Macromolecular syntheses and the course of cell cycle events in the chlorococcal algaScenedesmus quadricauda under nutrient starvation: Effect of nitrogen starvation

Daughter cells of the chlorococcal algaScenedesmus quadricauda incubated under photosynthesizing conditions in a nitrogen-free medium did not make any progress in the cell cycle. Photosynthetic starch formation continued for a period corresponding to a half of the cell cycle and then levelled off. Protein synthesis was very slow and it did not surpass double the initial amount. RNA content decayed from the start of treatment and approached about 2 pg/cell. When a synchronous population was deprived of nitrogen or of light in the middle of the cell cycle RNA synthesis stopped immediately or very soon afterwards and, in spite ofabundant intracellular nitrogen reserves, RNA content slowly declined. This degradation was much extensive in nitrogen starved cells where, eventually, the RNA content attained about half the starting value. In both experimental variants, DNA replications started at the same time as in control culture, but the final amount of DNA attained only half the control value. Protein synthesis stopped immediately in the dark. In the nitrogen-starved cells, it continued for several hours and protein content increased about 70 % of the amount present at the start of starvation. The number of daughter cells formed was proportional to the final protein content in the nitrogen-and light-deprived cells (corresponding division numbers were 6 and 4, respectively). Upon refeeding of daughter cells formed under nitrogen starvation, RNA synthesis started immediately, while protein synthesis displayed a lag of about 5 h. DNA replications were triggered at the time when the ratio of RNA to DNA content attained the same value as in the control culture.     

Biosynthesis of monensins a and b: the role of isoleucine

Isoleucine added to the cultivation medium of Streptomyces cinnamonensis C-100-5 induced a relative increase of the production of monensin B at the expense of monensin A. U-14C-Isoleucine was found not to be a specific monensin B precursor. The incorporation of 1-13C-2-methylbutyrate into monensins A and B showed the label to be evenly incorporated in both products at carbon atoms originating from C(1) of propionate. In regulatory mutants insensitive to 2-amino-3-chlorobutyrate isoleucine influenced the production of monensins only slightly but strains resistant to 2-aminobutyrate and norleucine decreased their total production by 2-12% in the presence of isoleucine which was associated with a decrease of monensin A content by 14-52%. The inhibitory effect of isoleucine on the biosynthesis of valine, a specific precursor of the butyrate unit of monensin A, is discussed.     

Characteristics of the saprophytic reference strain FA ofClaviceps paspali

Growth properties and morphological features of the saprophytic collection cultureClaviceps paspali strain FA were investigated. The strain was characterized by a range of utilization of 13 carbon sources in a basic synthetic and a peptone medium. A temperature of 23 °C was more favourable for growth than 28 °C. Stages of changes of the culture cultivated for a long time on Sabouraud’s medium were detected by electron microscopy. The white culture was characterized by true septated mycelium with different types of terminal parts of hyphae. Arthrospores occurred after a 14-d cultivation, small spherical conidia released individually from hyphae were quite rare. As compared with other strains of the same species, strain FA did not form spherical clusters of conidia. On the other hand, a spontaneous rupture of the surface cell wall in different parts of hyphae and release of the cytoplasm were observed. In corn-steep containing media the formation of individual, pair and chain-like forms of arthritic conidia was stimulated. Destructive autolytic changes of hyphae were detected in the medium with potato extract.     

Saprophytic production of Clavine alkaloids and activity of Hydroxymethylglutaryl-CoA reductase

In submerged Claviceps cultures the activity of hydroxymethylglutaryl-CoA reductase preceded the increase of alkaloid production and of sterol content. During the first alkaloid phase, cell mevalonate was involved in the biosynthesis of both alkaloids and steroids. In the second production phase, it was predominantly used for alkaloid synthesis. Hydroxymethylglutaryl-CoA reductase appears to be a suitable target for physiological manipulation to increase clavine alkaloid yields.     

Contribution to the ecology ofMarsilea quadrifolia L.

Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia).     

Seasonal changes in the photosynthetic response ofMercurialis perennis plants from different light regime conditions

Curves relating net photosynthetic rate to irradiance [P(I) curve relation] were estimated and analysed inMercurialis perennis L. plants stemming from three forest (spruce, beech and ash) stands with different tree leaf canopy development and different light regime. The saturating irradiance (I_s) reached the highest values in plants of all three stands in spring (spruce forest: 438 W m⁻², beech forest: 440 W m⁻² and ash forest: 367 W m⁻²), it declined sharply in the middle of the growing season (283, 285 and 297 W m^-2, respectively) and this I_s level persisted until autumn. A pronounced dynamics in plants from spruce and beech forests made itself manifest also in the adaptation (I_a) and compensating (I_c) irradiances, respectively. After a sudden decline in summer, values in autumn were close to those of the vernal season. The most pronounced parameter, which optimally expressed the adaptation ofMercurialis perennis to various light conditions, was the photosynthetic efficiency (α) calculated as the slope of the linear part of the curve relating net photosynthetic rate to irradiance. At the time of the highest P_{N sat.} value in course of the growing season (August) (spruce forest: 100, beech forest: 98.7 and ash forest: 85.8 μg CO₂ m⁻² s⁻¹), R_D was in its minimum; in autumn P_{N sat.} reached the lowest values which corresponded to the most intensive R_D. It was found thatMercurialis perennis plants stemming from forest stands with different light conditions did not make use equally of the altering light conditions in the course of the growing season. By the underlying analysis of P(I) curves this rhizomatous perennial herb (geophyte) may be characterized as a shade tolerant species.