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U Kutschera

Publications and source records attributed to U Kutschera.

At least 19 recordsLinked to original sources
PubMed2006

Moss-associated methylobacteria as phytosymbionts: an experimental study.

Methylotrophic bacteria inhabit the surface of plant organs, but the interaction between these microbes and their host cells is largely unknown. Protonemata (gametophytes) of the moss Funaria hygrometrica were cultivated in vitro under axenic conditions and the growth of the protonemal filaments recorded. In the presence of methylobacteria (different strains of Methylobacterium), average cell length and the number of cells per filament were both enhanced. We tested the hypothesis that auxin (indole-3-acetic acid, IAA), secreted by the epiphytic bacteria and taken up by the plant cells, may in part be responsible for this promotion of protonema development. The antiauxin parachlorophenoxyisobutyric acid (PCIB) was used as a tool to analyze the role of IAA and methylobacteria in the regulation of cell growth. In the presence of PCIB, cell elongation and protonema differentiation were both inhibited. This effect was compensated for by the addition of different Methylobacterium strains to the culture medium. Biosynthesis and secretion of IAA by methylobacteria maintained in liquid culture was documented via a colorimetric assay and thin layer chromatography. Our results support the hypothesis that the development of Funaria protonemata is promoted by beneficial phytohormone-producing methylobacteria, which can be classified as phytosymbionts.

Bryophyta↗
PubMed2005

Growth in liverworts of the Marchantiales is promoted by epiphytic methylobacteria.

Liverworts, the most basal lineage of extant land plants, have been used as model systems in the reconstruction of adaptations to life on land. In this study, we used gemmae (specialized propagules) that were isolated from mature gemma cups of two distantly related species of liverworts, Marchantia polymorpha L. and Lunularia cruciata L. (order Marchantiales). We show that methylobacteria (genus Methylobacterium), microbes that inhabit the surfaces of land plants where they secrete phytohormones (cytokinines), promote the growth of isolated gemmae cultivated on agar plates. As a control, two species of higher plants, maize (Zea mays L.) and sunflower (Helianthus annuus L.) were raised aseptically from sterile seeds (i.e., caryopses, achenes). Inoculation of these propagules with methylobacteria was without effect on growth in the above-ground phytosphere (expansion of stems and leaves). We conclude that normal development in Marchantia and Lunularia is dependent on (and possibly regulated by) epiphytic methylobacteria, whereas representative higher plants grow at optimal rates in the absence of these prokaryotic epiphytes.

Hepatophyta↗
PubMed2005

Molecular phylogeny of selected predaceous leeches with reference to the evolution of body size and terrestrialism.

The phylogenetic relationships of erpobdellid leeches collected throughout Europe were investigated using newly obtained mitochondrial cytochrome c oxidase subunit I (CO-I) gene sequence data from 10 taxa. Monophyly of the five European Erpobdella species (sub-family Erpobdellinae) was supported, but a newly discovered leech, E. wuttkei Kutschera, 2004 (the smallest member of its genus, discovered in an aquarium) was only distantly related to this clade. Three members of the semiaquatic Trochetinae were included in this study. The largest European leech species discovered so far, Trocheta haskonis Grosser, 2000, was found to be a terrestrial predator that feeds on earthworms. The rare species T. haskonis is the sister taxon of T. bykowskii Gedroyc, 1913, a well-known amphibious leech. Based on a comparison of body sizes and a phylogenetic tree the evolution of terrestrialism in the family Erpobdellidae is discussed.

Aging↗
PubMed2005

Endosymbiosis, cell evolution, and speciation.

In 1905, the Russian biologist C. Mereschkowsky postulated that plastids (e.g., chloroplasts) are the evolutionary descendants of endosymbiotic cyanobacteria-like organisms. In 1927, I. Wallin explicitly postulated that mitochondria likewise evolved from once free-living bacteria. Here, we summarize the history of these endosymbiotic concepts to their modern-day derivative, the "serial endosymbiosis theory", which collectively expound on the origin of eukaryotic cell organelles (plastids, mitochondria) and subsequent endosymbiotic events. Additionally, we review recent hypotheses about the origin of the nucleus. Model systems for the study of "endosymbiosis in action" are also described, and the hypothesis that symbiogenesis may contribute to the generation of new species is critically assessed with special reference to the secondary and tertiary endosymbiosis (macroevolution) of unicellular eukaryotic algae.

Animals↗
PubMed2004

The occurrence of an Australian leech species (genus Helobdella) in German freshwater habitats as revealed by mitochondrial DNA sequences.

The freshwater leech Helobdella europaea Kutschera 1987 was discovered twenty years ago in Germany and described as a new species. Here, we show that this leech is genetically identical with the Australian species Helobdella papillornata (CO-I-mt-DNA sequence identity of alignment positions: 98%). We conclude that H. europaea (syn. H. papillornata) represents an introduced annelid that occupies the same ecological niche as the common European leech H. stagnalis L.

Animals↗
PubMed2002

Plant development in the absence of epiphytic microorganisms.

Microorganisms (bacteria, fungi) are common residents of the roots, stems and leaves of higher plants. In order to explore the dependency of plant development on the presence of epiphytic microorganisms, the achenes (seeds) of sunflower (Helianthus annuus L.) were sterilized and germinated under aseptic conditions. The sterility of the seedlings was determined with the agar impression method. In seedlings from non-sterile seeds (control) that were likewise raised in a germ-free environment, all plant organs investigated (stem, cotyledons and primary leaves) were contaminated with bacteria. Hypocotyl elongation was not affected by epiphytic microorganisms. However, the growth rates of the cotyledons and primary leaves were higher in sterile seedlings compared with the control. The implications of this differential inhibition of organ development by epiphytic bacteria that are transmitted via the outer surface of the seed coat are discussed. We conclude that epiphytes in the above-ground phytosphere are not necessary for the development of the sunflower seedling.

Bacteria↗
PubMed2002

Sucrose metabolism and cellulose biosynthesis in sunflower hypocotyls.

The relationships between cellulose accumulation, changes in specific activities of enzymes of sucrose catabolism, levels of UDP-glucose and rate of dark respiration were investigated in the subapical 1 cm-hypocotyl region of 10- to 14-day-old-sunflower seedlings (Helianthus annuus L). The plants were grown under a light/dark regime in vermiculite that was soaked either with distilled water or half-strength Hoagland nutrient solution. At this stage of seedling development, the hypocotyl had ceased to elongate but increased in width. Stem thickening and the rate of cellulose accumulation were promoted by nutrient solution. The levels of the soluble (vacuolar) and wall-associated acid invertases (EC 3.2.1.26) were not correlated with these processes. However, the activities of the soluble (cytoplasmic) and membrane-bound sucrose synthases (EC 2.4.1.13) were larger in hypocotyls that were grown in the presence of nutrient solution. The concentration of UDP-glucose was reduced, and the rate of dark respiration was enhanced in the hypocotyls that were grown in Hoagland solution. The results support the hypothesis that both forms of the enzyme sucrose synthase play a critical role in cellulose biosynthesis of hypocotyl cells that had ceased to elongate and continue to grow by wall thickening.

Journal Article↗
PubMed2001

Gravitropism of axial organs in multicellular plants.

Gravitropism of plant organs such as roots, stems and coleoptiles can be separated into four distinct phases: 1. perception (gravity sensing), 2. transduction of a signal into the target region and 3. the response (differential growth). This last reaction is followed by a straightening of the curved organ (4.). The perception of the gravitropic stimulus upon horizontal positioning of the organ (1.) occurs via amyloplasts that sediment within the statocytes. This conclusion is supported by our finding that submerged rice coleoptiles that lack sedimentable amyloplasts show no graviresponse. The mode of signal transduction (2.) from the statocytes to the peripheral cell layers is still unknown. Differential growth (3.) consists of a cessation of cell expansion on the upper side and an enhancement of elongation on the lower side of the organ. Based on the facts that the sturdy outer epidermal wall (OEW) constitutes the growth-controlling structure of the coleoptile and that growth-related osmiophilic particles accumulate on the upper OEW, it is concluded that the differential incorporation of wall material (presumably glycoproteins) is causally involved. During gravitropic bending, electron-dense particles ('wall-loosening capacity') accumulate on the growth-inhibited upper OEW. It is proposed that the autotropic straightening response, which is in part due to an acceleration of cell elongation on the curved upper side, may be attributable to an incorporation of the accumulated particles ('release of wall-loosening capacity'). This novel mechanism of autotropic re-bending and its implications for the Cholodny-Went hypothesis are discussed.

Cotyledon↗
PubMed1991

Effects of submergence on development and gravitropism in the coleoptile of Oryza sativa L.

Caryopses of rice (Oryza sativa L. cv. Sasanishiki) were germinated in air or under water. In submerged seedlings a twofold increase in coleoptile growth rate and an inhibition of root growth was observed. The amount of starch in the amyloplasts of submerged coleoptiles was substantially reduced compared to the air-grown control plants and plastids had a proplastidic character. During the rapid elongation of coleoptiles under water, the osmotic concentration of the press sap remained constant, whereas in air-grown coleoptiles a decrease was measured. Determination of curvature of gravistimulated air-grown and submerged shoots was carried out by placing the coleoptiles horizontally in air of 98% relative humidity. Air-grown coleoptiles reached a vertical orientation within 5 h after onset of gravistimulation. In coleoptiles germinated under water the first signs of consistent negative gravitropic bending occurred after 4-5 h and curvature was complete after 24 h. During the first 5 h of gravistimulation the water-grown coleoptiles grew at an average rate of 0.39 mm h-1, whereas in air-grown coleoptiles a rate of 0.27 mm h-1 was measured. Concomitant with the delayed onset of gravitropic bending of the water-grown coleoptiles, a change in plastid ultrastructure and an increase in starch content was observed. We conclude that the gravitropic responsiveness of the rice coleoptile depends on the presence of starch-filled amyloplasts.

Cotyledon↗
PubMed1990

Auxin Enhancement of mRNAs in Epidermis and Internal Tissues of the Pea Stem and Its Significance for Control of Elongation.

The epidermis has been considered the site of auxin action on elongation of stems and coleoptiles. To try to identify mRNAs that might mediate auxin stimulation of cell enlargement, we compared, using in vitro translation assays, mRNA enhancement by indoleacetic acid (IAA) in the epidermis, with that in the internal tissues, of pea (Pisum sativum L., cv Alaska) third internode segments. We used seedlings that had been grown under red light, which enables the epidermis to be peeled efficiently from the internode. Most of the ;early' IAA enhancements previously reported using etiolated peas, plus several hitherto undescribed enhancements, occur in both the epidermis and the internal tissue of the light-grown plants after 4 hours of IAA treatment. These enhancements, therefore, do not fulfill the expectation of elongation-specific mRNAs localized to the epidermis. One epidermis-specific IAA enhancement does occur, but begins only subsequent to 1 hour (but before 4 hours) of auxin treatment. Similarly, the previously mentioned IAA enhancements common to epidermis and internal tissue do not begin, in the light-grown plants, within 1 hour of IAA treatment. Since IAA stimulates elongation in light-grown internodes within 15 minutes, it appears that none of these mRNAs can be responsible for auxin induction of elongation. We confirmed, with our methods, the previous reports that some of these mRNAs are enhanced by IAA within 0.5 hour in etiolated internodes. This indicates that we could have detected an early enhancement in light-grown tissue had it occurred.

Journal Article↗
PubMed1988

Growth, in vivo extensibility, and tissue tension in developing pea internodes.

The relationship between growth, in vivo extensibility, and tissue tension in the first 3 internodes of 5, 6, and 7 day-old pea plants (Pisum sativum L. cv Alaska), grown under continuous red light was investigated. The upper 15 millimeters of each internode was marked with ink and its elongation growth measured over the next subsequent 8 hours. In vivo extensibility was measured by stretching living tissue at constant force (creep test) in a custom-built extensiometer. Tissue tension was determined by (a) measuring the rate of expansion of the isolated cortical cylinder after adding water and the amount of contraction of the epidermis after peeling, and (b) by use of the ;split section test.' A good correlation between rate of elongation growth, in vivo extensibility, and tissue tension was established. The epidermis peeled from the growing third internode of 7 day-old plants and measured immediately showed a plastic extensibility (E(pl) twice that of peels from nongrowing excised sections. This high E(pl)-value was lost on incubation of the sections in distilled water, and was subsequently restored by incubating the sections in auxin (indole-3-acetic acid). We conclude that the in situ growth of the internodes is a function of tissue-tension, which provides the driving force of organ growth, and the extensibility (E(pl) of the outer epidermal wall, which is in the growing plant in a ;loosened' state. We furthermore suggest that in the intact plant auxin is causally involved in the wall loosening process in the epidermis.

Journal Article↗
PubMed1988

The biophysical basis of elongation growth in internodes of deepwater rice.

Partial submergence induces rapid internodal elongation in deepwater rice (Oryza sativa L., cv Habiganj Aman II). We measured in vivo extensibility, tissue tension, hydraulic conductance and osmotic potential in the region of cell elongation in the uppermost internode. The in vivo extensibility of the internode, measured by stretching of living tissue with a custom-made constant stress extensiometer, rose rapidly following submergence of the plant. Both the elastic (E(el)) and plastic (E(pl)) extensibility increased when growth of the internode was induced. The submerged internode displayed tissue tension (elastic outward bending of longitudinally split internode sections); in air-grown control internodes, no such bending occurred. The hydraulic conductance, estimated from the kinetics of tissue shrinkage in 0.5 molar mannitol and subsequent swelling in distilled water, was not changed by submergence. The osmotic potential, measured with a dew-point hygrometer using frozen-thawed tissue, was only 18% less negative in the submerged internode than in the air-grown control. This indicates that osmoregulation takes place in rapidly elongating rice internodes. We suggest that the rapid expansion of the newly formed internodal cells of submerged plants is controlled by the yielding properties (E(pl)) of the cell walls. Experiments with excised stem sections indicate that gibberellin is involved in increasing the E(pl) of the elongating cell walls.

Journal Article↗