A consortium of rhizobacterial strains and biochemical growth elicitors improve cold and drought stress tolerance in rice (Oryza sativa L.)

In the present study, a consortium of two rhizobacteria Bacillus amyloliquefaciens Bk7 and Brevibacillus laterosporus B4, termed ‘BB’, biochemical elicitors salicylic acid and β‐aminobutyric acid (SB) and their mixture (BBSB) were investigated for cold and drought stress tolerance in rice plants. After withholding water for 16 days, rice plants treated with BBSB showed 100% survival, improved seedling height (35.4 cm), shoot number (6.12), and showed minimum symptoms of chlorosis (19%), wilting (4%), necrosis (6%) and rolling of leaves. Similarly, BB inoculation enhanced plant growth and reduced overall symptoms in rice seedlings subjected to 0 ± 5 °C for 24 h. Our results imply several mechanisms underlying BB‐ and BBSB‐elicited stress tolerance. In contrast to the control, both treatments significantly decreased leaf monodehydroascorbate (MDA) content and electrolyte leakage, and increased leaf proline and cholorophyll content. Moreover, activities of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT) increased 3.0‐ and 3.6‐fold, respectively. Moreover, expression of OsMYB3R‐2, OsDIL, OsDREB1A and OsCDPK13 genes was significantly up‐regulated, suggesting that these genes play important roles in abiotic stress tolerance of rice. In addition, bacterial strains Bk7 and B4 were able to produce high amounts of IAA and siderophores, and colonise the plant roots, while only strain Bk7 exhibited the capability to form biofilms and solubilise inorganic phosphate. This study indicates that the BB and BBSB bio‐formulations can be used to confer induced systematic tolerance and improve the health of rice plants subject to chilling and drought stress.     

五种金花茶组植物的耐寒性比较研究

金花茶组植物是世界珍稀、濒危的观赏植物,具有极高的观赏价值和药用价值.为了比较金花茶组植物的耐寒性,以五种金花茶组植物为材料,采用人工模拟低温环境的方法对其2年生叶片进行低温胁迫处理,应用电导法研究五种金花茶种质在20℃(常温对照)、8℃、-2℃、-7℃、-12℃、-17℃、-22℃和-27℃低温下相对电导率的变化,配合Logistic方程,测定其低温半致死温度(LT50),以及叶片中游离脯氨酸、可溶性糖和丙二醛的含量.结果表明:五种金花茶的低温半致死温度(LT50)范围为-14.58~-12.74℃,其中金花茶为-14.58℃、龙州金花茶为-14.27℃、柠檬黄金花茶为-13.44℃、直脉金花茶为-13.09℃、东兴金花茶-12.74℃.低温半致死温度能反映金花茶种质的耐寒性,金花茶和龙州金花茶耐寒性强,其次为柠檬黄金花茶和直脉金花茶,东兴金花茶耐寒性较弱.在降温过程中,五种金花茶叶片相对电导率随温度降低呈S型上升,与温度呈负相关;脯氨酸、可溶性糖和丙二醛含量均呈现先上升后下降的趋势.同一低温条件下,半致死温度低的金花茶脯氨酸和可溶性糖的含量更高,而丙二醛含量更低.该研究结果为金花茶组植物耐寒种质选育提供了科学依据,为人工种植金花茶提供了技术支持.     

越冬期间库尔勒香梨不同器官抗寒指标随气温的变化

以越冬期间库尔勒香梨花芽、树干、枝条等器官为材料,测定了不同器官形成层组织抗氧化酶(SOD、CAT、POD)活性、可溶性蛋白含量、相对电导率等抗寒指标,同时监测了果园气温和树干阳阴面形成层温度,并采用隶属函数评价不同器官抗寒性,分析越冬期气温对新疆库尔勒香梨不同器官抗寒指标和抗寒性的影响。结果表明:(1)在库尔勒香梨越冬期间,不同器官同一抗寒指标和同一器官不同抗寒指标随气温、树干阳阴面形成层温度差的变化趋势有所不同,但总体上抗寒指标均与气温呈负相关关系,而与树干阳阴面形成层温度差均呈正相关关系。(2)各器官形成层可溶性蛋白含量与其抗氧化酶活性呈正相关关系,SOD、CAT活性与POD活性呈正相关关系,并以CAT与POD活性相关性最强。(3)利用隶属函数法综合分析结果显示,贡献率最大的是CAT活性和可溶性蛋白含量,不同器官抗寒性强弱顺序为花芽组织树干阴面形成层枝条形成层树干阳面形成层。研究发现,库尔勒香梨各器官形成层POD和CAT活性在越冬期间较低气温和较强烈形成层温度变化时较高,并以SOD对低温伤害和形成层温度变化最敏感;整个越冬期抗寒性强的器官表现出较高的可溶性蛋白含量和较低的相对电导率;形成层温度变化与抗寒生理指标变化之间具有较好的相关性,在一定范围内能够反映机体受到的低温冻害程度。     

Carbon dioxide exchange dynamics over a mature switchgrass stand

Switchgrass (Panicum virgatum L.) has gained importance as feedstock for bioenergy over the last decades due to its high productivity for up to 20 years, low input requirements, and potential for carbon sequestration. However, data on the dynamics of CO₂ exchange of mature switchgrass stands (>5 years) are limited. The objective of this study was to determine net ecosystem exchange (NEE), ecosystem respiration (Re), and gross primary production (GPP) for a commercially managed switchgrass field in its sixth (2012) and seventh (2013) year in southern Ontario, Canada, using the eddy covariance method. Average NEE flux over two growing seasons (emergence to harvest) was ?10.4 μmol m^?2 s^?1 and reached a maximum uptake of ?42.4 μmol m^?2 s^?1. Total annual NEE was ?380 ± 25 and ?430 ± 30 g C m^?2 in 2012 and 2013, respectively. GPP reached ?1354 ± 23 g C m^?2 in 2012 and ?1430 ± 50g C m^?2 in 2013. Annual Re in 2012 was 974 ± 20 g C m^?2 and 1000 ± 35 g C m^?2 in 2013. GPP during the dry year of 2012 was significantly lower than that during the normal year of 2013, but yield was significantly higher in 2012 with 1090 g  m^?2, compared to 790 g m^?2 in 2013. If considering the carbon removed at harvest, the net ecosystem carbon balance came to 106 ± 45 g C  m^?2 in 2012, indicating a source of carbon, and to ?59 ± 45 g C m^?2 in 2013, indicating a sink of carbon. Our results confirm that switchgrass can switch between being a sink and a source of carbon on an annual basis. More studies are needed which investigate this interannual variability of the carbon budget of mature switchgrass stands.     

Specific Ion Channels Control Sensory Gain,Sensitivity, and Kinetics in a Tonic Thermonociceptor

1. Download : Download high-res image (160KB)
2. Download : Download full-size image

     

TETREUTREPTIA POMQUETENSIS GEN. ET SP. NOV. (EUGLENOPHYCEAE): A QUADRIFLAGELLATE,PHOTOTROPHIC MARINE EUGLENOID1

A new euglenoid genus and species, Tetreutreptia pomquetensis, is described from winter waters of Maritime Canada. This phototrophic species is characterized by four emergent heterodynamic flagella, two about the length of the cell and two less than one-half this length. Tetreutreptia pomquetensis has features in common with species of Eutreptiella while it differs in several respects from any of the described species of that genus. It could be assigned to the order Eutreptiales or Euglenamorphales sensu Leedale or the order Euglenales sensu Farmer. This new alga has a narrow range of temperature tolerance; it grows best from 0° to 7° C and dies at temperatures above 10° C. The optimum salinity for growth was near full-strength seawater. Growth conditions for the alga define the conditions whence this species was isolated.     

Enhanced Calcite Dissolution in the Presence of the Aerobic Methanotroph Methylosinus trichosporium

Microbial aerobic methane oxidation (MOx) is intrinsically coupled to the production of carbon dioxide, favoring carbonate dissolution. Recently, microbial organic polymers were shown to be able to induce carbonate dissolution. To discriminate between different mechanisms causing calcite dissolution, experiments were conducted in the presence of solid calcite with (1) actively growing cells (2) starving cells, and (3) dead cells of the methanotrophic bacterium Methylosinus trichosporium under brackish conditions (salinity 10) near calcite saturation (saturation state (Ω) 1.76 to 2.22). Total alkalinity and the amount of dissolved calcium markedly increased in all experiments containing M. trichosporium cells. After initial system equilibration, similar calcite dissolution rates, ranging between 20.16 (dead cells) and 25.68 μmol L^?1 d^?1 (actively growing cells), were observed. Although concentrations of transparent exopolymer particles declined with time in the presence of actively growing and starving cells, they increased in experiments with dead cells. Scanning electron microscopy images of calcite crystals revealed visible surface corrosion after exposure to live and dead M. trichosporium cells. The results of this study indicate a strong potential for microbial MOx to affect calcite stability negatively, facilitating calcite dissolution. In addition to CO₂ production by methanotrophically active cells, we suggest that the release of acidic or Ca²⁺-chelating organic carbon compounds from dead cells could also enhance calcite dissolution.     

Innate-immune responses of tilapia (Oreochromis mossambicus) exposure to acute cold stress

In this present study, Oreochromis mossambicus tilapia were transferred to cold water at 12°C for various time intervals (1, 4, 8, 24, and 48 hr) and its innate immune response was analyzed by studying cellular and humoral parameters. In vivo, alternative complement pathway activity in blood plasma was rapidly increased at 1 hr of cold water (12°C) exposure. Lysozyme activity and cortisol levels of plasma were increased at 4 and 1 hr, respectively. Surprisingly, only plasma cortisol levels remained unchanged through 24 hr of cold water transfer. Phagocytic ability, phagocytic capacity, and respiratory burst (RB) activity of head kidney (HK) leukocytes and splenocytes showed no any significant changes. In peripheral blood leukocytes, phagocytic capacity, and RB activity were increased at 24 hr of cold water exposure. The expressions of genes involved innate immunity in splenocytes and HK leukocytes of tilapia cold water exposure were analyzed, messenger RNA (mRNA) expressions of HSP70, HSP90, and immunoglobulin M failed to change upon exposure to cold stress. Major histocompatibility complex-I and II mRNAs were significantly increased in tilapia splenocytes at 1 hr of cold water transferred. Whereas myxovirus (Mx) expression was increased in splenocytes and HK leukocytes of tilapia after 1 hr of cold water exposed. Our result reveals that the exposure of tilapia to acute cold stress condition significantly enhances plasma acid phosphatase activity and both phagocytic capacity and RB activity. Furthermore, cold stress significantly stimulates Mx gene expression in splenocytes and HK leukocytes.     

Geotaxis in the springtail Folsomia candida

Laboratory assays demonstrated the presence of a small positive geotaxis response to a 15° incline by Folsomia candida Willem (Collembola: Isotomidae). Negative phototaxis played an additive role to positive geotaxis when the experimental apparatus were exposed to light. The geotactic response was negatively affected by cold acclimation and decreasing surrounding temperature, but unaffected by food deprivation. The reduced mobility of springtails at low temperature did not seem to play a role in the corresponding decreased geotaxis. The low level of geotaxis and its further decrease with exposure to low temperature support an earlier suggestion that F. candida do not respond to cooling temperatures of fall by relocation to warmer deeper soil layers, but remain in the upper soil layers and increase their cold tolerance to continue foraging in the food‐rich upper soil layers.