Development cambium

Bildungs-geschwindigkeit,/. speed of formation or development, -gleichung, /. equation of formation structural equation, -schicht, /. formative layer specif.. (Bot.) cambium, -warme, /. heat of formation, -weise, /. mode of formation, bildwerfen, v.t. project (trtctures). 

Tn its normal polar, downward movement, the auxin stimulates the cells below the tip to elongate and sometimes to divide. Specific tissues, notably the cambium, are caused to divide laterally by auxin coming from the developing buds, which accounts for the wave of cell division occurring in tree trunks in the spring. Stimulation of other stem cells to divide... 

Pig. 64.—Photomicrograph of a transverse section of an old portion of California Privet root, showing completed secondary development. Note the prominent medullary rays (mr) cork (cfe) phellogen (,ph) secondary cortex (between ph and p ) protophloem (p )i secondary phloem ( ) cambium (c) secondary xylem tracheae (0 wood fibers (w/) and piotoxylem ( ). 

Abnonnal Structure of Dicotyl Roots.—In certain Dictoyl roots as Amaranthus, Jalap, Pareira, and Phytolacca, after the normal bundle system has been formed, there then develop successive cambiums outside of these bundles, producing concentric series of open collateral bundles. 

In Strychnos Nux Vomica internal phloem exactly as in Gelse-mium, etc., appears but in addition interxylary phloem is developed. In the wood region of this plant axis the cambium starts at a certain age fo lay down patches of phloem which become wedged in between xylem tissue as interxylary phloem. ... 

At times when a plant needs to slow down growth and assume a resting stage (dormant), abscisic acid is produced in the terminal bud, which slows down growth and directs the leaf primordia to develop scales that protect the dormant bud during winter. Since the hormone also inhibits cell division in the vascular cambium, both primary and secondary growth is put on hold during winter. 

Cells that have been formed recently at the vascular cambium have only a very thin primary cell wall. Even in the fully lignified cell the primary wall is very thin (0.1 j,m) and can be hard to distinguish from or isolate from the middle lamella many studies analyse the two together (ML+P) and relate results to the compound middle lamella (CML), a term which embraces both middle lamella and primary wall. The primary wall displays both elasticity and plasticity (permanent extension) during early cell growth and extension - at this stage in tracheid cell development... 

The three principal portions of a tree are the wood or xylem, the inner bark or phloem, and the outer bark. During the growing season, xylem is laid down on the inside, and phloem on the outside, of the vascular cambium. In the wood of the Gymnospermae (softwoods), all of which are arborescent and which began to develop some 300 million years ago, the principal wood element is the tracheid, whereas the 100-million-years younger, arborescent Angiospermae (hardwoods) are characterized by the presence of fibers and vessels. Both woods also contain parenchyma cells, especially in the rays. 

Our recent research suggests organ-, tissue-, and cell-specific localization of constitutive and induced terpenoid defense pathways in conifers. For example, linalool synthase (PaTPS-Lin) seems to be preferentially expressed in needles of Norway spruce and Sitka spruce with little or no expression in sterns. ft is also likely that expression of PaTPS-Lin in spruce needles is not associated with resin ducts but could reside in other cells involved with induced terpenoid emission. In contrast, we can speculate that most other mono-TPS and di-TPS are associated with epithelial cells of constitutive and induced resin ducts. The possible localization of conifer sesqui-TPS is difficult to predict. Furthermore, the exact spatial and temporal patterns of terpenoid pathway gene expression associated with traumatic resin duct development in the cambium zone and outer xylem remain to be studied at the tissue and cell level. In situ hybridization and immuno-localization of TPS will address these open questions. These methods have worked well in identifying cell type specific gene and protein expression of alkaloid formation in opium poppy Papaver somniferum) As the biochemistry of induced terpene defenses and the development of traumatic resin ducts have been well described in spruce, this system is ideal for future studies of tissue- and cell-specific localization of transcripts and proteins associated with oleoresin defense and induced volatile emissions in conifers. In addition, the advent of laser dissection microscopy techniques presents a fascinating means by which to further address RNA and protein analysis in a tissue-and cell-specific manner. These techniques, when applied to the cambium zone, xylem mother cells, and the epithelial cells that surround traumatic resin ducts, and will allow a temporal and spatial analysis of cellular functions occurring in the traumatic resin response. 

Although roots, particularly the root apices, are a major site of cytokinin biosynthesis in plants, there is evidence now that other meristematic tissues and organs including the cambium, developing buds, seeds and fruits and the embryonic axis of germinating seed have the ability to synthesize cytokinins under optimal growth conditions [6, 14]. Recently, stem and leaves have also been shown to be additional sites of cytokinin production [6]. The view that root-produced cytokinins move in the xylem to the shoot to participate in the control of development and senescence is widely accepted [15]. The major question that remains to be clarified is under what conditions the observed cytokinin activity in other plant parts is derived solely from the roots, and when, and to what degree it is derived by synthesis in situ. 

Evolutionarily and developmentally, the absence of leaves and roots in Cuscuta may be the reason for scanty primary xylem formation and the absence of a cambium. The primary phloem can transport host-derived assimilate all along the region of growth. Hence, in the absence of bidirectional development the cambium and its derivatives have become redundant in this dicot. 

The paucity of information about hormonal action on the regeneration of cambium is compensated for somewhat by the more extensive literature on the normal development of cambium. Since Reinders-Gouwentak (1965) reviewed the pre-1960 literature, some important papers have been published. To the already known effects of auxin, they have added information on the action of later discovered hormones. 

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