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Cambial Activity (cambial + activity)
Selected AbstractsBetween Xylem and Phloem: The Genetic Control of Cambial Activity in PlantsPLANT BIOLOGY, Issue 5 2003Y. Helariutta Abstract: Post-embryonic development is controlled by two types of meristems: apical and lateral. There has been considerable progress recently in understanding the function of root and shoot apical meristems at the molecular level. Knowledge of analogous processes in the lateral, or secondary, meristems, i.e. the vascular cambium or cork cambium, is, however, rudimentary. This is despite the fact that much of the diversity in the plant kingdom is based on the differential functions of these meristems, emphasizing the importance of lateral meristems in the development of different plant forms. The vascular cambium is particularly important for woody plants, but it also plays an important role during the development of various herbaceous species, such as Arabidopsis thaliana. In this review, we focus on the two basic functions of cambial activity: cell proliferation and pattern formation. [source] Resistance of Pinus contorta to the European race of Gremmeniella abietinaFOREST PATHOLOGY, Issue 2 2006G. Laflamme Summary Pinus contorta seedlings, together with Pinus resinosa and Pinus banksiana seedlings, were planted adjacent to 25-year-old red pine trees infected by the European (EU) race of Gremmeniella abietina. Resistance to this race was assessed over 5 years. All P. resinosa seedlings were dead after that period while 65% of P. contorta and 86% of P. banksiana seedlings appeared resistant to the disease. The tip blight that occurred on P. contorta was slightly longer than that observed on P. banksiana. In microscopy, one, two, or even more suberized boundaries were seen to be initiated near the surface of the shoot at the base of healthy needles where they extended downward in the direction of the vascular cambium. Suberized boundaries occasionally crossed the xylem and joined together in the pith region to form continuous barriers around necrotic tissues. However, in most cases, these suberized barriers were not continuous across the shoot and compartmentalization was then completed by other barriers mainly constituted of parenchyma cells and xylem tracheids that accumulated phenolic compounds. Meristematic-like cells were observed adjacent to the necrophylactic periderm. Tissue regeneration, restoration of cambial activities and formation of traumatic resin canals also seemed to be associated with the defence system of P. contorta against the EU race of G. abietina. Résumé Des semis de Pinus contorta, de P. resinosa et de P. banksiana ont été plantés près de pins rouges âgés de 25 ans et infectés par la race européenne (EU) de Gremmeniella abietina. La résistance à cette race a étéévaluée sur une période de 5 ans. Tous les semis de P. resinosa sont morts après cette période alors que 65% des semis de P. contorta et 86% des semis de P. banksiana semblaient résister à la maladie. La brûlure à l'extrémité des pousses sur le P. contortaétait un peu plus longue que celle observée sur le P. banksiana. En microscopie, une, deux et même plusieurs couches de cellules subérisées se sont différenciées près de la surface des pousses à la base d'aiguilles saines et continuaient à progresser basipétalement en direction du cambium. Ces couches subérisées traversaient occasionnellement le xylème avant de fusionner près de la moelle pour former des barrières continues autour des tissus nécrosés. Toutefois, dans la plupart des cas, les barrières subérisées présentes dans les pousses étaient discontinues et le compartimentage était alors complété par d'autres barrières constituées de cellules de parenchyme et de trachéides ayant accumulé des composés phénoliques. Des cellules semblables à celles présentes dans les zones méristématiques furent observées près du périderme nécrophylactique. La présence de nouveaux tissus, le rétablissement de l'activité cambiale et la formation de canaux résinifères traumatiques semblaient aussi contribuer au système de défense de P. contorta contre la souche EU de G. abietina. Zusammenfassung In der Nachbarschaft von 25jährigen Pinus resinosa, die mit der europäischen Rasse von Gremmeniella abietina infiziert waren, wurden Sämlinge von Pinus contorta zusammen mit Sämlingen von Pinus resinosa und Pinus banksiana ausgepflanzt. Während fünf Jahren wurde die Resistenz gegenüber dieser Erregerrasse beobachtet. Am Ende des Beobachtungszeitraums waren alle P. resinosa -Sämlinge tot, während 65% der P. contorta und 86% der P. banksiana -Sämlinge überlebten. Die Nekrosen an der Triebspitze waren auf P. contorta etwas länger als bei P. banksiana. Mikroskopisch waren ein, zwei oder sogar mehr suberinisierte Abwehrzonen erkennbar, deren Bildung nahe der Trieboberfläche an der Basis gesunder Nadeln begann und die sich nach unten in Richtung auf das Kambium ausdehnten. Gelegentlich entstanden diese suberinisierten Zonen auch im Xylem und vereinigten sich im Mark miteinander, so dass eine geschlossene Barriere gegen die nekrotischen Gewebe entstand. In den meisten Fällen dehnten sich die suberinisierten Zonen aber nicht durch den ganzen Trieb aus und die Kompartimentierung wurde durch andere Barrieren ergänzt, die vorwiegend aus parenchymatischen Zellen und Tracheiden bestanden, in denen phenolische Stoffe akkumuliert wurden. Neben dem nekrophylaktischen Periderm wurden Zellen mit meristematischer Aktivität beobachtet. Daneben waren die Neubildung von Geweben, die Wiederherstellung der Kambiumaktivität und die Bildung traumatischer Harzkanäle offensichtlich bei der Abwehr von P. contorta gegen die EU-Rasse von G. abietina wirksam. [source] The growth respiration component in eddy CO2 flux from a Quercus ilex mediterranean forestGLOBAL CHANGE BIOLOGY, Issue 9 2004S. Rambal Abstract Ecosystem respiration, arising from soil decomposition as well as from plant maintenance and growth, has been shown to be the most important component of carbon exchange in most terrestrial ecosystems. The goal of this study was to estimate the growth component of whole-ecosystem respiration in a Mediterranean evergreen oak (Quercus ilex) forest over the course of 3 years. Ecosystem respiration (Reco) was determined from night-time carbon dioxide flux (Fc) using eddy correlation when friction velocity (u*) was greater than 0.35 m s,1 We postulated that growth respiration could be evaluated as a residual after removing modeled base Reco from whole-ecosystem Reco during periods when growth was most likely occurring. We observed that the model deviated from the night-time Fc -based Reco during the period from early February to early July with the largest discrepancies occurring at the end of May, coinciding with budburst when active aboveground growth and radial growth increment are greatest. The highest growth respiration rates were observed in 2001 with daily fluxes reaching up to 4 g C m,2. The cumulative growth respiration for the entire growth period gave total carbon losses of 170, 208, and 142 g C m,2 for 1999, 2001, and 2002, respectively. Biochemical analysis of soluble carbohydrates, starch, cellulose, hemicellulose, proteins, lignin, and lipids for leaves and stems allowed calculation of the total construction costs of the different growth components, which yielded values of 154, 200, and 150 g C for 3 years, respectively, corresponding well to estimated growth respiration. Estimates of both leaf and stem growth showed very large interannual variation, although average growth respiration coefficients and average yield of growth processes were fairly constant over the 3 years and close to literature values. The time course of the growth respiration may be explained by the growth pattern of leaves and stems and by cambial activity. This approach has potential applications for interpreting the effects of climate variation, disturbances, and management practices on growth and ecosystem respiration. [source] An Overview of the Biology of Reaction Wood FormationJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 2 2007Sheng Du Abstract Reaction wood possesses altered properties and performs the function of regulating a tree's form, but it is a serious defect in wood utility. Trees usually develop reaction wood in response to a gravistimulus. Reaction wood in gymnosperms is referred to as compression wood and develops on the lower side of leaning stems or branches. In arboreal, dicotyledonous angiosperms, however, it is called tension wood and is formed on the upper side of the leaning. Exploring the biology of reaction wood formation is of great value for the understanding of the wood differentiation mechanisms, cambial activity, gravitropism, and the systematics and evolution of plants. After giving an outline of the variety of wood and properties of reaction wood, this review lays emphasis on various stimuli for reaction wood induction and the extensive studies carried out so far on the roles of plant hormones in reaction wood formation. Inconsistent results have been reported for the effects of plant hormones. Both auxin and ethylene regulate the formation of compression wood in gymnosperms. However, the role of ethylene may be indirect as exogenous ethylene cannot induce compression wood formation. Tension wood formation is mainly regulated by auxin and gibberellin. Interactions among hormones and other substances may play important parts in the regulation of reaction wood formation. [source] Development, dilation and subdivision of cortical layers of gentian (Gentiana asclepiadea) rootNEW PHYTOLOGIST, Issue 1 2003ottníková Summary ,,The structure and development of the cortical layers, especially the endodermis and exodermis, and changes in the cortex caused by the secondary growth of vascular tissues are described in the adventitious roots of gentian (Gentiana asclepiadea). ,,Sections along the whole axis of the soil-grown roots were observed using light microscopy; fluorescence microscopy was used to determine developmental stages of the endodermis and exodermis. ,,Both endodermis and exodermis develop in three stages: Casparian band formation, suberin lamellae deposition and secondary thickening of walls. After the onset of cambial activity (20 mm from apex) cortical cells expand tangentially and subdivision of individual cells starts between 20 mm and 60 mm from apex. Highly differentiated endodermal cells are divided by 0,19 new anticlinal walls, exodermal cells by 0,3 and parenchymatous mid-cortex by 0,1. ,,The additional anticlinal cell walls of the endodermis and exodermis possess neither Casparian bands nor suberin lamellae. Suberin lamellae remain continuous on the surface of extended tangential walls of both layers. There is a correlation between increasing diameter of the secondary vascular tissues and the number of endodermal cells created by subdivision of the original cells. [source] Between Xylem and Phloem: The Genetic Control of Cambial Activity in PlantsPLANT BIOLOGY, Issue 5 2003Y. Helariutta Abstract: Post-embryonic development is controlled by two types of meristems: apical and lateral. There has been considerable progress recently in understanding the function of root and shoot apical meristems at the molecular level. Knowledge of analogous processes in the lateral, or secondary, meristems, i.e. the vascular cambium or cork cambium, is, however, rudimentary. This is despite the fact that much of the diversity in the plant kingdom is based on the differential functions of these meristems, emphasizing the importance of lateral meristems in the development of different plant forms. The vascular cambium is particularly important for woody plants, but it also plays an important role during the development of various herbaceous species, such as Arabidopsis thaliana. In this review, we focus on the two basic functions of cambial activity: cell proliferation and pattern formation. [source] Environmental and hormonal regulation of the activity,dormancy cycle in the cambial meristem involves stage-specific modulation of transcriptional and metabolic networksTHE PLANT JOURNAL, Issue 4 2007Nathalie Druart Summary We have performed transcript and metabolite profiling of isolated cambial meristem cells of the model tree aspen during the course of their activity,dormancy cycle to better understand the environmental and hormonal regulation of this process in perennial plants. Considerable modulation of cambial transcriptome and metabolome occurs throughout the activity,dormancy cycle. However, in addition to transcription, post-transcriptional control is also an important regulatory mechanism as exemplified by the regulation of cell-cycle genes during the reactivation of cambial cell division in the spring. Genes related to cold hardiness display temporally distinct induction patterns in the autumn which could explain the step-wise development of cold hardiness. Factors other than low temperature regulate the induction of early cold hardiness-related genes whereas abscisic acid (ABA) could potentially regulate the induction of late cold hardiness-related genes in the autumn. Starch breakdown in the autumn appears to be regulated by the ,short day' signal and plays a key role in providing substrates for the production of energy, fatty acids and cryoprotectants. Catabolism of sucrose and fats provides energy during the early stages of reactivation in the spring, whereas the reducing equivalents are generated through activation of the pentose phosphate shunt. Modulation of gibberellin (GA) signaling and biosynthesis could play a key role in the regulation of cambial activity during the activity,dormancy cycle as suggested by the induction of PttRGA which encodes a negative regulator of growth in the autumn and that of a GA-20 oxidase, a key gibberellin biosynthesis gene during reactivation in spring. In summary, our data reveal the dynamics of transcriptional and metabolic networks and identify potential targets of environmental and hormonal signals in the regulation of the activity,dormancy cycle in cambial meristem. [source] Identification, measurement and interpretation of tree rings in woody species from mediterranean climatesBIOLOGICAL REVIEWS, Issue 1 2003PAOLO CHERUBINI ABSTRACT We review the literature dealing with mediterranean climate, vegetation, phenology and ecophysiology relevant to the understanding of tree-ring formation in mediterranean regions. Tree rings have been used extensively in temperate regions to reconstruct responses of forests to past environmental changes. In mediterranean regions, studies of tree rings are scarce, despite their potential for understanding and predicting the effects of global change on important ecological processes such as desertification. In mediterranean regions, due to the great spatio-temporal variability of mediterranean environmental conditions, tree rings are sometimes not formed. Often, clear seasonality is lacking, and vegetation activity is not always associated with regular dormancy periods. We present examples of tree-ring morphology of five species (Arbutus unedo, Fraxinus ornus, Quercus cerris, Q. ilex, Q. pubescens) sampled in Tuscany, Italy, focusing on the difficulties we encountered during the dating. We present an interpretation of anomalies found in the wood structure and, more generally, of cambial activity in such environments. Furthermore, we propose a classification of tree-ring formation in mediterranean environments. Mediterranean tree rings can be dated and used for dendrochronological purposes, but great care should be taken in selecting sampling sites, species and sample trees. [source] Xylem heterochrony: an unappreciated key to angiosperm origin and diversificationsBOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009SHERWIN CARLQUIST fls All angiosperms can be arranged along a spectrum from a preponderance of juvenile traits (cambial activity lost) to one of nearly all adult characters (cambium maximally active, mature patterns realized rapidly early in ontogeny). Angiosperms are unique among seed plants in the width of this spectrum. Xylem patterns are considered here to be indicative of contemporary function, not relictual. Nevertheless, most families of early-divergent angiosperms exhibit paedomorphic xylem structure, a circumstance that is most plausibly explained by the concept that early angiosperms had sympodial growth forms featuring limited accumulation of secondary xylem. Sympodial habits have been retained in various ways not only in early-divergent angiosperms, but also among eudicots in Ranunculales. The early angiosperm vessel, relatively marginal in conductive abilities, was improved in various ways, with concurrent redesign of parenchyma and fibre systems to enhance conductive, storage and mechanical capabilities. Flexibility in degree of cambial activity and kinds of juvenile/adult expressions has been basic to diversification in eudicots as a whole. Sympodial growth that lacks cambium, such as in monocots, provides advantages by various features, such as organographic compartmentalization of tracheid and vessel types. Woody monopodial eudicots were able to diversify as a result of production of new solutions to embolism prevention and conductive efficiency, particularly in vessel design, but also in parenchyma histology. Criteria for paedomorphosis in wood include slow decrease in length of fusiform cambial initials, predominance of procumbent ray cells and lesser degrees of cambial activity. Retention of ancestral features in primary xylem (the ,refugium' effect) is, in effect, a sort of inverse evidence of acceleration of adult patterns in later formed xylem. Xylem heterochrony is analysed not only for all key groups of angiosperms (including monocots), but also for different growth forms, such as lianas, annuals, various types of perennials, rosette trees and stem succulents. Xylary phenomena that potentially could be confused with heterochrony are discussed. Heterochronous xylem features seem at least as important as other often cited factors (pollination biology) because various degrees of paedomorphic xylem are found in so many growth forms that relate in xylary terms to ecological sites. Xylem heterochrony can probably be accessed during evolution by relatively simple gene changes in a wide range of angiosperms and thus represents a current as well as a past source of variation upon which diversification was based. Results discussed here are compatible with both current molecular-based phylogenetic analyses and all recent physiological work on conduction in xylem and thus represent an integration of these fields. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 26,65. [source] | ||||||||||