of neighboring ommatidia. We conclude that the ribbon synapses and associated transmitter substance in eccentric cell collaterals must be inhibitory, and that two pathways for self-inhibition may exist. We suggest, as a working hypothesis for the structure of the lateral plexus, a branching pattern with depth that mirrors the horizontal spread of lateral inhibition measured physiologically.     

Control and Kinetics of Branch Root Formation in Cultured Root Segments of Haplopappus ravenii

Branch root formation required only the presence of minerals, sucrose as a carbon source, and an auxin. The number of primordia formed was a function of auxin concentration. With naphthaleneacetic acid at 0.1 mg/l, up to 60 or more branches were formed per centimeter of Haplopappus ravenii root segment. Under our conditions, pea root segments formed only five or six branches per centimeter, but tomato and radish, like H. ravenii, formed large numbers of branches. Cytokinin inhibited branch formation, while gibberellic acid was without effect. Vitamins were not required for branch formation, although they enhanced elongation. Up to 5 days were required for the maximum number of stable branch primordia to form under the influence of naphthaleneacetic acid. If naphthaleneacetic acid was withdrawn earlier, fewer branch primordia developed. The requirement for a lengthy exposure to naphthaleneacetic acid, the kinetics of the response, and the ease with which naphthaleneacetic acid could be rinsed out of the tissue with consequent cessation of branch root formation, were similar to other hormone-regulated developmental systems. Anatomical and cytological studies were made of segments exposed for various times to auxin. The segments were mostly diarch, and branches formed obliquely to protoxylem poles. While primarily only pericycle-endodermis cells divided, both these and cortex cells responded in the first 24 hours exposure to naphthaleneacetic acid with enlarged nuclei and nucleoli, and a few cortical cells divided. Maximum nucleus and nucleolus size was reached approximately 9 hours after exposure to naphthaleneacetic acid. Branches rarely elongated more than 5 cm before their meristems died. The H. ravenii culture is maintained only by the frequent formation of new naphthaleneacetic acid-induced branches.     

樟子松人工林分枝结构的分析

基于对6块樟子松(Pinus sylvestris var. mongolica)人工林固定标准地中的30株样木枝解析调查数据,通过分析不同林分、不同大小林木1级枝和2级枝的分枝概率、分枝格局和分枝角度,揭示了樟子松人工林树冠的分枝结构特点。研究结果表明：樟子松人工林1级枝和2级枝的平均分枝数量分别为3.84个和2.80个,两者分枝概率均呈正态分布;1级和2级枝条在光照条件好的几个区间（方位角46°～225°）分布较多,1级枝条的水平分布遵从均匀分布,而2级枝条则不遵从均匀分布;树冠上层枝条的分枝角度略小于树冠中、下层,上层平均分枝角度为45.6°,而中下层平均分枝角度都为49.4°。不同大小林木的1级枝分枝结构规律表明：Ⅰ级木和Ⅴ级木的每轮平均分枝数非常接近,分别为3.89和3.94个,比Ⅲ级木每轮分枝数大0.5个左右;1级枝水平分布在各区间内(45°间隔)相差在0.24%～2.81%之间,方差分析结果表明枝条水平分布与林木大小无关;不同大小林木的分枝角度有所差别,Ⅰ级木、Ⅲ级木和Ⅴ级木的平均分枝角度分别为48.5°、42.2°和50.7°。     

Dpp and Notch specify the fusion cell fate in the dorsal branches of the Drosophila trachea.

Decapentaplegic (Dpp) signaling determines the number of cells that migrate dorsally to form the dorsal primary branch during tracheal development. We report that Dpp signaling is also required for the differentiation of one of three different cell types in the dorsal branches, the fusion cell. In Mad mutant embryos or in embryos expressing dominant negative constructs of the two type I Dpp receptors in the trachea the number of cells expressing fusion cell-specific marker genes is reduced and fusion of the dorsal branches is defective. Ectopic expression of Dpp or the activated form of the Dpp receptor Tkv in all tracheal cells induces ectopic fusions of the tracheal lumen and ectopic expression of fusion gene markers in all tracheal branches. Among the fusion marker genes that are activated in the trachea in response to ectopic Dpp signaling is Delta. In conditional Notch loss of function mutants additional tracheal cells adopt the fusion cell fate and ectopic expression of an activated form of the Notch receptor in fusion cells results in suppression of fusion cell markers and disruption of the branch fusion. The number of cells that express the fusion cell markers in response to ectopic Dpp signaling is increased in Notch(ts1) mutants, suggesting that the two signaling pathways have opposing effects in the selection of the fusion cells in the dorsal branches.     

Two novel reports of semidry stigmatic surface in Asteraceae

Research documents related to the morphology and function of style branches and stigmatic surface of Asteraceae are still rather few, and the literature reports are thus controversial. We report in the present study that the stigmatic surfaces of two non-related species of Asteraceae (Lessingianthus grandiflorus and Lucilia lycopodioides) have features of semidry stigmas. Sporodermis of both species was also analyzed so that we could understand how the stigmatic surface works during pollen deposition and rehydration. Stylar branches and pollen grains (sporodermis) were studied using scanning and transmission electron microscopy (SEM and TEM) and histochemistry techniques. The inner and marginal bands of stylar branches in these species display intermediary features between the dry and wet types of stigma: the cuticle characterizes the dry stigma and cells with secretory activity characterize the wet stigma; these showed differences from what has been described to the Asteraceae family, where stigmatic surface of species from several tribes is considered dry. Pollen grains are medium-size to large with exine ornamentation (echinate and echinolophate) and abundant secretion which latter characterizes pollenkitt. We can assume that two processes might help pollen grain hydration on stigmatic surface in Lessingianthus grandiflorus and Lucilia lycopodioides: (1) the presence of pollenkitt, as observed in the secretory content inside exine cavities and around pollen grains; and (2) the secretory activity of stigmatic surface cells, whose secretion accumulates among intercellular and subcuticular spaces and leads to cuticle disruption during the floral receptive phase. Our results suggest that ultrastructural and histochemical studies should be considered when describing stigmatic surface and that the “semidry” feature within Asteraceae should be investigated still more in detail, so that the taxonomic or adaptation value of this trait in the family can be verified.     

Quantitative Analysis of Filament Branch Orientation in Listeria Actin Comet Tails

Several bacterial and viral pathogens hijack the host actin cytoskeleton machinery to facilitate spread and infection. In particular, Listeria uses Arp2/3-mediated actin filament nucleation at the bacterial surface to generate a branched network that will help propel the bacteria. However, the mechanism of force generation remains elusive due to the lack of high-resolution three-dimensional structural data on the spatial organization of the actin mother and daughter (i.e., branch) filaments within this network. Here, we have explored the three-dimensional structure of Listeria actin tails in Xenopus laevis egg extracts using cryo-electron tomography. We found that the architecture of Listeria actin tails is shared between those formed in cells and in cell extracts. Both contained nanoscopic bundles along the plane of the substrate, where the bacterium lies, and upright filaments (also called Z filaments), both oriented tangentially to the bacterial cell wall. Here, we were able to identify actin filament intersections, which likely correspond to branches, within the tails. A quantitative analysis of putative Arp2/3-mediated branches in the actin network showed that mother filaments lie on the plane of the substrate, whereas daughter filaments have random deviations out of this plane. Moreover, the analysis revealed that branches are randomly oriented with respect to the bacterial surface. Therefore, the actin filament network does not push directly toward the surface but rather accumulates, building up stress around the Listeria surface. Our results favor a mechanism of force generation for Listeria movement where the stress is released into propulsive motion.     

Drosophila tracheal system formation involves FGF-dependent cell extensions contacting bridge-cells

Development of the ectodermally derived Drosophila tracheal system is based on branch outgrowth and fusion that interconnect metamerically arranged tracheal subunits into a highly stereotyped three-dimensional tubular structure. Recent studies have revealed that this process involves a specialized cell type of mesodermal origin, termed bridge-cell. Single bridge-cells are located between adjacent tracheal subunits and serve as guiding posts for the outgrowing dorsal trunk branches. We show that bridge-cell-approaching tracheal cells form filopodia-like cell extensions, which attach to the bridge-cell surface and are essential for the tracheal subunit interconnection. The results of both dominant-negative and gain-of-function experiments suggest that the formation of cell extensions require Cdc42-mediated Drosophila fibroblast growth factor activity.     

Evidence that cytokinin controls bud size and branch form in Norway spruce

Shoot elongation in many coniferous species is predetermined during bud formation the year before the shoot extends. This implies that formation of the primordial shoot within the bud is the primary event in annual shoot growth. Hormonal factors regulating bud formation are consequently of utmost importance. We followed the levels of the endogenous cytokinins zeatin riboside (ZR) and isopentenyladenosine (iPA) in terminal buds, whorl buds and lower lateral buds of the uppermost current-year whorl shoots of 15- to 20-year-old trees of Norway spruce [ Picea abies (L.) Karst.] from June to September. Cytokinins were isolated with affinity chromatography columns, purified by high performance liquid chromatography, and quantified by ELISA. The level of ZR was low in June but increased gradually in all buds until September. Throughout the measurement period, the ZR level was highest in terminal buds and lowest in the scattered lateral, buds, with the whorl buds intermediate. The level of iPA peaked in July and decreased later without any consistent differences among the three classes of buds. The development of different kinds of buds was followed by scanning electron microscopy. We found that bud growth was greatest during August and September. The final size of primordial shoots within the buds varied considerably and the weight of the terminal bud was three times that of the whorl buds and more than five times that of the other lateral buds.
We conclude that the increase in ZR level during the period of active bud development is indicative of the importance of cytokinin for this process. Furthermore, the positive correlation between the level of ZR and bud growth during the period of predetermination of next year's branch growth suggests that this hormone indirectly controls the form of single branches in the spruce tree.     

Evidence that cytokinin controls bud size and branch form in Norway spruce

Shoot elongation in many coniferous species is predetermined during bud formation the year before the shoot extends. This implies that formation of the primordial shoot within the bud is the primary event in annual shoot growth. Hormonal factors regulating bud formation are consequently of utmost importance. We followed the levels of the endogenous cytokinins zeatin riboside (ZR) and isopentenyladenosine (iPA) in terminal buds, whorl buds and lower lateral buds of the uppermost current-year whorl shoots of 15- to 20-year-old trees of Norway spruce [ Picea abies (L.) Karst.] from June to September. Cytokinins were isolated with affinity chromatography columns, purified by high performance liquid chromatography, and quantified by ELISA. The level of ZR was low in June but increased gradually in all buds until September. Throughout the measurement period, the ZR level was highest in terminal buds and lowest in the scattered lateral, buds, with the whorl buds intermediate. The level of iPA peaked in July and decreased later without any consistent differences among the three classes of buds. The development of different kinds of buds was followed by scanning electron microscopy. We found that bud growth was greatest during August and September. The final size of primordial shoots within the buds varied considerably and the weight of the terminal bud was three times that of the whorl buds and more than five times that of the other lateral buds.
We conclude that the increase in ZR level during the period of active bud development is indicative of the importance of cytokinin for this process. Furthermore, the positive correlation between the level of ZR and bud growth during the period of predetermination of next year's branch growth suggests that this hormone indirectly controls the form of single branches in the spruce tree.