The effect of root damage caused by simulated white grub attack on the growth,yield and water-use of groundnut plants

White grubs (larval scarabaeids) are now recognized as being important pests of groundnut (peanut) in many parts of the world because of their ability to damage roots. A method of simulating white grub damage to groundnut plants was developed to obtain an indication of how the feeding activity of these insects influences plant growth. The effect of root cutting and drought stress on water uptake and biomass production was evaluated, with roots being cut at three depths in the late vegetative and early podfilling stages. As groundnut plants are often grown under conditions of drought stress, the effects of which would be accentuated by root damage, this factor was introduced into the experiment. Plant water-use measurements indicated that the root systems of plants cut 30 days after emergence (DAE) and watered twice a week became fully functional again after 40 days. Pod and total biomass production were however significantly less than those of the uncut control plants, with drought stress reducing yields below the well-watered controls, particularly when cut at 10 cm below the soil surface. The root systems of plants cut 51 DAE did not regrow to any appreciable extent, and rates of plant water-use remained less than half of the uncut control plants. Over all treatments, there was a strong positive correlation between total (and pod) biomass and plant water-use. It was concluded that the phenological stage of the plant at which root damage occurred had a profound influence on the subsequent recovery in root growth and function, and ultimately on pod yield.     

Fecal steroid hormone analysis as an indicator of reproductive function in the cheetah

Techniques were developed and validated to measure fecal estrogen and progesterone concentrations of the female cheetah. Fecal samples were collected from seven mature females. Cheetahs were monitored before mating and continued until parturition. Four females had normal pregnancies, one conceived but the pregnancy resulted in spontaneous abortion, one was mated but apparently did not conceive and one was treated with gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) to induce follicular growth and ovulation. Vaginal superficial cells increased with increasing estrogen concentrations. Peak estrogen occurred one day postcopulation. Increases in fecal progesterone concentrations, indicative of ovulation, occurred after copulation and hormonally induced ovulation. For the first time reproductive function can be monitored in the cheetah using noninvasive sample collection. © 1994 Wiley-Liss, Inc.     

PHYSIOLOGICAL ACCLIMATION OF MARINE PHYTOPLANKTON TO DIFFERENT NITROGEN SOURCES1

We examined the energetic dependency of the biochemical and physiological responses of Thalassiosira pseudonana Hasle and Heimdal. Chaetoceros gracilis Schütt, Dunaliella tertiolecta Butcher, and Gymnodinium sanguineum Hirasaka to NH₄⁺, NO₃^?, and urea by growing them at subsaturating and saturating photon flux (PF). At subsaturating PF, when energy was limiting, NO₃^? and NH₄⁺ grown cells had similar growth rates and C and X quotas. Therefore, NO₃^? grown cells used up to 48% more energy than NH₄⁺ grown cells to assimilate carbon and nitrogen. Based on our measurements of pigments, chlorophyll-a-specific in vivo absorption cross-section, and fluorescence-chlorophyll a^?1, we suggest that NO₃^?, grown cells do not compensate for the greater energy requirements of NO₃^? reduction by trapping more light energy. At saturating PF, when energy is not limiting, the utilization of NO₃^?, compared to NH₄⁺ resulted in lower growth rates and N quotas in Thalassiosira pseudonana and lower N quotas in Chaetoceros gracilis, suggesting enzymatic rather than energetic limitations to growth. The utilization of urea compared to Nh₄⁺ resulted in lower growth rates in Chaetoceros gracilis and Gymnodinium sanguineum (saturating PF) and in lower N quotas in all species tested at both subsaturating and saturating PF. The high C:N ratios observed in all urea-grown species suggest that nitrogen assimilation may be limited by urea uptake or deamination and that symptoms of N limitation in microalgae may be induced by the nature of the N source in addition to the N supply rate. Our results provide new eridence that the maximum growth rates of microalgae may be limited by enzymatic processes associated with the assimilation of NO₃^?, or urea.     

Stability of bilirubin oxidase in organic solvent media: a comparative study on two low-water systems

The storage stability of bilirubin oxidase was studied in water-in-oil CTAB microemulsions with a chloroformrich continuous organic phase. The kinetics of the inactivation process were best described by a double exponential equation. Approximately half of enzymatic activity was lost during a "fast" phase with a half life of ca. 50 min, whereas the remaining activity was lost much more slowly (half life ca. 1000 min). Rates of inactivation were not affected significantly by variation of either solvent composition or concentration of water droplets, but inactivation was more rapid when droplet size was very small. Steady-state enzyme kinetics were studied at various stages in the inactivation process, and it was shown that inactivation occurred without change in the K(m) of the enzyme for bilirubin. Stability was also studied in a liquid/solid two-phase system; it was found that the inactivation process in this system; it was found that the inactivation process in this system was best described by a single exponential term. The rate was similar to the "fast" phase rate observed in the water-in-oil microemulsion system. Inactivation of the enzyme slow. Addition of the surfactant CTAB to the aqueous environment increased the rate of inactivation to levels comparable to those of the "slow" phase observed in water-in-oil microemulsions. (c) 1993 Wiley & Sons, Inc.     

Improved mating efficiency inAcetabularia acetabulum: recovery of 48–100% of the expected zygotes

Summary We have improved zygote recovery 11–1,000 fold by optimizing the physiology of gamete release and mating inAcetabularia acetabulum. Gamete release was affected by agar purity, concentration, and volume/gametangial pair. Cold pre-treatment of gametangia (14–30 d at 10°C in the dark) synchronized subsequent gamete release at 21°C in the light. Cold pre-treatment was nearly twice as effective in synchronizing subsequent gamete release when intact, gametangia-bearing caps rather than isolated gametangia were pretreated. Synchronizing gamete release doubled mating efficiency. In a wild-type laboratory strain ofA. acetabulum, there were 1,561±207 gametes/gametangium which had half-lives of 14.5 d in 0.1% seawater-agar. We recovered 48–93% of the expected numbers of zygotes from a mass mating of 8 to 1,226 gametangia and 11–128% of the expected numbers of zygotes from mating single gametangial pairs: the large range in the calculated mating efficiency may be attributable to the variation in the numbers of gametes made per gametangium. Zygote recovery from single gametangial pairs was highly dependent on the volume of mating matrix. In addition, most zygotes recovered were unattached to any other zygotes in the subsequent generation (> 95% single cells from matings of 1–500 gametangial pairs). Our improvements in mating conditions and zygote recovery (1) have facilitated cell manipulation and culture ofA. acetabulum in the laboratory; and (2) have made controlled crosses for selection and genetic analysis of mutants feasible. These advances have removed a major barrier to genetic analysis of development inAcetabularia.Abbreviations LB Luria-Bertani bacteriological broth - SE standard error of the mean - T_g agar gelling temperatures - DAPI 4,6-diamidino-2-phenylindole     

青皮核桃采后病害生防菌贝莱斯芽胞杆菌XRD006全基因组分析及防治效果研究

【目的】探究生防菌贝莱斯芽胞杆菌(Bacillus velezensis) XRD006对青皮核桃采后病害的生防能力及其贮藏保鲜效果,解析菌株的基因特性和次级代谢产物,了解菌株的抑菌机制。【方法】通过抑菌试验确定XRD006对青皮核桃采后病原菌的抑制能力。利用活体抑菌及贮藏试验探究生防菌对青皮核桃采后病原菌的抑制能力及对青皮核桃贮藏品质的影响。以全基因组测序了解菌株XRD006的基因组特征及潜在抑菌相关基因;利用antiSMASH软件预测XRD006的次级代谢产物;结合比较基因组学分析XRD006和贝莱斯芽胞杆菌标准株FZB42、SQR9之间的共线性关系和次级代谢产物基因簇差异。利用高效液相色谱(high performance liquid chromatography,HPLC)和质谱鉴定XRD006次级代谢产物并通过牛津杯法测定其抑菌能力。【结果】抑菌试验表明菌株XRD006对青皮核桃采后病原菌隐秘刺盘孢(Colletotrichum aenigma)、暹罗炭疽菌(Colletotrichum siamense)、葡萄座腔菌(Botryosphaeria dothidea)和藤仓...     

Carryover effects from environmental change in early life: An overlooked driver of the amphibian extinction crisis?

Ecological carryover effects, or delayed effects of the environment on an organism's phenotype, are central predictors of individual fitness and a key issue in conservation biology. Climate change imposes increasingly variable environmental conditions that may be challenging to early life-history stages in animals with complex life histories, leading to detrimental physiological and fitness effects in later life. Yet, the latent nature of carryover effects, combined with the long temporal scales over which they can manifest, means that this phenomenon remains understudied and is often overlooked in short-term studies limited to single life-history stages. Herein, we review evidence for the physiological carryover effects induced by elevated ultraviolet radiation (UVR; 280–400 nm) as a potential contributor to recent amphibian population declines. UVR exposure causes a suite of molecular, cellular and physiological consequences known to underpin carryover effects in other taxa, but there is a lack of research linking embryonic and larval UVR exposures to fitness consequences post-metamorphosis in amphibians. We propose that the key impacts of UVR on disease-related amphibian declines are facilitated through carryover effects that bridge embryonic and larval UVR exposure with potential increased disease susceptibility post-metamorphosis. We conclude by identifying a practical direction for the study of ecological carryover effects in amphibians that could guide future ecological research in the broader field of conservation physiology. Only by addressing carryover effects can many of the mechanistic links between environmental change and population declines be elucidated.     

Monitoring growth and acetic acid secretion by a thermotolerantBacillus using conduction microcalorimetry

Summary A method is described to determine power of heat-time curves by conduction microcalorimetry in order to monitor the viability and ability of a thermotolerantBacillus strain to secrete acetic acid both during exponential growth and during stationary-phase. In this system secreted acetic acid is neutralized by an insoluble source of lime (dolime) which results in a poor correlation between optical density and culture dry weight. As an alternative, cells and residual dolime were rapidly resuspended in isothermal fresh medium with glucose in a conduction microcalorimeter. Heat evolution was rapid over a period of 200–800 s. Steady state heat evolution rate decreased as a function of culture time and did not correlate with: 1) specific growth rate: 2) viable cell number: 3) glucose consumption rate; or 4) acetic acid secretion rate. Glucose consumption and acetic acid secretion during the stationary growth phase were correlated with specific heat evolution rate. These initial results indicate that this technique may be useful for further development as an on-line flow or stopped-flow method to monitor the physiology of bacilli in response to nutrient depletion or growth inhibition.     

Responses of the desert green algae,Chlorella sp. to drought stress

Desert algae are important components of the desert soil crust and play an essential role in desert soil ecosystem development. Owing to their special habitat, desert algae are often exposed to harsh environments, among which drought represents the most common stress. Green algae are considered to have drought tolerance potential; however, only a few studies have investigated this. In this study, we selected the green alga Chlorella sp., which was isolated from desert soil, and studied its physiological response to polyethylene glycol (PEG) 6000-induced drought stress. The results showed that drought stress can affect the photosynthetic efficiency of Chlorella sp., reduce its water retention ability, and destroy its ultrastructure. However, Chlorella sp. can cope with drought stress through a series of physiological regulatory strategies. Protective strategies include quick recovery of photosynthetic efficiency and increased chlorophyll content. In addition, induced synthesis of soluble proteins, lipids, and extracellular polysaccharide (EPS), and accumulation of osmotic regulatory substances, such as sucrose and trehalose, also contribute to improving drought tolerance in Chlorella sp. This study provides insights into the physiological responses of Chlorella sp. to drought stress, which may be valuable for understanding the underlying drought adaptation mechanisms of desert green algae.