Base temperature and heat units for leaf flushing emission and growth ofHevea brasiliensis Muell. Arg.

In this study we determined the base temperature and Heat units for leaf flushing initiation and growth of RRIM-600 and GT1Hevea clones. The minimum base temperature was found to be approximately 16° C for leaf flushing emission and 19° C for shoot growth in terms of height. Approximately 420 degree days at 16° C as base temperature is required for successive leaf flushing initiation. Linear equations with correlation coefficients above 0.95 allow an estimation of the height increase from the accumulated degree days, corrected or otherwise for photoperiod. The highest correlation coefficients demonstrated a positive effect of the photoperiod among the factors influencing the shoot growth.     

Effect of chilling on photosynthesis and antioxidant enzymes in Hevea brasiliensis Muell. Arg.

The aim of the present study was to assess the tolerance of Hevea brasiliensis to chilling temperatures since rubber production has been extended to sub-optimal environments. PB260 clone was used to analyze the responses of leaves chilled at 10°C during 96 h, as well as their recovery at 28°C. Some key parameters were used to evaluate photosynthetic apparatus functioning, membrane damage (electrolyte leakage) and oxidative stress. A short-term response versus a long-term one have been recorded, the time point of 24 h, when stomata closure was effective, being the border between the two responses. P _n decreased dramatically at 1 h, and Fv/Fm was slightly affected. NPQ reached its maximal level between 4 and 7 h. Lipid peroxidation and membrane lysis were observed between 48 and 96 h. Activities of antioxidant enzymes increased, along with the induction of antioxidant gene expression. Finally, the plants were capable to recover (net photosynthetic rate, photochemical efficiency, antioxidant enzymes activities) when placed back to 28°C showing that PB260 can withstand long-term chilling.     

Genetic transformation and regeneration of rubber tree (Hevea brasiliensis Muell. Arg) transgenic plants with a constitutive version of an anti-oxidative stress superoxide dismutase gene

Agrobacterium tumefaciens-mediated genetic transformation and the regeneration of transgenic plants was achieved in Hevea brasiliensis. Immature anther-derived calli were used to develop transgenic plants. These calli were co-cultured with A. tumefaciens harboring a plasmid vector containing the H. brasiliensis superoxide dismutase gene (HbSOD) under the control of the CaMV 35S promoter. The -glucuronidase gene (uidA) was used for screening and the neomycin phosphotransferase gene (nptII) was used for selection of the transformed calli. Factors such as co-cultivation time, co-cultivation media and kanamycin concentration were assessed to establish optimal conditions for the selection of transformed callus lines. Transformed calli surviving on medium containing 300 mg l^-1 kanamycin showed a strong GUS-positive reaction. Somatic embryos were then regenerated from these transgenic calli on MS2 medium containing 2.0 mg l^-1 spermine and 0.1 mg l^-1 abscisic acid. Mature embryos were germinated and developed into plantlets on MS4 medium supplemented with 0.2 mg l^-1 gibberellic acid, 0.2 mg l^-1 kinetin (KIN) and 0.1 mg l^-1 indole-3-acetic acid. A transformation frequency of 4% was achieved. The morphology of the transgenic plants was similar to that of untransformed plants. Histochemical GUS assay revealed the expression of the uidA gene in embryos as well as leaves of transgenic plants. The presence of the uidA, nptII and HbSOD genes in the Hevea genome was confirmed by polymerase chain reaction amplification and genomic Southern blot hybridization analyses.Communicated by L. Peña     

The distribution of plasmodesmata in the phloem ofHevea brasiliensis in relation to laticifer loading

Summary Cell to cell connections, including plasmodesmata and perforations, were examined in the non-conducting secondary phloem ofHevea brasiliensis. Samples were taken from trunks of numerous trees, from several clones, and prepared for thin sectioning and transmission or scanning electron microscopy and as optical sections for fluorescence microscopy. Numerous plasmodesmata were found clustered in primary pit-fields between the ray and axial parenchyma cells. Between the laticifers and adjacent parenchyma sheath cells, structures corresponding to functional plasmodesmata were not observed. But some unusual structural features were occasionally seen in these walls. These observations are discussed in relation to the possible function of the cell types, and to the loss of latex on the tapping ofHevea. It is suggested that the loading of the laticifer might first require a symplastic pathway for the transport of metabolites, at the end of which the assimilates must enter the apoplast. A transmembrane active transport system then transfers the metabolites in the laticifer. The presumable role of parenchyma cells in the loading of laticifers is emphasized.     

Field nursery inoculation of Hevea brasiliensis Muell. Arg. seedling rootstock with vesicular-arbuscular mycorrhizal (VAM) fungi

The growth response of Hevea brasiliensis to vesicular-arbuscular mycorrhizal (VAM) fungi inoculation was assessed in two field nursery sites containing indigenous mycorrhizal fungi (IMF). Seedling rootstocks were inoculated with mixed VAM-fungal species in a factorial combination with phosphorus (P) fertilizer application, and planted in randomised blocks on sandy (site 1) and clayey (site 2) soils. Plants were harvested after 26 weeks for measurements of shoot dry weight (DW), stem diameter, height, mycorrhizal root colonization and leaf nutrient contents. At site 1, VAM increased shoot DW, stem diameter and plant height only in treatments without P applied. Increases in shoot DW due to VAM were 70% greater than the uninoculated controls although this was reduced to 5% when P was applied. At site 2, VAM inoculation also increased shoot DW and stem diameter but the magnitude of the increases was smaller. Shoot DW response due to VAM was only 29%. At this second site, applying phosphate to uninoculated plants did not increase shoot yields further. Leaf concentrations of all nutrients were unaffected by VAM at both sites, except for copper (Cu) which was increased by VAM in treatments where P was not applied. However, leaf contents of P, potassium (K), magnesium (Mg) and Cu were increased by VAM at site 1, and of leaf nitrogen (N) and K at site 2. These experiments demonstrate that VAM-fungi could be introduced into field nursery sites to improve growth and P uptake by H. brasiliensis. The relevance of VAM-fungi to H. brasiliensis seedling rootstock development and the influence of IMF in determining field responses is discussed.     

橡胶树DELLA蛋白编码基因HbGAI的克隆与表达分析

该研究采用RT-PCR与RACE技术,从橡胶树‘热研7-33-97’胶乳中克隆了1个DELLA蛋白编码基因HbGAI(GenBank登录号为KT696439)。HbGAI全长cDNA序列2 050bp,包含1个长1 842bp的完整开放阅读框。序列分析显示,HbGAI基因编码613个氨基酸,其推导的蛋白含有DELLA和GRAS结构域,分子量为66.476kD,理论等电点为5.19,无跨膜结构域,属于亲水性蛋白。进化树分析表明,HbGAI蛋白与其他植物中DELLA蛋白具有较高的相似性,与麻疯树JcGAI和蓖麻RcGAI亲缘关系较近。荧光定量PCR结果显示,割胶和茉莉酸甲酯处理下调胶乳中HbGAI基因的表达,乙烯利处理4h内显著上调胶乳中HbGAI基因的表达,表明HbGAI基因可能在橡胶树割胶、茉莉酸、乙烯响应中发挥作用。     

Adaptation of red clover rhizobia to low temperatures

Summary Red clover Rhizobium strains, isolated from different locations between latitudes 60° and 63°30′ N in Finland, were tested for their adaptation to low temperatures. 31 strains were tested for growth at 5°C, 10°C, 15°C and 18°C in pure culture. No strain grew at 5°C. At the other temperatures there were differences between the strains, but the same strains grew fast at all temperatures. Ten strains were investigated for nodulation and acetylene reduction in phytotrons in two different climates, one simulating the growing season in southern and the other in northern Finland. There were differences between the strains in their ability to nodulate their host plant, and northern strains showed higher nitrogenase activity than southern strains in the cold climate.     

The effect of ethrel and temperature on the germination of Manihot glaziovii Muell. Arg. seeds

Dormancy in seeds of Manihot glaziovii is overcome at 25°C by application of ethrel at effective ethylene concentrations equal to and greater than 10 ll^–1. Imbibition of seeds in ethrel broadens the temperature optimum for germination but does not prevent the development of secondary dormancy at temperatures of 35°C and greater and 15°C and lower. Secondary dormancy must be due to factors other than reduced ethylene production.     

Responses of Porphyra linearis (Rhodophyta) to environmental factors under controlled culture conditions

The effect of environmental parameters on the growthof Porphyra linearis gametophytes was examinedunder controlled conditions, and related to themultilinear regression growth model recently developedfor this seaweed under coastal conditions in theeastern Mediterranean. Growth chambers, a gradienttable, special culture devices and analytical methodswere combined for this culture study.The major factors significantly controlling thegrowth rate of the P. linearis gametophytein glass dishes were: photoperiod, temperature, agein culture, photosynthetic photon flux (PPF), salinityand water dynamics. Maximal growth occurred underdaylength of 12 h, medium temperature (15–20 ^°C), low PPF (70–140 mol photon m^-2s^-1), ambient salinity (30–40 ppt), 1–3 h ofdaily air exposure, and water velocity of 4 cm s^-1.Photosynthesis and respiration rates weredominantly affected by daylength and temperature,while the concentration of pigments was dominantlyaffected by PPF and temperature.These conditions correspond well to the optimalnatural growth environment of this local species andare in agreement with the optimum estimated throughthe recently developed outdoor mathematical growthmodel.     

Adaptation of intestinal cell membrane enzymes to low temperatures in the Antarctic teleost Pagothenia bernacchii

The enzymatic activity (expressed as milliunits per milligram total proteins) of three intestinal brush-border membrane enzymes, leucine aminopeptidase, alkaline phosphatase and maltase, measured over a range of temperatures between 1.5 and 37 °C, has been found to be much higher in the Antarctic fish Pagothenia bernacchii than in the temperate fish Anguilla anguilla. To explain this experimental observation the apparent Michaelis-Menten constant, the maximal velocity, the activation energy values and the thermal stability of these three enzymes were measured. The apparent Michaelis-Menten constant values of leucine amino peptidase and alkaline phosphatase were different in the intestine mucosal homogenate of the two fish at each measured temperature (from a minimum of 2.5 to a maximum of 37 °C). However, the values found at 2.5 °C for the Antarctic species and 15 °C for the eel where comparable. Furthermore, its value was unchanged in eel intestine apical membranes, both in the presence and without enzyme lipid microenvironment. While the maximal enzymatic activities of the leucine aminopeptidase and maltase did not decrease without their enzyme lipid microenvironment, produced by treatment with Triton X-100, the impairment of alkaline phosphatase maximal activity cannot be significantly differentiated from a non-specific inhibitory effect of the detergent. The activation energy values of leucine amino peptidase, alkaline phosphatase and maltase were lower in the Antarctic fish (11.7, 5.6 and 11.8 kcal·mol^-1, respectively) than in the eel (13.6, 7.6 and 13.1 kcal·mol^-1, respectively). The thermal stability of alkaline phosphatase and maltase is different in Pagothenia bernacchii and Anguilla anguilla intestinal homogenate.Abbreviations BBM brush border membrane - E _a activation energy - EGTA ethyleneglycol-bis-(-amino ethylether)N, N-tetraacetic acid - HEPES 2-[4-(2-hydroxyethyl)-1-piperazinyl]-ethane sulphonic acid - Km_app apparent Michaelis-Menten constant - PMSF phenylmethyl-sulphonyl fluoride - TRIS TRIS (hydroxymethyl)-aminomethane     

Energetics of growth of Microbacterium thermosphactum at low temperatures

Microbacterium thermosphactum was grown at 5°C and 9°C in glucose-limited continuous cultures. The end products of glucose metabolism were L-lactate and ethanol, and these compounds accounted for 86–92% of the glucose utilized. With input glucose concentrations less than 3 mM Y _glu ^Max was found to be 40–43, Y _ATP ^Max 20–21 and m _s 0.1–0.2. These values are almost identical to those found previously for cultures at 25°C and show that this psychrotroph grows with a very high energetic efficiency over a wide range of temperatures. With a higher (but still limiting) input glucose concentration of 5.6 mM at 9°C, cellular efficiency declined as there was a marked reduction in Y _glu. This decrease was accounted for in mathematical terms by an increase in m _s to 0.7, whilst Y _glu ^Max and Y _ATP ^Max remained high at 38 and 19 respectively.     

Long-term chilling of young tomato plants under low light and subsequent recovery

The influence of unfavourable climatic conditions at the onset of the growth period on chilling-sensitive tomato (Lycopersicon esculentum Mill., cv. Abunda) was studied by exposing young plants to combinations of low temperature and low light (60–100 mol quanta · m^–2 · s^–1) for several weeks. When the temperature did not decrease below a critical point (8 ° C) no loss of developmental capacity of the plants was detected. However, while new leaves were readily formed upon return to normal growth conditions (22/18 °C, day/night, in a greenhouse), net accumulation of biomass showed a lag phase of approximately one week. This delay was accompanied by a strong, irreversible inhibition of photosynthesis in the fully expanded leaves which had been exposed to the chilling treatment. When plants were subjected to temperatures below 8 ° C, survival rates decreased after three weeks at 6 ° C and irreversible damage of apical meristematic tissue occurred. Drought-hardening prior to chilling ensured survival at 6 ° C and protected the plants against meristem loss.Abreviation Chl chlorophyll Thanks are due to G.P. Telkamp for technical assistance. This research is financially supported by the Netherlands Technology Foundation (STW, Utrecht, The Netherlands), and is coordinated by the Foundation for Biological Research (BION, 's-Gravenhage, The Netherlands).     

松天牛小首螨对极端温度耐受性的驯化效应及低温存储研究

[目的]松天牛小首螨是近年发现的首个能够寄生致死松墨天牛卵的一个螨类新种,研究该螨对极端温度耐受性的驯化效应和低温存储条件,有助于进一步评估该螨的潜在地理分布或应用区域,并为该螨的规模化运输和存储提供基础依据。[方法]通过不同温度条件驯化后,测定松天牛小首螨暴露在极端温度下的存活率,同时比较不同低温条件下存储的松天牛小首螨膨腹体涌出的成螨数量,以及存储的雌成螨的生存情况。[结果]高温驯化可显著提高雌成螨高温暴露存活率,其中30℃ 36 h驯化后的存活率提高了1.26倍;低温驯化可显著提高雌成螨极端低温暴露存活率,其中10℃ 96 h、10℃ 120 h驯化后的存活率分别提高了2.08和2.13倍。以膨腹体为存储对象,低温存储后涌出成螨的数量随着存储时间延长而逐渐显著减少;以雌成螨为存储对象,在10℃条件下存储30 d,存活率为65.10%,在4℃条件下存储30 d,存活率达84.21%。[结论]松天牛小首螨具有很强的温度适应性,短期温度驯化即可大幅提升其对极端温度的耐受性。膨腹体适合作为该螨短期低温存储对象,雌成螨则适合作为中长期低温存储对象。     

Responses in ion leakage of wild sugarcane (Saccharum spontaneum L.) clones to enhanced ultraviolet-B radiation under field conditions

Field studies were conducted to determine the potential for alterations in ion leakage and the intraspecific variation in ion leakage sensitivity of 20 wild sugarcane clones (Saccharum spontaneum L.) to enhanced ultraviolet-B (UV-B, 280–315nm) radiation in two consecutive years. The clones were collected from original sites with different altitude (from 0 to 1650 m) and latitude (from 18–37 °N). The supplemental UV-B radiation was 5.00 kJ m⁻², simulating a depletion of 20 % stratospheric ozone. Across all clones tested in the present study, a significant change (P<0.01 or 0.05) in ion leakage for 11 in tillering, 14 in elongation and 15 in flowering in 2003, and for 9 in tillering, 5 in elongation and 5 in floweing in 2004 were observed. In general, intraspecific responses of ion leakage of wild sugarcane clones to enhanced UV-B radiation existed under field conditions for two consecutive years, although intraspecific difference in 2003 was more obvious than that in 2004. Wild sugarcane clones originating from lower latitude or high elevation were not necessarily the more tolerant to enhanced UV-B radiation.     

A porous agar medium for improving the growth of plants under sterile conditions

Porous nutrient agar was prepared under sterile conditions by drawing molten 3.5% (w/v) nutrient agar into a plastic syringe, allowing it to set, extruding it into a test tube and giving the tube a firm flick. Simple colorimetric tests showed that gaseous diffusion was substantially faster through 3.5% (w/v) porous agar than through the 1% (w/v) non-porous agar frequently used for growing plants under sterile conditions. Root systems ofTrifolium subterraneum grew 80–90% larger in porous than in non-porous agar.     

Inheritance of emergence time at low temperatures in segregating generations of maize

Summary North Carolina Design III and generation means analyses were used to study the inheritance of seedling emergence time and a related seedling growth parameter in crosses between 5–154, a line from CIMMYT Pool 5 with rapid seedling emergence under cool conditions, and two Corn Belt Dent lines of maize (Zea mays L.). The crosses were evaluated at low temperatures in controlled environment rooms. Additive genetic variances were larger than dominance variances in both crosses and estimates of the average levels of dominance were in the partial dominance range. Dominance was in the direction of rapid seedling emergence and rapid utilization of seed reserve. Estimates of minimum numbers of effective factors provided evidence for polygenic inheritance.     

不同处理条件对介质阻挡放电低温等离子体杀菌效果及影响机理研究

【目的】研究不同处理条件下介质阻挡放电低温等离子体对单增李斯特菌和肠炎沙门氏菌的杀菌效果,以及抑菌活性物质含量随处理时间的变化。【方法】以单增李斯特菌和肠炎沙门氏菌为对象,研究不同电压、时间及氧气浓度对介质阻挡放电低温等离子体杀菌效果的影响,通过气态活性物质测定管测定O_3和NO_2浓度随处理时间的变化,利用荧光强度表征菌液中产生的活性物质浓度,采用荧光分光光度法测定·OH、H_2O_2和~1O_2随处理时间的变化。【结果】采用70 kV、150 s或80 kV、1_20 s能够完全杀灭肠炎沙门氏菌,而单增李斯特菌只在80kV、1_20s条件下才能被完全杀死。采用50%O_2+50%N_2的混合气体能够在90 s内完全杀死细菌。随处理时间的增加,两种菌体细胞内活性氧物质含量呈逐渐增加趋势。【结论】电压、时间及氧气浓度均能显著增强等离子体的杀菌效果,其杀菌作用主要与H_2O_2、·OH、1O_2等活性氧物质的含量有关,其中·OH和H_2O_2是介质阻挡放电等离子体杀菌的主要物质。