STRUCTURALLY PRESERVED SPHENOPHYTES FROM THE TRIASSIC OF ANTARCTICA: VEGETATIVE REMAINS OF SPACIINODUM,GEN. NOV.

Sphenophyte remains of Early-Middle Triassic age are described from silicified peat collected in the Transantarctic Mountains of Antarctica. The new sphenophyte, Spaciinodum collinsonii sp. nov., is represented by ribbed, jointed stems with characteristic pith and carinal canals. Stems are relatively small, ranging from 1.8–3.0 mm in diameter, lack secondary tissues, and are characterized by vallecular canals that are restricted to nodal regions. The internodal vascular system consists of 12–18 collateral bundles which alternate between successive internodes. A complete vascular ring is present in the nodal region and is surrounded by a continuous double endodermis. Xylem is endarch and composed of elements ranging from annular to reticulate. The Antarctic sphenophyte is compared with other Gondwana fossil articulates and extant Equisetum. Superficial stomata suggest affinities with modern Equisetum subgenus Equisetum; however, some anatomical differences preclude assignment with living species.     

Structurally preserved sphenophytes from the Triassic of Antarctica: reproductive remains of Spaciinodum

Permineralized cones found organically attached to Spaciinodum collinsonii stems are described from the early Middle Triassic silicified flora from the Fremouw Formation of Antarctica, and the species diagnosis is emended to include the reproductive specimens. The apical cones are organized into internodal and leaf-bearing nodal regions. Nodal septations span the central pith and cortex, and thin fimbrils subdivide the internodal areas into smaller chambers. The vascular system consists of 31-33 continuous bundles that do not alternate in position between successive nodes and internodes. Simple sporangia are associated with the cortical chambers and occur in one whorl on the axis. Spores are small, lack elaters, and have no discernible ultrastructure preserved, and they are interpreted to be immature. The Antarctic cones are different in structure from typical cones of modern and fossil members of Equisetales; however, they share similarities with some morphologically aberrant cones of extant Equisetum and several Late Paleozoic and Mesozoic compression-impression fossils. Spaciinodum is now the most complete anatomically described Mesozoic sphenophyte.     

Floral-stimulus activity in tobacco stem pieces

The growth patterns of axillary buds of dayneutral tobacco (Nicotiana tabacum L. cv. Wisconsin 38) plants were assessed by using expiants of single buds attached to leafless stem cuttings and allowing the buds to grow to flowering without additional manipulation. Buds located 5, 10 and 15 nodes below the inflorescence were employed. For a given bud position, when a cutting had few internodes the growth pattern of a bud tended to fall into one of two groups: buds that produced few-noded shoots and buds that produced many-noded shoots. For example, in a group of 13 cuttings composed of bud 5 with 2 associated internodes, 11 buds produced 14.2 nodes (range, 11–17) and 2 buds produced 32.0 nodes (range, 30–34). As the number of internodes on the cutting increased, the number of buds producing few-noded shoots increased and the number of nodes produced decreased (e.g. in contrast to the data above, all 5th buds with 6 internodes produced 12.8 nodes; range 11–15). When cuttings from the 3 positions had the same number of internodes, the more apical cuttings had buds that produced fewer nodes (e.g. for cuttings with 6 internodes all 5th buds produced 12.8 nodes, all 10th buds produced 15.5 nodes and 85% of 15th buds produced few-noded shoots with 19.3 nodes). The number of nodes produced by a bud was a function of the original position of the stem piece and not the original position of the bud. That is, bud 5 associated with the 6 internodes below it produced 12.8 nodes and bud 10 associated with essentially the same 6 internodes (i.e. the 6 above it) produced 12.9 nodes while bud 10 associated with the 6 internodes below it produced 15.5 nodes. Thus, the number of nodes produced by a bud was dependent upon the original main-axis position of the cutting as well as the number of internodes on the cutting. Buds forced to grow out in situ on main axes devoid of leaves produced substantially more nodes than similar buds on cuttings. Buds isolated without associated internodes produced many-noded plants with a number of nodes similar to that of plants grown from seed. The simplest interpretation of these data is that stem pieces contain floral-stimulus activity and that this activity is present in a gradient with the highest activity being located in the apical part of the stem.We thank Susan Smith and Harry Roy (Rensselaer) for comments, and the National Science Foundation for financial support (IBN-9003739 to C.N.M.).     

An extensin-rich matrix lines the carinal canals in Equisetum ramosissimum, which may function as water-conducting channels

Background and Aims

The anatomy of Equisetum stems is characterized by the occurrence of vallecular and carinal canals. Previous studies on the carinal canals in several Equisetum species suggest that they convey water from one node to another.

Methods

Cell wall composition and ultrastructure have been studied using immunocytochemistry and electron microscopy, respectively. Serial sectioning and X-ray computed tomography were employed to examine the internode–node–internode transition of Equisetum ramosissimum.

Key Results

The distribution of the LM1 and JIM20 extensin epitopes is restricted to the lining of carinal canals. The monoclonal antibodies JIM5 and LM19 directed against homogalacturonan with a low degree of methyl esterification and the CBM3a probe recognizing crystalline cellulose also bound to this lining. The xyloglucan epitopes recognized by LM15 and CCRC-M1 were only detected in this lining after pectate lyase treatment. The carinal canals, connecting consecutive rings of nodal xylem, are formed by the disruption and dissolution of protoxylem elements during elongation of the internodes. Their inner surface appears smooth compared with that of vallecular canals.

Conclusions

The carinal canals in E. ramosissimum have a distinctive lining containing pectic homogalacturonan, cellulose, xyloglucan and extensin. These canals might function as water-conducting channels which would be especially important during the elongation of the internodes when protoxylem is disrupted and the metaxylem is not yet differentiated. How the molecularly distinct lining relates to the proposed water-conducting function of the carinal canals requires further study. Efforts to elucidate the spatial and temporal distribution of cell wall polymers in a taxonomically broad range of plants will probably provide more insight into the structural–functional relationships of individual cell wall components or of specific configurations of cell wall polymers.     

Phylogenetic diversification of Equisetum (Equisetales) as inferred from Lower Cretaceous species of British Columbia, Canada

Three types of anatomically preserved vegetative shoots with features that characterize crown group Equisetum have been discovered in Lower Cretaceous deposits (≈136 Ma) of British Columbia, Canada, suggesting the genus is much older than currently believed. Specimens include two types of aerial shoots described as E. haukeanum sp. nov. and E. vancouverense sp. nov. and one type of subterranean rhizome. Shoots are 1-2 mm in diameter, jointed, and in cross section have fluted stems with a hollow pith. Distinctive patterns of cortical sclerenchyma and different ridge morphologies characterize each shoot morphotype. Nodes display irregular branching, highly fused leaf sheaths, and a nodal diaphragm. The aerial stem morphospecies have vallecular canals on alternating radii with carinal canals of an equisetostele surrounded by only a few tracheids. No secondary tissues are produced. Bands of surficial stomata flank the furrows of one morphospecies. Rhizomes and aerial shoots are of a similar size, suggesting that the plants were equivalent in stature to the smallest living Equisetum species. These fossils augment our understanding of evolutionary transformations that led from Paleozoic Archaeocalamitaceae and Calamitaceae to crown group Equisetaceae, suggesting that the initial diversification of Equisetum began far earlier than suggested by molecular-clock-based estimates.     

双穗雀稗(Paspalum distichum)通透性生理和茎解剖结构补充研究

双穗雀稗根外皮层,茎角质层和茎节中的质外体屏障结构阻挡黄连素示踪液透过植物体。茎中机械组织包括周缘厚壁机械组织层,厚壁组织层和维管系统,髓部和皮层的蜂窝状厚角组织。茎中通气组织包括茎节间髓部和皮层的蜂窝状通气组织,茎节内的通气组织。双穗雀稗茎节间具有外侧、内侧和维管系统的质外体屏障,以及茎节周围质外体屏障的封闭结构。因此,该植物体完善的机械组织、通气组织、质外体屏障结构及其离子不通透性是其适应湿地环境的重要结构。     

Role of hormones on flower bud formation in thin-layer expiants of tobacco

Flower bud formation was studied in thin-layer tissue expiants of epidermis plus subepidermal cortex from the inflorescence ramifications ofNicotiana tabacum cv. Samsun. With appropriate hormone concentrations of BA and NAA expiants from flowerv and fruitbearing stalks regenerate flower buds only, while those from the internodes of the inflorescence ramifications produce generative as well as vegetative buds. In both types of expiants the number of buds formed depend mainly on the hormone concentrations but, in addition, the age of stalks and internodes from which expiants are taken also affects bud formation. Both ABA and JA inhibit flower bud formation in expiants of flower stalks. JA was shown to particularly inhibit bud initiation.     

Endogenous abscisic acid levels in stems and axillary buds of intact or decapitated broad-bean plants (Vicia faba L.)

Endogenous levels of abscisic acid (ABA) were measured by gas-liquid chromatography (electron capture) in stems and axillary buds of intact or decapitated broad-bean plants ( Vicia faba L. cv. Aguadulce). Endogenous ABA was distributed in the main axis according to a concentration gradient from the apical part of the stem towards the base. Axillary buds contained ABA levels which were from 4 to 9 times higher than those in the corresponding nodes and internodes. Decapitation of the plant was followed within 6 h by a large decrease of ABA levels in all the parts of the main axis. The diminution of ABA content was the most important in axillary buds released from apical dominance. Twenty-four hours after the decapitation, the ABA concentration further decreased in the upper parts of the stem, while no modification was observed in the basal parts of the stem containing the smallest levels of ABA.     

Cytokinin Habituation in Juvenile and Flowering Tobacco

The possible link between cytokinin and flowering was examine in tobacco. The degree of cytokinin autotrophy and the competence for cytokinin habitution were measured in callus derived from pith tissue of Nicotiana tabacum cvs. H425 an W38.Explants were taken from internodes at all positions up the stem in juvenile and mature plants. To test whether the competence of cells to form flowers was linked with crtokinin habituation, thin cell layer explants from comparable internodes were tested for their ability to form floral buds. Callus derived from the upper parts of plants showed cytokinin autotrophy whether or not the plants were flowering. Flower buds were formed only on thin cell layer explants from the upper part of plants which were already flowering. Cytokinin habituation and competence to flower are therefore not directly linked although cytokinin habituation could be a prerequisite for meristematic activity and for flowering. Pith from internodes in the lower half of mature pants formed callus which was cytokinin-dependent, although these same internodes in juvenile plants were cytokinin-autotrophic. The ability to form cytokinin-autotrophic callus was therefore greatest in the meristematic regions and was lost as the pith cells aged. Competence to habituate after 35 °C treatment was also shown by pith callus from a few internodes in the middle of the plant below those already forming cytokinin-autotropic callus.     

Shoot atmospheric contact is of little importance to aeration of deeper portions of the wetland plant Meionectes brownii; submerged organs mainly acquire O2 from the water column or produce it endogenously in underwater photosynthesis

Partial shoot submergence is considered less stressful than complete submergence of plants, as aerial contact allows gas exchange with the atmosphere. In situ microelectrode studies of the wetland plant Meionectes brownii showed that O₂ dynamics in the submerged stems and aquatic roots of partially submerged plants were similar to those of completely submerged plants, with internal O₂ concentrations in both organs dropping to less than 5 kPa by dawn regardless of submergence level. The anatomy at the nodes and the relationship between tissue porosity and rates of O₂ diffusion through stems were studied. Stem internodes contained aerenchyma and had mean gas space area of 17.7% per cross section, whereas nodes had 8.2%, but nodal porosity was highly variable, some nodes had very low porosity or were completely occluded (ca. 23% of nodes sampled). The cumulative effect of these low porosity nodes would have impeded internal O₂ movement down stems. Therefore, regardless of the presence of an aerial connection, the deeper portions of submerged organs sourced most of their O₂ via inwards diffusion from the water column during the night, and endogenous production in underwater photosynthesis during the daytime.     

STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. I. ANTARCTICYCAS,GEN. NOV., A TRIASSIC CYCAD STEM FROM THE BEARDMORE GLACIER AREA

Silicified stems with typical cycadalean anatomy are described from specimens collected from the Fremouw Formation (Triassic) in the Transantarctic Mountains of Antarctica. Axes are slender with a large parenchymatous pith and cortex separated by a narrow ring of vascular tissue. Mucilage canals are present in both pith and cortex. Vascular tissue consists of endarch primary xylem, a narrow band of secondary xylem tracheids, cambial zone, and region of secondary phloem. Vascular bundles contain uni- to triseriate rays with larger rays up to 2 mm wide separating the individual bundles. Pitting on primary xylem elements ranges from helical to scalariform; secondary xylem tracheids exhibit alternate circular bordered pits. Traces, often accompanied by a mucilage canal, extend out through the large rays into the cortex where some assume a girdling configuration. A zone of periderm is present at the periphery of the stem. Large and small roots are attached to the stem and are conspicuous in the surrounding matrix. The anatomy of the Antarctic cycad is compared with that of other fossil and extant cycadalean stems.     

The Eucalypt Lignotuber: a Position-dependent Organ

Observational and experimental evidence is presented to showthat the capacity to form a lignotuber is not restricted tothe cotyledonary, and a few succeeding, nodes on the primaryseedling stems of certain eucalypts, but is also a propertyof shoots arising from their accessory buds. Erect secondaryshoots from the lignotuber, may bear lignotubers at a few nodes,rhizostolons at many nodes along their length, and, like stolons,rhizomes may give rise to leafy shoots bearing basal lignotubers.These facts describe a so-called position effect for the productionof lignotubers, in the sense that the term has been used forother position-dependent phenomena in plants. Seedlings of lignotuberousspecies remain competent to form lignotubers over a long periodof adversity during which lignotubers are not formed. Shootsof non-lignotuberous species do not inhibit lignotuber developmentwhen grafted to lignotuberous species. eucalypts, lignotubers, position effect, vegetative propagation, tissue culture, rhizostolons, rhizomes     

There is a continuum of gas space in young plants of Avicennia marina

Gas-spaces form a continuum throughout 10-month-old Avicennia marina seedlings. This has direct connection with the atmosphere via the stomata and spongy mesophyll of the leaves, and via the lenticels that occur on all the internodes and the hypocotyl. There is therefore provision for aeration of the root system prior to the development of pneumatophores. The amount of gas space is greatest in the cortex, and in elongated organs (petiole, root, stem internodes and hypocotyl) it occurs as wide elongated channels that are all interconnected. Continuity is maintained of pneumatophores. The amount of gas space is greatest in the cortex, and in elongated organs (petiole, root, stem internodes and hypocotyl) it occurs as wide elongated channels that are all interconnected. Continuity is maintained across the nodes by a mass of spongy tissue which connects up with the elongated channels above and below. In all organs the amount of gas space in the pith is much less, but there it also occurs as interconnected elongated channels. The volume of gas space is greatest in the major roots and specialised lignified cells which become collapsed may play a role in supporting the very large gas spaces.     

不同生态型的喜旱莲子草对莲草直胸跳甲化蛹能力的影响

 喜旱莲子草(Alternanthera philoxeroides)是一种水陆两栖的外来杂草,我国1986年从美国引进了该草的专食性天敌莲草直胸跳甲(Agasicles hygrophila)进行生物防治。该天敌的化蛹能力受喜旱莲子草不同生态型的影响,从而影响到其生物防治的效果。从形态解剖的角度结合天敌和寄主植物的田间生理生态学研究了其机理。结果表明：水生型喜旱莲子草无次生结构,而陆生型则具紧密的次生结构和丰富的晶体;不同生态型的喜旱莲子草茎秆形态和结构特征有显著差异,同一生态型草不同位置结构特征也存在显著差异。主成分分析和聚类分析结果表明当λ=3.56时,不同生态型不同节间位置可分为3类,这3类正好可解释田间喜旱莲子草受控制的情况。相关分析表明莲草直胸跳甲的化蛹率与茎秆节间长、茎秆外直径、髓腔成简单正相关,与皮层薄壁细胞厚度和密度、维管束厚度及髓腔薄壁细胞的厚度成简单负相关;用逐步回归建立了化蛹率与形态和解剖结构特性的模型（y=1.533　2-0.248　3x3-0.051　2x4-1.634　9x5-0.957　7x6R2=0.999　9）,表明茎秆直径大小不是影响莲草直胸跳甲化蛹能力的最重要因子,主要原因为维管柱的厚度,其次髓部薄壁细胞厚度、皮层密度和皮层厚度也不同程度影响了莲草直胸跳甲的化蛹能力。从解剖学角度解释了莲草直胸跳甲对不同生态型喜旱莲子草控制作用的机理：对水生型喜旱莲子草有良好控制效果,而对陆生的中间型能起到一定抑制作用,对陆生的旱生型基本无控制作用。     

Relative importance of nodal roots and apical buds in the control of branching in Trifolium repens L.

Clonal species are characterised by having a growth form in which roots and shoots originate from the same meristem so that adventitious nodal roots form close to the terminal apical bud of stems. The nature of the relationship between nodal roots and axillary bud growth was investigated in three manipulative experiments on cuttings of a single genotype of Trifolium repens. In the absence of locally positioned nodal roots axillary bud development within the apical bud proceeded normally until it slowed once the subtending leaf had matured to be the second expanded leaf on the stem. Excision of apical tissues indicated that while there was no apical dominance apparent within fully rooted stems and very little in stems with 15 or more unrooted nodes, the outgrowth of the two most distal axillary buds was stimulated by decapitation in stems with intermediate numbers of unrooted nodes. Excision of the basal branches from stems growing without local nodal roots markedly increased the length and/or number of leaves on 14 distally positioned branches. The presence of basal branches therefore prevented the translocation of root-supplied resources (nutrients, water, phytohormones) to the more distally located nodes and this caused the retardation in the outgrowth of their axillary buds. Based on all three experiments we conclude that the primary control of bud outgrowth is exerted by roots via the acropetal transport of root-supplied resources necessary for axillary bud outgrowth and that apical dominance plays a very minor role in the regulation of axillary bud outgrowth in T. repens.     

Expression of a ribosomal protein gene in axillary buds of pea seedlings

Axillary buds of intact pea seedlings (Pisum sativum L. cv Alaska) do not grow and are said to be dormant. Decapitation of the terminal bud promotes the growth of these axillary buds, which then develop in the same manner as terminal buds. We previously showed that unique sets of proteins are expressed in dormant and growing buds. Here we describe the cloning, sequencing, and expression of a cDNA clone (pGB8) that is homologous to ribosomal protein L27 from rat. RNA corresponding to this clone increases 13-fold 3 h after decapitation, reaches a maximum enhancement of about 35-fold after 12 h, and persists at slightly reduced levels at later times. Terminal buds, root apices, and elongating internodes also contain pGB8 mRNA but fully expanded leaflets and fully elongated internodes do not. In situ hybridization analysis demonstrates that pGB8 mRNA increases in all parts of the bud within 1 h of decapitation. Under appropriate conditions, growing buds can be made to stop growing and become dormant; these buds subsequently can grow again. Therefore, buds have the capacity to undergo multiple cycles of growth and dormancy. RNA gel blots show that pGB8 expression is reduced to dormancy levels as soon as buds stop growing. However, in situ hybridization experiments show that pGB8 expression continues at growing-bud levels in the apical meristem for 2 d after it is reduced in the rest of the bud. When cultured stems containing buds are treated with indoleacetic acid at concentrations ≥10 μm, bud growth and expression of pGB8 in the buds are inhibited.     

Distribution of free and bound forms of cis-trans and trans-trans abscisic acid in broad-bean plants in relation to apical dominance

Levels of endogenous abscisic acid (ABA; free and bound forms) have been determined by gas chromatography in stems and buds of broad-bean plants ( Vicia faba L. cv. Aguadulce) in relation to apical dominance. A downward gradient of free cis-trans ABA occurred along the stem, from the apical bud to the roots. Except for the actively growing apical bud the levels of free cis-trans ABA were higher in the buds than in the corresponding nodes. An inverse correlation can be set up between levels of free cis-trans ABA and growth of buds, except for the cotyledonary ones. High levels of bound ABA ( cis-trans form) are correlated with the growth of the apical bud and that of the axillary bud ax1. The hormonal regulation of the growth of the cotyledonary buds, which contained high levels of trans-trans ABA in bound forms, is apparently different from that of the other buds.     

Polyamine levels in buds and twigs of Tilia cordata from dormancy onset to bud break

The fluctuations of free and bound polyamines (PAs) were studied in vegetative buds and underlying twigs of linden (Tilia cordata L.) from August to May, to assess the connection between PA levels and seasonal cycles of growth and dormancy. Outer and inner bud scales and shoot tips (short shoot tips with leaf initials in contiguous short internodes) were analyzed separately, as were phloem with cortex and xylem with pith tissue from twigs. Seasonal variations in PA levels were present in buds and twigs during the research period. The most abundant PA in buds and twigs in free and bound forms was spermidine followed by putrescine. PA amounts were low in buds and twigs in autumn. In twig tissues, free PAs were predominant whereas in bud scales, bound PAs accumulated over free PAs in autumn, first in inner scales and later in outer scales as well. PA levels did not increase dramatically during the onset of dormancy in autumn but lower temperatures and probable cold hardening correlated positively with bound PAs in bud scales. In shoot tips with leaf initials, and contiguous short internodes, free putrescine and spermidine levels rose simultaneously with bud burst and new growth, while bound PAs diminished quite radically from temporary bud scales and from growing shoot tips.     

Volatile constituents of balsam poplar: The phenol glycoside connection

The volatile metabolites of balsam poplar winter-dormant buds are a complex array of mono- and sesquiterpenoids with 1,8-cineol, trans-nerolidol and (+)-(1R,1′R)-α-bisabolol being the major components. On the other hand the volatiles of internodes (stems between buds) consist mainly of salicaldehyde and (+)-6-hydroxycyclohexanone with minor amounts of cyclohexan-1,2-dione and an unidentified compound. This is the first report of these cyclohexanones as natural products; salicortin, a phenol glycoside, appears to be their biosynthetic precursor. A second phenol glycoside, trichocarpin, is present in poplar internodes; and it is the progenitor of trichocarpigenin (benzyl gentisate), an easily formed artifact.     

The role of nodal and internodal responses in gravitropism and autotropism in Galium aparine L

Abstract This time course and location of gravitropically induced curvatures in stems of goosegrass (Galium aparine L.), a member of the Rubiaceae, have been investigated. In the early stages of the response (0–5 h), curvature develops throughout the growing region, and is followed by an autotropic straightening which affects the internodes only, leading to the production of essentially straight internodes some 15 h after the onset of gravistimulation. Curvatures developing in the nodal regions, however, continue to increase over this period, and are not subject to reversal by autotropism. The nodal curvatures are not entirely dependent on the presence of any other part of the plant, since marked curvatures can be induced in isolated nodal segments. This pattern of response leads ultimately to correction of the growth direction of the plant by means of curvature responses confined exclusively to the nodes, despite the initial participation of both nodes and internodes in the gravitropic reaction.