Studies on Genetic Male-Sterile Soybeans : IV. Effect of Male Sterility and Source of Nitrogen Nutrition on Accumulation, Partitioning, and Transport of Nitrogen

Soybean (Glycine max [L.] Merr.) germplasm, isogenic except for loci controlling male sterility (ms₁) and nodulation (rj₁), was used to investigate the effects of reproductive tissue development and source of nitrogen nutrition on accumulation, transport, and partitioning of nitrogen in a greenhouse experiment. Nodulated plants were supplied nitrogen-free nutrient solution, and nonnodulated plants were supplied nutrient solution containing 20 millimolar KNO₃. Plants were sampled from flowering until maturity (77 to 147 days after transplanting).

Accumulation rates of nitrogen in whole plants during reproductive growth were not significantly different among the four plant types. Nitrogen accumulation in the sterile, nonnodulated plants, however, ceased 2 weeks earlier than in fertile, nonnodulated or fertile and sterile, nodulated plants. This early cessation in nitrogen accumulation resulted in sterile, nonnodulated plants accumulating significantly less whole plant nitrogen by 133 days after transplanting (DAT) than fertile, nonnodulated plants. Thus, changing the site of nitrogen assimilation from nodules (N₂-fixing plants) to roots and leaves (NO₃-fed plants) resulted in similar whole-plant nitrogen accumulation rates in fertile and sterile plants, despite the absence of seed in the latter.

Leaflet and stem plus petiole tissues of both types of sterile plants had significantly higher nitrogen concentrations after 119 DAT than both types of fertile plants. Significantly higher concentrations and exudation rates of nonureide, reduced-nitrogen in xylem sap of sterile than of fertile plants after 105 DAT were observed. These latter results indicated possible cycling of nonureide, reduced-nitrogen from the downward phloem translocation stream to the upward xylem translocation stream in roots of sterile plants. Collectively, these results suggest a lack of sinks for nitrogen utilization in the shoots of sterile plants. Hence, comparison of nitrogen accumulation rates for sterile and fertile plants does not provide a definitive test of the hypothesis that reproductive tissue development limits photosynthate availability for support of N₂ fixation and nitrate assimilation in determinate soybeans.

Nitrogen assimilation during reproductive growth met a larger proportion of the reproductive-tissue nitrogen requirement of nitrate-dependent plants (73%) than of N₂-fixing plants (63%). Hence, vegetative-tissue nitrogen mobilization to reproductive tissue was a more prominent process in N₂-fixing than in nitrate-dependent plants. N₂-fixing plants partitioned nitrogen to reproductive tissue more efficiently than nitrate-dependent plants as the reproductive tissues of the former and latter contained 65 and 55%, respectively, of the whole-plant nitrogen at the time that nitrogen accumulation in reproductive parts had ceased (133 DAT).

     

A determinant of polyomavirus virulence enhances virus growth in cells of renal origin.

We have identified a strain of polyomavirus, Py(L), which is unusual in causing acute morbidity and early death after inoculation of newborn mice. We determined that these animals died of kidney failure associated with extensive, virus-mediated destruction of renal tissue. Interestingly, the Py(L) strain infects baby mouse kidney cell cultures more efficiently than do other strains.     

Increased loss and decreased synthesis of hepatic glutathione after acute ethanol administration. Turnover studies.

The effect of acute ethanol administration on rates of synthesis and utilization of hepatic glutathione (GSH) was studied in rats after a pulse of [35S]cysteine. A 35% decrease in hepatic GSH content 5h after administration of 4 g of ethanol/kg body wt. was accompanied by a 33% increase in the rate of GSH utilization. The decrease occurred without increases in hepatic oxidized glutathione (GSSG) or in the GSH/GSSG ratio. The rate of non-enzymic condensation of GSH with acetaldehyde could account for only 6% of the rate of hepatic GSH disappearance. The increased loss of [35S]GSH induced by ethanol was not accompanied by an increased turnover; rather, a 30% inhibition of GSH synthesis balanced the increased rate of loss, leaving the turnover rate unchanged. The rate of acetaldehyde condensation with cysteine in vitro occurred at about one-third of the rate of GSH loss in ethanol-treated animals. However, ethanol induced only a minor decrease in liver cysteine content, which did not precede, but followed, the decrease in GSH. The characteristics of 2-methylthiazolidine-4-carboxylic acid, the condensation product between acetaldehyde and cysteine, were studied and methodologies were developed to determine its presence in tissues. It was not found in the liver of ethanol-treated animals. Ethanol administration led to a marked increase (47%) in plasma GSH in the post-hepatic inferior vena cava, but not in its pre-hepatic segment. Data suggest that an increased loss of GSH from the liver constitutes an important mechanism for the decrease in GSH induced by ethanol. In addition, an inhibition of GSH synthesis is observed.     

Cytoplasmic suppression of malignancy

Summary Using both normal and transformed rat liver epithelial cells to prepare cytoplasmic hybrids (cybrids) we have found evidence to support the theory that the cytoplasm from a normal cell can suppress tumorigenicity. A unique aspect of this study is that all of the cells utilized, both normal and malignantly transformed, were derived from an original cloned cell. We found that fusing cytoplasts from normal cells to malignantly transformed whole cells resulted in cybrid clones which, when injected into newborn rat pups, isogenic with those from which the cell culture was initiated, yielted tumors in 51% of the animals injected compared to 92% of the animals injected with the tumorigenic parent. Those animals that did develop tumors from the cybrid cells survived longer than those injected with cells from the tumorigenic parent. Thus, the cybrid, formed of cytoplasm from both parents, was less tumorigenic than the malignantly transformed parent cell. When reconstituted cells were prepared by fusing cytoplasts from normal cells with karyoplasts from malignantly transformed cells, a situation in which essentially all of the cytoplasm of the reconstituted cell is derived from normal cells, the tumorigenic phenotype was extinguished. This work was supported in part by United States Public Health Service grant CA12056, and grant CA09100 from the National Cancer Institute, Bethesda, MD. This work is partial fulfillment for the degree of Doctor of Philosophy for B.A.I.     

Increased atrial natriuretic peptide (6-33) binding sites in the subfornical organ of water deprived and Brattleboro rats

Binding sites for rat atrial natriuretic peptide (6-33) (ANP) were quantitated in the subfornical organ of chronically dehydrated homozygous Brattleboro rats unable to synthesize vasopressin; heterozygous Brattleboro rats, their controls, Long Evans rats and Long Evans rats after 4 days of water deprivation. Brain sections were incubated in the presence of 125I-ANP and the results analyzed by autoradiography coupled to computerized microdensitometry and comparison to 125I-standards. Brattleboro rats and water deprived Long Evans rats presented a higher number of ANP binding sites than their normally hydrated controls. Our results suggest a role of ANP binding sites in the subfornical organ in the central regulation of fluid balance and vasopressin secretion.     

Microdensitometric analysis for study of skeletal growth and aging in the living subject

Microdensitometric analysis of a radiographic image of mineralized tissue offers information on the morphologic characteristics of the specimen examined. The use of microstructure (such as individual trabecula of bone) and macrostructure (such as Harris lines of arrest) as in vivo bone markers allows for assessment of gross skeletal changes in nondestructive fashion. This technique is also applicable to the study of the interrelationship of tooth and bone. In addition, microdensitometry offers precise information on the fine structure of bone as regards the trabecular elements. This technique is applicable in determining the size and quantity of trabeculae, their persistence over long periods of time, and the factors responsible for change or lack of change in trabeculae during growth and aging.     

Effect of carbohydrates on the growth ofRhizoctonia solani Kühn

The growth OfRhizoctonia solani in different carbohydrates was studied. The rate of growth of the fungus was traced by taking the dry weights of mycelia obtained from the carbohydrate medium at regular intervals and shifts in the pH were recorded. Different carbohydrate sources had different effects on the growth of the organism. The exoenzymes from the organism were capable of cleaving carbohydrates irrespective of whether the fungus grew in them or not.     

Expression of class I histocompatibility antigens in neuroectodermal tumors is independent of the expression of a transfected neuroblastoma myc gene

We have evaluated the relationship between the neuronal myc gene (NMYC) and class I major histocompatibility complex (MHC) expression in human neuroblastoma (NB) tumor cell lines. Class I MHC surface Ag expression in NB cell lines varied from nearly undetectable to levels nearly as high as in a lymphoblastoid cell line. Class I MHC mRNA levels in NMYC-amplified NB cell lines were lower than levels observed in single copy NMYC NB cell lines. However, considerable variation in class I MHC surface Ag and mRNA expression was evident in NMYC-amplified cell lines. To determine directly whether NMYC might modulate class I MHC expression in NB, we transfected a plasmid containing a recombinant NMYC gene into two tumor cell lines derived from a NB and a related neuroepithelioma tumor. Constitutive overexpression of the recombinant NMYC gene produced no consistent change in class I MHC surface Ag or mRNA levels. To determine whether class I MHC expression might be developmentally regulated in adrenal medullary cells, the precursor cells of adrenal NB tumors, beta 2-microglobulin expression was measured in fetal and adult adrenal glands. beta 2-Microglobulin expression was not evident in the neuroblasts of a 24-wk-old fetal adrenal gland, whereas beta 2-microglobulin expression was present in the adult adrenal medulla. These data suggest that variation in class I MHC expression among NB cells may reflect the developmental stage at which neuroblasts were arrested during tumorigenesis.