ABA and Low Temperature Induce Freezing Tolerance via Distinct Regulatory Pathways in Wheat

The role of ABA in the induction of freezing tolerance was investigatedin two wheat (T. aestivum L.) cultivars, Glenlea (spring var)and Fredrick (winter var). Exogenous application of ABA (5x10^–5M for 5 days at 24°C) increased the freezing tolerance ofintact plants by only 3°C (LT₅₀) in both cultivars. Maximalfreezing tolerance (LT₅₀ of –9°C for Glenlea and –17°Cfor Fredrick) could only be obtained with a low temperaturetreatment (6/2°C; day/night) for 40 days. These resultsshow that exogenously applied ABA cannot substitute for lowtemperature requirementto induce freezing tolerance in intactwheat plants. Furthermore, there was no increase in the endogenousABA level of wheat plants during low temperature acclimation,suggesting the absence of an essential role for ABA in the developmentof freezing tolerance in intact plants. On the other hand, ABAapplication (5x10^–5 M for 5 days at 24°C) to embryogenicwheat calli resulted in an increase of freezing tolerance similarto that achieved by low temperature. However, as in intact plants,there was no increase in the endogenous ABA level during lowtemperature acclimation of calli. These results indicate thatthe induction of freezing tolerance by low temperature is notassociated with an increase in ABA content. Using an antibodyspecific to a protein family associated with the developmentof freezing tolerance, we demonstrated that the induction offreezing tolerance by ABA in embryogenic wheat calli was correlatedwith the accumulation of a new 32 kDa protein. This proteinis specifically induced by ABA but shares a common antigenicitywith those induced by low temperature. These results suggestthat ABA induces freezing tolerance in wheat calli via a regulatorymechanism different from that of low temperature. (Received June 15, 1993; Accepted September 16, 1993)     

The sublethal effects of tebufenozide on the precopulatory and copulatory activities of Choristoneura fumiferana and C. rosaceana

The sublethal effects of tebufenozide, an ecdysone agonist, on the reproductive biology of Choristoneura fumiferana (Clem) and of Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), treated during the larval stage, were evaluated using two treatment methods: the force‐feeding method and the diet method. The percentage of mortality and the developmental time of survivors increased linearly with the concentration of tebufenozide used. This ecdysone analogue proved to be more toxic to C. fumiferana than to C. rosaceana. In C. rosaceana, the weight of males and females decreased proportionally with the dose ingested, but females were affected to a greater extent. This difference might be due to a greater consumption of the treated diet, or to a differential vulnerability to tebufenozide. Tebufenozide did not modify the pre‐copulatory activities associated with chemical communication in the females. However, the consumption of tebufenozide delayed ovarian maturation, causing a reduction in the fecundity of females. Treated males had smaller spermatophores and fewer eupyrene sperms in their bursa copulatrix and spermatheca, along with lower mating success. In C. fumiferana, tebufenozide delayed the females’ onset time of calling the first night after emergence, but did not affect the mean time spent calling or the production of the main component of the sex pheromone. The males showed significantly greater difficulty in executing oriented flight in a wind tunnel, although their mating success was not affected. We concluded that tebufenozide interferes with various aspects of the reproductive biology of males and females of C. fumiferana and C. rosaceana, including some pre‐copulatory behaviors associated with sex pheromone communication.     

Origin and developmental patterns of lactase and other glycosidases in sheep amniotic and allantoic fluid.

Intestinal lactase activity (with its associated cellobiase, 4-methylumbelliferyl-beta-galactosidase and -beta-glucosidase activities) was used as a specific intestinal marker enzyme to study the release of protein and enzymes of intestinal origin in sheep amniotic fluid during gestation. In amniotic fluid, intestinal lactase activity peaked at 66--85 days of gestation and then decreased with gestation. This enzyme activity was very low or absent in allantoic fluid throughout gestation suggesting that there is no important transfer of amniotic fluid lactase towards the allantoic cavity. Maltase and 4-methylumbelliferyl-alpha-glucosidase showed no statistically significant variation with gestation in both amniotic and allantoic fluid whereas alpha-galactosidase and N-acetyl-beta-hexosaminidase which were first higher in allantoic than in amniotic fluid increased in amniotic fluid to reach allantoic fluid levels near term. Such patterns are consistent with the suggestion that the fetal urine is a source of alpha-galactosidase and N-acety-beta-hexosaminidase activities and that sheep urine is first accumulated in the allantoic sac via the urachus up to 86--90 days of gestation and thereafter passes more and more into the amniotic sac.     

Phosphate transport by capillaries of the blood-brain barrier.

Capillaries were isolated from bovine brain cortex and used for phosphate transport studies. The influx of phosphate through capillary membranes was studied by incubation with [32Pi]phosphate followed by a rapid filtration technique. Phosphate uptake by brain capillaries was mediated by a saturable high-affinity system which is independent of the sodium concentration in the incubation medium. The apparent half-saturation constant (Km) and maximal influx (Vmax) were estimated to 160 microM and 0.37 nmol/mg protein/30 s. Transport was inhibited by the phosphate analogues arsenate and phosphonoformic acid with apparent inhibition constants of 5 and 11 mM, respectively. The metabolic inhibitors cyanide and ouabain had no effect on the transport activity. Competition experiments showed that phosphate uptake was inhibited up to 41% by various anions (pyruvate, acetate, citrate, glutamate, and sulfate). In addition, phosphate uptake was significantly decreased by two selective inhibitors of anionic exchangers, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid. Chloride was not a substrate of the phosphate carrier as the replacement of external chloride, by nitrate, thiocyanate, or gluconate, did not increase phosphate transport. Aminohippuric acid and N'-methylnicotinamide, two specific substrates of anionic and cationic drug exchangers, did not compete with the phosphate carrier of cerebral capillaries. However, trans-stimulation with bicarbonate increased phosphate transport by 28%, and this stimulation was inhibited by 1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, suggesting that the carrier of the cerebral capillaries could exchange phosphate with bicarbonate.     

Effect of Metalaxyl on the incidence and severity of Pearl millet downy mildew disease in Northern Nigeria

Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight.     

Gene expression and the evolution of phenotypic diversity in social wasps

Background  

Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution.     

Control of mRNA export by adenovirus E4orf6 and E1B55K proteins during productive infection requires E4orf6 ubiquitin ligase activity

During the adenovirus infectious cycle, the early proteins E4orf6 and E1B55K are known to perform several functions. These include nuclear export of late viral mRNAs, a block of nuclear export of the bulk of cellular mRNAs, and the ubiquitin-mediated degradation of selected proteins, including p53 and Mre11. Degradation of these proteins occurs via a cellular E3 ubiquitin ligase complex that is assembled through interactions between elongins B and C and BC boxes present in E4orf6 to form a cullin 5-based ligase complex. E1B55K, which has been known for some time to associate with the E4orf6 protein, is thought to bind to specific substrate proteins to bring them to the complex for ubiquitination. Earlier studies with E4orf6 mutants indicated that the interaction between the E4orf6 and E1B55K proteins is optimal only when E4orf6 is able to form the ligase complex. These and other observations suggested that most if not all of the functions ascribed to E4orf6 and E1B55K during infection, including the control of mRNA export, are achieved through the degradation of specific substrates by the E4orf6 ubiquitin ligase activity. We have tested this hypothesis through the generation of a virus mutant in which the E4orf6 product is unable to form a ligase complex and indeed have found that this mutant behaves identically to an E4orf6⁻ virus in production of late viral proteins, growth, and export of the late viral L5 mRNA.