Interfascicular Regions Research Articles

Development of the vascular system in the inflorescence stem of Arabidopsis

Summary • The development of the vasculature in the inflorescence stem and pedicel of two common Arabidopsis thaliana ecotypes is reported, describing the tissues and events in primary and secondary growth of the stem vasculature. • Light and transmission electron microscopy was used to investigate the vascular system during plant growth; cellulose, lignin and callose were detected by cytochemistry. • The innermost cortical layer differentiated as a starch sheath during primary growth. The outermost parenchymatous layers of the interfascicular region lignified the walls at the onset of fascicular cambium activity. The secondary structure formed during silique production. In the internodes, the interfascicular cambium was mainly produced by starch sheath cells. In the interfascicular arcs of the internode, the secondary xylem mainly consists of xylem parenchyma whereas in the bundle region, it comprises vessels. Secondary phloem and xylary fibres were produced in limited quantities. Medullary sheath and phloem cap cells also became lignified. • The results show that the secondary vasculature develops in the stem and pedicel, and that, simultaneously, some primary tissues lignify, enhancing stem rigidity. Secondary vasculature is compared with the vascular alterations reported for some mutants.

Fibers. A model for studying cell differentiation, cell elongation, and cell wall biosynthesis.

A prominent anatomical feature in the inflorescence stems of Arabidopsis is the presence of fiber cells in the interfascicular regions (Fig. [1][1]). The feasibility of using interfascicular fibers in the inflorescence stems of Arabidopsis as a model for studying cell differentiation, cell

IFL1, a gene regulating interfascicular fiber differentiation in Arabidopsis, encodes a homeodomain-leucine zipper protein.

Arabidopsis inflorescence stems develop extraxylary fibers at specific sites in interfascicular regions. The spatial specification of interfascicular fiber differentiation is regulated by the INTERFASCICULAR FIBERLESS1 (IFL1) gene because mutation of that gene abolishes the formation of normal interfascicular fibers in Arabidopsis stems. To understand further the role of IFL1 in the specification of fiber differentiation, we cloned the IFL1 gene by using a positional cloning strategy. Sequence analysis showed that the IFL1 gene encodes a transcription factor that has the same features as a family of homeodomain-leucine zipper (HD-ZIP) proteins found only in plants. The predicted IFL1 protein is composed of three distinct domains, including a 60-amino acid HD at the N terminus followed by a 28-amino acid ZIP motif and a 724-amino acid C-terminal region. A nuclear targeting assay showed that IFL1 is able to direct a beta-glucuronidase fusion protein into the nucleus, which is consistent with IFL1's presumed function as a transcription factor. Gene expression analysis demonstrated that the IFL1 gene is expressed in the interfascicular regions in which fibers differentiate, which is consistent with its role in the control of interfascicular fiber differentiation. Furthermore, the IFL1 gene was shown to be expressed in the vascular regions, indicating its possible role in the regulation of vascular tissue formation. This possibility is supported by the observation that differentiation of both xylary fibers and vessel elements is altered in the vascular bundles of ifl1 mutants. Our results provide direct evidence that an HD-ZIP protein plays a role in the spatial control of fiber differentiation.

Anatomical Investigations on Campanula L. Taxa That Distributed in (B3) Eskisehir Region

The anatomy of roots, stems and leaves of Campanula L. taxa occuring Following taxa are compared; in Eskisehir have been investigated as anatomical. According to results obtaining from anatomical studies; Subgen.CAMPANULA: Campanula lyrata Lam., subsp. lyrata (sect. Quinqueloculares) C. rapunculoides L, subsp. cordifolia (C.Koch) (sect.Campanula), C. glomerata L.subsp. hispida (Witasek) Hayek.(sect.Involucrata), C. argaea Boiss. et Bal. (sect.Spicatae), C. cymbalaria Sm.(sect.Saxicolae), Subgen.RAPUNCULUS: C. persicifolia L.(sect.Rapunculus), C. olympica Boiss.(sect. Rapunculus). C.lyrata subsp.lyrata and C.argaea are endemics to Turkey. In consequence of the investigation at the and of the anatomical examing of taking sections from roots, stems and leaves, the structures which include general diagnostic properties of taxa are hairs on epiderm of stem and leaves; and laticifers in roots and stems are present or not, collenchymatic tissues at cortex is found or not, interfascicular region in roots is wide or narrow, mesophyll tissue at leave is bifacial or not.

Anatomical Changes Which Occur in Cuttings of Agathis australis (D. Don) Lindl 1. Wounding Responses

The basal and sub-basal regions in cuttings of Agathis australis undergo a complex series of anatomical changes. Many of these are categorized as wound responses and include cell divisions associated with the cut base and the proliferation of tracheids and phloem which arise in the interfascicular region about 4 mm above the cut base. The vascular tissue arcs outwards and downwards through the cortex. It may develop as isolated strands only a few cells wide or as sheets involving a number of cells. The precise pattern of vascular development appears to be determined by its extent at the point of origin and by the presence of obstacles such as primary and secondary resin canals which are located to the outside of the vascular bundles in the stem. Secondary resin canals are produced only in the rooting zone in cuttings that show extensive cell division. They arise schizogenously and do not form an interlinking network. Root primordia arise in the cortex at the end of isolated strands of newly developed vascular tissue. Primordia never form in association with sheets of tracheids or after the convergence of strands. In some cases virtually the entire sub-base is filled with vascular tissue as a result of cell division and the differentiation of parenchymatous tissue. Root primordia never appear in this situation.

Anatomy of Nodes Vs. Internodes in Coleus: The Nodal Cambium

Secondary growth begins in the nodal regions before the internodal regions in Coleus, so that longitudinally discontinuous vascular cambia are formed in the 6th through the 9th or 10th nodes, where the internodal cambium becomes continuous between nodal cambia. The nodal cambia are identifiable by radial seriation in interfascicular regions, typical cytology of fusiform initials, and the presence of a ray system. Anatomical features distinct from the primary plant body are shared by the nodal and internodal cambia. Branching of primary vascular strands, restricted to procambium and phloem, is virtually confined to nodal regions. In secondary growth, vascular branching of xylem and phloem occurs in both nodes and internodes. Xylem strand branches are formed only from derivatives of vascular cambia. It is proposed that the cambium provides the secondary plant body an efficient channel for lateral auxin transport, by which branching across interfascicular regions is facilitated.

ANATOMY OF NODES VS. INTERNODES IN COLEUS: THE NODAL CAMBIUM

Secondary growth begins in the nodal regions before the internodal regions in Coleus, so that longitudinally discontinuous vascular cambia are formed in the 6th through the 9th or 10th nodes, where the internodal cambium becomes continuous between nodal cambia. The nodal cambia are identifiable by radial seriation in interfascicular regions, typical cytology of fusiform initials, and the presence of a ray system. Anatomical features distinct from the primary plant body are shared by the nodal and internodal cambia. Branching of primary vascular strands, restricted to procambium and phloem, is virtually confined to nodal regions. In secondary growth, vascular branching of xylem and phloem occurs in both nodes and internodes. Xylem strand branches are formed only from derivatives of vascular cambia. It is proposed that the cambium provides the secondary plant body an efficient channel for lateral auxin transport, by which branching across interfascicular regions is facilitated.

HYPOCOTYL SWELLING IN MARROW SEEDLINGS IN RESPONSE TO 2,4‐D TREATMENT

SummarySwelling of the hypocotyl base was induced in marrow seedlings by incubation in 2,4‐D concentrations in the range 0·001 to 1·0 p.p.m. This swelling resulted partly from cell enlargement and partly from increased cell division. The radial enlargement of cells was not achieved at the expense of longitudinal cell extension, unlike many instances where swelling has been induced by ethylene. Increased cell division was most pronounced in the interfascicular region of the hypocotyl, indicating increased cambial activity in this area.

Anatomy of the primary-secondary transition zone in stems of Populus deltoides

The transition from primary to secondary stem tissues occurs as a continuum, and a precise anatomical definition of the transition does not exist. A definition was derived for Populus deltoides based on the birefringent properties of the fiber wall. This definition was quantitatively reproducible in the 9 plants tested, and the secondary transition was found to occur in the internode associated with the first mature leaf from the apex. The primary-secondary transition did not occur uniformly around the periphery. It was first observed in the vascular bundles opposite the incoming trace, and from there it progressed in a counter-clockwise direction. Within the transition internode, each vascular bundle and each tissue comprising the bundle differentiated in accord with the physiological age and the phyllotactic disposition of the developing leaf to which it led. Within any one vascular bundle, differentiation occurred first in the metaxylem vessels and associated fibers, followed closely by extension of fibers into the interfascicular regions and centripetal differentiation of the phloem fibers. The ontogenetic sequence of differentiation for each of the principal tissues of the secondary transition zone is described.

Changes in the Petiole of Leaves of Manihot esculenta (Crantz), on Rooting

The effects of age of leaf and of application of synthetic hormone on the ability to produce roots, were investigated in leaves of Manihot esculenta. It was found that the age of the leaf was not critical to the process, but that the application of hormone resulted in an early and prolific production of roots. The anatomy of the rooted petiole was investigated and was found to differ from that of an unrooted petiole in three respects: in an increase in the amount of secondarily produced tissues; in the incomplete lignification of the secondary xylem and in the production of adventitious roots from the interfascicular regions of the basal end.

FACTORS CONTROLLING CAMBIAL DEVELOPMENT IN THE HYPOCOTYL OF RICINUS COMMUNIS L.*

SUMMARY The development of the cambium in the interfascicular region of young castor bean hypocotyls was investigated under various experimental conditions. The cotyledons were found to be indispensable for the onset of cambial development. Young isolated hypocotyls developed a cambium when cultured in a simple medium lacking phytohormones but fortified with sucrose. Addition of indole-3-acetic acid to the medium did not enhance the rate of cambial development. When 2,3,5-triiodobenzoic acid was added, the typical acropetal extension of cambial development in the hypocotyl was maintained. Gibberellic acid (GA3) was found to have strong stimulatory properties, and, when combined with sucrose, to be capable of inducing a rate of cambial development comparable to that in the intact plant. Inhibitors of gibberellin biosynthesis applied to a hypocotyl-cotyledon system cultured in vitro or sprayed on the cotyledon of a decapitated seedling in vivo, depressed cambial development in the hypocotyl. Simultaneous application of gibberellic acid in the spray experiments restored the original level of cambial development. The significance of the present findings is discussed in relation to the prevailing concept of cambial stimulation.

Developmental Changes in the Vascular Cambium of Polygonum lapathifolium

Developmental changes in the vascular cambium of Polygonum lapathifolium were determined primarily by an analysis of the secondary xylem. The cambium and xylem consist of fascicular and interfascicular regions in this herbaceous dicotyledon. Near the pith vessels are restricted to the fascicular regions of the xylem. During secondary growth vessels are formed in some radial files in the interfascicular regions. Anticlinal divisions are of two types, oblique and lateral. In interfascicular files consisting of fibers only, about two-thirds of the anticlinal divisions are oblique. The oblique partition averages 31% of the length of the dividing initials. In interfascicular files consisting of vessel elements and fibers, there are almost equal numbers of oblique and lateral divisions. The oblique partition averages 37% of the length of the dividing initials in these files. Lateral divisions account for approximately three-fifths of the anticlinal divisions in the fascicular regions, consisting of vessel elements and fibers. The partitions formed in oblique anticlinal divisions average 64% of the length of the dividing cells in the fascicular regions. The frequency of anticlinal division is much higher in files consisting of vessel elements and fibers than in those consisting of fibers only. There is no loss of fusiform initials, except by ray formation. Ray initiation occurs by simple subdivision of fusiform initials. The findings are discussed in relation to the developmental changes in the vascular cambium in plants of different habits.

DEVELOPMENTAL CHANGES IN THE VASCULAR CAMBIUM OF POLYGONUM LAPATHIFOLIUM

Developmental changes in the vascular cambium of Polygonum lapathifolium were determined primarily by an analysis of the secondary xylem. The cambium and xylem consist of fascicular and interfascicular regions in this herbaceous dicotyledon. Near the pith vessels are restricted to the fascicular regions of the xylem. During secondary growth vessels are formed in some radial files in the interfascicular regions. Anticlinal divisions are of two types, oblique and lateral. In interfascicular files consisting of fibers only, about two‐thirds of the anticlinal divisions are oblique. The oblique partition averages 31% of the length of the dividing initials. In interfascicular files consisting of vessel elements and fibers, there are almost equal numbers of oblique and lateral divisions. The oblique partition averages 37% of the length of the dividing initials in these files. Lateral divisions account for approximately three‐fifths of the anticlinal divisions in the fascicular regions, consisting of vessel elements and fibers. The partitions formed in oblique anticlinal divisions average 64% of the length of the dividing cells in the fascicular regions. The frequency of anticlinal division is much higher in files consisting of vessel elements and fibers than in those consisting of fibers only. There is no loss of fusiform initials, except by ray formation. Ray initiation occurs by simple subdivision of fusiform initials. The findings are discussed in relation to the developmental changes in the vascular cambium in plants of different habits.

A STUDY OF SIZE DIFFERENCES IN TWO STRAINS OF CUCURBITA PEPO L.: II. HISTOLOGICAL AND CELLULAR SIZE DIFFERENCES

Size differences were studied on the cellular level in vegetative organs of two purebred strains of Cucurbita pepo L. which differ greatly in inherited size.Mature organ size has been analyzed for the two strains on the histological and cellular levels with particular emphasis on mature internode size. Differences between the strains in tissue and cell size were observed for the main tissue and cell types. Differences in internode length were determined both by differences in cell size and cell numbers. Cambial activity as expressed in numbers of radial immature derivatives and in number of divisions in the interfascicular regions was found to be much greater in CF than in SRC.No important differences were found between the large and small strain in the size of the meristematic and submeristematic regions. Early internode growth in terms of cell division and cell enlargement was also found to be similar in the two strains. It is concluded that the cellular differences found in the mature organ must be due to a longer duration of growth mainly in terms of cell enlargement but also in terms of cell, division. This conclusion is supported by the results obtained on internode growth described in a previous paper.Grafting experiments with apical buds of the two strains did not show any influence of the stock on the scion; mature organ size was determined only by the scion.

Resin Secretion in Balsamorrhiza sagittata

1. Balsamorrhiza sagittata is the dominant member of its habitat in the inter-mountain region. The plant depends largely upon growth of the rootstock for propagation. It does not produce flowers until the third or fourth season. A hardy rootstock accounts for its dominance, since the viability of the seeds is small, due to parasitic infection. 2. The radicle has the tetrarch type of development. The resin canals of the root arise in two concentric rows above and including the hardy mid-rootstock, with radial canals between the longitudinal canals of the two series. Only the outer of the two series of canals is found in the lowest portion of the rootstock and the subsidiary roots. A twofold series of canals is found in the stem and leaves, an outer series in the sinuses of the cortex opposite the interfascicular regions, and a second inner series in the pith opposite the hadrome elements. The root canals and the stem canals arise as two separate systems and remain distinct. The resin canals do not arise until long after resin is formed in the meristem. 3. Balsamoresene and balsamoresinic acid are formed in B. sagittata from inulin, probably by polymerization and reduction. The resene and resinic acid are essentially toxic in nature. The resene is the immediate substance from which resinic acid is formed. The secretory process is dependent on physiological activity in the meristem of the plant, in which inulin is used in anabolism and resene and resinic acid are derived as waste products in the plant. The resinic acid and resene are transferred to the secretory canals, where they are stored. 4. To summarize, the study of B. sagittata, with especial emphasis to the meaning of resin secretion, has developed certain facts regarding the purpose of resin secretion. In the growth of the plant a polysaccharide, inulin, produced during photosynthesis, is broken down, causing a by-product, balsamoresene, to be produced. This resene is changed to resinic acid. On account of the probable toxic nature of the resene and resinic acid to the plant, they are translocated to schizogenously formed ducts of endodermal origin, where they are stored as resinic acid.