True dichotomies in seedlings of Pinus radiata

1976 ◽  
Vol 54 (9) ◽  
pp. 1020-1022
Author(s):  
Richard T. Riding
Keyword(s):  
Shoot Apex ◽  
Pinus Radiata ◽  
Vascular Tissue

Histological observations of bifurcating seedlings of Pinus radiata revealed that this phenomenon resulted from a dichotomy of the shoot apex into two meristems. Vascular tissue passed equally into the two branches of the dichotomy.

Ovule and seed development in Pinus radiata: postmeiotic development, fertilization, and embryogeny

1976 ◽  
Vol 54 (18) ◽  
pp. 2141-2154 ◽  
Author(s):  
Barbara S. Lill
Keyword(s):  
Seed Development ◽  
Pinus Radiata ◽  
Vascular Tissue ◽  
Small Cells ◽  
Dense Cytoplasm ◽  
Procambial Strand ◽  
Embryo Maturity

Development of ovule tissues in Pinus radiata after meiosis, fertilization, and embryogeny is comparable with that of other pines, but P. radiata takes longer to develop. Fertilization occurs 15 months after pollination and morphological embryo maturity is reached 5 months later. In ovules harvested in spring after meiosis, a curved band of small cells with dense cytoplasm extends from the chalazal end of the ovule to the vascular tissue of the ovuliferous scale. It is interpreted as a procambial strand, which in the next year, differentiates basipetally into elongated, thick-walled cells with degenerated nuclei.

The opening and shedding mechanism of the female cones of Pinus radiata

1964 ◽  
Vol 12 (2) ◽  
pp. 125 ◽  
Author(s):  
R Allen ◽  
AB Wardrop
Keyword(s):  
Pinus Radiata ◽  
Radial Growth ◽  
Secondary Wall ◽  
Vascular Tissue ◽  
Middle Layer ◽  
Cell Axis ◽  
Vascular Connection ◽  
Differential Shrinkage ◽  
Longitudinal Cell ◽  
Cone Scale

The opening of the female cones of P. radiata has been shown to result from differential shrinkage between the adaxial vascular tissue and the abaxial sclerenchyma of the cone scale. The organization of the secondary wall of the tracheids typically consists of three helically organized concentric layers. In the outer and inner layers the microfibrillar orientation is approximately transverse, and in the middle layer the helix makes an angle of c. 40° with the longitudinal cell axis. In the sclerenchyma the secondary wall consists of wide layers in which the microfibrils of the lamellae are almost transverse to the longitudinal cell axis, alternating with narrow layers in which the microfibrils of the lamellae are almost parallel to the cell axis. Opening is preceded by a severance of the vascular connection between the cone and the stem or branch by the occlusion of the lurnina of the tracheids of the peduncle with resin. As radial growth of the stem proceeds, small fissures develop between the xylem of the stem or branch and that of the cone peduncle. The fissures become filled with resin and there is a progressive erosion of the tracheids of the peduncle until ultimately the xylem of the peduncle is separated from that of the stem or branch.

scholarly journals Single-cell analysis resolves the genetic program of primary vascular system formation in hybrid poplar

2021 ◽  
Author(s):  
Daniel Conde ◽  
Paolo M. Triozzi ◽  
Wendell J. Pereira ◽  
Henry W. Schmidt ◽  
Kelly M. Balmant ◽  
...  
Keyword(s):  
Gene Expression ◽  
Single Cell ◽  
Shoot Apex ◽  
Vascular Tissue ◽  
Vascular System ◽  
Developmental Trajectories ◽  
Specific Gene ◽  
Cell Type ◽  
Woody Perennials ◽  
Cell Type Specific

Despite the enormous potential of novel approaches to explore gene expression at a single-cell level, we lack a high-resolution and cell type-specific gene expression map of the shoot apex in woody perennials. We use single-nuclei RNA sequencing to determine the cell type-specific transcriptome of the Populus vegetative shoot apex. We identified highly heterogeneous cell populations clustered into seven broad groups represented by 18 transcriptionally distinct cell clusters. Next, we established the developmental trajectories of epidermal cells, leaf mesophyll, and vascular tissue. Motivated by the high similarities between Populus and Arabidopsis cell population in the vegetative apex, we created and applied a pipeline for interspecific single-cell expression data integration. We contrasted the developmental trajectories of primary phloem and xylem formation in both species, establishing the first comparison of primary vascular development between a model annual herbaceous and a woody perennial plant species. Our results offer a valuable resource for investigating the basic principles underlying cell division and differentiation conserved between herbaceous and perennial species, which also allows the evaluation of the divergencies at single-cell resolution.

scholarly journals Experimental investigations of the shoot apex of Dryopteris aristata Druce

1947 ◽  
Vol 232 (589) ◽  
pp. 343-384 ◽  
Keyword(s):  
Shoot Apex ◽  
Apical Meristem ◽  
Vascular Tissue ◽  
Normal Development ◽  
Vascular System ◽  
Leaf Primordia ◽  
Terminal Region ◽  
Main Shoot ◽  
Marked Contrast ◽  
Medullary Parenchyma

A method whereby the apical meristem of the fern Dryopteris aristata Druce can be partially isolated from the adjacent lateral organs and tissues is described. This procedure has been adopted as a means of investigating growth and morphogenesis at the shoot apex. The technique involves the severance of the incipient vascular tissue which originates immediately below the apical meristem; the isolated meristem is thus seated on a plug of growing medullary parenchyma. Leaf primordia can be similarly isolated. Meristems treated in this way are capable of growth. They develop into short vasculated shoots bearing leaves. The nutrients sustaining this growth must reach the apical meristem from below by diffusing through medullary parenchyma at the base of the isolated terminal region. Above the parenchymatous region a solenostelic vascular system is present in the new axis; this is in marked contrast to the dictyostelic configuration of the parental shoot below. On the further growth of the isolated meristem leaves are produced and the stele becomes dictyostelic. The new leaves, of which as many as fourteen have been observed after 11 weeks’ growth, show the normal phyllotactic arrangement, and this is continuous with that of the main shoot below. The procedure adopted has the effect of removing the physiological dominance of the apical meristem relative to the main shoot; thus numerous large buds develop on the lateral segments of the parental shoot but none on the isolated terminal region. The growth of isolated leaf primordia is very limited. The vascular system develops as a solenostele, foliar gaps are not formed in the region of confluence with the shoot stele, axillary buds are developed, and the leaf apex becomes directed outwards. These several features are in marked contrast to the normal development. The isolated lateral segments are also capable of further growth. The experimental procedure adopted involves the severance of the vascular tissues at various levels. An account is given of new and hitherto unrecorded morphological developments observed in these segments. Interesting features include the formation of large solenostelic buds, the solenostelic development of isolated meristeles, medullation of meristeles and the induction of a polycyclic stelar condition, in one instance by a process of cambium-like activity. These are all in marked contrast to the normal development of the intact shoot. The data which have been obtained are discussed with special reference to the path of translocation of nutrients to the terminal meristem and to leaf primordia, morphogenetic processes at the shoot apex, the factors influencing the differentiation of the vascular system, and theories of shoot formation and constitution. The results of these experiments give no support to phytonic theories but emphasize the difference in potentiality for development between shoot and leaf primordia. In this connexion the factors which determine the shape and system of segmentation of the apical initials of shoot and leaf are seen to require further investigation. The hypotheses that lateral buds are inhibited by substances proceeding from the apical meristem, that the initial differentiation of vascular tissue can be attributed to the basipetal diffusion of a substance or substances from the actively growing apical meristem, and that under conditions of tensile stress incipient vascular tissue undergoes a parenchymatous development, are supported by the data of these experiments. The observations afford a clear indication of the diversity of the morphogenetic activity in the growing region. Nutritional, mechanical and other factors are seen to be important in influencing the distribution of tissues during development. The view entertained by comparative morphologists that the vascular system in ferns is of a highly conservative nature and therefore of great value in phyletic studies is to some extent opposed by the data of these experiments. But notwithstanding the several unusual vascular configurations produced as a result of the experimental treatment, there is eventually a return to the typical vascular arrangements of the normal shoot. There is thus a need for harmonizing the data of the causal and phyletic aspects. The more thoroughly the operation of morphogenetic factors extrinsic to the specific hereditary substance is understood, the more critical will be the selection of criteria of comparison for phyletic purposes.

The comparative investigation of apices of vascular plants by experimental methods

1950 ◽  
Vol 234 (620) ◽  
pp. 583-602 ◽  
Keyword(s):  
Shoot Apex ◽  
Vascular Plants ◽  
Vascular Tissue ◽  
Vascular System ◽  
Subsequent Development ◽  
Comparative Investigation ◽  
Lateral Organs ◽  
Experimental Treatments ◽  
Leaf Insertion ◽  
Axial Growth

A considerable diversity of histological constitution is to be found in the apices of seed plants, and these again differ notably from those of eusporangiate and leptosporangiate ferns. Yet, in their growth and morphogenetic activity, the vegetative apices of all classes of vascular plants have much in common, i.e. they give rise to a vasculated axis with regularly disposed lateral members. Comparative investigations of apices by strictly anatomical methods have definite limits which are soon reached. In the present investigation the aim was to see if, when the same experimental treatments are applied to very differently constituted apices, closely comparable or divergent organographic developments ensue. When the shoot apex in selected eusporangiate and leptosporangiate ferns and in species of Primula was isolated by vertical incisions from the lateral organs and tissues, with concomitant severing of the incipient vascular tissue or procambium, the apex continued to grow and gave rise to a short vasculated leafy shoot in which the normal anatomical pattern was soon reconstituted. Relevant data for Dryopteris aristata have appeared in earlier volumes of these Transactions . Comparable data for eusporangiate and other leptosporangiate ferns are now described and illustrated. In Primula , in and just above the region of the incisions, the vascular tissue of the new axial growth was in the form of an uninterrupted ‘cylinder’, conforming in outline with the triangular or rectangular contour of the isolated plug. The experimental materials have afforded clear evidence of a basipetal development of vascular tissue from pith cells, strands of the new vascular system eventually becoming conjoined with those of the parent shoot. In the leaf-bearing region of the new shoot the vascular cylinder was interrupted by leaf gaps as in the normal development in Primula and in ferns. A prevascular ring, with foliar gaps in the regions of leaf insertion, is present at the shoot apex in Primula , this being comparable with the arrangements in ferns such as Dryopteris. When all the very young leaf promordia were successively removed, the shoot was found to have an uninterrupted ring of vascular tissue, as in equivalent experiments with Dryopteris and other ferns. The experimental data so far obtained thus show that when the same treatments are applied to very differently constituted apices, closely comparable results are obtained. The implications of this finding are discussed in relation to (i) the importance of the cellular constitution of apices in organogenesis, (ii) the the diversity of apical constitution in vascular plants at large, (iii) the apex as a self-determining region, (iv) the inception and subsequent development of the vascular system in different classes of plants, and (v) the relative contributions of axis and leaves to the vascular system.

Elemental Analysis of Phloem Tissue in Lemna Minor Root Tips

1980 ◽  
Vol 38 ◽  
pp. 798-799
Author(s):  
Patrick Echlin ◽  
Thomas Hayes ◽  
Clifford Lai ◽  
Greg Hook
Keyword(s):  
Vascular Tissue ◽  
Lemna Minor ◽  
Atomic Weight ◽  
Companion Cell ◽  
Root Tips ◽  
Phloem Tissue ◽  
Cell Stage ◽  
Phloem Parenchyma ◽  
Parenchyma Cells ◽  
Xylem Element

Studies (1—4) have shown that it is possible to distinguish different stages of phloem tissue differentiation in the developing roots of Lemna minor by examination in the transmission, scanning, and optical microscopes. A disorganized meristem, immediately behind the root-cap, gives rise to the vascular tissue, which consists of single central xylem element surrounded by a ring of phloem parenchyma cells. This ring of cells is first seen at the 4-5 cell stage, but increases to as many as 11 cells by repeated radial anticlinal divisions. At some point, usually at or shortly after the 8 cell stage, two phloem parenchyma cells located opposite each other on the ring of cells, undergo an unsynchronized, periclinal division to give rise to the sieve element and companion cell. Because of the limited number of cells involved, this developmental sequence offers a relatively simple system in which some of the factors underlying cell division and differentiation may be investigated, including the distribution of diffusible low atomic weight elements within individual cells of the phloem tissue.

Clinical aspects of reactive oxygen and nitrogen species

2004 ◽  
Vol 71 ◽  
pp. 121-133 ◽  
Author(s):  
Ascan Warnholtz ◽  
Maria Wendt ◽  
Michael August ◽  
Thomas Münzel
Keyword(s):  
Oxidative Stress ◽  
Reactive Oxygen Species ◽  
Risk Factor ◽  
Endothelial Dysfunction ◽  
Vascular Tissue ◽  
Rapid Development ◽  
Reactive Oxygen ◽  
Clinical Aspects ◽  
No Production ◽  
Oxygen Species

Endothelial dysfunction in the setting of cardiovascular risk factors, such as hypercholesterolaemia, hypertension, diabetes mellitus and chronic smoking, as well as in the setting of heart failure, has been shown to be at least partly dependent on the production of reactive oxygen species in endothelial and/or smooth muscle cells and the adventitia, and the subsequent decrease in vascular bioavailability of NO. Superoxide-producing enzymes involved in increased oxidative stress within vascular tissue include NAD(P)H-oxidase, xanthine oxidase and endothelial nitric oxide synthase in an uncoupled state. Recent studies indicate that endothelial dysfunction of peripheral and coronary resistance and conductance vessels represents a strong and independent risk factor for future cardiovascular events. Ways to reduce endothelial dysfunction include risk-factor modification and treatment with substances that have been shown to reduce oxidative stress and, simultaneously, to stimulate endothelial NO production, such as inhibitors of angiotensin-converting enzyme or the statins. In contrast, in conditions where increased production of reactive oxygen species, such as superoxide, in vascular tissue is established, treatment with NO, e.g. via administration of nitroglycerin, results in a rapid development of endothelial dysfunction, which may worsen the prognosis in patients with established coronary artery disease.

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