Biomechanics of the columnar cactus Pachycereus pringlei

We report the longitudinal variations in stiffness and bulk density of tissue samples drawn from along the length of two Pachycereus pringlei plants measuring 3.69 and 5.9 m in height to determine how different tissues contribute to the mechanical stability of these massive vertical organs. Each of the two stems was cut into segments of uniform length and subsequently dissected to obtain and mechanically test portions of xylem strands, stem ribs, and a limited number of pith and cortex samples. In each case, morphometric measurements were taken to determine the geometric contribution each tissue likely made to the ability of whole stems to resist bending forces. The stiffness of each xylem strand increased basipetally toward the base of each plant where stiffness sharply decreased, reaching a magnitude comparable to that of strands 1 m beneath the stem apex. The xylem was anisotropic in behavior, i.e., its stiffness measured in the radial and in the tangential directions differed significantly. Despite the abrupt decrease in xylem strand stiffness at the stem base, the contribution made by this tissue to resist bending forces increased exponentially from the tip to the base of each plant due to the accumulation of wood. A basipetal increase in the stiffness of the pith (and, to limited extent, that of the cortex) was also observed. In contrast, the stiffness of stem rib tissues varied little as a function of stem length. These tissues were stiffer than the xylem in the corresponding portions of the stem along the upper two-fifths of the length of either plant. Tissue stiffness and bulk density were not significantly correlated within or across tissue types. However, a weak inverse relationship was observed for these properties in the case of the xylem and stem rib tissues. We present a simple formula that predicts when stem ribs rather than the xylem strands serve as the principal stiffening agents in stems. This formula successfully predicted the observed aspect ratio of the stem ribs (the average quotient of the radial and tangential dimensions of rib transections), and thus provided circumstantial evidence that the ribs are important for mechanical stability for the distal and younger regions of the stems examined.     

Effects of Flooding, Tilting of Stems, and Ethrel Application on Growth, Stem Anatomy and Ethylene Production of Pinus densiflora Seedlings

Flooding of soil, tilting of seedlings, application of ethrelto stems, and combinations of these treatments, variously alteredthe rate of growth and stem anatomy of 2-year-old Pinus densifloraseedlings. Either flooding or tilting increased stem diametergrowth and induced formation of abnormal xylem. Whereas floodingdecreased the rate of dry weight increment of roots and needlesand increased growth of bark tissues, tilting of stems did not.However, tilting decreased the rate of height growth, stimulatedtracheid production, and induced formation of well-developedcompression wood with rounded, thick-walled tracheids, witha high lignin content but without an S3 layer in the tracheidwall. Ethylene appeared to have an important regulatory rolein stimulating growth of bark tissues as shown by thicker barkin flooded seedlings or those treated with ethrel. Ethyleneappeared to have a less important role in regulating formationof compression wood. Flooding increased the ethylene contentsof stems and induced formation of rounded, thick-walled tracheids.However, these tracheids lacked such features of well-developedcompression wood tracheids as a thick S2 layer, high lignincontent, and absence of an S3 layer. Furthermore, applicationof ethrel to vertical stems greatly increased their ethylenecontents but did not induce formation of well-developed compressionwood. Furthermore, ethrel application blocked development ofcertain characteristics of compression wood when applied totilted seedlings. For example an S3 wall layer was absent intracheids of tilted seedlings but present in tracheids of tilted,ethrel-treated seedlings. Also lignification of tracheids wasincreased on the under side of tilted stems, but reduced intilted, ethrel-treated seedlings, further de-emphasizing a directrole of ethylene in the formation of compression wood. Ethreltreatment induced formation of longitudinal resin ducts in thexylem whereas flooding or tilting of stems did not. Key words: Pinus densiflora, xylogenesis, reaction wood, compression wood, lignification, ethrel, ethylene     

COMPARATIVE CYTOHISTOLOGICAL STUDIES ON INHIBITION AND PROMOTION OF STEM GROWTH IN CHRYSANTHEMUM MORIFOLIUM

Sachs , R. M. (U. California, Davis), and A. M. Kopranek . Comparative cytohistological studies on inhibition and promotion of stem growth in Chrysanthemum morifolium. Amer. Jour. Bot. 50(8): 772-779. Illus. 1963.—The present study with Amo, CCC, and Phosfon,³ 3 substances which inhibit stem elongation, shows that all inhibit subapical cell expansion and division in Chrysanthemum morifolium var. ‘Indianapolis Yellow.‘ Furthermore, GA,³ in preventing the inhibition of stem elongation, maintains subapical activity at normal or greater than normal levels. For comparative purposes concentrations of the retardants and GA have been selected which completely prevent or promote the maximum rate of stem elongation. Phosfon causes complete inhibition of root growth and almost completely prevents dry matter accumulation in the tops. However, GA does not prevent such deleterious effects. Thus, GA and the growth retardants are mutually antagonistic only with respect to stem elongation and not to other aspects of growth. Furthermore, none of the retardants inhibits transverse stem growth; on the contrary transverse cell expansion and division in the subapical tissues are stimulated by the retardants, and as a result the stems of such plants are thicker than normal. GA not only prevents the thickening effect of the retardants, but, at the doses applied, GA-treated stems are considerably thinner than those of the controls, having fewer and smaller cells across the pith, cortical, and vascular tissues. Apparently, then, there is a relationship between longitudinal and transverse growth in the subapical tissues such that if one is promoted, the other is inhibited.     

A comparative karyological and cytophotometric study of normal and wounded stem tissues ofLathyrus odoratus L.

Wounding of stems ofLathyrus odoratus induced increased mitoses with polyploid in vascular and pith tissues, but not in cortex. Cell division area extended 200 μm from the wound edge. These facts confirm the previous observations inPisum sativum. DNA content of normal stem nuclei was high in vascular and pith tissues, but not in cortex.     

入侵植物水花生解剖学和组织化学染色研究

水花生(Alternanthera philoxeroides)因其表型可塑性、高生长速率和快速无性繁殖能适应水、陆生境。该文利用光学显微镜和荧光显微镜对水、陆生境的水花生不定根、茎解剖结构、组织化学特征及质外体通透性进行了研究。结果表明:(1)水生境下,其不定根皮层中具较大裂生型通气组织,无次生生长,内皮层具凯氏带且栓质化,皮层和皮下层明显木质化。(2)在陆生环境下,其不定根有次生生长,胞间具通气组织,内皮层具凯氏带且栓质化,皮层和皮下层略木质化;此外,不定根还具额外形成层,产生次生维管束、薄壁组织和不定芽;多年生不定根中具直接分裂的薄壁组织,周皮具凯氏带,且栓质化和木质化。(3)水、陆生境下,其匍匐茎具髓和中空髓腔,发生次生生长,具裂-溶生型通气组织、单层内皮层、厚角组织和木质化且栓质化的角质层,陆生匍匐茎周皮栓质化且木质化。(4)水花生质外体屏障结构组成复杂,黄连素无法穿透质外体屏障结构。水花生的上述解剖学特征,是水花生适应水、陆生境的有力证据。     

Pith: a marker of primary growth in Picea abies (L.) Karst.

The primary growth of trees may be studied either by following their development over time, which is costly and requires long-term monitoring, or by a posteriori growth analyses. Trees in temperate forests show rhythmic growth, which is characterised by morphological or anatomical markers. The study described here focuses on the pith of trees as an internal marker for the retrospective analysis of primary growth. Changes in pith size and density were quantified along a stem of Norway spruce [Picea abies (L.) Karst.] with high spatial resolution. The results showed that pith would appear to be a reliable marker of the annual growth rhythm even in the presence of polycyclism. Annual shoot limits were characterised by reductions in pith size associated, at the same time, with increases in pith density. In addition, pith size may provide information about tree ontogeny. The start of the competition with neighbouring trees was very likely responsible for an overall decrease in pith size. Regarding high frequency variations, pith size appeared to be less sensitive to local environmental fluctuations like climate than other studied variables such as annual shoot length and annual ring width. Finally, X-ray computed tomography proved to be a very promising method for the non-destructive detection of annual shoot limits in stems based on longitudinal changes in pith density, as demonstrated in a log of Norway spruce.

TUBULAR CAVITIES IN WHITE SNAKEROOT,EUPATORIUM RUGOSUM (ASTERACEAE)

Oil-filled schizogenous cavities 0.2-3.0 mm in length, each with a uniseriate epithelium, occur in all organs of white snakeroot (Eupatorium rugosum). Some epithelial cells swell, thus shrinking or occluding the cavity lumen. Foliar cavities form in staggered files in the midrib and in association with major veins. Cavities are progressively smaller and sparser in successive vein orders; the smallest ones develop as transformed bundle sheath cells in minor veins. Cavities in stems occur in irregular vertical files near vascular bundles in both cortex and pith. Leaf and stem cavities elongate variously, depending on when and where they form; in roots and floral organs, however, cavities are always short and sparse except in bracts, where they are common. Since each cavity remains discrete, we call these internal spaces ‘tubular cavities’ rather than ‘ducts’, which have generally been vaguely defined.     

Pith Autolysis in Herbaceous, Dicotyledonous Plants: Experimental Manipulation of Pith Autolysis in Several Cultivated Species

Pith autolysis, a condition in which dicotyledonous herbaceousplants have a hollow stem, results from the autolysis of a plant'sstorage pith. Our central hypothesis concerning the aetiologyof pith autolysis states that the carbon from the pith is transportedto the growth regions of the plant and used at times when theplant cannot meet its carbon needs by photosynthesis alone.According to this hypothesis, accelerated growth should increasepith autolysis. We here provide supporting evidence for thecentral hypothesis. More pith autolysis was found in fastergrowing tomato varieties than in dwarf varieties. More pithautolysis was found in both beans and tomatoes treated withGA₃ than in controls. More pith autolysis was found in leggybean plants grown in low light than in normal plants grown undernormal light conditions. Pith autolysis decreased in both beansand tomatoes when mechanically perturbed or sprayed with paclobutrazol,both treatments that reduced growth. The stems of buckwheatplants that were flowering showed greater pith autolysis andtherefore were more hollow than plants which were not floweringor which had the incipient flowers pinched off. This indicatedthat carbon from the storage pith may also be used in the formationof reproductive structures which require extra carbon. Alsoin support of the central hypothesis is the prevention of pithautolysis by the addition of extra carbon to the plant, in theform of an increased CO₂ concentration of the surrounding air.Copyright1995, 1999 Academic Press Bean, tomato, buckwheat, pith autolysis, CO₂, GA, thigmomorphogenesis, packobutrazol     

空心莲子草茎的解剖结构对不同水湿生境的适应研究

研究了空心莲子草茎的解剖结构对水分变化的适应,这些空心莲子草生活在因水分差异而形成的3种生境类型中。对茎表蜡质层厚度、髓腔面积/髓部面积、厚角细胞层数、厚角细胞壁厚、韧皮纤维束数、韧皮纤维壁厚、导管束数、导管腔大小8个结构参数的分析结果表明:茎的全部结构参数随水分条件的变化都有显著或极显著的差异,其趋异程度的大小顺序是,导管腔大小>厚角细胞壁厚>蜡质层厚度>髓腔面积/髓面积>韧皮纤维细胞壁厚>韧皮纤维束数>厚角细胞层数>导管束数;水分变化对机械组织细胞壁结构影响较大,而对细胞数量的影响较小;茎的结构在旱生生境中变异较大,保证了它对不均一环境的适应;空心莲子草茎的结构既具有旱生性特点又具有水生性特点,其结构究竟朝哪个方向发展,取决于环境水分条件。从茎的结构上看,治理该种应以限制其导管腔和髓腔分化为主要手段。     

Observation of water and Na+ in tissues of theBruguiera gymnorrhiza by1H-and23Na-NMR imaging

Distributions of free water, which is called water in this investigation, in mangrove (Bruguiera gymnorrhiza (L.) Lam.) tissues were examined by using¹H-NMR imaging, and accumulation of Na⁺ in hypocotyls was examined by using high resolution²³Na-NMR and²³Na-NMR imaging in relation to their morphology. Water located preferentially in the epidermis and the outer layer of cortex adjacent to the epidermis, and around vascular bundles of a root, a branch stem, and hypocotyls. Amount of water detected in the middle parts of cortex and pith was small unlikeAucuba japonica branch tissue. On the other hand, relatively high concentration of Na⁺ was detected in the pith besides the epidermis and the outer layer of the cortex adjacent to the epidermis, and around vascular bundles of the hypocotyl. The localization of Na⁺ did not correspond to that of water. Concentrations of Na⁺ accumulated (up to 22mM) in the hypocotyl were approximately 10 times higher than those observed in tissues of ordinary plants. The characteristic water distribution and accumulation of Na⁺ in the mangrove are considered to relate to their ecological nature for the adaptation to saline environments.     

A large anatomically preserved calamitean stem from the Upper Permian of southwest China and its implications for calamitean development and functional anatomy

A large permineralized calamitean stem, Arthropitys yunnanensis Tian et Gu from the Upper Permian of southwest China is reinvestigated and interpreted. The stem has a broad pith and well developed and large carinal canals. Secondary xylem is thick and characterized by wide parenchymatous interfascicular zones that remain constant in width throughout the wood. Striking features of the stem include the abundant leaf traces arranged in two whorls in the cortex with this arrangement previously unrecognized within calamitean stems, and the presence of growth rings in secondary xylem that suggest frequent fluctuations in environmental stress presumably due to variations in water availability. Features of A. yunnanensis infer the stem to be in the epidogenetical phase of calamitean development, and suggest it to be the basal part of a large trunk. Comparisons with biomechanical models for calamitean stems suggest this species had a semi-self supporting habit.     

STEM ANATOMY OF PARTHENIUM ARGENTATUM,P. INCANUM AND THEIR NATURAL HYBRIDS

Guayule (Parthenium argentatum Gray) contains rubber in the parenchymatous cells of stems and roots. Stem anatomy of P. argentatum is described along with that of P. incanum H.B.K. (mariola). Anatomy of these species differs significantly. Phloem rays in both species increase in width by cell division and expansion; however, the increase observed in mariola is less as compared to that in guayule. Axial xylem parenchyma in guayule is generally a two-cell strand as compared to the fusiform axial xylem parenchyma observed in mariola. Vascular ray cells and cells of the pith region of guayule are parenchymatous, whereas those of mariola are sclerenchymatous. As a result of introgression between guayule and mariola, three forms of guayule exist in the native stands of Mexico. Morphological differences between these guayule plants have been described previously. The stem anatomy of these three groups of plants differ importantly. Group I guayule plants, least introgressed by mariola, have taller rays with the cells of pith region and vascular rays parenchymatous. Group III plants, highly introgressed by mariola, have a few to many cells of vascular rays and pith with lignified secondary walls and shorter rays. Many of the anatomical characteristics of group II plants, somewhat introgressed by mariola, are intermediate between group I and III plants.     

鱼腥草茎叶解剖学特征及其与其他古草本类群相关结构的比较分析

采用常规石蜡切片法．对鱼腥草的药用部位地上茎、根状茎和叶进行了解剖学观察。鱼腥草茎和叶的表皮下有特殊的皮下层细胞．茎的皮层和髓中有分泌细胞存在。地上茎和根状茎之间在皮层细胞层数、周维纤维柱的有无、维管柱和髓所占比例、维管束束数、次生生长等办面存在差异,这些差异与它们各自担负的生理功能相关联。叶的皮下层细胞显著,它们是复表皮的一部分。叶表皮上有胶质化表皮细胞和水钵的结构。对鱼腥草茎和叶中的皮下层细胞的来源和功能、与其他古草本类群相关的结构特征以及水钵的结构与分铂等问题进行了探讨。     

Temperature-induced Alterations in the Expression of Susceptibility of Cassava to Colletotrichum gloeosporioides f. sp. manihotis

Cassava plants (Manihot esculenta Crantz) were incubated at 15, 25 or 35 °C after inoculation of green stems with Colletotrichum gloeosporioides (Penz.) f. sp. manihotis Chev. At 25 °C, the cultivar TMS 30211 was less susceptible than the cultivar TMS 30337. At 35 °C, compared to 25 °C, the lesion diameter was reduced in both cultivars, the cassava stem extracts showed an enhanced fungitoxicity, the grem tubes were more sensitive to the stem extracts and a layer of lignified, cells developed earlier around the infected tissues. At 15 °C, the lesions in both cultivars extended more rapidly than at the other temperatures, even though 15 °C, compared to 25 °C, caused a 50% reduction of mycelial growth rate on oat meal agar.     

Freezing avoidance in Andean giant rosette plants

Abstract Frost avoidance mechanisms were studied in Espeletia spicata and Espeletia timotensis, two Andean giant rosette species. The daily courses of soil, air and tissue temperatures were measured at a site at circa 4000 m. Only the leaves were exposed to subzero temperatures; the apical bud and stem pith tissues were insulated by surrounding tissues. The leaf tissues avoided freezing by supercooling rather than by undergoing active osmotic changes. The temperatures at which ice formed in the tissues (the supercooling points) coincided with injury temperatures indicating that Espeletia tissue does not tolerate any kind of ice formation. For insulated tissue (apical bud, stem pith, roots) the supercooling point was around - 5°C coinciding with the injury temperature. Supercooling points of about –13 to - 16°C were observed for leaves. These results contrast with those reported for Afroalpine giant rosettes which tolerate extracellular freezing. The significance of different adaptive responses of giant rosettes to similar cold tropical environments is discussed.     

Tree fern growth strategy in the Late Devonian cladoxylopsid species Pietzschia levis from the study of its stem and root system

Portions of stems from five new anatomically preserved specimens of Pietzschia levis from a new Late Devonian plant locality of eastern Tafilalt, Anti-Atlas (Morocco), were analyzed to complete the preliminary reconstruction previously done with a single specimen. The basal part of the longest new specimen consists of an obconical portion of stem surrounded by a thick mantle of adventitious roots. Roots are connected to the peripheral strands of primary xylem specific to the stele of Pietzschia stems. Roots grow outwardly; they cross the cortex and the broad central pith at a steep angle and emerge from the stem lower down. The number of roots produced at one level increases conspicuously from the base towards the distal end of the obconical portion of stem. By contrast, cross-sectional dimensions of roots at their origin level decrease distally. Individual roots increase in diameter, and their stele gets more lobed as they grow through stem tissues. The large number of roots at the specimen base and their wider dimensions at this level contribute to the conspicuous enlargement of the stem base. Patterns assessed from the reconstruction of the Pietzschia levis root system may be close to those of the older cladoxylopsids Pseudosporochnales comprising an upright trunk. Growth strategies in the small-statured species P. levis and in younger arborescent ferns of the Psaronius type are compared. They differ mainly in the relative lengths of epidogenetic vs. apoxogenetic growth phases of the stem.     

Gibberellic-Acid-Promoted Transport of Assimilates in Stems of Phaseolus vulgaris. Effects on Assimilate Accumulation by the Sink

Under conditions of apoplastic unloading from the sieve element-companioncell (se-cc) complexes in fully-elongated stems of Phaseolusvulgaris plants, gjbberellic acid (GA₃ stimulated in vitro uptakeof [¹⁴C]sucrose by the stem tissues. The GA₃, response dependedupon the incubate containing calcium ions and being bufferedat pH 6. The GA₃ action could be accounted for by a reductionin the Michaelis-Menten constant of the uptake process. Promotedtransport by GA₃ in the decapitated stems resulted in all thetissues accumulating higher levels of [¹⁴C]photosynthates. Comparisonof this response with that for in vitro uptake of [¹⁴C]sucroseindicated that GA₃ stimulation of the sucrose uptake processcontributed significantly to the accumulation of photosynthatesby the pith alone. The bulk of enhanced photosynthate accumulationby the remaining stem tissues can be accounted for by a GA,-inducedelevation of the apoplast sucrose concentration. In terms ofonset and change in rate, the time-course kinetics of GA₃ stimulationof [¹⁴C]photosynthate transport and of in vitro [¹⁴CJsucroseuptake were found to be similar. It is proposed that GA₃ promotionof photosynthate accumulation by the pith tissues is a minorcontributing factor to GA₃ regulation of phloem translocation Phaseolus vulgaris L., french bean, stem, assimilate transport, gibberellic acid, rink accumulation     

Seasonal respiration of foliage, fine roots, and woody tissues in relation to growth, tissue N, and photosynthesis

Autotrophic respiration may regulate how ecosystem productivity responds to changes in temperature, atmospheric [CO₂] and N deposition. Estimates of autotrophic respiration are difficult for forest ecosystems, because of the large amount of biomass, different metabolic rates among tissues, and seasonal variation in respiration rates. We examined spatial and seasonal patterns in autotrophic respiration in a Pinus strobus ecosystem, and hypothesized that seasonal patterns in respiration rates at a common temperature would vary with [N] for fully expanded foliage and fine roots, with photosynthesis for foliage, and with growth for woody tissues (stems, branches, and coarse roots). We also hypothesized that differences in [N] would largely explain differences in maintenance or dormant‐season respiration among tissues. For April–November, mean respiration at 15 °C varied from 1.5 to 2.8 μmol kg^?1 s^?1 for fully expanded foliage, 1.7–3.0 for growing foliage, 0.8–1.6 for fine roots, 0.6–1.1 (sapwood) for stems, 0.5–1.8 (sapwood) for branches, and 0.2–1.5 (sapwood) for coarse roots. Growing season variation in respiration for foliage produced the prior year was strongly related to [N] (r² = 0.94), but fine root respiration was not related to [N]. For current‐year needles, respiration did not covary with [N]. Night‐time foliar respiration did not vary in concert with previous‐day photosynthesis for either growing or fully expanded needles. Stem growth explained about one‐third of the seasonal variation in stem respiration (r² = 0.38), and also variation among trees (r² = 0.43). We did not determine the cause of seasonal variation in branch and coarse root respiration, but it is unlikely to be directly related to growth, as the pattern of respiration in coarse roots and branches was not synchronized with stem growth. Seasonal variations in temperature‐corrected respiration rates were not synchronized among tissues, except foliage and branches. Spatial variability in dormant‐season respiration rates was significantly related to tissue N content in foliage (r² = 0.67), stems (r² = 0.45), coarse roots (r² = 0.36), and all tissues combined (r² = 0.83), but not for fine roots and branches. Per unit N, rates for P. strobus varied from 0.22 to 3.4 μmol molN^?1 s^?1 at 15 °C, comparable to those found for other conifers. Accurate estimates of annual autotrophic respiration should reflect seasonal and spatial variation in respiration rates of individual tissues.     

Soil nitrogen turnover in proximal and distal stem areas of European beech trees

In European beech (Fagus sylvatica L.) forests, a large proportion of the water and ion input to the soil results from stemflow which creates a soil microsite of high element fluxes proximal to the tree trunk. The soil proximal to the stem is considered to have different rates of nitrogen turnover which might influence the estimation of N-turnover rates at the stand scale. In a previous study we reported high nitrate fluxes with seepage proximal to the stems in a forest dominated by European beech in Steigerwald, Germany. Here, we investigated the soil nitrogen turnover in the top 15 cm soil in proximal (defined as 1 m² around beech stems) and distal stem areas. Laboratory incubations and in situ sequential coring incubations were used to determine the net rates of ammonification, nitrification, and root uptake of mineral nitrogen. In the laboratory incubations higher rates of net nitrogen mineralization and nitrification were found in the forest floor proximal to the stem as compared to distal stem areas. No stem related differences were observed in case of mineral soil samples. In contrast, the in situ incubations revealed higher rates of nitrification in the mineral soil in proximal stem areas, while net nitrogen mineralization was equal in proximal and distal areas. In the in situ incubations the average ratio of nitrification/ammonification was 0.85 in proximal and 0.34 in distal stem areas. The net nitrogen mineralization was 4.4 g N m^-2 90 day^-1 in both areas. Mineralized nitrogen was almost completely taken up by tree roots with ammonium as the dominant nitrogen species. The average ratio of nitrate/ammonium uptake was 0.69 in proximal and 0.20 in distal areas. The higher water content of the soil in proximal stem areas is considered to be the major reason for the increased rates of nitrification. Different nitrogen turnover rates in proximal stem areas had no influence on the nitrogen turnover rates in soil at the stand scale. Consequently, the observed high nitrate fluxes with seepage proximal to stems are attributed to the high nitrogen input by stemflow rather than to soil nitrogen turnover. This revised version was published online in August 2006 with corrections to the Cover Date.