Xylem Ring Research Articles

Response of Cambial and Shoot Growth in Trees Treated with Paclobutrazol

Three experiments were conducted to investigate the effect of paclobutrazol on shoot and cambial growth of nine tree species located in Indiana and Louisiana, U.S. In Experiment I, white oak (Quercus alba L.) and red oak (Q. rubra L.) in Indiana were treated in April 1995 with paclobutrazol using the soil drench method. In Experiment II, paclobutrazol was applied in April 1996, using the soil injection method, to eight species growing in Indiana: white oak, red oak, sweetgum (Liquidambar styraciflua L.), black walnut (Juglans nigra L.), European black alder (Alnus glutinosa L.), yellow poplar (Liriodendron tulipifera L.), white ash (Fraxinus americana L.), and white pine (Pinus strobus L.). In Experiment III, two species, sweetgum and cherrybark oak (Q. falcata var. pagodaefolia L.) in Louisiana, were treated with paclobutrazol by the soil drench method in March 1997. At the end of the 1998 growing season, annual shoot growth and annual xylem ring increment were measured for each of the two to four growing seasons after treatment in the three experiments. The effects of paclobutrazol on cambial growth and annual shoot growth at various positions along the trunk and in the canopy varied with species and treatment duration. Paclobutrazol reduced cambial growth in white oak, red oak, cherrybark oak, sweetgum, European black alder, and white pine with the amount varying among species, vertical location in the tree, and year after treatment.

Effect of sucrose nutrition on the histological structure of carob shoot

Analysis of carob (Ceratonia siliqua L.) shoot cultures grown on 2 and 8 % sucrose in light and darkness (etiolation) showed marked differences in histological structure. Etiolated, dark grown shoot cultures were hypolignified on both sucrose concentrations. They had highly reduced sclerenchyma and xylem production, endodermis with Casparian bands and absence of lenticel formation. In light grown cultures shoots in transection showed nearly concentric ring of sclerenchyma (outer) and xylem (inner) ring and the absence of Casparian bands in endodermal cells. Increased sucrose nutrition promoted lignification and efficiently prevented lenticel hypertrophy characteristic for low sucrose concentration.

Cambial variants in the roots of Glinus lotoides L. and G. oppositifolius (L.) A. DC. (Molluginaceae)

Structure and development of successive cambia and their derivatives are studied histologically in the root of two species of Glinus (Molluginaceae). In both species first ring of cambium functions for a short time followed by the development of second ring from the cortical parenchyma. The subsequent cambial rings formed followed the similar pattern of development. The mature roots are composed of three to five successive rings of xylem alternating with phloem. Absence of ray initials in the cambium leads to the development of rayless xylem and phloem. Xylem consists of vessel elements, tracheids, libriform fibres, fibre tracheids and axial parenchyma. In transverse view vessels appear oval to circular and solitary in G. lotoides and angular, narrow and mostly in radial multiples in G. oppositifolius. Xylem fibres retain their nucleus even after the formation of secondary walls in both the species. Storage of starch in the lumen is a characteristic feature of fibres. The significance of successive cambia, rayless xylem and nucleated xylem fibres is discussed in relation to the plant habit.

CAMBIAL VARIANT AND XYLEM STRUCTURE IN THE STEM OF COCCULUS HIRSUTUS (MENISPERMACEAE)

Development of cambial variant and xylem structure were studied in the stem of Cocculus hirsutus (Menispermaceae). In the early stages of stem development several collateral vascular bundles are joined by interfascicular cambium resulting in the formation of a complete cambial cylinder. After functioning for two to three years the cambial ring ceases its activity. Subsequently a second ring of cambium is formed from the innermost cortical parenchyma cells. These parenchyma cells undergo periclinal divisions to give rise to cells that become lignified, abaxially, and cambial cells, adaxially. The cambial cells divide periclinally giving rise to individual vascular bundles with xylem and phloem. Later the cambium in each bundle is joined by interfascicular cambium. Subsequent cambia develop similarly resulting in the formation of successive rings of xylem and phloem. During the leafless condition, all the cambial rings are dormant, and flanked by mature xylem and phloem elements. With the sprouting of new leaves, either the existing outermost cambium reactivates or an entire new ring of cambium develops. The xylem is diffuseporous with indistinct growth rings. It is composed of fibre-tracheids, tracheids, vessel elements, libriform fibres, and parenchyma cells. Xylem rays are multiseriate, compound and heterocellular. Deformed libriform fibres and vessel elements commonly occur among the ray cells in all the successive rings of xylem. The length of fibres and the height and width of xylem rays increase gradually from the centre towards the periphery of the stem.

Winter embolism, mechanisms of xylem hydraulic conductivity recovery and springtime growth patterns in walnut and peach trees.

Xylem vessels of Prunus persica Batsch (peach) and Juglans regia L. (walnut) are vulnerable to frost-induced embolism. In peach, xylem embolism increased progressively over the winter, reaching a maximum of 85% loss of hydraulic conductivity (PLC) in early March. Over winter, PLC in walnut approached 100%, but the degree of xylem embolism varied during the winter, reflecting the ability of walnut to generate positive xylem pressures in winter and spring. In contrast, positive xylem pressures were not observed in peach. Controlled freeze-thaw experiments showed that frost alone is insufficient to increase embolism in peach; evaporative conditions during thawing are also required. However, when both species were protected from frost, PLC was zero. At bud break, there was complete recovery from embolism in walnut, whereas PLC remained high in peach. Three mechanisms responsible for the restoration of branch hydraulic conductivity were identified in walnut: the development of stem pressure, the development of root pressure and the formation of a new ring of functional xylem, whereas only one mechanism was observed in peach (new functional ring). The climatic conditions necessary for the manifestation of these mechanisms were investigated.

Differences in delta13C and diameter growth among remnant Scots pine populations in Scotland.

Published data suggest that differences in wood cellulose carbon isotope composition (delta13C) and xylem ring width among natural populations of Scots pine in Scotland (Pinus sylvestris L.) are attributable to the persistence of palaeotypes of various post-glacial migratory origins. We assessed differences in wood cellulose delta13C and ring width among Scottish Scots pine populations grown in a clone bank and in natural stands at various locations in northern and central Scotland. Ring width and wood cellulose delta13C varied significantly among natural stands. Potential water deficit was positively correlated with wood cellulose delta13C and xylem ring width in the natural stands. Neither wood cellulose delta13C nor xylem ring width of clone bank trees correlated with any climate variables at the sites from which the trees originated, indicating little adaptation to climate for these traits. Xylem ring width showed a site x population interaction for the growth sites (i.e., natural stands versus clone bank), but wood cellulose delta13C did not. These results suggest that climate variation in Scotland has not resulted in significant genetic variation in wood cellulose delta13C or xylem ring width in post-glacial populations.

Annual rings in native and introduced forbs of lower Michigan, U.S.A.

Almost nothing is known about the presence of annual growth rings in North American perennial herbs and, correspondingly, the age of forbs is also largely unknown. In this study we sampled established individuals of dicotyledonous perennial herbs (60 species) in different habitats in lower Michigan (U.S.A.) and analyzed the main roots for the presence of growth rings in the secondary xylem. Two thirds of the species showed clearly or relatively clearly demarcated growth rings in the root xylem that are most likely annual rings. The anatomical patterns contributing to the delineation of growth rings in the root xylem differed widely, particularly among plant families. These included variations in vessel diameter and vessel density and differences in the presence and extent of tangential bands of fibres or lignified parenchyma, respectively. Among introduced species and in disturbed habitats (meadows, ruderal sites), clearly demarcated growth rings were found more frequently than among native species and in semi-natural and natural habitats (old fields, prairie remnants, open sandy vegetation). While most of the sampled plants were young (2 to 3 years old), the age distribution in the whole sample was relatively wide (2- to 16-year-old plants). Older individuals ([Formula: see text]6 years old) were mainly found in semi-natural and natural habitats. Results indicate that the analysis of annual rings in the root xylem of perennial herbs (herb-chronology) may be widely used as a reconstructive method in plant ecology over extensive geographic areas with seasonal temperate climate. Research into plant invasions may particularly profit from a high proportion of forb species in disturbed habitats that show clearly demarcated annual rings.Key words: age determination, anatomical patterns, annual rings, perennial herbs, population ecology, secondary root xylem.

Growth and annual ring structure of Larix sibirica grown at different carbon dioxide concentrations and nutrient supply rates.

We compared effects of ambient (360 vpm) and elevated (720 vpm) carbon dioxide concentration ([CO2]) and high and low nutrient supply rates on stem growth, annual ring structure and tracheid anatomy of Siberian larch (Larix sibirica Ledeb.) seedlings over two growing seasons. Elevated [CO2] had no significant effect on either stem height or diameter growth; however, both stem height and diameter growth were enhanced by the high nutrient supply rate, and these increases were stimulated by elevated [CO2]. Elevated [CO2] tended to increase the width of the annual xylem ring, the number of cells in a radial file spanning the ring, and tracheid lumen diameter, whereas it tended to reduce cell wall thickness, although there were no statistically significant CO2 effects on tracheid anatomy. Changes in tracheid cell morphology seemed to be dependent on changes in shoot elongation rates.

Occurrence of rayless secondary xylem in some Indian herbaceous species

(Received 28 December 2000 and in revised form 26 February 2001) Absence of rays was observed in the secondary xylem of thirteen species from seven genera of Aizoaceae, Chenopodiaceae, and Polygonaceae. Among the species studied, all the members of Polygonaceae had normal secondary xylem, whereas in Aizoaceae and Chenopodiaceae the vascular cylinder of the mature stem was composed of successive rings of xylem alternating with phloem bands. All the species of Chenopodiaceae and Polygonaceae accumulated scanty secondary xylem composed of vessels, tracheids, libriform fibers, and axial parenchyma, while in Aizoaceae, in addition to the above-mentioned cell types, fibriform vessels and fiber tracheids were also observed. In the latter part of secondary growth in both Chenopodium species, some of the axial parenchyma underwent transverse division and formed a group of vertically elongated, procumbent cells, referred to here as pedomorphic rays. In all species studied, nuclei were retained in the lumen of xylem...

Growth Rings in the Stem of Thuja orientalis L.

During the winter dormancy period of 1998-99, the differentiation process of xylem and the formation of annual and pseudo-annual growth rings was studied in sections of the central stem of Thuja orientalis of different age (1-14 year old), starting from the top (the tip of leader shoot) towards the bottom. In the apical 1-2 cm portion of the one year-old leader shoot, only the protoxylem was formed by the end of vegetation. The protoxylem elements appeared first in 6 bundles than gradually merged into 2 semiquadrangular (triangular) bands (each containing 3 protoxylem bundels) around the pith. In this stem portion, the pith was cross-formed first and became gradually flattened at the lower stem parts, following the generally flattened shape of the stem and the respective facial and marginal position of leaves. A continuous xylem ring (with formation of metaxylem elements) apeared 3-5 cm below the shoot tip. In fact, it was the stem part where a "real" annual ring was formed by the end of vegetation. The first pseudo-annual rings were observed 16 cm below the top. The "regular" annual rings were completely continuous all around the stem, consisted of strongly flattened in radial direction thick-walled latewood tracheids and had a distinct border (demarcation line) at the end of the year. The "pseudo-annual" rings formed incomplete dark rings or semicircular bands within the earlywood. They were composed of tracheids with thick cell walls but somewhat wider radial diameter than those of the "real" annual rings, and the border between their outside margin and the next earlywood was less distinct.
 In the xylem of two year old stem portion, the innermost central annual ring appeared not at the transition zone between the current and the former years of growth, but about 2 cm lower. Above that, only the thick-walled bundles of the former years protoxylem were found. Down the stem, the older sections showed similar features: the next annual ring appeared always somewhat lower than the borderzone of the given and the former years growth. The "pseudoannual" rings (or more correctly the growth rings) continued regularly to appear in the lower (older) sections of the stem as well. They were found untill the age of up to 14 years (the bottom of the studied plants). Their number was 3-4 per year first, than (from the 5th annual ring counted from the centre) decreased to 3,2,1, and in the youngest outer part of the xylem there was no pseudo-annual ring at all. The development of pseudo-annual rings was usually more marked on the thicker (more branched) than on the thinner side of stem. Stems older than 14 years were not studied.

SECONDARY GROWTH IN THE STEM OF SOME SPECIES OF ALTERNANTHERA AND ACHYRANTHES ASPERA (AMARANTHACEAE)

Secondary growth in Achyranthes aspera, Alternanthera polygamous, A. pungens, A. sessilis, and A. triandra was achieved by the development of a cambial variant resulting in successive rings of xylem and phloem. Each new cambium was developed at a distance about two to three cells external to the phloem produced by the previous cambium. The development of phloem was not synchronous in the species studied. Phloem development started either simultaneously with xylem or after the formation of a few xylem derivatives. In Achyranthes, xylem production started first followed by the development of phloem. Phloem mother cells differentiated into sieve tube elements, companion cells and axial parenchyma. Xylem was storied and exclusively composed of axial elements. Radial elements were absent in all the xylem rings of the stem. Vessels were angular and mostly solitary, but radial and tangential multiples were also observed occasionally. Xylem fibres were nonseptate and nucleated. Development of phloem and the rayless nature of the xylem is discussed.

Ecological Application of ‘Herbchronology’: Comparative Stand Age Structure Analyses of the Invasive PlantBunias orientalisL.

The age structures of stands of the herbaceous perennial forbsBunias orientalisandRumex crispuswere determined in different habitats in the vicinity of Würzburg (Unterfranken, Germany). Plant age was determined by counting annual rings in the secondary root xylem (herbchronology). In rarely-disturbed (unmown, not disrupted) habitats, stands ofB. orientalisshowed a high proportion of older (⩾4-year old) individuals, whereas comparable stands at frequently-disturbed habitats were dominated by 1- or 2-year old plants. Plant size was positively and linearly related to plant age at frequently-disturbed sites and plants in the reproductive stage were younger than at the rarely-disturbed sites. Thus, the age structure data indicate favourable effects of anthropogenic disturbance on stand development ofB. orientalis. At recently-disturbed, productive sites,B. orientalisshowed narrow age distributions for a few years after the disturbance event, apparently resulting from a strong decline in seedling establishment after canopy closure. Stand development of the co-occurring speciesR. crispuswas less affected by vegetation density at such productive sites, but seemed to suffer more from relatively dry soil conditions. Besides being markers of plant age, annual rings may be sensitive records of past growing conditions, as suggested forB. orientalisby the relationship between annual ring width and position in a gradient of light supply. These results suggest that age structure data obtained by ‘herbchronology’ can provide valuable supplementary information for studies on the population ecology of perennial dicotyledonous herbs with clearly-demarcated annual rings.

Fossil dicotyledonous liana Anamirta pfeifferi sp. nov. (Menispermaceae) from the Deccan Intertrappean beds of India

A fossil dicotyledonous woody liana, Anamirta pfeifferi sp. nov., showing anomalous secondary growth has been described from the Deccan Intertrappean beds of Nawargaon-Maragsur area, district Wardha, Maharashtra, India. The wood exhibits pluriseriate secondary growth with alternate concentric rings of xylem and phloem, vascular bundles in a ring separated by broad primary xylem rays, differentiated pith and endarch primary xylem. Pluriseriate type of anomalous secondary growth in a fossil dicotyledonous wood has been described here for the first time.

Age-determination of Dicotyledonous Herbaceous Perennials by Means of Annual Rings: Exception or Rule?

Abstract Thirty-five herbaceous dicotyledonous perennial plant species, with permanent root systems, from 16 families, were examined for the presence of growth rings in the secondary root xylem. Most of the species surveyed showed ring zonations in the roots, and these could be verified as annual growth rings in the ten species for which plants of known age were available. The potential value of ‘herbchronology’ as a tool in ecological investigations of species and stands of perennial herbs of temperate zones is discussed.

Sensitive detection of potato spindle tuber viroid using RT-PCR and identification of a viroid variant naturally infecting pepino plants

A reverse-transcription polymerase chain reaction (RT-PCR) method was developed to detect full length potato spindle tuber viroid (PSTVd) using primer pair 5'-CCCTGAAGCGCTCCTCCGAG-3' (complementary to PSTVd nucleotides 69-88) and 5'ATCCCCGGGGAAACCTGGAGCGAAC-3' (homologous to PSTVd nucleotides 89-113). A full-length amplified PSTVd cDNA was detected using RT-PCR in GeneReleaser-treated nucleic acid extracts of potato tuber tissues taken from tuber periderm, cortical parenchyma, external phloem, xylem ring, perimedullary zone containing internal phloem, perimedullary starch-storage parenchyma or pith regions. The viroid was also detected using RT-PCR from total nucleic acid or GeneReleaser-treated sap extracts of true potato seed (TPS), and pollen. PSTVd detection from total nucleic acid extracts of TPS can be achieved without further treatment with GeneReleaser or after further purification. GeneReleaser-treated sap extracts of as little as five pollen grains were sufficient to yield an amplified full-length PSTVd cDNA by this method. A one-step short version of RT-PCR was shown to detect PSTVd from infected tomato leaf nucleic acids. The RT-PCR protocol was successful in detecting a naturally occurring variant of PSTVd from pepino (Solanum muricatum) plants that consists of 357 nucleotides and differs from the prototype 359 nucleotide PSTVd isolate in five positions.

Lignification and cinnamyl alcohol dehydrogenase activity in developing stems of tomato and poplar: a spatial and kinetic study through tissue 2

Cinnamyl alcohol dehydrogenase (CAD) is an enzyme involved in the synthesis of lignin monomers. Tissue prints were used to localize CAD activity in tomato and poplar tissues. In parallel, lignin deposition was estimated by classical histochemical tests. Image analysis was also used to quantify the amount of CAD activity and the extent of lignification throughout the development of stems. Tomato stems showed a limited lignification. CAD activity, restricted to the xylem, reached a maximum during the early stages of development and showed a patched pattern on the xylem ring. In contrast, CAD activity was much stronger in poplar stems and closely associated with all lignified areas: starting with localized areas within the xylem and finally completely covering the xylem ring. The enzyme showed a significant activity in primary and secondary xylem, and both lignin deposition and CAD activity increased as the plant matured. These results show that CAD activity, which is important for lignification, can easily be detected in plant tissues by tissue prints. They also reveal that tomato (herbaceous stems) and poplar (woody stems) dramatically differ in the developmental pattern of CAD within their lignified tissues.

Growth and Fire Response of Selected Epacridaceae of South-Western Australia

Recruiting populations of seeder (Astroloma xerophyllum (DC.) Sond. and Leucopogon conostephioides DC.) and resprouter (Leucopogon verticillatus R.Br. and Conostephium pendulum. Benth.) epacrids were examined over an 8 year period, using time of fire, shoot morphology and root xylem ring number to age plants. The seeders commenced flowering earlier, achieved three-fold higher shoot:root ratios but accumulated much smaller root starch reserves than the resprouters. The resprouting potential of L. verticillatus was 'bud initiation-limited', since progressive shoot removal exhausted the bud-producing potential but did not fully deplete the starch reserves of the root stock. Apparent conversion efficiency of starch to new shoot biomass was 88%. The corresponding response in C. pendulum was 'energy reserve-limited', with shoot removal eliminating root starch but leaving many unexpanded buds. Dendroecological analyses of root xylem growth rings were undertaken on 15 year-old plants of C. pendulum recruiting from seed in unburnt and adjacent periodically burnt habitats. Growth ring extension of burnt plants resumed after each fire at rates faster than their unburnt counterparts, suggesting that improved access by resprouting shoots to light, water and nutrients compensated for destruction of the previous shoot system.

Two New Species and a Key to Passiflora subg. Astrophea

Two new species, Passiflora amoena and Passiflora callistemma, were discovered during a taxonomic revision of subgenus Astrophea. The first is placed in section Botryastrophea, the second in section Astrophea. A key is provided for all the species of Passiflora subgenus Astrophea. Passiflora L. subgenus Astrophea (DC.) Masters is composed of 50 species of trees, shrubs, or lianas confined to tropical areas of South Amer- ica, with two species ranging north into Me- soamerica. As did Killip (1938), I recognize six sections in the subgenus. Members of sect. Bot- ryastrophea (Harms) Killip, are lianas with strong axillary tendrils, anomalous secondary growth, and brightly colored, orange to purple flowers with an elongated hypanthium. Flowers are borne on very short to very long racemes pro- duced from thick stems close to the forest floor, or at the edge of forest vegetation, and are prob- ably pollinated by hummingbirds. Species of sect. Astrophea DC., are trees or lianas with con- centric rings of secondary xylem and white to greenish-white flowers with mostly yellow co- ronal filaments. The floral hypanthium is short, and the species are probably pollinated by large bees. More than 50 years have passed since the last comprehensive taxonomic treatment of subge- nus Astrophea, (Killip 1938), and many new spe- cies have been published since that time. To facilitate identification of plants in this large and difficult group, a key is provided for all the species of the subgenus. at apex of petiole, with raised oval nectaries 1.5- 2.3 mm long and 1.0-1.2 wide; stipules seta- ceous, ca. 0.3 mm long, deciduous. Flowering branches to 4 cm long, mostly on thick stems close to base of plant; peduncles stout, 2.0-3.5 mm long, 1.3-1.7 mm diam.; bracts triangular, 1.0-1.3 mm long, 0.4-0.8 mm wide. Flowers sal-

The Relationship Between Size of Shoot Apices and Morphological Features of Mature Leaves and Stems of Four Species of Angiosperm Trees

Shoot apex, leaf and stem growth parameters for four species of deciduous trees were measured. Only in elm was there a correlation between the size of shoot apical meristems and mature leaves. In ash, basswood and cottonwood there was no significant difference between size of shoot apices of sucker and canopy branches, despite significant differences in lamina size. In the sucker branches of all species studied there occurred an early, lateral expansion of the subapical region of the shoot apical meristem. This correlated well with the greater diameter of stem and pith regions of sucker branches. In addition, the season's annual ring of xylem was greater in basswood, cottonwood and elm. Diameters of vessel elements were greater in sucker than canopy branches in three of the four species. Total branch and internode and number of nodes per branch were significantly greater for sucker branches than canopy growth of all species studied.A hypothesis is proposed to explain the development of the very large surface area of leaves on sucker branches. This hypothesis is based on the position of sucker branches in relation to the root system and involves differences in water stress known to be present in all plants.

INTERNAL PHLOEM IN THE PULVINUS OF SOYBEAN PLANTS

Glycine max, like many species of Fabaceae, has pulvini at the base of the petiole. In this structure, the vascular cylinder is constricted and consists of a ring of phloem surrounding a ring of xylem. A combination of light and transmission electron microscopy and histochemistry showed that, in addition, there are groups of internal phloem strands in the pulvinar pith. This was confirmed by direct observation of sieve plates and crystalline P‐protein inclusions typical of leguminous sievetube members. Serial sections through the stem–pulvinus–petiole revealed that a spatial reorientation of the vascular tissue in the pulvinus resulted in the formation of internal phloem strands, which are continuous with the external phloem bundles above and below the pulvinus. Using 6(5)carboxyfluorescein (6CF) as a fluorescent tracer of phloem transport, we have shown that the internal phloem was active. In most of the experiments, when 6CF was applied to a source leaf, the internal phloem was not stained when the stem was girdled between the source leaf and the roots. Thus, we suggest that the internal phloem of the pulvinus of soybean is specialized for transport toward the root.