The effect of bacterial strain and temperature changes on the nitrogenase activity of Lotus pedunculatus root nodules

After 40 days of growth at 25°C, Lotus pedunculatus cav., cv. Maku plants infected with Rhizobium loti strain NZP2037 displayed similar relative growth rates but had twice the nodule mass and only one third the whole plant dry weight of plants infected with Bradyrhizobium sp. (Lotus) strain CC814s. In the NZP2037 symbiosis, the rate of CO₂ evolution (per g dry weight of nodulated root) was 1.6 times as high as that in the CC814s symbiosis while the rate of C₂H₂ reduction (per g dry weight of nodule) was only 48% of that in the CC814s symbiosis. Studies of the effect of short term temperature changes on the gas exchange characteristics (CO₂ and H₂ evolution, C₂H₂ reduction) of these symbioses revealed wide differences in the optima for C₂H₂ reduction. Nodules infected with NZP2037 displayed maximal C₂H₂ reduction rates [157 μmol (g dry weight nodule)^?1 h^?1] at 12°C, whereas nodules infected with CC814s were optimal at 30°C [208 μmol (g dry weight nodule)^?1 h^?1]. These short term studies suggested that differences in temperature optima for N₂ may have partially accounted for the poorer effectivity, at 25°C, of strain NZP2037 when compared with strain CC-814s. The relative efficiency [RE = 1 – (H₂ evolution/C₂H₂ reduction)] of N₂ fixation varied widely with temperature in the two symbioses, but there was a general trend toward higher RE with lower temperatures. The ratio of CO₂ evolution: C₂H₂ reduction (mol/mol) in nodulated roots infected with CC814s was constant (ca 10 CO₂/C₂H₂) between 5°C and 30°C, whereas in plants infected with NZP2037 it reached a minimal value of 3.3 CO₂/C₂H₂ at 10°C and was 19 CO₂/C₂H₂ at the growing temperature (25°C).     

Chromophore structure in phytochrome intermediates and bleached forms of phytochrome

Phytochrome (120 kdalton or 60 kdalton) was isolated from etiolated seedlings of Avena sativa L. cv. Pirol (Baywa München). Irradiation with red light of the P_r form at −23°C in aqueous medium or at −40°C in 66% glycerol leads to the intermediate meta-Rb. Acidification of the glycerol solution at −40°C leads to the absorption of the 15(E) phytochrome chromophore (= P_fr chromophore). Subsequent irradiation transforms this into the 15(Z) chromophore (= P_r chromophore). The presence of the 15(E) chromophore was demonstrated by the same methods also in phytochrome bleached either as P_fr in the dark by 4 M urea, methanol, acetone, ethylene glycol, 8-anilinonaphthalene-1-sulfonate, or as P_r by irradiation with red light in the presence of the same agents. Phytochrome bleached by sodium dodecylsulfate or by dehydration was also investigated. It was concluded that bleached phytochrome contains the P_fr chromophore without specific interaction with the protein.     

Triterpenes from Periandra dulcis roots

Three oleanane triterpenes were isolated from the roots of Periandra dulcis,and identified as 3β-hydroxy-25-al-olean-18-en-30-oic acid (periandric acid I), 3β-hydroxy-25-al-olean-12-en-30-oic acid (periandric acid II) and 3-oxo-25-hydroxy-olean-12-en-30-oic acid. The former two compounds (periandric acids I and II) were identical with the aglycones obtained by hydrolysis of periandrin I and II, respectively and the latter one was a new triterpene.     

Condensed tannins: co-occurrence of procyanidins,prodelphinidins and profisetinidins in the heartwood of Acacia baileyana

The flavonoids and condensed tannins of the heartwood of Acacia baileyana var. purpurea are described. In conformity with other Acacia species, the hydroxylation pattern of the flavonoids is of the resorcinol type but, in sharp contrast, the tannins are heterogeneous consisting of a mixture of the resorcinol and phtoroglucinol series. Dimeric proanthocyanidins of the phloroglucinol type were absent and this exception to the general observation that they invariably co-occur with the polymers may be explained by the relative nucleophilicity of the aromatic A-rings.     

Studies on the C-24 configurations of Δ7-sterols in theseeds of Cucurbita maxima

Uncertainties surrounding the structures of the Δ⁷-sterols in the seeds of Cucurbita maxima have been resolved. Seven components were found by TLC, GLC, HPLC, mass spectrometry and ¹H NMR. They were 24β-ethyl-5α-cholesta-7,22,25(27)-trien-3β-ol, 24β-ethyl-5α-cholesta-7,25(27)-dien-3gb-ol, avenasterol, spinasterol, 24-dihydrospinasterol, 24ζ-methyllathosterol and 25(27)-dehydrofungisterol. The ¹H NMR spectra indicated that the sterols with an ethyl substituent at C-24 occurred in the absence of their C-24 epimers. This seems to be the first instance of the detection of 25(27)-dehydrofungisterol in a higher plant.     

Lysine biosynthesis and the evolution-of pennate marine diatoms

The classification of lysine biosynthetic pathways in various organisms have been used to investigate their descent in evolution. We have attempted these determinations in the diatoms Amphora coffeaeformis var:perpusilla (Grunow Cleve.) and Phaeodactylum tricornutum (Bohlin). Additionally, we have verified earlier results of Vogel in a green alga, Chlorella pyrenoidosa strain Tx 71105 (Texas Culture Collection). Our research indicates that the diaminopimelic acid route is involved in all three organisms. While these studies do not exclude the possible co-existence of the α-aminoadipic acid route, the results imply a closer evolutionary relationship of pennate diatoms to bacteria and “classical” photosynthetic plants rather than to heterotrophic or mixotrophic fungi and atypical algal strains such as the Euglenophyta.     

Long poly(A) tracts in the human genome are associated with the Alu family of repeated elements

Long poly(dA).poly(dT) tracts (poly(A) tracts), regions of DNA containing at least 20 contiguous dA residues on one strand and dT residues on the complementary strand, are found in about 2 X 10(4) copies interspersed throughout the human genome. Using poly(dA).poly(dA) as a hybridization probe, we identified recombinant lambda phage that contained inserts of human DNA with poly(A) tracts. Three such tracts have been characterized by restriction mapping and sequence analysis. One major poly(A) tract is present within each insert and is composed of from 28 to 35 A residues. In each case, the poly(A) tract directly abuts the 3' end of the human Alu element, indicating that the major class of poly(A) tracts in the human genome is associated with this family of repeats. The poly(A) tracts are also adjacent to A-rich sequences and, in one case, to a polypurine tract, having the structure GA3-GA3-GA4-GA6-GA5-GA4. We suggest that repetitive cycles of unequal crossing over may give rise to both the long poly(A) and polypurine tracts observed in this study.     

Aplysia oxymyoglobin with an unusual stability property

Native oxymyoglobin was isolated directly from the radular muscle of Aplysia kurodai with complete separation from metmyoglobin on a DEAE-cellulose column. It was examined for its spectral and stability properties. The spectrum of Aplysia MbO2 , which lacks the distal histidine, is very similar to those of mammalian oxymyoglobins , the alpha-peak being higher than the beta-peak and the absorbance ratio being 1.03. Its stability, however, is quite different from those of the mammalian oxymyoglobins , and Aplysia MbO2 is found to be extremely susceptible to autoxidation. Its rate is one-hundred times higher at pH 9.0, and its pH dependence is unusual and much less steep, when compared with sperm whale MbO2 as reference.     

Microsecond rotational motions of eosin-labeled myosin measured by time-resolved anisotropy of absorption and phosphorescence

We have studied submicrosecond and microsecond rotational motions within the contractile protein myosin by observing the time-resolved anisotropy of both absorption and emission from the long-lived triplet state of eosin-5-iodoacetamide covalently bound to a specific site on the myosin head. These results, reporting anisotropy data up to 50 microseconds after excitation, extend by two orders of magnitude the time range of data on time-resolved site-specific probe motion in myosin. Optical and enzymatic analyses of the labeled myosin and its chymotryptic digests show that more than 95% of the probe is specifically attached to sulfhydryl-1 (SH1) on the myosin head. In a solution of labeled subfragment-1 (S-1) at 4 degrees C, absorption anisotropy at 0.1 microseconds after a laser pulse is about 0.27. This anisotropy decays exponentially with a rotational correlation time of 210 ns, in good agreement with the theoretical prediction for end-over-end tumbling of S-1, and with times determined previously by fluorescence and electron paramagnetic resonance. In aqueous glycerol solutions, this correlation time is proportional to viscosity/temperature in the microsecond time range. Furthermore, binding to actin greatly restricts probe motion. Thus the bound eosin is a reliable probe of myosin-head rotational motion in the submicrosecond and microsecond time ranges. Our submicrosecond data for myosin monomers (correlation time 400 ns) also agree with previous results using other techniques, but we also detect a previously unresolvable slower decay component (correlation time 2.6 microseconds), indicating that the faster motions are restricted in amplitude. This restriction is not consistent with the commonly accepted free-swivel model of S-1 attachment in myosin. In synthetic thick filaments of myosin, both fast (700 ns) and slow (5 microseconds) components of anisotropy decay are observed. In contrast to the data for monomers, the anisotropy of filaments has a substantial residual component (26% of the initial anisotropy) that does not decay to zero even at times as long as 50 microseconds, implying significant restriction in overall rotational amplitude. This result is consistent with motion restricted to a cone half-angle of about 50 degrees. The combined results are consistent with a model in which myosin has two principal sites of segmental flexibility, one giving rise to submicrosecond motions (possibly corresponding to the junction between S-1 and S-2) and the other giving rise to microsecond motions (possibly corresponding to the junction between S-2 and light meromyosin).(ABSTRACT TRUNCATED AT 400 WORDS)