Manfred Kluge

Geosiphon pyriforme, a fungus forming endocytobiosis with Nostoc (Cyanobacteria) is an ancestral member of the Glomales : Evidence by SSU rRNA analysis

Geosiphon pyriforme inhabiting the surface of humid soils represents the only known example of endocytobiosis between a fungus (Zygomycotina; macrosymbiont) and cyanobacteria (Nostoc; endosymbiont). In order to elucidate the taxonomical and evolutionary relationship ofGeosiphon pyriforme to fungi forming arbuscular mycorrhiza (AM fungi), the small-subunit (SSU) ribosomal RNA genes ofGeosiphon pyriforme andGlomus versiforme (Glomales; a typical AM fungus) were analyzed and aligned with SSU rRNA sequences of several Basidiomycetes, Ascomycetes, Chytridiomycetes, and Zygomycetes, together with all AM-fungal (Glomales) sequences published yet.The distinct group of the order Glomales, which includesGeosiphon, does not form a clade with any other group of Zygomycetes. Within the Glomales, two main lineages exist. One includes the families Gigasporaceae and Acaulosporaceae; the other one is represented by the genusGlomus, the members of which are very divergent.Glomus etunicatum andGeosiphon pyriforme both form independent lineages ancestral to the Glomales. The data provided by the present paper confirm clearly thatGeosiphon represents a fungus belonging to the Glomales. The question remains still open as to whether or notGeosiphon is to be placed within or outside the genusGlomus, since this genus is probably polyphyletic and not well defined yet.Geosiphon shows the ability of aGlomus-like fungus to form a “primitive” symbiosis with a unicellular photcautotrophic organism, in this case a cyanobacterium, leading to the conclusion that a hypothetical association of aGlomus-like fungus with a green alga as a step during the evolution of the land plants appears probable.

Über Zusammenhänge zwischen dem CO2-Austausch und der Abgabe von Wasserdampf durch Bryophyllum daigremontianum Berg

1. The transpiration in leaves of Bryophyllum daigremontianum exactly follows the changes in consumption of atmospheric carbon dioxide (caused by the Crassulaceen acid metabolism) during the light and dark periods. After removal of the epidermis no distinct rhythm in the course of transpiration can be observed any more, whereas the characteristic CO2 exchange continues in an unchanged matter. For this reason we assume that the changing rate of CO2 uptake from the atmosphere determines the concentration of carbon dioxide in the intercellular spaces of the leaves and in this way controls the opening of stomata. 2. CO2 uptake from the atmosphere in the light phase decreases faster than CO2 consumption in the dark when the plants are held under water stress conditions. At the endpoint CO2 is fixed only in the dark period. On the basis of the connection between CO2 uptake and movement of stomata we assume a closure of the stomata during the light period (since no extracellular CO2 is fixed). Since evaporation values in the light phase are high under natural conditions, this manner of gas exchange minimizes the loss of water during water stress conditions, and nevertheless guarantees a positive balance of carbon.Summary1.The transpiration in leaves of Bryophyllum daigremontianum exactly follows the changes in consumption of atmospheric carbon dioxide (caused by the Crassulaceen acid metabolism) during the light and dark periods. After removal of the epidermis no distinct rhythm in the course of transpiration can be observed any more, whereas the characteristic CO2 exchange continues in an unchanged matter. For this reason we assume that the changing rate of CO2 uptake from the atmosphere determines the concentration of carbon dioxide in the intercellular spaces of the leaves and in this way controls the opening of stomata.2.CO2 uptake from the atmosphere in the light phase decreases faster than CO2 consumption in the dark when the plants are held under water stress conditions. At the endpoint CO2 is fixed only in the dark period. On the basis of the connection between CO2 uptake and movement of stomata we assume a closure of the stomata during the light period (since no extracellular CO2 is fixed). Since evaporation values in the light phase are high under natural conditions, this manner of gas exchange minimizes the loss of water during water stress conditions, and nevertheless guarantees a positive balance of carbon.Zusammenfassung1.Transpiration und CO2-Aufnahme zeigen bei Bryophyllum daigremontianum sowohl im Licht als auch im Dunkel völlige Gleichläufigkeit. Die charakteristische Kurve des CO2-Austausches (massive CO2-Aufnahme im Dunkel, teilweise Unterdrückung der CO2-Aufnahme im Licht) bleibt erhalten, wenn die Epidermis der Blätter entfernt wird. Der Rhythmus des Transpirationsverlaufes geht bei dieser Maßnahme verloren. Es wird deshalb angenommen, daß die mit dem CO2-Austausch verbundenen Abläufe des Säurestoffwechsels der Crassulaceen im Blattparenchym über die Kontrolle des CO2-Partialdruckes in den Intercellularen die Spaltöffnungsweite und damit die Transpirationsintensität in den einzelnen Phasen der Licht- und Dunkelperiode bestimmen.2.Bei fortschreitender Austrocknung des Bodens wird die CO2-Aufnahme im Licht stärker eingeschränkt als im Dunkel. Als Endzustand ist CO2-Aufnahme ausschließlich in der Dunkelphase zu beobachten. Da die Transpiration mit der CO2-Aufnahme gekoppelt ist, wird in dieser Phase tagsüber (und damit zur Zeit erhöhter Evaporation unter natürlichen Bedingungen) stomatär kein Wasser abgegeben. Die Koppelung zwischen dem Säurestoffwechsel und dem Gasaustausch erweist sich somit als vorteilhaft im Hinblick auf die Kohlenstoff- und Wasserbilanz der Pflanze.

Photoperiodism and crassulacean acid metabolism : I. Immunological and kinetic evidences for different patterns of phosphoenolpyruvate carboxylase isoforms in photoperiodically inducible and non-inducible Crassulacean acid metabolism plants.

Plants of Kalanchoe blossfeldiana v. Poelln. Tom Thumb and Sedum morganianum E. Walth. were grown under controlled photoperiodic conditions under either short or long days. Gaz exchange measurements confirmed that in K. blossfeldiana Crassulacean acid metabolism (CAM) was photoperiodically inducible and that S. morganianum performed CAM independently of photoperiod. With K. blossfeldiana, a comparison of catalytic and regulatory properties of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) from short-day and long-day grown plants showed differences, but not with S. morganianum. Ouchterlony double diffusion tests and immunotitration experiments (using a S. morganianum PEPC antibody) established that CAM is induced in K. blossfeldiana—but not in S. morganianum—through the synthesis of a new PEPC isoform; this form shows an immunological behavior different from that prevailing under non-inductive conditions and can be considered as specific for CAM performance.

Phenotypic changes in the fluidity of the tonoplast membrane of crassulacean-acid-metabolism plants in response to temperature and salinity stress

Electron paramagnetic resonance-spectroscopic studies on spin-labeled purified tonoplast membranes showed that in the obligate crassulacean-acid-metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perr. the fluidity of the tonoplast decreased during acclimation to higher temperatures. This phenotypic change in tonoplast fluidity was paralleled by a decrease in the mobilization of malic acid from the vacuoles during CAM in the light. The shift from the C3 to the CAM mode of photosynthesis in the facultative CAM plant Mesembryanthemum crystallinum L. also led to a decrease in the fluidity of the tonoplast membrane. The results are consistent with the hypothesis that the ability to store malic acid during CAM in the vacuoles depends largely on the actual fluidity of the tonoplast membrane.

Is Sedum acre L. a CAM plant

SummarySedum acre L. collected from its natural stands south of Darmstadt (Germany) showed δ13C values typical for C3 plants. This suggests that in situ at the natural stand CO2 was fixed mainly via the C3 mode of photosynthesis rather than via the CAM mode. However, experimental water stress shifts the CO2 exchange pattern from the C3 type to CAM type. Simultaneously, a diurnal rhythm of malic acid oscillation, typical for CAM, and increase of PEP-carboxylase and malic enzyme activities developed. Hence, Sedum acre is obviously to be classified as a facultative CAM plant. Because of the temperature characteristics of CO2 exchange in Sedum acre, in situ CO2 should be harvested from the atmosphere mainly during the seasons where water stress situations capable of inducing CAM are unlikely to occur.

Temperature effects on malic-acid efflux from the vacuoles and on the carboxylation pathways in crassulacean-acid-metabolism plants

The studies described in the paper were conducted with tissue slices of Crassulacean acid metabolism (CAM) plants floating in isotonic buffer. In a first series of experiments, temperature effects on the efflux of [14C]malate and14CO2 were studied. An increase of temperature increased the efflux from the tissue in a non-linear manner. The efflux was markedly influenced also by the temperatures applied during the pretreatment. The rates of label export in response to the temperature and the relative contributions of14CO2 and [14C]malate to the label export were different in the two studied CAM plants (Kalanchoë daigremontiana, Sempervivum montanum). In further experiments, temperature response of the labelling patterns produced by14CO2 fixation and light and darkness were studied. In tissue which had accumulated malate (acidified state) an increase of temperature decreased the rates of dark CO2 fixation whilst the rates of CO2 fixation in light remained largely unaffected. An increase of temperature shifted the labelling patterns from a C4-type (malate being the mainly labelled compound) into a C3-type (label in carbohydrates). No such shift in the labelling patterns could be observed in the tissue which had depleted the previously stored malate (deacidified state). The results indicate that in the acidified tissue the increase of temperature increases the efflux of malate from the vacuole by changing the properties of the tonoplast. It is assumed that the increased export of malic acid lowers the in-vivo activity of phosphoenol pyruvate carboxylase by feedback inhibition.

Untersuchungen über den Gaswechsel von Bryophyllum während der Lichtperiode

Summary1.All conditions which result in a low level of malic acid at the beginning of the light period (removal of CO2 in the dark, considerably prolonged dark peroid, high temperatures in the dark) caused CO2 uptake in the light period to start earlier than it did in the untreated control. The same result was obtained with treatment (increase of light intensity) which brings about faster degradation of the malate accumulated in the night. The course of CO2 uptake seems therefore to be dependet on the extent to which the CO2 pool (represented by malic acid) is filled.2.The conversion of malate accumulated in the night into carbohydrates in light is characterized by a lag phase at the beginning of the light period. During this lag phase atmospheric CO2 is consumed, but this consumption comes to an end when the first photosynthetic products of malate appear. There is evidence that external CO2 is consumed by the leaf tissues only when carbon dioxide derived from an internal source (malate) is not available.Zusammenfassung1.Alle Maßnahmen, die zu einem niedrigen Malatspiegel zu Beginn der Lichtperiode verhelfen (CO2-Entzug im Dunkel, stark erhöhte Temperatur im Dunkel, überlange Dunkelperiode) haben zur Folge, daß die CO2-Aufnahme in der zweiten Hälfte der Lichtperiode früher einstezt als bei der unbehandelten Kontrolle. Das gleiche gilt für Maßnahmen, die einen schnelleren Abbau des nachts akkumulierten Malat bewirken (Erhöhung der Lichtintensität). Der Verlauf der CO2-Aufnahme scheint daher maßgeblich vom Füllstand des durch das Malat repräsentierten CO2-Speichers bestimmt zu sein.2.Die Umwandlung des Malat in Kohlenhydrate durchläuft bei plötzlich einsetzender Belichtung eine Verzögerungsphase. Da diese Phase von intensivem Verbrauch externen Kohlendioxids begleitet ist, der dann zum Erliegen kommt, wenn die ersten photosynthetischen Folgeprodukte des Malat auftreten, schließen wir, daß endogenes Kohlendioxid mit dem CO2 der Luft um die Assimilationszentren konkurriert, so daß exogenes CO2 nur dann verbraucht werden kann, wenn endogenes (aus dem Malat stammendes) noch nicht oder nicht mehr zur Verfügung steht.

Geosiphon pyriforme, an Endocytosymbiosis Between Fungus and Cyanobacteria, and its Meaning as a Model System for Arbuscular Mycorrhizal Research

Geosiphon pyriforme (Kutz.) v. Wettstein is a coenocytic soil fungus and until now the only known example of a fungus living in endocytobi-otic association with a cyanobacterium, i.e. with Nostoc punctiforme. The symbiotic nature of the system was first recognized by F.v. Wettstein (1915), who described it as a symbiosis between a heterotrophic siphonal chlorophyceaen alga and Nostoc. The fungal nature of the macrosymbiont was recognized by Knapp (1933). The fungus lives together with the cyanobacterium on the surface and in the upper layer of wet soils poor in inorganic nutrients, particularly in phosphate. When a fungal hypha comes into contact with free-living Nostoc cells, the latter are incorporated by the fungus at the hyphal tip, which thereafter swells and forms a unicellular “bladder”, about 1–2mm in size and appearing on the soil surface (Fig. 1). Inside this bladder the cyanobacteria are physiologically active and dividing. Life history, ultra-structure and physiological activity of the system will be described in this chapter.

Crassulacean acid metabolism in Kalanchoë species collected in various climatic zones of Madagascar: a survey by δ13C analysis

SummaryThe carbon isotope compositions of samples of Kalanchoë species collected at the natural stands in Madagascar were determined. The results suggest that all species of the genus Kalanchoë are capable of crassulacean acid metabolism. The observed δ13C values cover the whole range from −10 to −30‰. This high diversity of the δ13C values was found among the species of the genus as well as, in certain cases, within a single species. This suggest that the CAM patterns in Kalanchoë are generally very flexible. The δ13C values show a clear correlation with the climate of the habitats from where the samples derived. Values indicative of CO2 fixation taking place exclusively during the night were found in the dry regions of Madagascar, whereas δ13C values indicative of mixed CO2 fixation during night and day or of CO2 fixation entirely during the day are distributed in the humid zones.

In situ studies on crassulacean acid metabolism in Sedum acre L. and Sedum mite Gil

SummaryCO2 exchange, the diurnal variations in the levels of malic, citric and isocitric acid, and the labelling pattern after 14CO2 fixation were measured in Sedum acre and Sedum mite growing in situ. As predicted from laboratory experiments, drought changed the gas exchange pattern from a C3 type to a crassulacean acid metabolism (CAM) type. This shift correlated with the development of a diurnal rhythm in the malic acid content. The results of 14CO2 pulse-chase experiments suggest that in well-watered plants a CAM pattern of carbon flow already exists; hence water stress might enhance latent CAM rather than induce it. The in situ CAM performance by the Sedum species appeared to be highly susceptible to modulation by season and external factors, particularly light and temperature.CAM did not substantially contribute to total carbon gain in S. acre and S. mite. During most of their lifecycles the plants grow under conditions that favour CO2 uptake by the C3 pathway rather than by CAM. Hence, despite a capability to feature CAM, the δ13C values found in S. acre and S. mite are those of C3 plants.