Calcium influx at the tip of growing root-hair cells of Arabidopsis thaliana

The role of extracellular Ca²⁺ in root-hair tip growth has been investigated in Arabidopsis thaliana (L.) Heynh. Root-hair length was found to be dependent on the concentration of Ca²⁺ in the growth medium, with maximum length achieved at [Ca²⁺] of 0.3–3.0 mM. Using a non-intrusive calcium-specific vibrating microelectrode, an extracellular Ca²⁺ gradient was detected at the tips of individual growing root-hair cells. The direction of the gradient indicated a net influx of Ca²⁺ into root-hair cells. No gradient was detected near the sides of the root hairs or at the tips of non-growing root hairs. When root hairs were exposed to the Ca²⁺-channel blocker nifedipine, tip growth stopped and the extracellular Ca²⁺ gradient was abolished. These results indicate that Ca²⁺ influx through plasma-membrane Ca²⁺ channels is required for normal root-hair tip growth.Abbreviation APW artificial pond water We thank L.F. Jaffe, W. Kuhtreiber and A. Miller of the National Vibrating Probe Facility, Marine Biological Laboratory, Woods Hole, Mass., USA for their technical assistance and helpful discussions. We also thank Liam Dolan, Martin Steer, and Susan Ford for helpful discussions. This research was supported by National Science Foundation grant PCM-9004568.     

Accuracy of genomic predictions in Bos indicus (Nellore) cattle

Background

Nellore cattle play an important role in beef production in tropical systems and there is great interest in determining if genomic selection can contribute to accelerate genetic improvement of production and fertility in this breed. We present the first results of the implementation of genomic prediction in a Bos indicus (Nellore) population.

Methods

Influential bulls were genotyped with the Illumina Bovine HD chip in order to assess genomic predictive ability for weight and carcass traits, gestation length, scrotal circumference and two selection indices. 685 samples and 320 238 single nucleotide polymorphisms (SNPs) were used in the analyses. A forward-prediction scheme was adopted to predict the genomic breeding values (DGV). In the training step, the estimated breeding values (EBV) of bulls were deregressed (dEBV) and used as pseudo-phenotypes to estimate marker effects using four methods: genomic BLUP with or without a residual polygenic effect (GBLUP20 and GBLUP0, respectively), a mixture model (Bayes C) and Bayesian LASSO (BLASSO). Empirical accuracies of the resulting genomic predictions were assessed based on the correlation between DGV and dEBV for the testing group.

Results

Accuracies of genomic predictions ranged from 0.17 (navel at weaning) to 0.74 (finishing precocity). Across traits, Bayesian regression models (Bayes C and BLASSO) were more accurate than GBLUP. The average empirical accuracies were 0.39 (GBLUP0), 0.40 (GBLUP20) and 0.44 (Bayes C and BLASSO). Bayes C and BLASSO tended to produce deflated predictions (i.e. slope of the regression of dEBV on DGV greater than 1). Further analyses suggested that higher-than-expected accuracies were observed for traits for which EBV means differed significantly between two breeding subgroups that were identified in a principal component analysis based on genomic relationships.

Conclusions

Bayesian regression models are of interest for future applications of genomic selection in this population, but further improvements are needed to reduce deflation of their predictions. Recurrent updates of the training population would be required to enable accurate prediction of the genetic merit of young animals. The technical feasibility of applying genomic prediction in a Bos indicus (Nellore) population was demonstrated. Further research is needed to permit cost-effective selection decisions using genomic information.     

Microbial population dynamics on seeds during drum and steeping priming

In the UK, seeds are primed commercially via drum or steeping priming processes to improve seed germination and seedling establishment but the microbial population dynamics occurring during these processes are unknown. Consequently, changes in culturable bacterial and fungal populations that occurred during laboratory and commercial scale drum priming of carrot, leek and parsnip seed and during laboratory scale and commercial scale steeping priming of carrot and sugar beet seed were investigated. Populations of bacteria and pseudomonads increased by 2 and 4 log₁₀ cfu g^–1 seed during priming to reach between 7 and 10 log₁₀ cfu g^–1 seed with less than 1 log₁₀ cfu g^–1 seed decrease after redrying, irrespective of seed type or priming process. Pseudomonads represented approximately 10% of the culturable bacterial population. Fungal populations also increased by between 1 and 3 log₁₀ cfu g^–1 seed during priming of carrot, leek and parsnip seed and were little affected by redrying. Addition of a tefluthrin coating (a standard commercial insecticide treatment) during the drying stage of commercial scale drum priming had little effect on microbial populations. During steeping priming, populations of bacteria and pseudomonads on sugar beet also increased by 2 and 4 log₁₀ cfu g^–1 seed with less than 1 log₁₀ cfu g^–1 seed decrease after redrying. However, fungi did not increase in the same manner on sugar beet, suggesting that the sugar beet seed itself may have an inhibitory effect on fungal growth. The presence of thiram in the steeping liquid (a standard commercial fungicide treatment) inhibited fungal proliferation on carrot and sugar beet seed. Spore forming bacteria generally occurred at low levels on all seeds (between 2 and 5 log₁₀ cfu g^–1seed) and did not exhibit any characteristic population changes during priming or redrying. Clearly some culturable populations of microorganisms can increase reproducibly during these priming processes and survive the redrying procedure, thereby demonstrating the potential for a novel method of introducing microbial inoculants onto seed.     

Relationship of nitrate supply with growth rate, plasma membrane-bound and cytosolic nitrate reductase, and tissue nitrate content in tobacco plants

cNR, cytosolic nitrate reductase
PM-NR, plasma membrane-bound nitrate reductase

Activities of plasma membrane-bound nitrate reductase (PM-NR) and cytosolic nitrate reductase (cNR) in tobacco (Nicotiana tabacum L. cv. Samsun) are regulated differently, depending upon the nitrate supply to the culture medium (in sand culture). The cNR activity of roots was higher at low nitrate concentrations with the maximum at 5 mM nitrate supply and declined to low values beyond 5 mM . In contrast, the PM-NR activity of roots increased with higher nitrate concentrations with the maximum at 25 mM nitrate and clearly decreased only at 40 mM . This high PM-NR activity correlated with a low growth rate and might be one of the responses to excess nitrate. Internal nitrate and total nitrogen content of the tissues, however, showed a relative minimum in shoots and in roots of between 15 and 25 mM external nitrate. With declining PM-NR activities beyond 25 mM external nitrate, the nitrate content in the tissue increased indicating an inverse relationship between tissue nitrate content and root PM-NR activity. In leaves both NR activities (cNR and PM-NR) correlated with the internal nitrate content, but with a different response at low nitrate.     

Temperature Response and Effect of Ca2+ and Mg2+ on ATPases from Roots of Oats and Wheat as Influenced by Growth Temperature and Nutritional Status

Activation by Ca²⁺, Mg²⁺, Zn²⁺, or Mn²⁺ of adenosine triphosphatases in a microsomal fraction from wheat roots depends upon the growth temperature when the plants are grown under low salt conditions, but not when the plants get a full-strength culture medium. At low ionic strength, cultivation at 25°C gives only half as high activation as cultivation at 18°C or at high ionic strength at both temperatures. Corresponding data for activation of ATPases from oats also show that low ionic strength during growth gives the highest temperature dependence. Low temperature together with low salt conditions during growth gives the highest ATPase activity after stimulation with divalent cations. High growth temperature and full-strength medium decrease the ATPase activity. Activation energies (Ea) were calculated for the two temperature intervals 35–20°C and 20–5°C. The dominating ATPase stimulation (Ca²⁺ in wheat, Mg²⁺ in oats) is characterized by high specific activity combined with a low Ea value. The differences in ATPase activity between oats and wheat can be correlated with different cultivation requirements known from agriculture.     

Effects of water temperature and salinity on elimination of Salmonella charity and Escherichia coli from Sydney rock oysters (Crassostrea commercialis)

The elimination of Salmonella charity and Escherichia coli from the Sydney rock oyster, Crassostrea commercialis, was examined during commercial purification of oysters under different water temperatures and salinities. Both organisms were rapidly eliminated at 18 to 22 degrees C. Purification was effective but slower at 24 to 27 degrees C and incomplete and inconsistent at temperatures below 17 degrees C. The oysters suffered stress and were not effectively purified at water salinities of 15 to 20% but were rapidly purified at 32 to 47% salinity. Winter-harvested and summer-harvested oysters were purified similarly in water at 18 to 22 degrees C and 32 to 36% salinity.     

A histological study of the Shionogi adenocarcinoma 115 grown in male and female mice

We have previously demonstrated that growth rate and morphology differ between androgen-responsive Shionogi mouse mammary tumours maintained in male and female mice. Furthermore, we can modulate the growth rate of these tumours in male mice by exposing the mice to psychosocial stressors. In the present study, we were interested in determining if tumours in male mice with a comparable growth rate to that in females, also had a morphology similar to that in females. SC115 tumours were examined using histochemical and immunohistochemical techniques. Tumours in male mice were easily distinguishable from tumours in female mice regardless of growth rate. Tumours maintained in female mice contained osteoid-like regions which stained positive for sialic acid and sulphate moieties. No such regions were observed in any of the tumours from male mice. In addition, although all tumours contained MSA (muscle specific actin)-positive and S100 protein-positive cells, these regions were more extensive in the tumours of female mice. This study suggests that tumour growth rate and morphology are independently regulated by the host environment.     

Effects of water temperature and salinity on elimination of Salmonella charity and Escherichia coli from Sydney rock oysters (Crassostrea commercialis).

The elimination of Salmonella charity and Escherichia coli from the Sydney rock oyster, Crassostrea commercialis, was examined during commercial purification of oysters under different water temperatures and salinities. Both organisms were rapidly eliminated at 18 to 22 degrees C. Purification was effective but slower at 24 to 27 degrees C and incomplete and inconsistent at temperatures below 17 degrees C. The oysters suffered stress and were not effectively purified at water salinities of 15 to 20% but were rapidly purified at 32 to 47% salinity. Winter-harvested and summer-harvested oysters were purified similarly in water at 18 to 22 degrees C and 32 to 36% salinity.