Nitrogen mineralization rates in salinevs. salt-amended soils

Studies were conducted to compare N mineralization rates in salt-amended nonsaline soils to naturally-occurring saline soils. NaCl, CaCl₂, and Na₂SO₄ were added to nonsaline soils at rates that produced electrical conductivities of the saturation extracts (EC_e) of 5, 10, 15, and 20 dS m⁻¹. Saline soils with similar properties were leached to the same EC_c levels. N mineralization in the Chino soil was inhibited by salt addition, particularly with sodium and calcium chlorides. In the Domino soil there was some inhibition of N mineralization with the chloride salts, but enhancement with Na₂SO₄ was observed. Nitrification in both soils was more sensitive to salt addition than ammonification. N mineralization occurred more slowly in both leached saline soils compared to the salt-amended soils. Leached saline soils often accumulated greater amounts of inorganic N compared to their native saline counterparts, particularly with the 5 dS m⁻¹ Chino soil (native, 44 dS m⁻¹) and with the 5, 10, 15 and 20 dS m⁻¹ Domino soils (native, 32 dS m⁻¹). Kinetic parameters were estimated by the linear least squares (LLS) and the nonlinear least squares (NLLS) methods. Generally, the LLS transformation estimated greater values of potentially mineralizable N (N_o) and lower rate constants (k). With the NLLS equation, N_o values for the leached saline soils were usually lower, and k values usually higher than in the salt-amended soils. The nonsaline controls generally had the highest N_o and lowest k estimates. Average LLS rate constants for the salt-amended and leached saline soils were 0.055 and 0.083 for the Chino, and 0.104 and 0.137 week⁻¹, respectively, for the Domino soils. With the NLLS equation, average k values for the salt-amended and leached saline soils were 0.087 and 0.089 for the Chino, and 0.181 and 0.387 week⁻¹, respectively, for the Domino soils. These results suggest that N mineralization rates obtained in salt-amended nonsaline soils may not be representative of those in naturally-occurring saline soils.     

Anaerobic metabolism enzymes as markers of flooding stress in maize seeds

Maize (Zea mays L.) seeds differ in their relative tolerance to the anaerobic environment caused by flooding. Seed tolerance to flooding stress depends on cellular and metabolic processes since gross anatomical responses have not developed at the pre-emergence stage. The study reported here characterizes the activities of four anaerobic respiratory enzymes: pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH), lactate dehydrogenase (LDH), and malic enzyme (ME) in the flood-tolerant A632 and floodsusceptible Mo 17 inbred maize seeds during flooding at 10 and 25°C. Each inbred consisted of two seed lots possessing 95% and 75% germination levels. Flooding increased the activities of all four enzymes. However, no consistent correlation between anaerobic enzyme activity and flood tolerance was observed across genotype, seed quality and flooding temperature. The results indicate that it may not be feasible to use whole-seed anaerobic enzyme activities to predict maize seed performance under flooding stress. Contribution from the Soil Drainage Research Unit, USDA-ARS, Columbus, OH, in cooperation with the Ohio Agricultural Research and Development Center, The Ohio State University. OARDC Journal Article No. 66–86.     

Further evidence from sectioned material in support of the existence of a linear terminal complex in cellulose synthesis

Summary Transmembrane linear terminal complexes considered to be involved in the synthesis of cellulose microfibrils have been described in the plasma membrane ofBoergesenia forbesii. Evidence for the existence of these structures has been obtained almost exlusively using the freeze etching technique. In the present study an attempt has been made to complete these studies using conventional fixation, staining, and sectioning procedures. In developing cells ofBoergesenia forbesii, strongly stained structures traversing the plasma membrane and averaging 598.9 nm ± 171.3 nm in length, 28.7 nm ± 4.2 nm in width, and 35.2 nm ± 6.6 nm in depth have been demonstrated. These structures are considered to be linear terminal complexes. At their distal (cell wall) surface, they appear to be closely associated with cellulose microfibrils. At the proximal (cytoplasmic) surface, they are associated with microtubules and polysomes. A model of the possible interrelation of the terminal complexes and microtubules leading to the generation of cell wall microfibrils is proposed.     

Identification and characterization of a Ca2+-calmodulin-sensitive cyclic nucleotide phosphodiesterase in a human lymphoblastoid cell line.

This study examines the pattern and regulatory properties of cyclic nucleotide phosphodiesterases in a human lymphoblastoid B-cell line (RPMI 8392) established from a patient with acute lymphocytic leukaemia. In this cell line, phosphodiesterase activity measured at 0.25 microM-cyclic AMP is approx. 7-fold greater than that in isolated human peripheral-blood lymphocytes, and 16% of the phosphodiesterase activity in RPMI 8392 cells is associated with particulate fractions. Phosphodiesterase activity in crude fractions of this cell line is reproducibly stimulated by about 60-80% by Ca2+-calmodulin. In the presence of 20 nM-calmodulin, half-maximal stimulation occurs at 0.7 microM-Ca2+. The cytosolic phosphodiesterase activity of RPMI 8392 cells is separated into two forms by DEAE-Sephacel chromatography. The first form is eluted at approx. 0.2 M-sodium acetate, catalyses the hydrolysis of both cyclic AMP and cyclic GMP, and is stimulated 3-fold by Ca2+-calmodulin. This form exhibits non-linear kinetics for cyclic AMP in the absence of calmodulin, with extrapolated Km values of 0.8 and 4 microM, and non-linear kinetics in the presence of calmodulin, with extrapolated Km values of 0.5 and 1 microM. The Vmax. values are increased approx. 3-fold by calmodulin. The second form is eluted at approx. 0.6 M-sodium acetate, is specific for cyclic AMP, and insensitive to stimulation by Ca2+-calmodulin. The Ca2+-calmodulin-sensitive phosphodiesterase from the DEAE-Sephacel column can be adsorbed to a calmodulin-Sepharose affinity column and eluted with EGTA. This enzymic activity can also be immunoprecipitated by a monoclonal antibody directed against a calmodulin-bovine heart phosphodiesterase complex. This study documents the existence of Ca2+-calmodulin-sensitive phosphodiesterase in a cultured lymphoblastoid cell line derived from a leukaemic patient.     

Metabolism of inositol 1,4,5-trisphosphate in guinea-pig hepatocytes.

Metabolism of inositol 1,4,5-trisphosphate was investigated in permeabilized guinea-pig hepatocytes. The conversion of [3H]inositol 1,4,5-trisphosphate to a more polar 3H-labelled compound occurred rapidly and was detected as early as 5 s. This material co-eluted from h.p.l.c. with inositol 1,3,4,5 tetrakis[32P]phosphate and is presumably an inositol tetrakisphosphate. A significant increase in the 3H-labelled material co-eluting from h.p.l.c. with inositol 1,3,4-trisphosphate occurred only after a definite lag period. Incubation of permeabilized hepatocytes with inositol 1,3,4,5-tetrakis[32P]phosphate resulted in the formation of 32P-labelled material that co-eluted with inositol 1,3,4-trisphosphate; no inositol 1,4,5-tris[32P]phosphate was produced, suggesting the action of a 5-phosphomonoesterase. The half-time of hydrolysis of inositol 1,3,4,5-tetrakis[32P]phosphate of approx. 1 min was increased to 3 min by 2,3-bisphosphoglyceric acid. Similarly, the rate of production of material tentatively designed as inositol 1,3,4-tris[32P]phosphate from the tetrakisphosphate was reduced by 10 mM-2,3-bisphosphoglyceric acid. In the absence of ATP there was no conversion of [3H]inositol 1,4,5-trisphosphate to [3H]inositol tetrakisphosphate or to [3H]inositol 1,3,4-trisphosphate, which suggests that the 1,3,4 isomer does not result from isomerization of inositol 1,4,5-trisphosphate. The results of this study suggest that the origin of the 1,3,4 isomer of inositol trisphosphate in isolated hepatocytes is inositol 1,3,4,5-tetrakisphosphate and that inositol 1,4,5-trisphosphate is rapidly converted to this tetrakisphosphate. The ability of 2,3-bisphosphoglyceric acid, an inhibitor of 5-phosphomonoesterase of red blood cell membrane, to inhibit the breakdown of the tetrakisphosphate suggests that the enzyme which removes the 5-phosphate from inositol 1,4,5-trisphosphate may also act to convert the tetrakisphosphate to inositol 1,3,4-trisphosphate. It is not known if the role of inositol 1,4,5-trisphosphate kinase is to inactivate inositol 1,4,5-trisphosphate or whether the tetrakisphosphate product may have a messenger function in the cell.     

Immediate induction of a 45 K secreted glycoprotein by serum and growth factors in quiescent mouse 3T3 cells : Two-dimensional gel analysis

Stimulation of quiescent 3T3 cells by serum dramatically induces the synthesis of a group of secreted polypeptides with a molecular weight (MW) of 45 K (p45 A, B, C, D). The synthesis of these polypeptides increases 10-fold during the first 2 h. Cycloheximide superinduces the 45 K polypeptides and actinomycin D (actD) blocks completely their induction by serum. Peptide mapping analysis and pulse-chase experiments revealed that p45 A is a precursor of polypeptides p45 B, C, D. Tunicamycin treatment inhibits the synthesis of all four polypeptides but a new related protein appears, p-p45, the unglycosylated precursor. In the presence of tunicamycin, p-p45 is also found in the medium, demonstrating that glycosylation is not essential for the secretion. In vitro translation experiments show that the levels of p45 mRNA present in stimulated cells are severalfold higher than that of non-stimulated cells. Purified growth factors, such as platelet-derived growth factor (PDGF), fibroblast growth factor (FGF) and epidermal growth factor (EGF) induce the synthesis of p45 in quiescent cells.     

Revised genetic map of the distal end of the F transfer operon: implications for DNA helicase I, nicking at oriT, and conjugal DNA transport.

The DNA transfer stage of conjugation requires the products of the F sex factor genes traMYDIZ and the cis-acting site oriT. Previous interpretation of genetic and protein analyses suggested that traD, traI, and traZ mapped as contiguous genes at the distal end of the transfer operon and saturated this portion of the F transfer region (which ends with an IS3 element). Using antibodies prepared against the purified TraD and TraI proteins, we analyzed the products encoded by a collection of chimeric plasmids constructed with various segments of traDIZ DNA. We found the traI gene to be located 1 kilobase to the right of the position suggested on previous maps. This creates an unsaturated space between traD and traI where unidentified tra genes may be located and leaves insufficient space between traI and IS3 for coding the 94-kilodalton protein previously thought to be the product of traZ. We found that the 94-kilodalton protein arose from a translational restart and corresponds to the carboxy terminus of traI; we named it TraI*. The precise physical location of the traZ gene and the identity of its product are unknown. The oriT nicking activity known as TraZ may stem from unassigned regions between traD and traI and between traI and IS3, but a more interesting possibility is that it is actually a function of traI. On our revised map, the position of a previously detected RNA polymerase-binding site corresponds to a site at the amino terminus of traI rather than a location 1 kilobase into the coding region of the gene. Furthermore, the physical and genetic comparison of the F traD and traI genes with those of the closely related F-like conjugative plasmids R1 and R100 is greatly simplified. The translational organization we found for traI, together with its identity as the structural gene for DNA helicase I, suggests a possible functional link to several other genes from which translational restart polypeptides are expressed. These include the primases of the conjugative plasmids ColI and R16, the primase-helicase of bacteriophage T7, and the cisA product (nickase) of phage phi X174.