The dependence of polyamine and phospholipid contents in maring bacteria on the osmotic strength of the medium

Biogenic amines in rhizobia and legume root nodules

Root-nodule bacteria (rhizobia) are of great importance for nitrogen acquisition through symbiotic nitrogen fixation in a wide variety of leguminous plants. These bacteria differ from most other soil microorganisms by taking dual forms, i.e. a free-living form in soils and a symbiotic form inside of host legumes. Therefore, they should have a versatile strategy for survival, whether inhabiting soils or root nodules formed through rhizobia-legume interactions. Rhizobia generally contain large amounts of the biogenic amine homospermidine, an analog of spermidine which is an essential cellular component in most living systems. The external pH, salinity and a rapid change in osmolarity are thought to be significant environmental factors affecting the persistence of rhizobia. The present review describes the regulation of homospermidine biosynthesis in response to environmental stress and its possible functional role in rhizobia. Legume root nodules, an alternative habitat of rhizobia, usually contain a variety of biogenic amines besides homospermidine and the occurrence of some of these amines is closely associated with rhizobial infections. In the second half of this review, novel biogenic amines found in certain legume root nodules and the mechanism of their synthesis involving cooperation between the rhizobia and host legume cells are also described.

Early carbonic anhydrase induction in the gills of the blue crab,Callinectes sapidus, during low salinity acclimation is independent of ornithine decarboxylase activity

Carbonic anhydrase (CA) induction in the gills of the euryhaline blue crab, Callinectes sapidus, was measured in response to lowered environmental salinity. Simultaneous measurements of ornithine decarboxylase (ODC) activity were made in gills and nonbranchial tissues to determine whether ODC activity and the resultant synthesis of polyamines played a role in the initiation and regulation of CA induction. CA induction in the seventh gill pair (G7) was proportional to the decrease in ambient salinity, but activity in the third gill pair (G3) remained unchanged. Induction began by 24 hr after low salinity transfer, much earlier than previously reported, and peaked after 4 days. The magnitude of salinity change affected the magnitude of CA induction only, not the time course. A general cell volume regulatory response, as measured by the appearance of total ninhydrin-positive substances (TNPS) in the hemolymph, was initiated within 4 hr of low salinity transfer and was complete by 24 hr post-transfer. General cell swelling may be the initial signal in the pathway of CA induction. ODC activity in the gills of acclimated animals was not influenced by salinity. For crabs transferred from 35 to 25 ppt, ODC activity did not change significantly over the time course of acclimation. There was an early but transient increase in ODC activity in all tissues for crabs acclimated to 28 ppt and transferred to 15 ppt. Induction of ODC activity does not appear to be a precursor for CA induction; therefore, it does not appear that polyamines are substantially involved in the up-regulation of transport enzyme activity in low salinity. ODC, and resultant polyamine synthesis, may, however, have a role in cell volume regulation.

Characterization of putrescine production in nongrowing Vibrio parahaemolyticus cells in response to external osmolality

Nongrowing Vibrio parahaemolyticus cells rapidly produced putrescine (Put) from added arginine when subjected to a low osmotic stress. This phenomenon was characterized in connection with a regulatory mechanism of the responsible enzymes, arginine decarboxylase (ADC) and agmatine ureohydrolase (AUH). NaCl, KCl, LiCl, sucrose, and glycerol were used as solutes to prepare the resuspending media with various osmolalities. Regardless of whether the solutes were electrolytes or non-electrolytes, exposure of cells to low osmolality brought about instantaneous increases in both intra- and extracellular Put contents without significant changes in the contents of other polyamines. This acceleration in Put production was accompanied by no increases in the specific activities of ADC and AUH. On the other hand, when cells were exposed to the osmolality equivalent to 2 or 5% NaCl, all solutes except for glycerol did not cause a remarkable variation in the intracellular Put content, while the amount of Put in the medium varied depending on the solute used; sucrose and glycerol still greatly prompted Put production, as judged by high Put contents in the media, even at the osmolality equivalent to 5% NaCl. The cation efflux from cells, measured as the K+ release, was observed whenever the increase in Put production occurred. Furthermore, in vitro experiments showed that NaCl and KCl inhibited ADC to a similar extent, about 70% inhibition being observed at 200 mM. However, AUH was not affected by these compounds. These results suggest that the reduction in the concentrations of Na+ and K+ predominantly present in cells may cause the increase in activity of the preexisting ADC, which leads to the enhancement of Put production.

Changes in mitochondrial structure and function in 9l rat brain tumor cells treated in vitro with alpha-difluoromethylornithine, a polyamine biosynthesis inhibitor

Mitochondrial structure and function were studied in 9L rat brain tumor cells depleted of polyamines by alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase. Cells treated with methylglyoxal bis(guanylhydrazone), a reversible inhibitor of S-adenosylmethionine decarboxylase, were used for comparison because this polyamine biosynthesis inhibitor is known to cause structural and functional disruption of mitochondria. A significant increase in mitochondrial size, measured quantitatively, was found in alpha-difluoromethylornithine-treated cells (10 mM for 72 hr) compared with untreated cells (P < 0.001). This increase in mitochondrial size was reversed when putrescine was added to the cultures for 24 hr after alpha-difluoromethylornithine treatment. Putrescine alone had no effect on the size of mitochondria. Treatment of cells with methylglyoxal bis(guanylhydrazone) (80 muM for 48 hr) caused only a slight increase in mitochondrial size compared with mitochondria in untreated cells (P < 0.05) and failed to produce the dramatic ultrastructural changes reported in other cell lines. Ultrastructural examination revealed an increase in cytoplasmic and membrane-associated ribosomes in alpha-difluoromethylornithine-treated cells, an increase in cytoplasmic ribosomes in methylglyoxal bis(guanylhydrazone)-treated cells, and an increase in membrane-bound ribosomes in putrescine-treated cells. In cells treated first with alpha-difluoromethylornithine and then with putrescine, the distribution of ribosomes was normal. The distributions of ribosomes were not quantitatively assessed. Pyruvate utilization, a measure of mitochondrial function, was decreased in cells treated with 10 mM alpha-difluoromethylornithine for 72 hr, compared with untreated cells. Restoration of intracellular polyamine levels by the addition of putrescine 24 hr before analysis reversed this phenomenon. Putrescine treatment alone did not affect pyruvate utilization. Pyruvate utilization in methylglyoxal bis(guanylhydrazone)-treated cells was depressed to a greater extent than that in alpha-difluoromethylornithine-treated cells.