Comparative seed ecology of the endangered shrub, Pimelea spicata and a threatening weed, Bridal Creeper: Smoke, heat and other fire-related germination cues

Summary Pimelea spicata R. Br. is a nationally listed endangered Australian shrub threatened with extinction by habitat fragmentation and environmental weed invasion. Bridal Creeper (Asparagus asparagoides L. W. Wight) is the primary weed threat to the largest remaining populations of P. spicata in the Cumberland Plain. Fire, as part of an integrated pest management program, offers the potential to stimulate P. spicata populations while controlling Bridal Creeper. It is important, therefore, to understand how the components of fire affect the germination and growth of both species. Using laboratory experiments we investigated the effects of smoke, heat, ash and/or light on the germination of P. spicata and Bridal Creeper. We found a significant promotive effect of smoke and indication of an inhibitory heat shock (90°C for 10 min) effect on the germination of P. spicata seeds. The response of Bridal Creeper seeds to the same factors was complex; while the results of one experiment suggested an inhibitory effect of smoke and a promotive effect of heat, subsequent trials were contradictory, implying that Bridal Creeper, like many weeds, is able to germinate under a wide range of environmental conditions. Other experiments investigated the optimal germination temperature and innate dormancy of P. spicata in the absence of fire‐related germination cues. Of the incubation temperatures investigated, the optimal diurnally fluctuating regime for P. spicata germinations was 10°C and 20°C in the night and day, respectively. The innate dormancy of freshly produced seeds disappeared after 3 months. In contrast to Bridal Creeper, we found a persistent germinable seed bank of about 97 P. spicata seeds/m² located in the top 5 cm of the soil profile. While fire alone is unlikely to kill Bridal Creeper plants, fire may help to manage local infestations of the weed by limiting germination and providing opportunity for herbicide treatment of regrowth.     

Heteropolypeptides from hydrogen cyanide and water? Solid state15N NMR investigations

Cross-polarization magic-angle spinning¹⁵NMR spectra have been used to determine the composition of hydrogen cyanide polymers both before and after treatment with water. The unambiguous presence of secondary amide groups (as in peptide links) has been established by double-cross-polarization studies on the polymers synthesized from equimolar amounts of H¹³CN and HC¹⁵N. The NMR results are consistent with the hypothesis that the original heteropolypeptides on Earth were synthesized directly from hydrogen cyanide and water without the intervening formation of -amino acids.     

Plasmids, loss of lactose metabolism, and appearance of partial and full lactose-fermenting revertants in Streptococcus cremoris B1.

The unstable ability to metabolize lactose (lac) via the phosphoenolpyruvate-phosphotransferase system (PTS) was examined in Streptococcus cremoris B1. The presence of functional lactose-specific PTS enzymes was correlated with the presence of a distinct plasmid species. Characterization of deoxyribonucleic acid extracted from lactose-positive (Lac+) S. cremoris B1 revealed two plasmids having molecular weights of 9 X 10(6) and 36 X 10(6). An acriflavine (BC1)-induced, lactose-negative (Lac-) mutant possessed no plasmids and was devoid of all three lac-specific PTS enzymes. A Lac- mutant (DA2) isolated by growing at elevated temperatures only possessed the 9 X 10(6)-dalton plasmid and also lacked the lac PTS enzymes. A spontaneous Lac- mutant possessed both the 9 X 10(6)-and 36 X 10(6)-dalton plasmids. This mutant displayed FIII-lac and phospho-beta-D-galactosidase (P-beta-gal) activity but was deficient in EII-lac activity. The spontaneous Lac- strain reverted to both full and partial lactose-fermenting phenotypes having FIII-lac, EII-lac, and P-beta-gal activities. BC1 and DA2 Lac- mutants reverted only to the partial lactose-fermenting phenotype having P-beta-gal activity; EII-lac and FIII-lac activities were absent. The results indicate that the genetic determinants for EII-lac, FIII-lac, and P-beta-gal are located on the 36 X 10(6)-dalton plasmid in S. cremoris B1. Evidence for a second chromosomally associated P-beta-gal gene operating in the partial lactose-fermenting revertants is also presented.     

The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum

Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.     

Effects of SV40 transformation on the cytoskeleton and behavioural properties of human keratinocytes

A cloned cell line (SVK14) with apparently unlimited growth potential was isolated from simian virus 40 (SV40)-infected human foreskin keratinocytes which did not appear to pass through any obvious 'crisis' (Girardi et al., J. Cell. Comp. Physiol., 1965, 65, 69-84). Indirect immunofluorescence microscopy showed that the transformed cells have the SV40 large T antigen in their nuclei and stain positively with LE61, a monoclonal antibody that reacts with a tonofilament determinant normally only found in non-keratinizing simple epithelia. SVK14 cells can be grown in the absence of 3T3 feeders and show an impaired ability to differentiate into squames, and this impairment becomes more marked with passage. At later passages the cells acquire the ability to form colonies in agar and to produce a factor with mitogenic activity which stimulates DNA synthesis in quiescent 3T3 cells. Concomitantly, the SVK14 cells become less sensitive to the growth inhibitory effect of human alpha interferons.     

Genetic Evidence for Plasmid-Linked Lactose Metabolism in Streptococcus lactis subsp. diacetylactis

It has been previously observed that loss of plasmid pGK4101 occurred concomitantly with loss of lactose-fermenting ability in Streptococcus lactis subsp. diacetylactis 18-16. Transfer of this 41-megadalton plasmid to LM0230, a lactosenegative (Lac⁻) strain of S. lactis, required cell-to-cell contact and resulted in a conversion of LM0230 to the Lac⁺ phenotype. This confirms the linkage of lactose-fermenting ability to the 41-megadalton plasmid in S. lactis subsp. diacetylactis and, in addition, demonstrates transfer by a process resembling conjugation in the group N streptococci.     

Breakdown of aberrant protein in rabbit reticulocytes decreases with cell age.

1. The lower regions of the stem of celery (Apium graveolens L.) contain a soluble enzyme that hydrolyses phosphatidylinositol. 2. The lipoidal product of hydrolysis is diacylglycerol, and the water-soluble products are 1:2-cyclic phosphoinositol and phosphoinositol in the approximate proportions of 60% and 40% respectively: this indicates that a phosphodiesterase (phospholipase C-like) activity is cleaving the phosphatidylinositol. 3. The enzyme requires a bivalent cation, Ca2+ being the most effective activator. 4. The enzyme has a pH optimum, depending on conditions of assay, of pH 5.9-6.6 and in this pH range shows no detectable activity against phosphatidylcholine or phosphatidylethanolamine. 5. The activity is stimulated by phosphatidic acid and slightly inhibited (30% at concentrations equimolar with phosphatidylinositol) by phosphatidylcholine. 6. The phosphodiesterase was also detected (but not quantified) in the tips of the flowers in cauliflowers, in outer leaves of onion and in the elongating stem of daffodils. 7. The enzyme's properties are compared with equivalent mammalian enzymes, and its possible role in the catabolism of phosphatidylinositol in higher plants is discussed.     

Fructose-1,6-bisphosphate,a regulator of metabolism

Summary Fructose-1, 6-bisphosphate affects the rate of a large variety of enzyme reactions. In some instances its role as a physiologic effector is well documented. In many cases the effects of fructose bishosphate on particular enzymes have been demonstrated in vitro but the link to physiologic conditions has not yet been established. It is the purpose of this paper to summarize the scattered findings in fructose bisphosphate as an effector of enzyme reactions and to draw some conclusions about the role of the compound in metabolic regulation.     

Isolation and characterization of terminally differentiated chicken and rat skeletal muscle myoblasts

The ability of skeletal muscle myoblasts to differentiate in the absence of spontaneous fusion was studied in cultures derived from chicken embryo leg muscle, rat myoblast lines L6 and L8, and the mouse myoblast line G8. Following 48–96 hr of culture in a low-Ca²⁺ (25 μm), Mg²⁺-depleted medium, chicken myoblasts exhibited only 3–5% fusion whereas up to 64% of the cells fused in control cultures. Depletion of Mg²⁺ led to preferential elimination of fibroblasts, with the result that 97% of the mononucleated cells remaining at 120 hr exhibited a bipolar morphology and stained with antibodies directed against M-creatine kinase, skeletal muscle myosin, and desmin. Mononucleated myoblasts rarely showed visible cross-striations or M-line staining with anti-myomesin unless the medium was supplemented with 0.81 mM Mg²⁺, suggesting that Mg²⁺ plays a role in sarcomere assembly. Conditions of Ca²⁺ and Mg²⁺ depletion inhibited myoblast fusion in the rodent cell lines as well, but mononucleated myoblasts failed to differentiate under these conditions. Differentiated individual myoblasts from rat cell lines and from chicken cell cultures were obtained when fusion was inhibited by growth in cytochalasin B (CB). CB-treated rat myoblast cultures accumulated MM-CK to nearly twice the specific activity found in extensively fused control cultures of comparable age. Spherical cells which accumulated during CB treatment were isolated and shown to contain nearly eight times the CK specific activity present in nonspherical cells from the same cultures. Approximately 90% of these cells exhibited immunofluorescent staining with antibodies to skeletal muscle myosin, failed to incorporate [³H]thymidine or to form colonies in clonal subculture, and thus represent terminally differentiated rat myoblasts. Quantitative microfluorometric DNA measurements on individual nuclei demonstrated that the terminally differentiated myoblasts obtained in these experiments from both chicken and rat contain 2cDNA levels, suggesting arrest in the G₀ stage of the cell cycle.