Measured comparison of the crossover periods for mid- and long-wave IR (MWIR and LWIR) polarimetric and conventional thermal imagery.

We report the results of a multi-day diurnal study in which polarimetric and conventional thermal imagery is recorded in the mid- and long-wave IR to identify and compare the respective time periods in which minimum target contrast is achieved. The data shows that the chief factors affecting polarimetric contrast in both wavebands are the amount of thermal emission from the objects in the scene and the abundance of MWIR and LWIR sources in the optical background. In particular, it has been observed that the MWIR polarimetric contrast was positively correlated to the presence of MWIR sources in the optical background, while the LWIR polarimetric contrast was negatively correlated to the presence of LWIR sources in the optical background.

Identification and characterization of a novel Bradyrhizobium japonicum gene involved in host-specific nitrogen fixation.

To understand the genetic mechanism of host specificity in the interaction between rhizobia and their hosts, it is important to identify genes that influence both early and late steps in symbiotic development. This paper focuses on the little-understood genetics of host-specific nitrogen fixation. A deletion mutant of Bradyrhizobium japonicum, strain NAD163, was found to induce effective, nitrogen-fixing nodules on soybean and siratro plants but produced ineffective nodules on cowpea plants. Additional transposon and deletion mutants defined a small region that conferred this phenotype, and this region was sequenced to identify two putative open reading frames (ORFs). Data indicate that only one of these ORFs is detectable in bacteroids. This ORF was termed hsfA, with a predicted protein product of 11 kDa. The transcriptional start site of hsfA was determined and found to coincide with a predicted RpoN-dependent promoter. Microscopic studies of nodules induced by the wild type and hsfA mutants on cowpea and soybean plants indicate that the cowpea mutant nodules are slow to develop. The data indicate that hsfA appears to play a crucial role in bacteroid development on cowpea but does not appear to be essential for nitrogen fixation on the other hosts tested.

A lipopolysaccharide mutant of Bradyrhizobium japonicum that uncouples plant from bacterial differentiation.

The Tn5-containing fragment from a non-nodulating mutant of Bradyrhizobium japonicum, strain ML142, was introduced into B. japonicum strain 61A101c by marker exchange to construct strain JS314. Strain JS314 failed to nodulate several soybean varieties tested. However, on a few varieties nodulelike structures were induced to a frequency of 54% of the plants inoculated. The ultrastructure of these nodules was studied in detail by light and electron microscopy. The nodules were devoid of internal bacteria, possessed central vascular tissue (unlike the lateral vascular tissue of a normal nodule), and exhibited localized cell death of epidermal cells. Study of the cell surface polysaccharides of strain JS314 revealed that the exopolysaccharide of this strain was identical to that of the wild type. However, the lipopolysaccharide (LPS) of strain JS314 showed gross differences from that isolated from the wild-type strain. Specifically, the LPS of strain JS314 appeared to lack the high molecular weight LPS I form, strongly suggesting that the LPS lacks the O-chain. Glycosyl-composition analysis showed that the LPS of mutant JS314 lacked 2,3-di-O-methylrhamnose, 3-O-methylrhamnose, fucose, and quinovosamine. These results indicate that LPS I in B. japonicum is essential for bacterial infection of soybean, but is not required to initiate plant cortical cell division, an early plant response to infection.

Immunogold localization of the NodC and NodA proteins of Rhizobium meliloti.

Monospecific, polyclonal antibodies to the nodC and nodA gene products of Rhizobium meliloti were used in combination with immunogold labeling and transmission electron microscopy to localize the NodC and NodA proteins in cultures of R. meliloti. Both NodC and NodA were detected in the cytoplasm and cell envelope in thin sections of free-living rhizobia treated with luteolin, a known inducer of nod gene expression; however, only NodC was detected on cell surfaces when immunolabeling was performed with intact induced cells. In view of biochemical data characterizing NodC as an outer membrane protein with a large extracellular domain, the pattern of immunolabeling on thin sections suggests that NodC is produced on free cytoplasmic ribosomes prior to assembly in the membrane. The pattern of NodA labeling on thin sections is consistent with biochemical data detecting NodA in both soluble and membrane fractions of NodA-overexpressing strains of R. meliloti.

Bacterium release into host cells of nitrogen-fixing soybean nodules: the symbiosome membrane comes from three sources.

The release process of bacteria into the cytoplasm of soybean nodule cells has been studied, and three functional zones of the infection thread are delineated. Zone 1 is found over the greatest length of very long infection threads. Zone 2 is a short region where membrane mobilization by exocytosis of endoplasmic reticulum (ER) into the infection-thread membrane takes place; the result is that much new membrane and wall degradation enzymes can be provided. In addition, de novo membrane formation takes place inside the infection thread in apposition to the bacterial outer membrane. Zone 3 is the endocytic region where both bacteria and infection-thread wall degradation vesicles are released into the host cytoplasm and constitute a second product of endocytosis at the infection thread tip. Evidence is presented indicating that the symbiosome membrane, even at its time of origin, is composed of membrane from three sources: the host infection-thread membrane, ER, and de novo synthesis; the membrane formation that is so large for these purposes is probably carried out both from the ER directly and also through the Golgi-apparatus synthesis. Evidence is also given that the bacteria have lost their exopolysaccharide coatings before release into symbiosomes.

Cytoplasmic membrane systems involved in bacterium release into soybean nodule cells as studied with two Bradyrhizobium japonicum mutant strains.

Two Bradyrhizobium japonicum, Tn5-induced, mutant strains, ML126 and ML150, were studied. Both induce host cell division to form normal-sized nodules that do not fix nitrogen and whose cells have very few bacteroids (Bar-). Early-infection (15 days post infection) cells have much endoplasmic reticulum (ER), numerous Golgi bodies, and large vacuoles that are probably secondary lysosomes. Later the cytoplasm of the host cells of both are dominated by hundreds of vesicles containing only finely fibrous material and that appear to originate by the degradation of the cell walls of the infection threads; they have been named "infection-thread wall degradation vesicles" (IWDV). Phosphotungstic acid-chromic acid (PACA) staining of thin sections shows that IWDV membranes and the plasma membranes of both the cells and infection threads usually stain quite intensely, while the membranes of other cell organelles do not. The membranes of the few symbiosomes present in the mutants also stain with PACA. This evidence suggests that largely the host-cell plasma membrane gives rise to both the vesicle and symbiosome membranes in these mutants. In cells induced by both mutants, ER appears to be deficient, a finding suggesting that an ER-synthesis signal is involved in the normal release process, that ER synthesis is prerequisite to a normal volume of release, and that insufficient ER can impair symbiosome formation. In the mutant-induced infections, normal lysosomes develop and engulf both symbiosomes and cytoplasmic vesicles, but the retardation of this activity is the probable cause of the cytoplasm becoming overloaded with vesicles.

Localizations of aluminum in soybean bacteroids and seeds.

Aluminum, long known to be detrimental to soybean productivity, was localized in the polyphosphate granules (PPG) of bacteroids in root nodules of soybean plants. By using energy-dispersive X-ray analysis, bacteroids in early infections were shown to have typical PPG constituents. However, in PPG in older infections and after the bacteroids were digested intracellularly, aluminum was also detected. These results indicate that aluminum accumulates in PPG after a period when organisms have been resident in host cells and that high levels of aluminum were present in the bacteroids at the time of their demise. At least some of the aluminum in these laboratory-grown plants could have come from the seeds used.

Gradionation: hypothesis for positioning and patterning.

The interaction of contiguous proteins is explored in microtubules, rosettes, and membranes based on the well established molecular phenomena of cooperativity and allosterism. It is proposed that conformational gradients in protein arrays cause the formation of gradions by nearest-neighbor interactions. Gradions are repeating functional molecular sequences that contain several conformational forms of one or more proteins, with the result that different reactive sites can exist in the same molecular architecture at any one time. Gradionators are small controlling molecules that may be microscopically visible as layers of linkages, but could alse be smaller. Some of the presently available supporting evidence and its functional implications are discussed, including the possibility that the raison d'etre for membrane-particle arrays is to enhance the regulation and amplification capabilities of cell systems.

Morphology of rigor--shortened bovine muscle and the effect of trypsin on pre- and postrigor myofibrils.

Bovine semitendinosus muscles were sampled immediately after death, after 24 hr postmortem with storage at 2 degrees , 16 degrees , or 37 degrees C, and after 312 hr postmortem with storage at 2 degrees and 16 degrees C. A biopsy technique was used to prevent shortening during glutaraldehyde fixation. Postfixation in osmium tetroxide was followed by embedding in an Epon-Araldite mixture. Bovine muscle was supercontracted after 24 hr storage at 27deg; but was only slightly contracted after storage at 16 degrees for 24 hr. Muscle held at 37 degrees for 24 hr was slightly less supercontracted than the 2 degrees muscle. Striking similarities existed between muscles stored at 16 degrees and at 2 degrees C for 312 hr. Both were slightly shortened with narrowed I bands and an area of increased density, probably due to overlap of thin filaments in the middle of the A band. Postmortem shortening was accompanied by banding-pattern changes similar to those predicted for contracting muscle by Huxley and Hanson's sliding filament model. Treatment of myofibrils with 0.05% trypsin resulted in a rapid loss of Z lines and, in supercontracted myofibrils, caused a return of the banding pattern of resting muscle.

Electron microscopy of mitosis in amebae. 3. Cold and urea treatments: a basis for tests of direct effects of mitotic inhibitors on microtubule formation.

The mitotic apparatus (MA) of the giant ameba, Chaos carolinensis, has characteristic sequences of microtubule arrays and deployment of nuclear envelope fragments. If mitotic organisms are subjected to 2 degrees C for 5 min, the MA microtubules are completely degraded, and the envelope fragments are released from the chromosomes which remain condensed but lose their metaphase-plate orientation. On warming, microtubules reform but show partial loss of their parallel alignment; displacement of the envelope fragments persists or is increased by microtubule reformation. This study demonstrates that cooling causes destruction of microtubules and intermicrotubular cross-bonds and further shows that such controlled dissolution and reformation can provide an in vivo test sequence for studies on the effects of inhibitor-compounds on microtubule subunit aggregation. Urea, at the comparatively low concentration of 0.8 M, inhibited reformation following cooling and rewarming but was ineffective in altering microtubules that had formed before treatment.

Structural variations during mitosis in the chick embryo.

Selected tissues from chick embryos were fixed in 2% glutaraldehyde and 1% OsO(4), both buffered at pH 7.6 with Veronal-acetate, and were embedded in Maraglas or Araldite. Two types of cell division have been noted. Generally, epithelial cells divide predominantly by a shortening of the chromosome-to-pole distance rather than by spindle elongation; mesenchymal cells undergo extensive spindle elongation. The presence of numerous continuous microtubules in cells that undergo extensive spindle elongation functionally implicates these tubules in the elongation process. In most embryonic epithelia, the cleavage furrow converges to a fixed site forming a mid-body near the anchoring desmosomes at the free surface; symmetrical furrow formation is typical of mesenchymal cells which lack desmosomes. The hypothesis of cleavage furrow formation and the fate of the mid-body that is formed during cytokinesis are discussed.