ROOT CONTRACTION IN HYACINTH. I. EFFECTS OF IAA ON DIFFERENTIAL CELL EXPANSION

Contractile roots of Hyacinthus orientalis L. cv ‘Pink Pearl’ shorten as a result of growth of inner cortical cells which expand radially and contract longitudinally. Brief treatment with IAA (indole-3-acetic acid—0.5 and 1.0 mg/1) induces subapical swelling, root cap proliferation and decreased rates of elongation in potentially contractile roots. Growth resumes with removal of IAA from the culture medium and contraction subsequently occurs. The pattern of subsequent contraction is affected by prior IAA treatment; contraction occurs in the normal manner both acropetal and basipetal to the points of IAA-induced swelling, but does not occur in the swollen region itself. Microscopic examination of the swollen region reveals that cells of the middle and outer cortex are radially expanded and longitudinally shortened relative to middle and outer cortical cells of contracted and uncontracted portions of the same root and control roots. In contrast, inner cortical cells in swollen regions of IAA-treated roots show approximately 50% less radial expansion than inner cortical cells of control contracted roots. Middle and outer cortical cells in the swollen region of IAA-treated roots undergo radial expansion, while middle and outer cortical cells in adjacent contracting zones are compressed by radially expanding inner cortical cells. Average volumes of cortical cells in the IAA-induced swollen region increased approximately two-fold when contraction occurred in adjacent regions. These results suggest that in hyacinth roots, under certain circumstances, inner and outer cortical cells alike possess the ability for growth reorientation and expansion. However, during the usual course of contractile root development, cells of the outer cortex are restricted in this ability, through an as yet unknown mechanism, and are passively compressed by the radially expanding inner cortical cells.     

Mechanism of Root Contraction in Gladiolus

A mechanism for root contraction in Gladiolus is proposed, basedon an ultrastructural study of the cortical parenchyma. Thedriving force of the process is presumed to be the differentialcompressive stress between atmospheric pressure and the negativepressure within the xylem. Early lysis of the middle lamellain the region of maturity, especially marked towards the innercortex, permits the inner cortical cells to respond to thispressure mainly by gliding among their neighbours while theouter cortical cells may glide somewhat but are mostly compressedlongitudinally and expanded radially. The outer cells becomemoribund, with dehydrated cytoplasm and loss of structure inthe cell organelles. Senescence and death take a centripetalcourse through outer and middle cortex, during which the dyingcells are progressively further compressed longitudinally, balloonedradially, and finally collapsed radially. As cell separationceases, the living cells of the inner cortex are also compressedsomewhat. However, they remain turgid, develop thick cell walls,and eventually resist further compression, bringing root contractionto an end.     

Ultrastructure of the haustorial interface and apoplastic continuum between host and the root hemiparasiteOlax phyllanthi (Labill.) R. Br. (Olacaceae)

Summary Structural features of haustorial interface parenchyma of the root hemiparasiteOlax phyllanthi are described. Walls contacting host xylem are thickened non-uniformly with polysaccharides, not lignin, and show only a thin protective wall layer when abutting pits in walls of host xylem vessels or tracheids. Lateral walls of interface parenchyma exhibit an expanded middle layer of open fibrillar appearance, sometimes with, but mostly lacking adjoining layers of dense wall material. Free ribosomes and rough endoplasmic reticulum are prominent and occasional wall ingrowths present. Experiments involving transpirational feeding of the apoplast tracers lanthanum nitrate or uranyl acetate to host roots cut below haustorial connections, indicate effective apoplastic transfer from host to parasite root via the haustorium. Deposits of the tracers suggest a major pathway for water flow through host xylem pits, across the thin protective wall layer, and thence into the haustorium via the electronopaque regions of the terminal and lateral walls of the contact parenchyma. Graniferous tracheary elements and walls of parenchyma cells of the body of the haustorium appear to participate in tracer flow as do walls of cortical cells, stele parenchyma and xylem conducting elements of the parasite root, suggesting that both vascular and non-vascular routes are involved in extracytoplasmic transfer of xylem sap from host to parasite. The Casparian strip of the endodermis and the suberin lamella of the exodermis of theOlax root act as barriers to flow within the system.     

Anatomy ofZea mays andGlycine max seedlings treated with triazole plant growth regulators

Soil drenches containing 250 μg of paclobutrazol or uniconazol (50 ml of a 17 μM solution) reduced the height of both corn (Zea mays L. cv. How.Sweet It Is) and soybean (Glycine max (L.) Merr. cv. A2) seedlings. With corn, uniconazol was considerably more active than paclobutrazol in reducing height whereas with soybean both compounds had similar dwarfing effects. The compounds increased foliar chlorophyll content and leaf thickness in soybean but had no effect on these parameters in corn. The increase in leaf thickness with soybean was due primarily to an increase in the thickness of the palisade cell layer. Chloroplast size and ultrastructure of both species were unaffected by the compounds. The growth regulators increased root diameter in both corn and soybean because of increased size of cortical parenchyma cells and particularly in soybean because of radial rather than longitudinal growth of the first few layers of the cortical parenchyma.     

Living cells in wood. 1. Absence,scarcity and histology of axial parenchyma as keys to function

The diversity of expression in axial parenchyma (or lack of it) in woods is reviewed and synthesized with recent work in wood physiology, and questions and hypotheses relative to axial parenchyma anatomy are offered. Cell shape, location, abundance, size, wall characteristics and contents are all characteristics for the assessment of the physiological functions of axial parenchyma, a tissue that has been neglected in the consideration of how wood histology has evolved. Axial parenchyma occurrence should be considered with respect to mechanisms for the prevention and reversal of embolisms in tracheary elements. This mechanism complements cohesion–tension‐based water movement and root pressure as a way of maintaining flow in xylem. Septate fibres can substitute for axial parenchyma (‘axial parenchyma absent’) and account for water movement in xylem and for the supply of carbohydrate abundance underlying massive and sudden events of foliation, flowering and fruiting, as can fibre dimorphism and the co‐occurrence of septate fibres and axial parenchyma. Rayless woods may or may not contain axial parenchyma and are informative when analysing parenchyma function. Interconnections between ray and axial parenchyma are common, and so axial and radial parenchyma must be considered as complementary parts of a network, with distinctive but interactive functions. Upright ray cells and more numerous rays per millimetre enhance interconnection and are more often found in woods that contain tracheids. Vesselless woods in both gymnosperms and angiosperms have axial parenchyma, the distribution of which suggests a function in osmotic water shifting. Water and photosynthate storage in axial parenchyma may be associated with seasonal changes and with succulent or subsucculent modes of construction. Apotracheal axial parenchyma distribution often demonstrates storage functions that can be read independently of osmotic water shifting capabilities. Axial parenchyma may serve to both enhance mechanical strength or, when parenchyma is thin‐walled, as a tissue that adapts to volume change with a change in water content. Other functions of axial parenchyma (contributing resistance to pathogens; a site for the recovery of physical damage) are considered. The diagnostic features of axial parenchyma and septate fibres are reviewed in order to clarify distinctions and to aid in cell type identification. Systematic listings are given for particular axial parenchyma conditions (e.g. axial parenchyma ‘absent’ with septate fibres substituting). A knowledge of the axial parenchyma information presented here is desirable for a full understanding of xylem function. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 291–321.     

Developmental and structural features of secretory canals in root and shoot wood of Copaifera langsdorffii Desf. (Leguminosae–Caesalpinioideae)

Copaifera langsdorffii Desf., popularly known as copaíba, is an oleoresin-producing tree has been overexploited in Brazil by the pharmaceutical, cosmetic and varnish industries. Despite the long history of the use of this species, the structural knowledge on the resin-producing sites remains inadequate and is limited to the trunk. The aim of this study was to describe the origin, structure and developmental features of secretory spaces present in shoot and root wood of C. langsdorffii, based on the usual techniques of wood anatomy studies. Both root and shoot wood present secretory canals distributed along the marginal parenchyma bands which delimit growth layers. Secretory canals are constituted by a locally biseriate epithelium and lume that contains terpenes. They are arisen in the cambial zone from fusiform cambial initial cells and, eventually, ray initials. The origin of lumen is schizogenous. The epithelial cells have meristematic potential and are responsible for the locally biseriate epithelium. Mature secretory canals are wider and are separated between themselves only by a row of radial cells. The fusion of these adjacent secretory canals is frequent and results from the radial cell collapse. The finding of an interconnected system of resin canals in C. langsdorffii might be of value in terms of sustainable extraction of the resin and realistically assess its sustainable harvest potential.     

Root Contraction in Hyacinthus orientalis

Root contraction is effected in many species by redirected growthof parenchyma cells, supplemented in some cases by other processes.In Hyacinthus, root contraction is associated with the growthof inner cortical cells, which after becoming fully elongatedin the normal growth of the root, then expand radially and contractlongitudinally. The contraction is, however, a growth process,since it occurs in turgid tissue and is partly reversible byplasmolysis. Moreover, the radial walls of the cells concernedincrease in area and the cells increase in volume. The changes in cell shape associated with contraction involvechanges in cell-wall structure which, in so far as they aredetectable by polarization microscopy, are described and discussedin the light of current views on cell-wall growth.     

Maximum axial and radial growth pressures of plant roots

Summary The axial root growth force exerted by seedlings of pea (Pisum sativum cv. Greenfeast), cotton (Gossypium hirsutum cv. Sicot 3) and sunflower (Helianthus annuus cv. Hysun) was measured. Effects of different seedling age and different batches of seeds on axial root growth pressure were investigated. Mean values of the maximum axial root growth pressure (P_a) estimated from the maximum axial root growth force (F_max) and root diameter were 497, 289, and 238 kPa respectively for pea, cotton and sunflower seedlings of same size. P_a and F_max were significantly influenced by seedling age and for pea seedlings of same age they varied with the seed batch. A new technique was developed for estimating radial root growth pressure and was tested on pea seedlings. Each pea root was confined both in the axial and radial directions in a cylindrical chalk sample at a constant water potential. The roots exerted radial stress which caused tensile failure in a proportion of the chalks. The measurement of tensile strength of duplicate chalks enabled estimation of the maximum radial pressures exerted by the roots. The maximum axial and radial root growth pressures were of comparable magnitude.     

Rearrangement of cells in storeyed cambium of<Emphasis Type="Italic"> Lonchocarpus sericeus</Emphasis> (Poir.) DC connected with formation of interlocked grain in the xylem

The history of cellular events in the storeyed cambium of Lonchocarpus sericeus (Poir.) DC was analysed on the basis of changes in the cell arrangement in successive layers and strata of axial parenchyma in the xylem. The mechanism of formation of the regular interlocked grain was investigated. Inclination of fusiform cells changes intensively whereas height and position of storeys in the successive layers of axial parenchyma are constant. As a result, new contacts between cells are formed by means of the intrusive growth of ends of cells belonging to one storey between the tangential walls of cells of the neighbouring storey and unequal periclinal divisions, which give a new shape to the initials. The concept of intrusive growth between the radial walls of the fusiform initials in the formation of xylem with interlocked grain should be revised on this basis.     

SEEDLING GROWTH AND ROOT CONTRACTION IN THE SOAP PLANT,CHLOROGALUM POMERIDIANUM (LILIACEAE)

Radicles and adventitious roots of the soap plant are contractile and through their activity, mature bulbs of this species are buried to depths of 20–30 cm. Experiments were performed to determine rates of contraction and displacement of the shoot apex resulting from activity of the contractile radicle and the first several adventitious roots. The average displacement was 23.2 mm over a 10-wk period and 63.8 mm over 29 weeks. Small glass beads and abortive seeds served as controls and showed no displacement through the soil column. Measurements from longitudinal and transverse sections of contracted and uncontracted portions of radicles revealed average increases of 26–64% in radial dimensions and 40–56% decreases in longitudinal dimensions of inner and middle cortical cells (excluding the endodermis) following contraction. Cells of the outermost cortex (excluding the exodermis) decreased in average longitudinal dimensions by 18–26% before becoming distorted and collapsed as contraction was completed. Average volumes of innermost cortical cells decreased by 15–54%, while two or three cell layers of the middle cortex, adjacent to collapsed outer cortical cells, increased in volume up to 75%. These middle cortical cells are identified as the “active” cells which, by their growth, are responsible for the shortening of the root. Throughout the process of contraction, the stele remains straight and undistorted, although the closer spacing of tracheary element secondary wall thickenings following contraction suggests longitudinal compression of the stele. The average number of cortical cells per transverse section does not differ in contracted and uncontracted roots and no evidence is found to support the “interdigitation” hypothesis of root contraction. However, reorientation of middle cortical cell expansion may be the mechanism of root contraction in Chlorogalum pomeridianum.     

Relationship between microtubule orientation and patterns of cell expansion in developing cortical cells of Lemna minor roots

In actively growing cortical cells in the elongation zone of Lemna minor L. roots, both longitudinal (radial and tangential) and transverse walls expand in both length and width. The longitudinal walls of the three types of cortical cells in the root (i.e. outer, middle and inner) showed the largest expansion in the longitudinal axis. In contrast, the inner cortical cells exhibited the least expansion in width, whereas the middle cortical cells displayed the largest expansion in width. Thus, the profiles of the expansion of longitudinal walls were characteristic for the three types of cortical cells. In this study, both the orientation of cortical microtubule (MT) arrays and their dynamic reorientation, and the density of cortical MTs, were documented and correlated to the patterns of cell wall expansion. Significantly, transverse arrays of cortical MTs were most prominent in the radial walls of the inner cortical cells, and least so in those of the middle cortical cells. Toward the base of roots, beyond the elongation zone, the orientation of cortical MTs shifted continuously from transverse to oblique and then to longitudinal. In this case, the rate of shift in the orientation of cortical MTs along the root axis was appreciably faster in the middle cortical cells than in the other two types of cortical cells. Interestingly, the continuous change in cortical MT orientation was not confirmed in the transverse walls which showed much smaller two-dimensional expansion than the radial walls. Additionally, the presence of fragmented or shortened cortical MTs rapidly increased concomitantly with the decrease of transversely oriented cortical MTs. This relationship was especially prominent in the transverse walls of the inner cortical cells, which displayed the least expansion among the three types of cortical cells investigated. In the root elongation zone, the density of cortical MTs in the inner cortical cells was about three times higher than that in the other two cortical cell types. These results indicate that in the early stage of cell expansion, the orientation of cortical MTs determines a preferential direction of cell expansion and both the shifting orientation and density of cortical MTs affect the magnitude of expansion in width of the cell wall.     

TENSIONAL STRESS IN THE CAMBIUM AND ITS DEVELOPMENTAL SIGNIFICANCE

In the mitotically active vascular cambium of conifers and broadleaved trees there is tension across the radial middle lamellae. This tension seems to be important for intrusive growth of fusiform cells. In the vascular cambium of Fraxinus and Robinia there is tension across the tangential middle lamellae also, which makes possible the increase in diameter of differentiating vessel members.     

Root contraction in hyacinth IV. Orientation of cellulose microfibrils in radial longitudinal and transverse cell walls

Summary Cellulose microfibrils (MFs) were visualized on the inner surface of root cortex cell walls ofHyacinthus orientalis L. using a replica technique. Microfibril orientation was determined in radial longitudinal and transverse cell walls of the root tip, uncontracted, contracting, and fully contracted regions of the root. In longitudinal walls, the innermost MFs were ordered and parallel to one another and were oriented transversely, axially or obliquely, depending upon the developmental stage of the region. In transverse walls MFs in a single layer formed crisscross or ordered parallel arrays, depending upon the region. Parallel arrays were oriented either parallel, perpendicular, or oblique to the radius of the root. Inner walls of certain cells in the contracting region had MFs which appeared interrupted over their lengths. In general, these findings parallel earlier immunofluorescence and electron microscopic observations of changing cortical microtubule (MT) orientation accompanying root contraction. The major exception to MT-MF congruence occurred in cells of the actively contracting region. In middle and outer cell layers, MFs appeared short and partially obscured, while MTs in these cells occurred in conspicuous laterally aggregated strands parallel to one another over the length of the cells or were absent. This alteration in MF-MT parallelism may be related to the reorientation in cell growth occurring in the contractile zone or to the collapse of specific cells during the process of root contraction.Abbreviations MF microfibril - MT microtubule     

Stem anatomy of the dwarf subshrub Cressa cretica L. (Convolvulaceae)

Stem anatomy and development of medullary phloem are studied in the dwarf subshrub Cressa cretica L. (Convolvulaceae). The family Convolvulaceae is dominated by vines or woody climbers, which are characterized by the presence of successive cambia, medullary- and included phloem, internal cambium and presence of fibriform vessels. The main stems of the not winding C. cretica shows presence of medullary (internal) phloem, internal cambium and fibriform vessels, whereas successive cambia and included phloem are lacking. However, presence of fibriform vessels is an unique feature which so far has been reported only in climbing members of the family. Medullary phloem develops from peri-medullary cells after the initiation of secondary growth and completely occupies the pith region in fully grown mature plants. In young stems, the cortex is wide and formed of radial files of tightly packed small and large cells without intercellular air spaces. In thick stems, cortical cells become compressed due to the pressure developed by the radial expansion of secondary xylem, a feature actually common to halophytes. The stem diameter increases by the activity of a single ring of vascular cambium. The secondary xylem is composed of vessels (both wide and fibriform), fibres, axial parenchyma cells and uni-seriate rays. The secondary phloem consists of sieve elements, companion cells, axial and ray parenchyma cells. In consequence, Cressa shares anatomical characteristics of both climbing and non-climbing members. The structure of the secondary xylem is correlated with the habit and comparable with that of other climbing members of Convolvulaceae.     

Radial and axial turgor pressure measurements in individual root cells of Mesembryanthemum crystallinum grown under various saline conditions

Abstract. Radial and axial turgor pressure profiles were measured with the pressure probe in untreated and salt-treated intact roots of Mesembryanthemum crystallinum. The microcapillary of the pressure probe was inserted step-wise into the root tissue 5, 25 and 50 mm away from the root cap. For evaluation of the data, only those recordings on a given root were used in which four discontinuous increases in turgor pressure occurred. These four turgor pressure increases could be related to the rhizodermal cells and to the cells in the three cortical layers. The measurements showed that a radial turgor pressure gradient of the same magnitude (directed from the third cortical layer to the external medium) existed along the root axis. The magnitude of this turgor pressure gradient decreased with increasing salinity (up to 400 mol m^-3 NaCl) in the growth medium. Addition of 10 mol m^-3 CaCl₂ to the 400 mol m^-3 NaCl medium partly reduced the salt-induced decrease in turgor pressure, but only in cells 25–50 mm away from the root tip. Combined with this effect, a small axial turgor pressure gradient was generated, therefore, in the cortex layers which was directed to the root tip. Measurements of the volumetric elastic modulus, ?, of the wall of the individual cells showed that the presence of salt considerably reduced the magnitude of this parameter and that addition of Ca²⁺ to the strongly saline medium partially diminished this decrease. This effect was strongest in cells 50 mm away from the root tip. The magnitude of ? of rhizodermal and cortical cells increased along the root axis both in untreated and in salt-treated roots. The ? value was significantly smaller for rhizodermal cells compared to the cortical cells, with the exception of cells 50 mm from the tip. In this tissue, rhizodermal and cortical cells exhibited nearly the same values. The decrease of the ?-values with salt and the increase along the root axis under the various growth conditions could be correlated with corresponding changes in cell volume. Diurnal changes in turgor pressure could not be detected in the individual root cells, with the notable exception of the rhizodermal and cortical cells located in the region 50 mm away from the root tip of the control plants. In these cells, an increase in turgor pressure was observed during the morning hours. Determination of the average osmotic pressure in tissue sections along the roots of control and salt-treated plants revealed that at 400 mol m^-3 NaCl the osmotic pressure gradient between the tissue and the medium is exo-directed, provided that the water is not (partly) immobilized.     

Parenchyma cells of secondary phloem in Pinus strobus

Summary Parenchyma cells of the secondary phloem in Pinus strobus have all the cellular organelles common in other plant cells. They have mitochondria, endoplasmic reticulum, ribosomes, dictyosomes, and plastids. Parenchyma cells are very conspicuous because of their organic inclusions, starch and lipids. Plasmodesmata in transverse and tangential walls of axial parenchyma cells and in end walls of ray parenchyma cells are regularly distributed and of uniform size, about 500 Å in diameter. In radial walls of axial parenchyma cells and horizontal walls of ray parenchyma cells plasmodesmata are located in primary pit-fields; there they are of variable size and often divided into several branches. The branches are confluent into a median nodule. Perforation of the transverse wall between two axial parenchyma cells and the resultant union of the cellular material of the two connected cells is reported.This research has been supported by NSF Grant GB 3193.     

How cobalt facilitates cadmium- and ethylene precursor-induced growth inhibition and radial cell expansion in barley root tips

Significant root growth inhibition was observed during the very short 5 minute exposure time of barley roots to the low 10 μM concentration of cadmium. In addition to the cadmium-induced root growth inhibition, considerable radial expansion of roots was observed as a characteristic symptom of transient short-term exposure of roots to cadmium. The cadmium-induced radial expansion of roots was observed mainly the cortical cells of elongation zone that were twice as large as in control roots. Similarly as in cadmium-treated roots, short-term treatment with ACC significantly inhibited root growth and caused a marked radial expansion of cortical cells. The ethylene synthesis inhibitor cobalt significantly alleviated both the cadmium- and ethylene precursor-induced root growth inhibition and radial root expansion. The results indicate that ethylene probably plays a crucial role in the short-term cadmium-induced inhibition of root growth and radial cell expansion of barley root tips, which are the very early symptoms of cadmium toxicity.     

RELATION OF DWARFMISTLETOE (ARCEUTHOBIUM) TO THE XYLEM TISSUE OF CONIFERS. I. ANATOMY OF PARASITE SINKERS AND THEIR CONNECTION WITH HOST XYLEM

Srivastava , L. M., and K. Esau . (U. California, Davis.) Relation of dwarf mistletoe (Arceuthobium) to the xylem tissue of conifers. I. Anatomy of parasite sinkers and their connection with host xylem. Amer. Jour. Bot. 48(2): 159–167. Illus. 1961.—The anatomy of the sinkers of Arceuthobium infecting 7 species of conifers was studied by the use of serial cross, radial, and tangential sections of the host wood. The sinkers were found to be composed of parenchyma cells only, or of parenchyma cells and tracheary elements, including vessel elements. In all species tracheary cells of the sinkers had direct contacts with the host tracheids of axial and radial systems. Typically the sinkers were associated with rays of the host wood. In some species, the centripetal ends of sinkers were wedged in radially among the axial tracheids of the host, but centrifugally such sinkers were usually found associated with rays. In the region of the host cambium the sinker contained parenchyma cells meristematic in appearance and, in 6 out of 7 species, also mature tracheary elements. The oldest of these elements became stretched and ruptured, a circumstance indicating that growth occurred in the part of the sinker embedded in the host cambium. This growth appeared to be coordinated with that of the host cambium, so that the sinker became embedded in the host xylem and phloem. Radial centripetal penetration of sinkers among differentiating axial tracheids of the host possibly occurred to a limited extent.     

Patterns of cortical and perinuclear microtubule organization in meristematic root cells ofAdiantum capillus veneris

Summary The interphase meristematic root cells ofAdiantum capillus venerispossess a well developed cytoskeleton of cortical microtubules (Mts), which disappear at prophase. The preprophase-prophase cells display a well organized preprophase microtubule band (PMB) and a perinuclear Mt system. The observations favour the suggestion that the cell edges included in the PMB cortical zone possess a Mt organizing capacity and thus play an important role in PMB formation. The perinuclear Mts are probably organized on the nuclear surface. The preprophase-prophase nuclei often form protrusions towards the PMB cortical zone and the spindle poles, assuming a conical or rhomboid shape. Mts may be involved in this nuclear shaping.Reinstallation of cortical Mts in dividing cells begins about the middle of cytokinesis with the reappearance of short Mts on the cell surface. When cytokinesis terminates, numerous Mts line the postcytokinetic daughter wall. Many of them converge or form clusters in the cytoplasm occupying the junctions of the new and the old walls. In the examined fern, the cortical Mt arrays seem to be initiated in the cortex of post-cytokinetic root cells. A transitory radial perinuclear Mt array, comparable to that found in post-telophase root cells of flowering plants, was not observed inA. capillus veneris.