TRICHOME MORPHOLOGY AS AN INDICATOR OF HIGH RUBBER BEARING GUAYULE (PARTHENIUM ARGENTATUM GRAY) PLANTS IN NATIVE POPULATIONS

Parthenium argentatum Gray (guayule) and P. incanum (mariola) grow in close associations in their native habitat of Mexico. Variation in rubber concentration and morphology of guayule has been known for a long time. Studies of over 75 native guayule plants indicated the presence of at least three prominent forms of guayule plants. Group I guayule plants have oblanceolate leaves and leaf margins are entire to two-toothed. T-shaped leaf trichomes are with centrally attached stalk and cap cell with two blunt ends. Plants in this group are high in rubber, containing on the average 17% rubber. Group II guayule plants have narrow elliptic leaves and leaf margins are entire to four-toothed. T-shaped trichomes have an acentrally attached stalk and a cap cell with short end blunt, long end pointed and straight. Rubber content in these plants averages 10%. Group III guayule plants have ovate leaves and leaf margins are four- to eight-toothed. T-trichomes have an acentrally attached stalk and a cap cell with short end blunt, long end pointed and wavy or curved. These plants on the average contain 6% rubber. Morphological as well as biochemical data indicate the presence of mariola genes in the last two groups of plants and this has resulted in an increase in trichome length and a decrease in the rubber content. Group II guayule plants are of more common occurrence than the others. Based on the data presented here, high rubber bearing guayule plants in native stands can be easily selected by analyzing trichome morphology.     

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.     

Gland Cells in Resin Canal Epithelia in Guayule (Parthenium argentatum) in Relation to Resin and Rubber Production

Schizogenous resin canals develop in the pith and cortex ofthe primary stem tissue in guayule (Parthenium argentatum Gray).In secondary tissue concentric rings of resin canals are producedfrom derivatives of the vascular cambium. Both resin and rubberaccumulate in the epithelial cells of the canals. These havethe characteristics of gland cells. Resin is secreted into thecanals and rubber accumulates in the surrounding parenchymacells as well as the gland cells, especially in winter. Younggland cells contain modified plastids and smooth tubular endoplasmicreticulum. These organelles probably accommodate the compartmentalizedsteps of the isoprenoid biosynthetic pathway leading to theproduction of isopentenyl pyrophosphate. As these ultrastructuralcharacteristics only exist in young gland cells of the currentseason's growth they seem to be the sole source of the precursorsfor both resin and rubber formation. Parthenium argentatum, guayule, resin canals, gland cells, plastids, smooth endoplasmic reticulum, rubber, resin, epithelial cells, ultrastructure     

白鲜营养器官解剖结构及其与白鲜碱的积累关系

应用植物解剖学、组织化学及植物化学方法对白鲜营养器官根、茎、叶的结构及其生物碱的积累进行了研究。结果显示:(1)白鲜根的次生结构以及茎和叶的结构类似一般双子叶植物;白鲜多年生根主要由周皮、次生韧皮部、维管形成层以及次生木质部组成,根次生韧皮部中可见大量的淀粉、草酸钙簇晶、韧皮纤维以及油细胞;茎由表皮、皮层、维管组织和髓组成;叶由表皮、栅栏组织、海绵组织和叶脉组成;在茎和叶初生韧皮部的位置均分布有韧皮纤维,在叶表皮上分布有头状腺毛和非腺毛;在茎和叶紧贴表皮处分布有分泌囊。(2)组织化学分析结果显示:在白鲜多年生根中,生物碱类物质主要分布在周皮、次生韧皮部、维管形成层和木薄壁细胞中;在茎中,生物碱主要分布在表皮、皮层、韧皮部、木薄壁细胞及髓周围薄壁细胞中;在叶中,生物碱主要分布在表皮细胞、叶肉组织和维管组织的薄壁细胞;此外在分泌囊和头状腺毛中亦含有生物碱类物质。(3)植物化学结果显示,秦岭产白鲜根皮/白鲜皮、根木质部、茎和叶中白鲜碱含量分别为0.041%、0.012%、0.004%和0.002%,其中木质部中白鲜碱含量和其他部分地区白鲜皮中白鲜碱含量类似。研究表明,在秦岭产白鲜营养器官中,除根皮/白鲜皮外,在根木质部亦含有大量的白鲜碱,且在茎和叶中亦含有一定的白鲜碱,具有潜在的开发利用价值。     

Response of Maize and Sorghum to Excess Boron and Salinity

We have analyzed the stress-associated proteins in a high-rubber-yielding guayule (Parthenium argentatum Gray cv. 11591) leaves. Protein profiles in leaf fractions, resolved by SDS-PAGE and visualized by Coomassie Brilliant Blue staining, were different under various stresses. Changes in 25, 34 and 74 kDa polypeptides were noticed in response to low night temperature treatment while 24, 40, 47 and 81 kDa proteins responded to low irradiance. 23, 50, 75 and 82 kDa proteins were altered in response to drought stress. Certain proteins may play a significant role in the acquisition of tolerance in parenchyma cells of guayule leaves and might be useful markers to study adaptation in guayule plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

拐枣果序梗的发育解剖学研究

拐枣肉质膨大果序梗的发育过程可划分为前、中、后、末４个时期,前期为初生生长时期,内部结构类似一般双子叶植物茎的初生构造;中期为维管形成层活动时期,产生了不同其茎的次生木质部,由成片木质化的厚壁纤维细胞、一定量的木射线及星散在其中极少数的导管组成;后期为异常分生组织活动时期,初生木质部木薄壁组织及邻近少量髓细胞及邻近少量髓细胞转化为异常分生组织,向外产生切向排列的薄壁细胞,经扩大的切向伸长,使原导管     

Stem anatomy of Dolichos lablab Linn (Fabaceae): Origin of cambium and reverse orientation of vascular bundles

Secondary growth in the stem of Dolichos lablab is achieved by the formation of eccentric successive rings of vascular bundles. The stem is composed of parenchymatous ground tissue and xylem and phloem confined to portions of small cambial segments. However, development of new cambial segments can be observed from the obliterating ray parenchyma, the outermost phloem parenchyma and the secondary cortical parenchyma. Initially cambium develops as small segments, which latter become joined to form a complete cylinder of vascular cambium. Each cambial ring is functionally divided into two distinct regions. The one segment of cambium produces thick-walled lignified xylem derivatives in centripetal direction and phloem elements centrifugally. The other segment produces only thin-walled parenchyma on both xylem and phloem side. In mature stems, some of the axial parenchyma embedded deep inside the xylem acquires meristematic activity and leads to the formation of thick-walled xylem derivatives centrifugally and phloem elements centripetally. The secondary xylem comprises vessel elements, tracheids, fibres and axial parenchyma. Rays are uni-multiseriate in the region of cambium that produces xylem and phloem derivatives, while in some of the regions of cambium large multiseriate, compound, aggregate and polycentric rays can be noticed.     

扁圆封印木（相似种）茎干的解剖特征

贵州省水城矿区晚二叠世煤核中扁圆封印木（相似种Ｓｉｇｉｌｌａｒｉａ ｃｆ．ｂｒａｒｄｉｉＢｒｏｎｇｎ．）茎干的主要解剖特征如下：管状中柱,具多边形薄壁细胞组成的髓。初生木质部成环带状,外缘呈规则的齿槽状,向心式发育。次生木质部显束状特征,横切面管胞为方圆至长方形,纵切面为梯状壁增厚,并具流苏纹。射线１—２列细胞宽,数个至十余个细胞高。叶迹起源于初生木质部外缘的槽中,中始式,但以向心发育为主。     

Anatomical Characteristics of the Stem of Sigillaria cf. brardii from Coal Balls in Guizhou Province,China

The stem specimens of Sigillaria cf. brardii were collected from the coal balls of Upper Permian in Shuicheng Coal Mines in Guizhou Province. The main anatomical characteristics of Sigillaria cf. brardii are described as follows: The stem is siphonostelic, with pith composed entirely of polygonal parenchyma cells, there are secondary walls in some pith cell cavities these secondary walls show the characters of cell division. Surrounding the pith is the continuous cylindrical primary xylem which consists entirely of tracheids. The outermost, and part are the protoxylem elements show spiral secondary thickenings. In cross section, the outer edge of exarch primary xylem appears regularly sinuous, with trace of mesarch leaf originating from the furrows. The centripetal metaxylem is characterized by scalariform wall thickenings on the tracheids, and delicated strands of secondary wall materials extending between abjacent bars, these structures are called fimbris, or williamson striations, and are characteristic in lepidodendrids. The secondary xylem consists of tracheids and vascular rays. The tracheids, too, have scalariform wall thickenings and fimbris. The rays are one-to twocell width and several to more than ten cells in height.     

Developmental anatomy of vascular cambium and periderm ofBotrypus virginianus and its bearing on the systematic position of ophioglossaceae

The developmental anatomy of the vascular cambium and periderm ofBotrypus virginianus was studied, and its bearing on the systematic position of Ophioglossacease is discussed. The cambial zone including cambium is initiated in a procambial ring of the stem before primary vascular tissue is well differentiated. The presumed cambium is composed of fusiform and ray initials. The cambium is extremely unequally bifacial, producing secondary xylem centripetally, and quite a small number of parenchymatous cells but no secondary phloem centrifugally. The cambial activity persists long, although it is very low in the mature part of the stem. It seems that the circumferential increase of the cambium is accommodated by an increase in the number of cambial initials. Secondary xylem is nonstoried and composed of tracheids with circular-bordered pits with evenly thick pit membranes, and uniseriate or partly biseriate radial rays. It makes up the bulk of the stem xylem. Periderm is formed almost entirely around the stem, simultaneous with its increment due to the secondary xylem. The combination of these anatomical features of secondary tissue supports the idea that Ophioglossaceae are living progymnosperms.     

Cellular localization of aquaporin mRNA in hybrid poplar stems

? Premise of the study: Aquaporins (AQPs) are channel proteins, and their function is mostly associated with transmembrane water transport. While aquaporin genes are known to be expressed in woody poplar stems, little is known about AQP expression at the cellular level. Localization of AQP expression to particular cell and tissue types is a necessary prerequisite in understanding the biological role of these genes. ? Methods: Subsets of plants were subjected to 6 wk of high nitrogen fertilization (high N plants) or to a controlled drought. Experimental treatments affected cambial activity and wood anatomy. RNA in situ hybridization was used to characterize spatial expression of three AQP genes in stem cross sections. ? Key results: The strongest labeling consistently occurred in the cambial region and in adjacent xylem and phloem cells. Expression was also detected in rays. Contact cells exhibited high expression, while expression in other ray cells was more variable. High N plants exhibited a broader band of expression in the cambial region than plants receiving only adequate N fertilization (control plants) and plants subjected to drought. ? Conclusions: Water channels in stems were expressed in a manner that allows hydraulic coupling between xylem and other tissues that may serve as water reservoirs, including phloem and pith parenchyma. Expression of AQPs in rays may increase radial flow of water from xylem and phloem to the cambial region where AQPs may help sustain rapid cell division and expansion of developing vessel elements.     

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.     

Distribution of leaf assimilates in the stem of Picea abies L.

Summary Autoradiographic and microautoradiographic studies of 2-year-old Picea abies plants show that in summer leaf assimilates from the second-year shoot are translocated basipetally. Leaf assimilates are first transported to the stem via leaf trace phloem, then to the base of the stem in the sieve cells of the latest increment of secondary phloem. On the way down leaf assimilates move radially from sieve cells into cells of the phloem parenchyma, the vascular cambium, the rays, the inner periderm and certain cells of pith and cortex, including the epithelial cells surrounding the resin ducts. Other cells of pith and cortex remain nearly free of label, despite the long translocation time (20 h). With the exception of the vascular cambial cells, the stem cells that gain leaf assimilates by radial distribution coincide with those that contain chlorophyll and starch.     

六盘山鸡爪大黄蒽醌类化合物积累特征的研究

采用多种组织化学方法研究了六盘山鸡爪大黄营养器官中蒽醌类化合物的积累特征.结果显示:蒽醌类化合物在根中分布于周皮的木栓层和栓内层、次生维管组织的维管射线和根中央的部分木薄壁细胞内,且维管射线是根中贮藏和积累蒽醌类化合物的主要组织;在根茎中分布于周皮的木栓层和栓内层、次生维管组织的形成层和维管射线,以及髓的异常维管束射线中,且维管射线是根茎中贮藏和积累蒽醌类化合物的主要组织;在茎中主要分布于表皮、近表皮皮层和维管束的维管束鞘及其薄壁细胞,大型和小型维管束之间和周围的部分薄壁细胞,以及髓射线中有不同程度的分布;在叶中主要积累在叶柄的表皮、叶柄和大叶脉的部分基本组织、维管束的部分薄壁细胞等部位.结果表明,六盘山鸡爪大黄的根和根茎是蒽醌类化合物贮藏和积累的主要器官,维管射线是其贮藏和积累的主要组织,而且各营养器官中蒽醌类化合物积累的数量与植物各相关器官组织的发育程度、细胞中含淀粉粒的多少存在着一定的相关性.     

Anomalous secondary vascular tissue inHelminthostachys zeylanica (Ophioglossaceae)

The vascular anatomy ofHelminthostachys zeylanica was examined with special reference to anomalous secondary tissue. Primary xylem development gradually takes place centrifugally. In branched rhizomes with destroyed apices, the vascular cylinder apical to the insertion of branch traces is generally composed of primary xylem, accessory xylem, inner parenchyma of radially arranged cells, outer parenchyma of irregularly arranged cells, and partly crushed phloem, listed in order going outwards. The accessory xylem as well as the inner parenchyma ofHelminthostachys zeylanica is probably secondarily produced, partly to contribute to the branch traces, in a position corresponding to that of secondary vascular tissue developed from a normal cambium inBotrychium sensu lato. It is suggested that although a cambium is lacking inHelminthostachys zeylanica, the secondary vascular tissues are comparable between the genera. The phylogenetic implication of this tissue is discussed.     

ANOMALOUS GROWTH AND VEGETATIVE ANATOMY OF SIMMONDSIA CHINENSIS

The anatomy of the stem, root, and leaf of Simmondsia chinensis (Link) Schneider was investigated, as well as the mode of tissue formation in the stem. Perivascular tissue is present as part of the primary body; outermost cell layers of this tissue mature as a fibrous sheath. The first short-lived extrafascicular cambium is generated within the remaining parenchymatous perivascular tissue. Successive independent extrafascicular cambia, organized as complete rings or large arcs, arise within peripheral conjunctive parenchyma produced by previous cambia. Extrafascicular cambia produce secondary xylem centripetally and conjunctive tissue bands and strands of secondary phloem centrifugally. Conjunctive tissue initials produce raylike structures of conjunctive tissue; true vascular rays are absent. The phellogen is actually a region of transition where the peripheral conjunctive parenchyma of previous extrafascicular cambia undergoes further cellular subdivision; a true phellogen is lacking. Xylem bands do not represent annual or seasonal growth increments, and secondary growth in Simmondsia is an unequivocal example of the “concentric” anomaly.     

Auxin-Responsive DR5 Promoter Coupled with Transport Assays Suggest Separate but Linked Routes of Auxin Transport during Woody Stem Development in Populus

Polar auxin transport (PAT) is a major determinant of plant morphology and internal anatomy with important roles in vascular patterning, tropic growth responses, apical dominance and phyllotactic arrangement. Woody plants present a highly complex system of vascular development in which isolated bundles of xylem and phloem gradually unite to form concentric rings of conductive tissue. We generated several transgenic lines of hybrid poplar (Populus tremula x alba) with the auxin-responsive DR5 promoter driving GUS expression in order to visualize an auxin response during the establishment of secondary growth. Distinct GUS expression in the cambial zone and developing xylem-side derivatives supports the current view of this tissue as a major stream of basipetal PAT. However, we also found novel sites of GUS expression in the primary xylem parenchyma lining the outer perimeter of the pith. Strands of primary xylem parenchyma depart the stem as a leaf trace, and showed GUS expression as long as the leaves to which they were connected remained attached (i.e., until just prior to leaf abscission). Tissue composed of primary xylem parenchyma strands contained measurable levels of free indole-3-acetic acid (IAA) and showed basipetal transport of radiolabeled auxin (³H-IAA) that was both significantly faster than diffusion and highly sensitive to the PAT inhibitor NPA. Radiolabeled auxin was also able to move between the primary xylem parenchyma in the interior of the stem and the basipetal stream in the cambial zone, an exchange that was likely mediated by ray parenchyma cells. Our results suggest that (a) channeling of leaf-derived IAA first delineates isolated strands of pre-procambial tissue but then later shifts to include basipetal transport through the rapidly expanding xylem elements, and (b) the transition from primary to secondary vascular development is gradual, with an auxin response preceding the appearance of a unified and radially-organized vascular cambium.     

Stem and leaf anatomy of the arborescent Cucurbitaceae Dendrosicyos socotrana with comments on the evolution of pachycauls from lianas

Stem and leaf anatomy of Dendrosicyos socotrana, the only arborescent Cucurbitaceae, are examined for correlations with life form and ecology and are used to test hypotheses regarding features adaptive in scandent plants. The stem consists mainly of ray and conjunctive parenchyma with small strands of xylem forming an anastomosing net throughout the trunk. Xylem strands bear vascular cambia that produce secondary phloem, representing the first report of successive cambia in Cucurbitales. Some features characteristic of lianas, such as very wide vessel elements with thick walls, are absent from Dendrosicyos. Other features, such as very wide rays and abundant axial parenchyma, are present in both Dendrosicyos and lianas but appear to serve differing roles in these different life forms. It is suggested that lianas have numerous features that are readily co-opted in the evolution of pachycaul trees and that the evolution of pachycauls from lianas has happened repeatedly in the core eudicots.     

Sclerospiroxylon xinjiangensis nov. sp., a gymnospermous wood from the Kungurian (lower Permian) southern Bogda Mountains,northwestern China: Systematics and palaeoecology

A new silicified wood, Sclerospiroxylon xinjiangensis Wan, Yang et Wang nov. sp., is described from the Cisuralian (lower Permian) Hongyanchi Formation in southeast Tarlong section, Turpan City, Xinjiang Uygur Autonomous Region, northwestern China. The fossil wood is composed of pith, primary xylem and Prototaxoxylon-type secondary xylem. The pith is solid, circular, heterocellular, with sclerenchyma and parenchyma. The primary xylem is endarch to mesarch, with scalariform thickenings on tracheid walls. The secondary xylem is pycnoxylic, composed of tracheids and parenchymatous rays. Growth rings are distinct. Tracheids have mostly uniseriate, partially biseriate araucarian pitting on their radial walls. Helical thickenings are always present on both the radial and the tangential walls. Rays are 2–14 cells high, with smooth walls. There are 2 to 7, commonly 2 to 4 cupressoid pits in each cross-field. Leaf traces suggest that S. xinjiangensis nov. sp. was evergreen with a leaf retention time of at least 15 years. Based on the sedimentological evidence, growth rings within the S. xinjiangensis nov. sp. could have been caused by seasonal climatic variations, with unfavorable seasons of drought or low temperature. Low percentage of latewood in each growth ring is probably due to the intensity of climatic seasonality and/or long leaf longevity.     

MODIFIED REMNANTS OF CENTRIPETAL XYLEM IN THE LEAF TRACE OF CEPHALOTAXUS

A study of the leaf traces at the nodes in various species and varietal forms of Taxus, Torreya, Amentotaxus and Cephalotaxus reveals, only in Cephalotaxus, an unusual type of parenchymatous tissue associated with the xylem of the leaf trace. The cells of this tissue occur in one to three layers, have abundant cytoplasm and conspicuous nuclei. The thin walls of these cells are devoid of pits and show spiral or spiral-reticulate thickenings. These thickenings, although readily taking the counterstain, reveal the presence of lignin as determined by the phloroglucin test and by fluorescence microscopy. This tissue is always internal—that is, adaxial—to the protoxylem of the trace. From the node it accompanies the trace for a short distance into the leaf base, where it gives way centrally to the typical leaf parenchyma and laterally to the transfusion tissue on the flanks of the bundle. In the basipetal direction it is in contact with the inner face of the annular protoxylem of the stele, eventually disappearing in the typical pith parenchyma. This tissue occasionally reveals instances of well-lignified tracheid-like centripetal elements. On the basis of the characteristics of this tissue, it is suggested that its origin lies in former centripetal xylem. The significance of this tissue to the evolution of the stele and the systematic position of Cephalotaxus is discussed.