Chlamydospore formation of <Emphasis Type="Italic">Entoloma clypeatum</Emphasis> f. <Emphasis Type="Italic">hybridum </Emphasis>on mycorrhizas and rhizomorphs associated with <Emphasis Type="Italic">Rosa multiflora</Emphasis>

 Chlamydospores of Entoloma clypeatum f. hybridum were described on the mycorrhizas and rhizomorphs associated with Rosa multiflora. Their developmental pattern seems to be the Nyctalis type. This is the first report on chlamydospore formation on the mycorrhizae in entolomatoid fungi. Received: January 17, 2002 / Accepted: November 5, 2002 Acknowledgments K.H. is grateful to Emeritus Professor N. Sagara in Kyoto University, in whose laboratory part of this study was undertaken. Thanks are due to Mr. D. Sakuma for allowing the specimens to be kept in Osaka Museum of Natural History. Correspondence to:H. Kobayashi     

Detection of specific chromosome reduction in rice somatic hybrids with the A, B, and C genomes by multi-color genomic in situ hybridization

 A multi-color genomic in situ hybridization (McGISH) method has been developed. Three different rice genomes, A, B and C, involved in rice somatic hybrids were distinguished using three different fluorescent signals. All the rice chromosomes from the different genomes could be identified by different fluorescent colors, and the distribution of each genome in the nucleus was clearly visualized under a fluorescence microscope. The relationship between chromosomal constitution and morphological variations observed in the somatic hybrids, and the utility of McGISH, are discussed based on the results currently obtained. Received: 21 November 1997 / Accepted: 9 December 1997     

Modelling O2 and O2 unidirectional fluxes in plants. III: Fitting of experimental data by a simple model

Photosynthetic assimilation of CO₂ in plants results in the balance between the photochemical energy developed by light in chloroplasts, and the consumption of that energy by the oxygenation processes, mainly the photorespiration in C₃ plants. The analysis of classical biological models shows the difficulties to bring to fore the oxygenation rate due to the photorespiration pathway. As for other parameters, the most important key point is the estimation of the electron transport rate (ETR or J), i.e. the flux of biochemical energy, which is shared between the reductive and oxidative cycles of carbon. The only reliable method to quantify the linear electron flux responsible for the production of reductive energy is to directly measure the O₂ evolution by ¹⁸O₂ labelling and mass spectrometry. The hypothesis that the respective rates of reductive and oxidative cycles of carbon are only determined by the kinetic parameters of Rubisco, the respective concentrations of CO₂ and O₂ at the Rubisco site and the available electron transport rate, ultimately leads to propose new expressions of biochemical model equations. The modelling of ¹⁸O₂ and ¹⁶O₂ unidirectional fluxes in plants shows that a simple model can fit the photosynthetic and photorespiration exchanges for a wide range of environmental conditions. Its originality is to express the carboxylation and the oxygenation as a function of external gas concentrations, by the definition of a plant specificity factor Sp that mimics the internal reactions of Rubisco in plants. The difference between the specificity factors of plant (Sp) and of Rubisco (Sr) is directly related to the conductance values to CO₂ transfer between the atmosphere and the Rubisco site. This clearly illustrates that the values and the variation of conductance are much more important, in higher C₃ plants, than the small variations of the Rubisco specificity factor. The simple model systematically expresses the reciprocal variations of carboxylation and oxygenation exchanges illustrated by a “mirror effect”. It explains the protective sink effect of photorespiration, e.g. during water stress. The importance of the CO₂ compensation point, in classical models, is reduced at the benefit of the crossing points Cx and Ox, concentration values where carboxylation and oxygenation are equal or where the gross O₂ uptake is half of the gross O₂ evolution. This concept is useful to illustrate the feedback effects of photorespiration in the atmosphere regulation. The constancy of Sp and of Cx for a great variation of P under several irradiance levels shows that the regulation of the conductance maintains constant the internal CO₂ and the ratio of photorespiration to photosynthesis (PR/P). The maintenance of the ratio PR/P, in conditions of which PR could be reduced and the carboxylation increased, reinforces the hypothesis of a positive role of photorespiration and its involvement in the plant-atmosphere co-evolution.     

Lovastatin biosynthesis by Aspergillus terreus with the simultaneous use of lactose and glycerol in a discontinuous fed-batch culture

The influence of various combinations of glycerol and lactose feed on the biosynthesis of two polyketide metabolites, lovastatin and (+)-geodin, by Aspergillus terreus ATCC20542 in a discontinuous fed-batch culture was presented. In these experiments lactose and/or glycerol were also used as the initial carbon substrates in the cultivation media. The application of glycerol feed, when lactose is the initial substrate, leads to the appreciable lovastatin concentration in the broth (122.4 mg l⁻¹), nevertheless the abundant (+)-geodin level is at the same time obtained (255.5 mg l⁻¹). The cultures with glycerol as the initial substrate and fed with lactose produce less lovastatin and (+)-geodin. The application of the various combined glycerol and/or lactose feeds allows for improving lovastatin production up to 161.8 mg l⁻¹ and decreases (+)-geodin concentration to 98.7 mg l⁻¹. The analysis of product formation rates and yield coefficients indicates that lovastatin is more efficiently produced on lactose, especially in the initial stages of the cultivation. Glycerol efficiently sustains fungal activity to form these polyketides in the late idiophase but it mainly favours (+)-geodin formation, if solely used in the feed. The feeds performed both with lactose and glycerol occur to be the most desired to maximise lovastatin and minimise (+)-geodin formation.     

Effects of precipitation on photosynthesis and water potential in Andropogon gerardii and Schizachyrium scoparium in a southern mixed grass prairie

In grassland ecosystems, spatial and temporal variability in precipitation is a key driver of species distributions and population dynamics. We experimentally manipulated precipitation to understand the physiological basis for differences in responses of species to water availability in a southern mixed grass prairie. We focused on the performance of two dominant C₄ grasses, Andropogon gerardii Vitman and Schizachyrium scoparium (Michx.) Nash, in treatments that received ambient rainfall, half of ambient rainfall (“drought” treatment), or approximately double ambient rainfall (“irrigated” treatment). Water potentials of S. scoparium were lower than A. gerardii, suggesting superior ability to adjust to water deficit in S. scoparium. Additionally, drought reduced photosynthesis to a greater extent in A. gerardii compared to S. scoparium. Leaf-level photosynthesis rates were similar in ambient and irrigated treatments, but were significantly lower in the drought treatment. Although stomatal conductance was reduced by drought, this was not limiting for photosynthesis. Leaf δ¹³C values were decreased by drought, caused by an increase in C_i/C_a. Chlorophyll fluorescence measures indicated light-harvesting rates were highest in irrigated treatments, and were lower in ambient and drought treatments. Moreover, drought resulted in a greater proportion of absorbed photon energy being lost via thermal pathways. Reductions in photosynthesis came as a result of non-stomatal limitations in the C₄ cycle. Our results provide mechanistic support for the hypothesis that S. scoparium is more drought tolerant than A. gerardii.