Ultrastructure of sieve-element plastids inCaryophyllales (Centrospermae), evidence for the delimitation and classification of the order

The orderCaryophyllales (Centrospermae) was found to contain specific P-type sieve-element plastids which are characterized by protein inclusions composed of ring-shaped bundles of filaments and of central crystalloids. The sieve-element plastids of 14 families (140 species investigated) fit into this overall characterization, and more specific details are used to delimit the families and arrange them within the order.Phytolaccaceae, the basic family of the order display much diversity: the crystalloids inside their plastids are either globular (most genera) or polygonal (Stegnosperma), starch may also be present (Phytolacca).Nyctaginaceae, with starch inBougainvillea sieve-element plastids, can be derived directly fromPhytolacca. Globular crystalloids are present in most of the families, as inDidiereaceae, Cactaceae, Aizoaceae-Tetragoniaceae, Portulacaceae-Basellaceae-Halophytaceae-Hectorellaceae. Caryophyllaceae andLimeum ofMolluginaceae contain polygonal crystalloids (otherMolluginaceae with globular crystalloids). Crystalloids are entirely absent fromChenopodiaceae (incl.Dysphaniaceae) andAmaranthaceae. The probable relationships between these families are presented diagrammatically in Fig. 13. Bataceae, Gyrostemonaceae, Vivianiaceae, Theligonaceae, Polygonaceae, Plumbaginaceae, Fouquieriaceae, Frankeniaceae, andRhabdodendraceae—all at some time included into theCaryophyllales (Centrospermae) or doubtfully referred to them—develop S-type (or different P-type) sieve-element plastids. Their direct connection to theCaryophyllales therefore is excluded. Finally, evolutionary trends of theCaryophyllales are discussed.Presented in the Symposium Evolution of Centrospermous Families, during the XIIth International Botanical Congress, Leningrad, July 8, 1975.     

Further studies of the sieve-element plastids of theCaryophyllales includingBarbeuia,Corrigiola, Lyallia,Microtea, Sarcobatus,andTelephium

The sieve-element plastids of 69 species of theCaryophyllales were investigated by transmission electron microscopy. All contained the specific subtype-P3 plastids characterized by a peripheral ring of protein filaments. The presence or absence of an additional central protein crystal and their shape being either polygonal or globular as well as the average sizes of the sieve-element plastids are useful features in the characterization of some families.—Barbeuia contains sieve-element plastids that confirm its placement within thePhytolaccaceae. Lyallia differs fromHectorella by including small starch grains in their sieve-element plastids, which otherwise by their globular crystals negate a closer connection to theCaryophyllaceae. The lack of a central protein crystal in its form-P3fs plastids placesMicrotea best within theChenopodiaceae. Sarcobatus, a so far uncontested member of theChenopodiaceae, contains form-P3cf plastids, i.e., including a central crystal not found elsewhere in this family.Telephium andCorrigiola, shifted back and forth betweenMolluginaceae andCaryophyllaceae, have form-P3cf(s) plastids with a polygonal crystal which favor their placement within theCaryophyllaceae.     

Contributions to the knowledge of sieve-element plastids inGunneraceae and allied families

P-type sieve-element plastids were found in theGunneraceae, while S-type plastids are present in theHaloragaceae andHippuridaceae. The specific characters of the sieve-element plastids (e.g., their size and the morphology of their contents) are discussed in relation to other taxa of theRosidae containing P-type plastids and to the systematic position of theGunneraceae. Contributions to the Knowledge of P-Type Sieve-Element Plastids in Dicotyledons, III. — For other parts of this series see (I.:)Behnke (1982 b) and (II.:)Behnke (1985).     

S-type sieve-element plastids and anthocyanins inVivianiaceae: Evidence against its inclusion intoCentrospermae

The presence of S-type sieve-element plastids and anthocyanins in theVivianiaceae indicates that it is not a member ofCentrospermae (Caryophyllales).     

Flavonoids of some controversial members of theCaryophyllales (Centrospermae)

The absence or occurrence of C-glycolsylflavonoids in theAizoaceae andMolluginaceae, respectively, has been utilized to classify several controversial genera of centrospermous plants that have previously been placed in different families by systematists. The presence of these compounds in several further species of theMolluginaceae is reported. Their anomalous presence inGliscrothamnus (Aizoaceae) is discussed.     

Sieve-element plastids ofTriticum andAegilops (Poaceae)

Fourteen taxa of the Triticum-Aegilops group have been investigated for their sieve-element plastids. At maturity they contain dense and thin crystalloid inclusions and are classified into the PIIc' plastid type; onlyAe. comosa var.biaristata lacked the thin crystalloids and thus conforms to the PII c type. The proteinaceous nature of the crystalloids was demonstrated by application of proteolytic enzymes. Ultrastructural evidence suggests that both kinds of crystalloid inclusions are involved in the sealing of sieve-plate pores of injured sieve tubes. Measurements and calculations of the spacings and angles carried out on crystalloid prints permitted the construction of a two- and three-dimensional pattern forT. aestivum thin crystalloids.     

Sieve-element plastids,exine sculpturing and the systematic affinities of theBuxaceae

The sieve-element plastids of members of several genera in theBuxaceae (Buxus, Pachysandra andSarcococca) were found to be of the specific subtype PVI, which contains a central globular protein crystal.Simmondsia (Simmondsiaceae) andDaphniphyllum (Daphniphyllaceae), on the other hand, were found to contain S-type sieve-element plastids. The occurrence of the highly restricted PVI plastids in theBuxaceae mitigates against a close relationship between theBuxaceae andSimmondsia, Daphniphyllum andEuphorbiaceae. Exine sculpturing of theBuxaceae andSimmondsiaceae also shows no close similarities. Both of these EM characters are discussed in connection with other available data and with respect to earlier systematic treatment of these families.     

Rumex subgen.Rumex sect.Axillares (Polygonaceae) in South America

Rumex sect.Axillares first described by the author in 1937 is known to be represented in N. America by 20 endemic species. From S. America only five species, all endemic, were previously known; this number is raised in the present revision to 15. Outside America there exist small groups of endemic species in S. Africa and in the islands of Hawaii as well as in Australia and scattered single species in C. Africa, on the remote Atlantic islands of Tristan de Cunha and Gough Island, and in eastern Asia.—In Europe the section is completely absent, except for three American species which occur as rare aliens. TheAxillares are not only morphologically well-characterized by their growth—no leaf rosettes, flowering period practically unlimited by formation of later flowering axillary shoots, flowers often monoecious—but also by their genetic structure expressed by a different behaviour in hybridization. Hybrids are frequent between species of sect.Rumex (syn.Simplices) and are easy to recognize by their sterility which results in a certain peculiarity in habit. In contrast, no spontaneous hybrids are known with certainty among species of sect.Axillares. Most artificial hybrids are fairly fertile. So far only three hybrids between species of the two sections have been known. Three more have been found by the author in Chile, all being highly sterile and showing the growth characteristics resulting from sterility as occur in hybrids between species of sect.Rumex.

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Resumen Rumex secciónAxillares fue descrito por primera vez por el autor en 1937. Se conoce en América del Norte con 20 especies endémicas. De América del Sur se conocían sólo 5 especies, todas ellas endemicas; este número asciende a 15 en la presente revision. Fuera de las Américas se encuentran pequeños grupos de especies endémicas en Sudáfrica, en las Islas de Hawaii y en Australia; especies aisladas se encuentran en Africa Central, en las lejanas Islas Atlánticas de Tristan de Cunha y Gough Island y en Asia Oriental. La sección no tiene representantes en Europa, con excepción de tres especies americanas introducidas, poco frecuentes. La secciónAxillares se caracteriza bien, tanto morfológicamente por su forma de creciemiento—sin rosetas foliares, período floral prácticamente ilimitado por la formación de inflorescencias axilares parciales, flores a menudo monoicas—como por su estructura genética que se manifiesta en un comportamiento diferente de hibridación. Híbridos son frecuentes en las especies de la secciónRumex (syn.Simplices) y reconocibles por su esterilidad que se expresa en cierta particularidad del habito. Al contrario, no hay seguridad de híbridos espontáneos en la secciónAxillares. La mayor parte de los híbridos artificiales son totalmente fértiles. Hasta ahora se conocían solo tres híbridos entre las especies de ambas secciones. Otros tres han sido encontrados por el autor en Chile. Todos completamente estériles y con las características de hábito típicas resultantes la esterilidad, como ocurre en los híbridos de la secciónRumex.

     

A numerical taxonomic study of thePolygonum aviculare complex (Polygonaceae) in Belgium

16 morphological characters were assessed in 300 plants sampled from 27 populations ofPolygonum aviculare sensu lato representative of the whole ecological range of the species in Belgium. The three multivariate treatments performed, namely principal component analysis, cluster analysis and discriminant analysis provide evidence thatP. aviculare can be divided in 4 units, roughly corresponding to the four taxa recognized byChrtek. However, the results point out that subsp.monspeliense and subsp.calcatum should be included at the varietal rank within respectively subsp.aviculare (=P. heterophyllum) and subsp.aequale (=P. arenastrum) as defined byLindman. Fruit dimensions, fruit shape and tepal length are the most discriminant characters for separating the four taxa, while several other characters are discriminant at the population level only. The evolutionary significance of the variation pattern of the whole complex is discussed in terms of life history differentiation and ecological specialization.     

Can sieve-element plastids in Panicum maximum (Poaceae) leaves act in the blockage of injured sieve-tube elements?

The ultrastructural features and the plastid changes caused by sample preparation were studied in sieve elements of Panicum maximum leaves. Samples of expanded leaves, taken near the ligule region, were fixed and processed by common light and transmission electron microscopy methods. In mature sieve-tube elements, the protoplast is electron-translucent and plastids are the most frequent organelles. Mitochondria and smooth endoplasmic reticulum segments are also visible and occupy a parietal position within the cell. The plastids are globular and show electron-dense proteinaceous inclusions in the stroma. The protein crystals are predominantly cuneate, but thin crystalloids and amorphous and/or filamentous proteins also occur. The presence of intact plastids plus others in different phases of plastid envelope rupture were interpreted as evidence that this rupture is a normal event in response to injury. This plastid envelope rupture is possibly activated by the release of pressure in the sieve-tube element. After plastid membrane vesiculation, the stroma and the protein crystals are dispersed within the sieve-element ground cytoplasm. The vesicles originating from the plastid envelope move to one cell pole, while protein crystalloids move to the opposite pole and agglomerate in the sieve-plate region. Our findings indicate that these protein crystalloids, which deposit in the sieve plate, may act in sieve-plate pores occlusion, preventing the release of phloem sap, similar to the role of P-protein in dicotyledons.     

Ultrastructure of chromoplasts and other plastids in Crocus sativus L. (Iridaceae)

Saffron (Crocus sativus L. Iridaceae) chromoplasts and other plastids were studied by electron microscope to determine their structure, origin and pigment localization. Plastids from pistils of floral buds and flowers at anthesis, dried and decoloured stigmas, and green and senescent leaves were examined. Results indicated that mature saffron chromoplasts occur in the red parts of stigmas and have a reticulo-tubular structure. They contain a reticulum of tubules and plastoglobules. Tubules formed dilated vesicles mainly while plastoglobules appeared numerous and scattered on the whole chromoplast. Chromoplasts appeared in red stigma of very young floral buds. They originated from amyloplasts, the only plastids occurring in the colourless basal portion of style, as well as in the parenchyma of ovary and corm. Transition forms of plastid as amylo-chromoplast, occur in the yellow parts of stigma and style. Senescent leaves did not show plastids with structure similar to the chromoplast of red stigma. Red pigmented and scented stigmas might cooperate in saffron reproduction by attracting pollinator.     

Chromosome number,morphology, pairing,and DNA values of species and hybrids in the genusFallopia (Polygonaceae)

The taxa in this study have in the past been treated together in sect.Tiniaria Meissner ofPolygonum L. s.l., and more recently the large erect rhizomatous herbaceous perennials have been separated from the twining annuals and perennials as the generaReynoutria andFallopia respectively. These taxa range in ploidy level from diploid to octoploid, with base numbers of both 10 and 11 present. The plants are primarily Asiatic in distribution, although many of the large erect perennials are now naturalized in many parts of Europe. Cytological examination has revealed the presence of a number of previously unknown hybrid taxa in the British Isles. The readiness with which hybridisation occurs between taxa of differing base number and ploidy level, and similarities revealed in chromosome morphology, meiotic pairing and in DNA C-value, suggest to the authors that these two genera are best amalgamated underFallopia.     

Sex ratio variation and spatial segregation of the sexes in populations ofRumex acetosa andR. acetosella (Polygonaceae)

Populations ofRumex acetosa andR. acetosella were studied during two growth seasons. The ramet sex ratios ofR. acetosa were always female-biased. InR. acetosella the sex ratios expressed more variation but were mostly female-biased. In both species the sex ratios commonly varied between subpopulations reflecting a partial spatial segregation of the sexes. No marked differences between sexes in vegetative vigour were detected in either species. Interactions between sex ratios, various soil characteristics and population densities were determined. Possible mechanisms for causing biased sex ratios and partial spatial segregation of the sexes are discussed.     

Pollen morphology of the genera Polygonum s. str. and Polygonella (Polygoneae: Polygonaceae)

The pollen of 30 taxa (27 species, one subspecies and two varieties) in two genera, viz Polygonum s. str. and Polygonella was investigated with LM and SEM, and some selected taxa with TEM. In all genera investigated the pollen is prolate to spheroidal, and the aperture is mostly tricolporate, rarely panto-hexacolporate (especially Polygonum section Polygonum). The exine sculpturing pattern is the most variable feature. Three types of exine can be recognized. Type 1 (Avicularia-Type, sensu Hedberg) - All species of section Polygonum and section Tephis share the smooth tectate exine with spinules, sometimes the surface is more or less rough (Polygonum afromontanum in section Tephis). Type 2 (Pseudomollia-Type, sensu Hong) - Pollen of Polygonum molliaeforme (section Pseudomollia) has the exine, which is verrucose on both poles and nearby the mesocolpium, and mostly psilate around the ectoaperture. Type 3 (Duravia-Type, sensu Hedberg) - Pollen grains of Polygonum section Duravia and Polygonella have the exine which is semitectate-reticulate at the mesocolpium and the poles, and rugulate/reticulate or sometimes foveolate with microspinules around the ectoapertures. The pollen grains in four taxa (viz Polygonum section Pseudomollia, P. section Duravia and genus Polygonella) have a well-marked dimorphism of the ektexine, which is considered to be a synapomorphic condition. The differences of pollen grain between the genus Polygonella and Polygonum section Duravia are almost non existent and clearly interrelated. It is therefore postulated that the similarity in pollen of both taxa is not the result of convergency, but is interpreted as a homology. It is noteworthy that the pollen of Polygonum molliaeforme (section Pseudomollia) appears as intermediate between the Avicularia-type and the Duravia-type, and is well supported the value of separated section for its own. Additionally, in TEM, some exine ultrastructures (e.g. columellae, foot layer, endexine) appear to be valuable characters for comparison between/among taxa. The systematic potentialities of the pollen data of the studied taxa at various systematic levels are also discussed.     

Foliar anatomy ofPolygonum (Polygonaceae): Survey of epidermal and selected internal structures

Several anatomical characters in leaves were described, and their distribution determined, for 153 species ofPolygonum, mostly from herbarium specimens. Structures surveyed were epidermal (glandular and nonglandular trichomes, nodules, specialized parenchyma, stomatal apparatus) and internal (cavities, crystals, laticifer-like cells, nodules, subepidermal fibers). Cleared leaves were supplemented by resin-embedded sections and SEM preparations of selected species. No feature defines any taxonomic section, but some features occur only within one section. Laticifer-like cells, epidermal and internal nodules, resin cups, and unique epidermal and subepidermal cavities seem to be unknown elsewhere; other features (invaginated epidermal cells; enlarged crystal cells confined to paraveinal layer) are rare among angiosperms.     

Allozyme variation in the annual weed species complexPolygonum aviculare (Polygonaceae) in relation to ploidy level and colonizing ability

Variation at six polymorphic enzymatic loci was studied in 50 populations of the selfing annualPolygonum aviculare from Belgium. The results show that theP. aviculare complex has an allopolyploid origin and comprises two main genetic entities, viz.P. aviculare subsp.depressum (2n = 4x = 40), restricted to urban sites subject to trampling stress, andP. aviculare subsp.aviculare (2n = 4x = 40, 2n = 6x = 60), with a wider ecological amplitude. The latter had a higher genetic diversity and a higher frequency of fixed heterozygosity than the former. WithinP. aviculare subsp.aviculare, genetic diversity and ecological amplitude correlated positively with ploidy level. Additionally, stronger genetic differentiation among and lower variation within populations was found in urban areas than in cultivated fields.     

Morphology and ultrastructure of Mammillaria gracillis (Cactaceae) in in vitro culture

Morphogenetic status of cactus Mammillaria gracillis Pfeiff. tissue culture was studied by light and electron microscopy. In vitro propagated shoots spontaneously developed callus. This callus regenerated normal and hyperhydric shoots without exogenous hormones. Tumour tissue induced by wild or rooty strains of Agrobacterium tumefaciens never expressed any morphogenetic potential. Light microscopy showed cellular characteristics of morphologically different tissues. Ultrastructural studies revealed changes in plastids: secondary dedifferentiation of mature chloroplasts, thylakoid swelling and disruption, phytoferritin accumulation, plastid elongation and increase in size. Changes in chlorophyll and carotenoid content were in accordance with degradation of the thylakoid system. Plastids were confirmed as very sensitive organelles to an artificial hyperhydric environment as well as to Agrobacteria-mediated cell transformation.     

A phloem-specific,lectin-like protein is located in pine sieve-element plastids by immunocytochemistry

Two co-purifying phloem polypeptides of 24 and 25 kilodaltons (kDa) were isolated from homogenates of Pinus sabiniana Dougl. phloem by differential centrifugation, selective solubilization and electrophoresis, and rabbit antibodies raised against them. The antisera were found to be specific for doublet bands between 23 and 25 kDa in Western blots of whole phloem extracts of Pinus species; no xylem polypeptides were labelled, nor did labelling occur in blots of phloem extracts from other genera in the Pinaceae. Solubilized phloem polypeptides bind strongly to chitin (oligomeric N-acetylglucosamine) columns and are sensitive to thiol reagents, both characteristics which relate them to phloemspecific lectins isolated from angiosperm species (C. Allen, 1979, Biochem. J. 183, 133–137; A.K. Gietl et al., 1979, Planta 144, 367–371). Fluorescence microscopy and immuno-gold electron microscopic cytochemistry demonstrated antigenic sites specifically associated with protein crystals peculiar to the sieve-element plastids of the Pinaceae.Abbreviations DAB diamino benzidine tetrachloride - FITC fluorescein isothiocyanate - kDa kilodalton - PBS phosphate-buffered saline - PP phloem polypeptide(s) - SDS-PAGE Sodium dodecyl sulphate-polyacrylamide gel electrophoresis - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol