Determination of Root Exudates in a Steril Continuous Flow Culture. II. Short-Term and Long-Term Variations of Exudation Intensity

The exudate production of alfalfa under the conditions of the sterile flow culture was quantitatively measured. In the first 40 days 3.10⁻³ μmoles amino-N, 2.5 μequivalents of organic acids and approximately 10⁻⁴ μmoles of reducing sugars were liberated per plant and per day into the percolating nutrient solution. The amino acid concentration in the outflow varies according to a daily periodicity. The exudation of a colored substance also shows daily periodical variations. This pattern is different from the pattern of the amino acid exudation, however, and directly coupled to shoot illumination. Short-term 2,4-dinitrophenol additions to the nutrient lower the liberation of amino acids into the percolating solution.     

Ionic strength effects on cytochrome aa3 kinetics

1. The occurrence of an optimal ionic strength for the steady-state activity of isolated cytochrome aa₃ can be attributed to two opposite effects: upon lowering of the ionic strength the affinity between cytochrome c and cytochrome aa₃ increases, whereas in the lower ionic strength region the formation of a less active cytochrome c-aa₃ complex limits the ferrocytochrome c association to the low affinity site.2. At low ionic strength, the reduction of cytochrome c-aa₃ complex by ferrocytochrome c₁ proceeds via non-complex-bound cytochrome c. Under these conditions the positively charged cytochrome c provides the electron transfer between the negatively charged cytochromes c₁ and aa₃.3. Polylysine is found to stimulate the release of tightly bound cytochrome c from the cytochrome c-aa₃ complex. This property points to the existence of negative cooperativity between the two binding sites. We suggest that the stimulation is not restricted to polylysine, but also occurs with cytochrome c.4. Dissociation rates of both high and low affinity sites on cytochrome aa₃ were determined indirectly. The dissociation constants, calculated on the basis of pre-steady-state reaction rates at an ionic strength of 8.8 mM, were estimated to be 0.6 nM and 20 μM for the high and low affinity site, respectively.     

The reaction between cytochrome C1 and cytochrome C

The kinetics of electron transfer between the isolated enzymes of cytochrome c₁ and cytochrome c have been investigated using the stopped-flow technique. The reaction between ferrocytochrome c₁ and ferricytochrome c is fast; the second-order rate constant (k₁) is 3.0 · 10⁷ M^?1 · s^?1 at low ionic strength (I = 223 mM, 10°C). The value of this rate constant decreases to 1.8 · 10⁵ M^?1 · s^?1 upon increasing the ionic strength to 1.13 M. The ionic strength dependence of the electron transfer between cytochrome c₁ and cytochrome c implies the involvement of electrostatic interactions in the reaction between both cytochromes. In addition to a general influence of ionic strength, specific anion effects are found for phosphate, chloride and morpholinosulphonate. These anions appear to inhibit the reaction between cytochrome c₁ and cytochrome c by binding of these anions to the cytochrome c molecule. Such a phenomenon is not observed for cacodylate. At an ionic strength of 1.02 M, the second-order rate constants for the reaction between ferrocytochrome c₁ and ferricytochrome c and the reverse reaction are k₁ = 2.4 · 10⁵ M^?1 · s^?1 and k_?1 = 3.3 · 10⁵ M^?1 · s^?1, respectively (450 mM potassium phosphate, pH 7.0, 1% Tween 20, 10°C). The ‘equilibrium’ constant calculated from the rate constants (0.73) is equal to the constant determined from equilibrium studies. Moreover, it is shown that at this ionic strength, the concentrations of intermediary complexes are very low and that the value of the equilibrium constant is independent of ionic strength. These data can be fitted into the following simple reaction scheme: cytochrome c²⁺₁ + cytochrome c³⁺ai cytochrome c³⁺₁ + cytochrome c²⁺.     

Ultrastructure and histochemistry of Citrus limon (L.) stigma

Citrus limon has a wet stigma which can be divided in two zones: a glandular superficial one formed by papillae, and a non-glandular one formed by parenchymatic cells. The stigmatic exudate is produced by the papillae after the latter have reached their ultimate size. The papillae of the mature pistil are of varying size and composition. Both the unicellular and multicellular ones are present. The cells at the base of the papillae are rich in cytoplasm, whereas the tip cells are vacuolated. Histochemical analysis has shown that the exudate of Citrus is composed of lipids, polysaccharides, and proteins. Our results indicate that the lipidic component is produced and secreted first, followed by production and secretion of the polysaccharidic component. The lipidic component of the exudate is produced in the basal papillae cells and accumulates as droplets in dilated parts of the smooth endoplasmic reticulum (SER). Subsequently the lipid droplets are transported to the plasma membrane, and transferred by the latter into the cell walls. Then the exudate component is accumulated in the intercellular spaces and in the middle lamellar regions of the walls. Subsequently, the polysaccharidic component of the exudate is produced and secreted by the tip cells of the papillae.Abbreviations RER rough endoplasmic reticulum - SER smooth endoplasmic reticulum     

The reaction between cytochrome c1 and cytochrome c

The kinetics of electron transfer between the isolated enzymes of cytochrome c1 and cytochrome c have been investigated using the stopped-flow technique. The reaction between ferrocytochrome c1 and ferricytochrome c is fast; the second-order rate constant (k1) is 3.0 . 10(7) M-1 . s-1 at low ionic strength (I = 223 mM, 10 degrees C). The value of this rate constant decreases to 1.8 . 10(5) M-1 . s-1 upon increasing the ionic strength to 1.13 M. The ionic strength dependence of the electron transfer between cytochrome c1 and cytochrome c implies the involvement of electrostatic interactions in the reaction between both cytochromes. In addition to a general influence of ionic strength, specific anion effects are found for phosphate, chloride and morpholinosulphonate. These anions appear to inhibit the reaction between cytochrome c1 and cytochrome c by binding of these anions to the cytochrome c molecule. Such a phenomenon is not observed for cacodylate. At an ionic strength of 1.02 M, the second-order rate constants for the reaction between ferrocytochrome c1 and ferricytochrome c and the reverse reaction are k1 = 2.4 . 10(5) M-1 . s-1 and k-1 = 3.3 . 10(5) M-1 . s-1, respectively (450 mM potassium phosphate, pH 7.0, 1% Tween 20, 10 degrees C). The 'equilibrium' constant calculated from the rate constants (0.73) is equal to the constant determined from equilibrium studies. Moreover, it is shown that at this ionic strength, the concentrations of intermediary complexes are very low and that the value of the equilibrium constant is independent of ionic strength. These data can be fitted into the following simple reaction scheme: cytochrome c2+1 + cytochrome c3+ in equilibrium or formed from cytochrome c3+1 + cytochrome c2+.     

A modified MOPP regimen in the treatment of Hodgkin's disease stage III B and IV (author's transl)

In a retrospective study 80 patients with Hodgkin's disease of stage III B (n = 32) and IV (n = 48) were investigated, who had been treated with a modified MOPP regimen. 28 patients (35%) were previously untreated. A completed remission was reached in 51 patients, a partial remission in 16, and 13 patients failed to respond. 16 patients had died in the observation period. Complete remissions were twice as frequent with 90% in stage III as compared with 45% in stage IV. The group of patients surviving 4 years was 92% in stage III and 62% in stage IV.     

Two newly recognized species of Hemidactylus (Squamata,Gekkonidae) from the Arabian Peninsula?and Sinai,Egypt

A recent molecular phylogeny of the Arid clade of the genus Hemidactylus revealed that the recently described H. saba and two unnamed Hemidactylus species from Sinai, Saudi Arabia and Yemen form a well-supported monophyletic group within the Arabian radiation of the genus. The name ‘Hemidactylus saba species group’ is suggested for this clade. According to the results of morphological comparisons and the molecular analyses using two mitochondrial (12S and cytb) and four nuclear (cmos, mc1r, rag1, rag2) genes, the name Hemidactylus granosus Heyden, 1827 is resurrected from the synonymy of H. turcicus for the Sinai and Saudi Arabian species. The third species of this group from Yemen is described formally as a new species H. ulii sp. n. The phylogenetic relationships of the members of ‘Hemidactylus saba species group’ are evaluated and the distribution and ecology of individual species are discussed.     

NMR imaging of high-amylose starch tablets. 2. Effect of tablet size

Carbohydrate polymers are widely used for pharmaceutical applications such as the controlled release of drugs. The swelling and water mobility in high-amylose starch tablets are important parameters to be determined for these applications. They have been studied at different time intervals by nuclear magnetic resonance imaging (NMRI) after the immersion of the samples in water. These tablets have a hydrophilic matrix, which swells anisotropically and forms a hydrogel in water. NMRI shows clearly the anisotropy of the water penetration and the swelling along the radial and axial dimensions of the tablets. Empirical relationships are established to describe the kinetics of water penetration and swelling of the tablets. Results show that water uptake and tablet swelling strongly depend on the size of the tablets. Gravimetric measurements of water uptake were also performed in comparison with the NMRI results.