Comparison of Nitrogen Fixation Activity in Tall and Short Spartina alterniflora Salt Marsh Soils

A comparison of the N₂ fixers in the tall Spartina alterniflora and short S. alterniflora marsh soils was investigated. Zero-order kinetics and first-order kinetics of acetylene reduction were used to describe the activity of the N₂ fixers in marsh soil slurries. It was found that the V_max values were approximately 10 times greater for the N₂ fixers in the tall Spartina than in the short Spartina marsh when raffinose was used as the energy source. In addition, the (K_s + S_n) values were approximately 4 to 15 times lower for the N₂ fixers in the tall Spartina than in short Spartina marsh. First-order kinetics of nitrogen fixation for several substrates indicate that the N₂ fixers in the tall Spartina marsh were two to seven times more active than those in the short Spartina marsh. Ammonium chloride (25 μg/ml) did not inhibit nitrogen fixation in the tall Spartina marsh, but there was a 50% inhibition in nitrogen fixation in the short Spartina marsh. On the other hand, sodium nitrate inhibited nitrogen fixation almost 100% at 25 μg/ml in both soil environments. Amino nitrogen (25 to 100 μg/ml) had little or no effect on nitrogen fixation. The results indicate that the N₂ fixers in the tall Spartina marsh were physiologically more responsive to nutrient addition than those in the short Spartina marsh. This difference in the two populations may be related to the difference in daily tidal influence in the respective areas and thus provide another explanation for the enhanced S. alterniflora production in the creek bank soil system.     

Gibberellin A13 7-aldehyde: A proposed intermediate in the fungal biosynthesis of gibberellin A3

Gibberellin A₁₃ 7-aldehyde, previously proposed as an intermediate in the fungal biosynthesis of gibberellin A₃, has been prepared from gibbere     

Functional domains in introns: trans-acting and cis-acting regions of intron 4 of the cob gene

We have sequenced the mutational changes in eight mutants in the open reading frame of intron 4 of the cob gene on yeast mitochondrial DNA. Three have a cis-acting splicing defect, while the other inactivate a trans-recessive intron domain that specifies a trans-acting splicing factor. From phenotypic evidence, including analyses of the allele-specific extra proteins, we have identified a protein (P27) encoded wholly within the intron that appears to be the intron 4 splicing factor (maturase). The evidence suggests that P27 is a secondary translation product resulting from the proteolytic cleavage of a larger precursor encoded by exon and intron sequences, but an alternative model, in which P27 is a primary translation product, has not been ruled out.     

Mosaic organization of a mitochondrial gene: evidence from double mutants in the cytochrome b region of Saccharomyces cerevisiae

The region coding for apocytochrome b in the mitochondrial genome of Saccharomyces cerevisiae is believed to exhibit a mosaic organization, consisting in certain strains of five exons and four introns. This model can be tested by the use of double mutants, each containing two physically, genetically and phenotypically defined mit- lesions in cis, (that is, in the same mitochondrial chromosome). Such mutants have been constructed, and the phenotypes of several examples of each of the four possible classes--exon-exon, exon-intron (downstream), intron (upstream)-exon and intron-intron--have been examined. Our results have shown that upstream mutations are always epistatic to downstream ones for polypeptide products, and that regulation of expression of cytochrome oxidase subunit I by introns is epistatic regardless of position. These findings have provided an independent verification of the mosaic model, and also suggest that at least the majority of novel polypeptides accumulating in intron mutants are hybrid products that contain sequences of the wild-type polypeptide.     

Frontal sinus size in Eskimo populations

The frontal sinuses of 143 Eskimo skulls from two sites in the Hudson Bay region of Canada were examined radiographically. No between-site or sex differences were noted in the size of the sinuses. On average, the sinuses are small and often bilaterally absent. The Canadian samples have smaller sinuses than reported for Alaskan Eskimos or American Indian groups.     

Hypothalamic sarcoidosis and hypopituitarism

4 patients with presumed pituitary hypothalamic sarcoidosis are described. 3 had histological diagnoses compatible with sarcoidosis and in the other this diagnosis was strongly suspected from chest X-rays. 2 patients presented with diabetes insipidus. ACTH reserve was diminished in 3 out of 4 and growth hormone reserve was diminished in the 3 who were tested. All 4 patients developed secondary amenorrhea. 3 patients had hypothalamic hypothyroidism. Prolactin dynamics were intact. Tomograms of the sella turcica in all 4 and computerized tomography of the hypothalamic area in 2 patients failed to reveal any abnormality.     

Regulatory interaction between mitochondrial genes. II. Detailed characterization of novel mutants mapping within one cluster in the cob2 region.

These studies describe the properties of three mit- mutants designated EM17, EM25, and PZ1, all mapping at two closely linked sites near one of the boundaries of the region of the mitochondrial genome concerned with the specification of cytochrome b. They all exhibit complex phenotypes affecting cytochrome b, cytochrome aa3, and additional polypeptides not found in the wild type. In the case of EM 17 this complexity can be ascribed to the presence of two mutations induced in the course of the initial mutagenic treatment: one, the cob2 mutation proper, is responsible for the loss of cytochrome b which is replaced by an altered, functionally inactive polypeptide, cytochrome b. This polypeptide can be further modified, or even eliminated, by the controlled introduction of another mutation in the cob1 segment of the cob region. The reduction in cytochrome oxidase subunit I, responsible for the effects on cytochrome aa3 and enzymatic activity in EM17, is due to a second (not mit-) mutation that has been located in the par1-proximal segment of the oxi3 region. This second mutation as well as the cob mutation can be overcome, and the respective aspect of wild type function restored to EM17, by recombination with rho- strains retaining the appropriate segment(s) of the wild type genome. The phenotype of the other two mutants is due to a single mutagenic event. This conclusion is confirmed by their ability to restore wild type functions by reversion. The mutation in EM25 appears to be due to a frameshift, which has led to premature chain termination, producing a polypeptide of Mr = 15,000 related to apocytochrome b. This change is accompanied by a decrease in the amount of subunit I of cytochrome oxidase. Revertants fall into three classes: on galactose two produce a polypeptide indistinguishable from apocytochrome b, but vary in its amount, while the third fails to increase apocytochrome b above mutant levels. Production of subunit I is increased but fails to reach wild type levels. Complete restoration of wild type functions can, however, be obtained by recombination of EM25 with rho- (cob2+) strains. Mutation PZ1 results in a complete absence of any polypeptide related to apocytochrome b and of cytochrome oxidase subunit I. These cells produce a novel polypeptide with a Mr = 45,000 not found in the wild type, and unrelated to all its normal polypeptides. Reversion or recombination with rho- (cob2+) strains results in virtually complete restoration of all wild type functions and the elimination of the novel polypeptide.     

Proline Accumulation in Water-stressed Barley Leaves in Relation to Translocation and the Nitrogen Budget

Mobilization of N from leaves of barley (Hordeum vulgare L.) during water stress, and the role of proline as a mobilized species, were examined in plants at the three-leaf stage. The plants responded to water stress by withdrawing about 25% of the total reduced N from the leaf blades via phloem translocation. Most of this N loss was during the first 2 days while translocation of ¹⁴C-photosynthate out of the stressed blade still remained active. Free proline accumulation in the blade was initially slow, and became more rapid during the 2nd day of stress. Although a major free amino acid, proline accounted for only about 5% of the total N (soluble + insoluble) retained in severely stressed blades. When the translocation pathway in water-stressed leaves was interrupted just below the blade by a heat girdle, a cold jacket, or by blade excision, N loss from the blade was prevented and proline began to accumulate rapidly on 1st day of stress. Little free proline accumulated in the blades until after the ability to translocate was lost. Proline was, however, probably not a major species of N translocated during stress, because proline N accumulation in heat-girdled stressed leaves was five times slower than the rate of total N export from intact blades.     

Energy-linked Adenosine Diphosphate Accumulation by Corn Mitochondria: I. General Characteristics and Effect of Inhibitors

Corn mitochondria show respiration-linked net accumulation of [³H]ADP in the presence of phosphate and magnesium, especially if the formation of ATP is blocked with oligomycin. Inhibition of ADP-ATP exchange by carboxyatractyloside also activates ADP accumulation, and addition of carboxyatractyloside or palmitoyl-coenzyme A to oligomycin-blocked mitochondria produces additional ADP uptake. With carboxyatractyloside the accumulated ADP is phosphorylated to ATP. With oligomycin, only a little ATP is formed. Millimolar concentrations of ADP are required for maximum uptake, and the K_m (3.77 millimolar) for ADP translocation is independent of whether oligomycin or carboxyatractyloside is used. This is not true for ADP concentrations in the 0.05 to 0.25 millimolar range. Accumulated [³H]ADP rapidly exchanges with unlabeled AMP, ADP, or ATP, but not with other diphosphate nucleotides or 2 millimolar substrate anions. [³H]AMP is not accumulated, but [³H]ATP is accumulated to about one-half the extent of [³H]ADP. Tricarboxylate substrates inhibit ADP net uptake, and inhibition by citrate is competitive with K_i = 10 millimolar. The evidence suggests the presence of a pathway, carboxyatractyloside-insensitive and different from the translocase, which operates to maintain adenine nucleotides in the matrix.     

Light stimulation of proline synthesis in water-stressed barley leaves

The effect of light on [¹⁴C]glutamate conversion to free proline during water stress was studied in attached barley (Hordeum vulgare L.) leaves which had been trimmed to 10 cm in length. Plants at the three-leaf stage were stressed by flooding the rooting medium with polyethylene glycol 6000 (osmotic potential-19 bars) for up to 3 d. During this time the free proline content of 10-cm second leaves rose from about 0.02 to 2 mol/leaf while free glutamate content remained steady at about 0.6 mol/leaf. In stressed leaves, the amount of [¹⁴C]glutamate converted to proline in a 3-h period of light or darkness was taken to reflect the in-vivo rate of proline biosynthesis because the following conditions were met: (a) free-glutamate levels were not significantly different in light and darkness; (b) both tracer [¹⁴C]-glutamate and [¹⁴C]proline were rapidly absorbed; (c) rates of [¹⁴C]proline oxidation and incorporation into protein were very slow. As leaf water potential fell, more [¹⁴C]glutamate was converted to proline in both light and darkness, but at any given water potential in the range-12 to-20 bars, illuminated leaves converted twice as much [¹⁴C]glutamate to proline.