Some Characteristics of Pseudomonas 0–3 which Utilizes Polyvinyl Alcohol

Pseudomonas 0–3 strain which was isolated from soil can grow on polyvinyl alcohol (PVA) as a sole carbon source. When 0.5 per cent of PVA (500, 1500 or 2000) was employed as the carbon source in the culture medium, PVA was almost completely lost from the culture fluid after a week and the concentration of total organic carbon measured by a TOC analyzer decreased from the initial value of about 2700 ppm to 250~300 ppm after 7~10 days culture. This bacterium was found to produce and secrete an inducible enzyme which degrade PVA. The way by which this enzyme degrades PVA was examined and the results were obtained which suggested that PVA was broken down oxidatively in a way of endowise splitting. However, the mechanism of PVA degradation has not been clarified yet. The optimum pH and temperature for enzyme activity were examined and they were 7.5~8.5 and 35~45°C, respectively. Morphological and biological characteristics of this bacterium were examined and it was similar to a strain of Pseudomonas boreopolis.     

The effect of bacterial strain and temperature changes on the nitrogenase activity of Lotus pedunculatus root nodules

After 40 days of growth at 25°C, Lotus pedunculatus cav., cv. Maku plants infected with Rhizobium loti strain NZP2037 displayed similar relative growth rates but had twice the nodule mass and only one third the whole plant dry weight of plants infected with Bradyrhizobium sp. (Lotus) strain CC814s. In the NZP2037 symbiosis, the rate of CO₂ evolution (per g dry weight of nodulated root) was 1.6 times as high as that in the CC814s symbiosis while the rate of C₂H₂ reduction (per g dry weight of nodule) was only 48% of that in the CC814s symbiosis. Studies of the effect of short term temperature changes on the gas exchange characteristics (CO₂ and H₂ evolution, C₂H₂ reduction) of these symbioses revealed wide differences in the optima for C₂H₂ reduction. Nodules infected with NZP2037 displayed maximal C₂H₂ reduction rates [157 μmol (g dry weight nodule)^?1 h^?1] at 12°C, whereas nodules infected with CC814s were optimal at 30°C [208 μmol (g dry weight nodule)^?1 h^?1]. These short term studies suggested that differences in temperature optima for N₂ may have partially accounted for the poorer effectivity, at 25°C, of strain NZP2037 when compared with strain CC-814s. The relative efficiency [RE = 1 – (H₂ evolution/C₂H₂ reduction)] of N₂ fixation varied widely with temperature in the two symbioses, but there was a general trend toward higher RE with lower temperatures. The ratio of CO₂ evolution: C₂H₂ reduction (mol/mol) in nodulated roots infected with CC814s was constant (ca 10 CO₂/C₂H₂) between 5°C and 30°C, whereas in plants infected with NZP2037 it reached a minimal value of 3.3 CO₂/C₂H₂ at 10°C and was 19 CO₂/C₂H₂ at the growing temperature (25°C).     

FMDV vp1基因在豆科牧草百脉根中的转化与表达

通过根癌农杆菌介导法,将FMDV阿克苏(Akesu/O/58)株结构基因vp1转化豆科牧草百脉根子叶和子叶柄,其愈伤、芽和生根等过程经50 mg/L Kan筛选后,获得Kan抗性百脉根植株.对抗性植株进行vp1基因的PCR、RT-PCR检测和VP1蛋白的Western-blotting杂交.结果表明vp1基因转入百脉根中,检测有转录活性;目的蛋白获得了正确表达;扩繁和移栽后获得了批量转基因百脉根,为下一阶段的动物试验提供了实验材料.     

Efficient isolation, culture and regeneration of Lotus corniculatus protoplasts

This paper reports an improved protocol for isolation, culture and regeneration of Lotus corniculatus protoplasts. A range of parameters which influence the isolation of L. corniculatus protoplasts were investigated, i.e., enzyme combination, tissue type, incubation period and osmolarity level. Of three enzyme combinations tested, the highest yield of viable protoplasts was achieved with the combination of 2% Cellulase Onozuka RS, 1% Macerozyme R-10, 0.5% Driselase and 0.2% Pectolyase. The use of etiolated cotyledon tissue as a source for protoplast isolation proved vital in obtaining substantially higher protoplast yields than previously reported. Culture of the protoplasts on a nitrocellulose membrane with a Lolium perenne feeder-layer on the sequential series of PEL medium was highly successful in the formation of micro-colonies with plating efficiencies 3–10 times greater than previous studies. Shoot regeneration and intact plants were achieved from 46% of protoplast-derived cell colonies.     

Cumulative effects of fire on a tussock pampa grassland

Abstract. In order to test for cumulative effects of fire on Paspalum quadrifarium‐dominated grasslands (‘pajonal’), we analysed the impact of single and repeated fires on the community structure and post‐fire recovery of canopy after a final, simultaneous fire event. Nine plots were defined within a homogeneous pajonal stand, and treatments of low (LF), medium (MF) and high frequency (HF) of fire were defined by the application of one, two or four cold‐season burns, respectively, along a 6‐yr period. Both burned and unburned plots were exposed to grazing by cattle during the summer following the first and the third years of that period. High cattle preference for burned sites conditioned fire temperature and vegetation responses to the following burning events. Cumulative effects between successive burning events were observed for the cover of basal area of the dominant and other sprouting species, the cover and thickness of the litter layer, the seed bank size of the principal recruiter species, and the floristic composition. While light interception by the canopy was positively related to fire frequency during the early growth season, further growth of P. quadrifarium determined a greater light interception in LF than in MF and HF. These patterns of light interception were associated with a faster occupation of the inter‐tussock areas by opportunistic species in plots subjected to frequent fires (HF and MF) than in plots with low fire frequency (LF), and a more lasting regrowth of P. quadrifarium in the LF plot than in the HF ones. High fire frequencies reduced the dominance of P. quadrifarium. Percent of species classified as subordinated graminoids or forbs did not vary among treatments. However, the abundance of different forb species was differentially favoured by contrasting frequencies of fire, describing some coarse relationships between their specific responses and their dispersal strategies.     

Efficacy of Multiple Applications of Oxamyl and Phenamiphos for Controlof Pratylenchus penetrans in Birdsfoot Trefoil

Preplant soil applications of granular phenamiphos effectively reduced Pratytenchus penetrans in soil during the seeding year and 1 year after, and in the roots of birdsfoot trefoil 2 years after seeding. Forage yields were increased in the season following application of phenamiphos, but stands of plants/m² were not greater (P = 0.05) than those in the checks 1 and 2 years after treatment. Additional spring applications of phenamiphos 1 and 2 years after seeding further reduced numbers of nematodes in the soil but did not improve forage yields or plant stand over that of a single application. Broadcast preplant soil sprays of oxamyl followed by several foliar sprays at different rates and frequencies of application over a 3-year period restricted populations of P. penetrans in the soil and roots of birdsfoot trefoil but did not consistently result in increased forage yields. Stands of birdsfoot trefoil continued to decline each year even with oxamyl treatments.     

Influence of temperature and salinity on the germination of Lotus creticus (L.) from the arid land of Tunisia

Effects of salinity, temperature and their interactions on the rate and final percentage of germination were evaluated for two populations (Msarref, Oued dkouk) of the invasive glycophyte Lotus creticus Linné, grown under arid environmental conditions of the Tunisia. Seeds that were not treated with NaCl germinated well in a wide range of temperatures. For both populations, maximum germination occurred in distilled water at 25°C and lowest germination for all salinities was at 35°C. Germination was substantially delayed and significantly reduced with an increase in NaCl to levels above 300 mm . Compared to the Oued dkouk population, final germination and germination rate of the Msarref population was completely inhibited at 300 mm NaCl. The interactive effect of temperature and NaCl concentration on final germination and germination rate was significant (P < 0.01), indicating that the germination response to salinity depended on temperature. The inhibition of Oued dkouk population seed germination at high salt concentration was mostly due to osmotic effects while ionic effects were noted at Msarref population. The germination behaviour of the Oued dkouk population would therefore imply adaptive mechanisms to saline environments, while in the Msarref population such mechanisms seem to be absent. Since seed germination is more sensitive to salinity stress than the growth of established plants, the greater tolerance to salinity of Oued dkouk population would be an adaptive feature of this population to saline environment.     

Changes of Thylakoid Membrane Stacks and Chl a/b Ratio of Chloroplast from Sacred Lotus (Nelumbo nucifera) Seeds During Their Germination Under Light

Changes of chloroplast thylakoid membrane stacks and Chl a/b ratio in the plumule of sacred lotus (Nelumbo nucifera Gaertn) seeds during their germination under light were as follows: Before germination there were giant grana and very low Chi a/b ratio (0.9) in the chloroplasts. Two days after germination, the thylakoid membranes of the giant grana gradually loosened and even destacked (disintegrated), the Chl a/b ratio was 1.06. Four clays after germination, the newly formed grana thylakoid membranes were 3–5 times shorter than those of the supergrana thylakoid membranes before germination and less grana stacks were seen; the Chl a/b ratio was 1.42. Six days after germination, the stacked thylakoi membranes became more orderly arranged. In addition the grana increased in number, the stroma thylakoid membranes were scarce, the Chl a/b ratio was 2.16. Eiglt days after germination, the thylakoid membranes in each granum decreased, but the total number of grana increased only slightly. In the meantime, some large starch grains and more stroma thylakoid membranes appeared; the Chl a/b ratio was 2.77. Ten days after germination normal thylakoid membrane structure was formed both in grana and stroma lamellae. They were arranged orderly as in the chloroplasts of other higher plants; the Chl a/b ratio was 2.80. The following conclusions could be drawn from the above mentioned results: 1) There was a negative correlation between the degree of stacking of the grana thylakoid membranes and the Chl a/b ratio. This statement further proved that the membranes stacking might mainly be induced by LHCII. 2) Development of the grana thylakoid membranes within chloroplasts from sacred lotus plumule followed that of the stroma thylakoid membranes, and the tendency of changes of their Chl 2/b ratio being from the lowest to the highest and then to normal were quite different from those of other higher plants. The chloroplasts iri the latter plants contain long parallel stacks of nonappressed primary thylakoids at second step, and the changes of their ratio of Chl a/b tend to be from the highest to the lowest and then to normal. There are indications that sacred lotus plumule might employ a distinctive developing pathway. This provides an important basis for Nelumbo to possess an unique position in phylogeny of Angiospermae.