红树植物地上根根端的发育,结构与生态适应

观察了分布于海南和广东省热带、亚热带海岸潮间带的６ 科９ 属１５ 种红树植物各种地上根根端与胚轴顶端的发育及结构。红树科（Ｒｈｉｚｏｐｈｏｒａｃｅａｅ）４ 属的支柱根根端,以显著的柱状分生组织区、根冠柱、栓质化的根冠为特征。老鼠簕属（Ａｃａｎｔｈｕｓ）、海榄雌属（Ａｖｉｃｅｎｎｉａ）的支柱根和海榄雌属、海桑属（Ｓｏｎｎｅｒａｔｉａ）的出水通气根根端都有短的根冠柱,薄的栓质化根冠或根冠的木栓层具有生长层。大多数红树植物的根端很早开始原形成层的活动,表皮之下常见外皮层,周皮常在表皮下层出现等独特的发育式样、结构特征,显示了环境的选择作用和红树植物的趋同适应     

REEXAMINATION OF PORE WATER SULFIDE CONCENTRATIONS AND REDOX POTENTIALS NEAR THE AERIAL ROOTS OF RHIZOPHORA MANGLE AND AVICENNIA GERMINANS

Soil redox potentials and pore water sulfide concentrations on a mangrove island in the Belizean barrier reef system were significantly correlated with the presence of the aerial roots of mangrove trees. Sulfide concentrations were three to five times lower near the prop roots of Rhizophora mangle (red mangrove) and the pneumatophores of Avicennia germinans (black mangrove) than in adjacent (≤ 1 meter away) unvegetated sediment. Soil redox potentials were also significantly higher near the aerial roots. A comparison of the two species revealed that sulfide concentrations in the rhizosphere of R. mangle were as low as that of A. germinans. However, sulfide concentrations in areas occupied by the black mangrove were variable and a function of pneumatophore density. The occurrence of an oxidized rhizosphere around the roots of both species suggests that the adult trees are equally capable of exploiting reduced sediments as long as their respective pathways for root aeration are functional.     

钦州湾红树林丛枝菌根初步研究

海漆 (Excoecaria agallocha)、桐花树 (Aegiceras corniculatum)、秋茄 (Kandlia candel)、白骨壤 (Avi-cennia marina)是钦州湾分布广、生长量大的 4种红树植物 ,该项研究初步调查了丛枝菌根真菌在这四种植物根系的定居情况。在这四种植物的根际土壤均分离到丛枝菌根真菌孢子 ,其孢子密度以海漆根际的最高 ,其次为桐花树、秋茄、白骨壤。同时 ,海漆根系的侵染率和物种丰富度也最高 ,但在所取的白骨壤根样中没有观察到丛枝菌根的侵染。菌根侵染主要是以根内菌丝、胞内菌丝膨大扭曲、泡囊等形态出现。海水和土壤质地是影响菌根侵染率的主要因素。在所采土样中仅发现球囊霉属 (Glomus)、无梗囊霉属 (Acaulospora)丛枝菌根真菌 ,计有 1 7种和多个未确定种。     

Diversity of endophytic fungi in the roots of mangrove species on the west coast of India

Because mangrove plant species are a valuable source of useful metabolites, their endophytes have gained more importance. Randomly sampled surface-sterilized whole root segments of four mangrove plant species, Acanthus ilicifolius, Avicennia officinalis, Rhizophora mucronata, and Sonneratia caseolaris from the mangroves of Udyavara (Karnataka) on the west coast of India, were characterized for fungal communities by direct plating, damp chamber, and bubbling chamber incubation methods. The richness of endophytic fungal species from whole root segments after direct plating and damp chamber incubation was greatest for R. mucronata than for other plants (18 vs. 8-13). Incubation of whole root segments in bubbling chambers yielded conidia of two freshwater hyphomycetes: Mycocentrospora acerina (in Avicennia officinalis) and Triscelophorus acuminatus (in R. mucronata and in S. caseolaris). Surface-sterilized whole root and root bark segments of R. mucronata sampled from the mid-tide level on direct plating yielded more fungi than that of the root segments sampled from low-tide and high-tide levels. The greatest number of isolates, species richness, and diversity of fungi were shown by the whole root segments of R. mucronata from the mid-tide level. Rarefaction indices also revealed the highest expected number of species out of 150 random isolations from the mid-tide level samples of whole root and root bark segments of R. mucronata. The present study showed that fungi in mangrove roots are composed of a consortium of soil, marine, and freshwater fungi.     

Changes in root cap pH are required for the gravity response of the Arabidopsis root

Although the columella cells of the root cap have been identified as the site of gravity perception, the cellular events that mediate gravity signaling remain poorly understood. To determine if cytoplasmic and/or wall pH mediates the initial stages of root gravitropism, we combined a novel cell wall pH sensor (a cellulose binding domain peptide-Oregon green conjugate) and a cytoplasmic pH sensor (plants expressing pH-sensitive green fluorescent protein) to monitor pH dynamics throughout the graviresponding Arabidopsis root. The root cap apoplast acidified from pH 5.5 to 4.5 within 2 min of gravistimulation. Concomitantly, cytoplasmic pH increased in columella cells from 7.2 to 7.6 but was unchanged elsewhere in the root. These changes in cap pH preceded detectable tropic growth or growth-related pH changes in the elongation zone cell wall by 10 min. Altering the gravity-related columella cytoplasmic pH shift with caged protons delayed the gravitropic response. Together, these results suggest that alterations in root cap pH likely are involved in the initial events that mediate root gravity perception or signal transduction.     

A Histochemical Study of Phosphatases in Root Apical Meristems

Root apices, representing different types of apical tissue organization,were examined with the techniques of enzyme histochemistry.The distribution of acid phosphatase, adenosine triphosphatase,and glucose 6-phosphatase was determined for the various tissuesof the root apices. Phosphatases demonstrated intense activityin the root cap, protoderm, and cortex of all the roots tested.Moderate phosphatase activity was observed in the procambialstrands and differentiating tracheary elements. No activitywas evident in the promeristem and root cap columella. Theseresults are discussed with regard to the morphology of rootapices, and an attempt is made to elucidate possible physiologicalfunctions in relation to enzyme localization.     

世界红树植物区系

探讨了世界红树林植物区系的种类组成及其特点。确认全世界共有红树植物16科24属84种(含12变种)，其中真红树为11科16属70种(含12变种)，半红树为5科8属14种。东方类群有14科18属74种(含12变种)，以／legiceras，Osbornia，／legialitis，Bruguiera，Ceriops，Kandelia，Scyphiphora和。Nypa等属为特征；西方类群有5科6属10种，具有单种特有科皮利西科Pelliceraceae以及laguncularia属。中国红树植物区系有12科15属26种(含1变种)，其中特有种4种。海南的红树植物种类最为丰富，占全国的96．2％；广东次之，占42．3％。台湾记载的红茄苳(Rhizophoram,ucronata)其实为红树榄R．stylose之误。     

广西的红树林

本文主要讨论广西沿海的红树林的植物种类成分、外貌、适应形态学特点、群落类型和演替规律,以及生产管理问题。 该地区的红树植物种类计有8科、12属、12种,以红树科植物占优势。群落类型有:白骨壤群落、桐花树群落、秋茄-桐花树群落、红海榄群落、木榄群落、木榄-桐花树群落、桐花树-海漆稀树群落和红海榄+秋茄-桐花树群落等。     

DEVELOPMENTAL ANATOMY OF LIGHT-INDUCED ROOT NODULATION BY ZAMIA PUMILA L. SEEDLINGS IN STERILE CULTURE

The developmental anatomy of Zamia pumila L. root apices was studied during light-induced nodulation. Dark-grown roots had an apical organization identical to that of other cycads and similar to that of other gymnosperms. A distinct protoderm was not observed in these roots, which had a large open meristem and a root cap with a well-defined columella. During nodulation, the meristem became reduced in size, and its constituent cells became vacuolate until all but a few resembled ground tissue. The root cap senesced during nodulation, and a recognizable root cap was absent from mature nodules. A file of densely cytoplasmic cells with centrally positioned nuclei developed in the nodule cortex. This layer was continuous across the nodule apex, and was identical to the presumptive algal-zone described previously by other authors. Light-induced nodules branched dichotomously and were identical to algal-free nodules described by other authors. In dichotomously branched nodules, each lobe was covered by a parenchymatous mantle analogous to a root cap. A unicellular layer similar to the presumptive algal zone spanned the gap between opposite nodule lobes, and extended beneath each lobe before terminating in the cortex. Typical meristematic regions were not observed in these nodules. Based on cell sizes and patterns, a meristematic zone was thought to exist between the mantle and the inner cortex.     

A MUCILAGINOUS ROOT SHEATH IN ERICACEAE

A prominent mucilaginous sheath surrounding the root tips of plants in the family Ericaceae is described. The sheath was ubiquitous in all species examined. These included representatives of both subfamilies and all tribes of the family. Anatomical studies indicated that the sheath was not the breakdown product of root cap cells but rather that it was formed exterior to a thickened cell wall or cellular layer at the root tip. Although the mucilaginous sheath stained readily with ruthenium red (a specific test for pectins), it was not possible to show it to be one of the common pectins by microchemical tests. Relationships between the soil environment and the extent and condition of the sheath are discussed. Possible significance or functions of the sheath are suggested.     

Standing crop and aboveground biomass partitioning of a dwarf mangrove forest in Taylor River Slough,Florida

The structure and standing crop biomass of a dwarf mangrove forest, located in the salinity transition zone ofTaylor River Slough in the Everglades National Park, were studied. Although the four mangrove species reported for Florida occurred at the study site, dwarf Rhizophora mangle trees dominated the forest. The structural characteristics of the mangrove forest were relatively simple: tree height varied from 0.9 to 1.2 meters, and tree density ranged from 7062 to 23 778 stems ha^–1. An allometric relationship was developed to estimate leaf, branch, prop root, and total aboveground biomass of dwarf Rhizophora mangle trees. Total aboveground biomass and their components were best estimated as a power function of the crown area times number of prop roots as an independent variable (Y = B × X^–0.5083). The allometric equation for each tree component was highly significant (p<0.0001), with all r² values greater than 0.90. The allometric relationship was used to estimate total aboveground biomass that ranged from 7.9 to 23.2 ton ha^–1. Rhizophora mangle contributed 85% of total standing crop biomass. Conocarpus erectus, Laguncularia racemosa, and Avicennia germinans contributed the remaining biomass. Average aboveground biomass allocation was 69% for prop roots, 25% for stem and branches, and 6% for leaves. This aboveground biomass partitioning pattern, which gives a major role to prop roots that have the potential to produce an extensive root system, may be an important biological strategy in response to low phosphorus availability and relatively reduced soils that characterize mangrove forests in South Florida.     

Root apical organization inArabidopsis thaliana 1. Root cap and protoderm

Summary We investigated the development of the root cap and protoderm inArabidopsis thaliana root tips.A. Thaliana roots have closed apical organization with the peripheral root cap, columella root cap and protoderm developing from the dermatogen/calyptrogen histogen. The columella root cap arises from columella initials. The initials for the peripheral root cap and protoderm are arranged in a collar and the initiation event for these cells occurs in a sequential pattern that is coordinated with the columella initials. The resulting root cap appears as a series of interconnected spiraling cones. The protoderm, in three-dimensions, is a cylinder composed of cell files made up of packets of cells. The number of cell files within the protoderm cylinder increases as the root ages from one to two weeks. The coordinated division sequence of the dermatogen/calyptrogen and the increase in the number of protoderm cell files are both features of post-embryonic development within the primary root meristem.Abbreviations RCP root cap/protoderm - CI columella initial - PI protoderm initial     

广西英罗湾红树植物群落的研究

 对广西英罗湾红树植物群落的种类组成、类型、外貌、结构、物种多样性和演替等进行了较系统的探讨。组成群落的优势红树植物有木榄、红海榄、秋茄、桐花树、白骨壤和海漆6种,隶属6属4科。主要的群落类型有木揽群落、木榄+红海榄群落、红海榄群落、红海榄+秋茄群落、秋茄群落、秋茄+桐花树群落、秋茄+白骨壤群落、桐花树群落、白骨壤群落、白骨壤+桐花树群落和海漆群落等11个群系。群落外貌由单叶、革质、全缘、中型叶的高位芽植物决定。群落层次结构简单．单层或两层。和陆地植物群落相比较,组成群落的红树植物的物种多样性较低。受潮滩土壤质地、养分状况、环境盐度和潮淹程度以及红树植物自身对盐渍生境的适应性等因子制约,群落的分布形成了明显的生态系列。随着海平面的相对降低和土壤理化性质的改善,群落具有向陆生植物群落演化的趋势。     

DIFFERENTIAL OXIDATION OF MANGROVE SUBSTRATE BY AVICENNIA GERMINANS AND RHIZOPHORA MANGLE

Both Avicennia germinans (black mangrove) and Rhizophora mangle (red mangrove) are commonly found in anaerobic substrate. Black mangrove roots create oxidized rhizospheres substantially larger than those described for other plant species. When air cannot enter the root system through the pneumatophores, the rhizospheres become as reduced as nearby un vegetated soil. The presence of red mangrove, in contrast, appears to have no effect on the oxidation state of surrounding anaerobic soils. It is likely that these data help to explain the distributions of both species in intertidal associations.     

Touch modulates gravity sensing to regulate the growth of primary roots of Arabidopsis thaliana

Plants must sense and respond to diverse stimuli to optimize the architecture of their root system for water and nutrient scavenging and anchorage. We have therefore analyzed how information from two of these stimuli, touch and gravity, are integrated to direct root growth. In Arabidopsis thaliana, touch stimulation provided by a glass barrier placed across the direction of growth caused the root to form a step-like growth habit with bends forming in the central and later the distal elongation zones. This response led to the main root axis growing parallel to, but not touching the obstacle, whilst the root cap maintained contact with the barrier. Removal of the graviperceptive columella cells of the root cap using laser ablation reduced the bending response of the distal elongation zone. Similarly, although the roots of the gravisensing impaired pgm1-1 mutant grew along the barrier at the same average angle as wild-type, this angle became more variable with time. These observations imply a constant gravitropic re-setting of the root tip response to touch stimulation from the barrier. In wild-type plants, transient touch stimulation of root cap cells, but not other regions of the root, inhibited both subsequent gravitropic growth and amyloplast sedimentation in the columella. Taken together, these results suggest that the cells of the root cap sense touch stimuli and their subsequent signaling acts on the columella cells to modulate their graviresponse. This interaction of touch and gravity signaling would then direct root growth to avoid obstacles in the soil while generally maintaining downward growth.     

Early root cap development and graviresponse in white clover (Trifolium repens) grown in space and on a two-axis clinostat.

White clover (Trifolium repens) was germinated and grown in microgravity aboard the Space Shuttle (STS-60, 1994; STS-63, 1995), on Earth in stationary racks and in a slow-rotating two-axis clinostat. The objective of this study was to determine if normal root cap development and early plant gravity responses were dependent on gravitational cues. Seedlings were germinated in space and chemically fixed in orbit after 21, 40, and 72 h. Seedlings 96 h old were returned viable to earth. Germination and total seedling length were not dependent on gravity treatment. In space-flown seedlings, the number of cell stories in the root cap and the geometry of central columella cells did not differ from those of the Earth-grown seedlings. The root cap structure of clinorotated plants appeared similar to that of seedlings from microgravity, with the exception of three-day rotated plants, which displayed significant cellular damage in the columella region. Nuclear polarity did not depend on gravity; however, the positions of amyloplasts in the central columella cells were dependent on both the gravity treatment and the age of the seedlings. Seedlings from space, returned viable to earth, responded to horizontal stimulation as did 1 g controls, but seedlings rotated on the clinostat for the same duration had a reduced curvature response. This study demonstrates that initial root cap development is insensitive to either chronic clinorotation or microgravity. Soon after differentiation, however, clinorotation leads to loss of normal root cap structure and plant graviresponse while microgravity does not.     

A morphometric analysis of cellular differentiation in root caps ofCucurbita peop

In order to quantify the ultrastructural changes that occur during cellular differentiation in an “open” type of root cap, we have performed a morphometric analysis of the ultrastructures of calyptrogen, columella, and peripheral cells of the root cap ofCucurbita pepo. The relative volumes of nuclei, nucleoli, and mitochondria decrease as cells move (i.e., differentiate) through the root cap. Before cells are sloughed from the cap, the relative volume of the vacuole increases by 250%. The relative volumes of plastids and plastid starch increase as calyptrogen cells differentiate into columella cells, but decrease as columella cells differentiate into peripheral cells. Dictyosomal volumes increase only as columella cells differentiate into peripheral cells. These results indicate that the five cell types comprising the root cap ofC.pepo are each characterized by a unique structure, and that the ultrastructural changes associated with cellular differentiation in root caps are organelle specific. These results are discussed relative to the functions of the various cell types of the root cap.     

ONTOGENETIC REORGANIZATION OF THE ROOT MERISTEM IN THE COMPOSITAE

The organization of the root meristem in selected Compositae was investigated to determine whether changes in the pattern of cell arrangement occurred during root growth in species other than Helianthus annuus. Embryonic, short, and long primary roots of one species of each of twelve genera were prepared for microscopic examination. Additional intermediate growth stages were prepared for Echinacea pallida. The meristem of embryonic roots showed layers of initials typical for dicotyledons. The meristem in many of the short roots of eight species was reorganized by the development of a secondary columella. The long roots showed patterns similar to the embryonic roots. In three species which maintained closed meristems, two layers of cortical initials were common in the embryonic root, and as a general trend, a single layer of cortical initials became more common during root elongation. The cellular changes that resulted in the initiation of a secondary columella are characterized by the conversion of cortical initials to secondary columella initials by a shift in their plane of cell division. It is proposed that the size and shape of the quiescent center changes as the conversion takes place. No intermediate stages were observed which could account for the reduction of two layers of cortical initials to one layer.     

A suberized perimedullary reaction zone in Populus balsamifera novel for compartmentalization in trees

 Following artificial inoculation of nonhost Populus balsamifera with Ophiostoma ulmi, structural defensive tissues were formed in the xylem. Among these tissues there was a perimedullary sheath of cells, located adjacent to the invaded xylem, that originated from the dedifferentiation of perimedullary and xylem parenchyma cells. Histochemical tests revealed that this sheath was intensively suberized. A band of lignified cells was frequently detected on both sides of this suberized tissue. The formation of such a tissue at the pith margin represents a new type of anatomical barrier in relation to compartmentalization processes described for trees. Ultrastructural examination showed that the wall of cells forming this zone was generally composed of a compound middle lamella, a suberized secondary wall and a tertiary wall layer. Using colloidal gold conjugated to monoclonal antibodies against pectin and to an exoglucanase for cellulose, only limited labelling was obtained for pectin whereas labelling for cellulose was abundant in the compound middle lamella and the tertiary wall layer. In a few fibres close to this suberized zone, the latter probe also made it possible to distinguish the occasional presence of several alternating wall layers mainly composed of either suberin or cellulose. In Salix sp., another tree species belonging to the Salicaceae, this type of suberized reaction zone was also observed. The new reaction zone is similar in structure and location to a suberized barrier formed in nonwoody carnation (Dianthus caryophyllus) plants in the defense against vascular fungi. Received: 30 July 1996 / Accepted: 7 January 1997     

Fatty acids,sterols and hydrocarbons in the leaves from eleven species of mangrove

The fatty acid, sterol and hydrocarbon compositions of the fresh leaves from eleven species of mangroves, cultivated in a shadehouse, are reported. The fatty acid and sterol analyses, whilst generally typical of higher plants, showed several chemotaxonomically significant differences between the species. The epicuticular wax hydrocarbons and fatty acids were low in abundance compared to previous reports of mangrove leaf lipids, which may reflect the importance of environmental influences on this group of compounds. Cluster analysis of selected subsets of the data showed clear chemotaxonomic divisions amongst the mangroves. The results grouped the mangroves into genera, except for the Rhizophora and Ceriops tagal which were not separated, and grouped the family Rhizophoraceae distinct from all other species except Xylocarpus granatum. Avicennia marina var. resinifera was able to be distinguished from Avicennia marina by cluster analysis, supporting its assignment as a distinct variety. The results show that the lipids of mangroves are chemotaxonomically significant.