Effects of repeated application of water stress on water status and growth of wheat

The effects on water status and growth of controlled cycles of water stress applied at various stages of development were studied on a semi-dwarf spring wheat (Triticum aestivum L.). The plants were grown in controlled environment chambers of the Duke University Phytetron at 24/18°C with a 12-h photo-period at about 600 μE m^?2 s^?1. Groups of plants were subjected to severe water stress by withholding irrigation, beginning at the 7th leaf, early anthesis, or early dough stages of development. A second cycle started 9 to 13 days after termination of the first cycle and maintained until the flag leaf water potential reached –25 bars at each of the growth stages. The lower leaves showed sign of wilting as indicated by curling in the first drying cycle at –7 bars and in the second cycle at –9 bars of leaf water potential during all stages of growth. Although these leaves recovered completely upon rewatering, onset of senescence was accelerated by three days in stressed plants. A preliminary drying cycle did not increase the ability of the plants to withstand subsequent stress because of severity of stress. Water stress of –25 bars at all three stages of growth reduced seed yield. The reduction was greater when a second stress cycle was also applied. Stress applied during early anthesis stage produced the smallest and the least number of seeds. The lack of osmotic adjustment probably was due to very rapid and severe development of water stress.     

Effects of ionic strength and relative humidity on the efflux of K+ (86Rb) and Ca2+ (45Ca) from roots of intact seedlings of cucumber, oat and wheat

Spring wheat (Triticum aestivum L. cv. Svenno), oat (Avena sativa L. cv. Brighton) and glasshouse cucumber (Cucumis sativus L. cv. Bestseller F1) were cultured for a week after germination on complete nutrient solutions of three different dilutions (1, 25 and 50% of the full strength medium). K⁺(⁸⁶Rb) and ⁴⁵Ca were present during the whole culture period. Relative humidity (RH) was 50% except during the last day, when half the material was transferred to 90% RH. Efflux of labelled ions was then followed during eight hours on unlabelled solutions of the same composition as before, and at both 50% and 90% RH in the atmosphere. – Uptake of K⁺(⁸⁶Rb) during growth tended to be saturated in the 25% medium. Contrariwise, the level of Ca²⁺ in the roots increased continuously with strength of the medium. At low concentrations cucumber roots were higher in Ca²⁺ than roots of oat or wheat, whereas all three species showed similar levels of Ca²⁺ in 50% medium. – At the lowest ionic strength, smooth efflux curves were obtained that could be resolved according to the three-compartment theory. At higher ionic strength, irregularities were observed, and more for Ca²⁺ than for K⁺; but for practical purposes compartment analysis with the same time constants could be applied as for the lowest concentration. – Discrimination between K⁺ and Rb⁺ differed between the roots, but not much between the shoots of different species. The roots of oat and wheat took up Rb⁺ preferentially over K⁺ in the 25% and 50% media; whereas K⁺ was preferred over Rb⁺ or little discrimination made in 1% medium and for cucumber. The shoots generally showed less discrimination than the roots. The main variability in discrimination between K⁺ and Rb⁺ thus appears to be localized in the tonoplasts of the roots cells. – Low RH around the shoots increased efflux of K⁺(⁸⁶Rb) from the cytoplasm and vacuoles of the root cells as compared to the efflux at high RH. DNP (2,4-dinitrophenol) in the medium had the same effect as high RH around the shoots. The signal system that must exist between shoots and roots is discussed as a response to “drought” conditions. In relation to investigations of others, it is assumed that the effect of DNP may indicate that part of the chain between roots and shoots consists of metabolically influenced sites, whose output is influenced by the rate of water transport.     

Taxonomic isolation and the accumulation of herbivorous insects: a comparison of introduced and native trees

Abstract.

• 1 Evidence from leaf-mining insects on Fagaceous hosts suggests that range expansions of insects onto introduced trees often involve species that feed on native hosts closely related to the introduced host.
• 2 An examination of the herbivorous entomofauna of British trees illustrates that the size of the entomofauna is partially determined by the taxonomic isolation of the host tree.

     

Growth of Trypanosoma cruzi in Cultures of Chick Embryo Cells, and Effects of Furazolidone and Tris (p-Aminophenyl)Carbonium Chloride

SYNOPSIS. Monolayers of cells of coverslips were produced by culturing known numbers of trypsinized chick cells in growth medium (solution 199 plus 20% calf serum) at 37 C for 2 days. The fluid was then replaced with maintenance medium (solution 199 plus 5% calf serum) containing various known numbers of T. cruzi and the preparations were incubated at 33 C for 5 days; fresh maintenance medium was substituted on the 2nd or 3rd day. The inocula of parasites were obtained from T. cruzi -cell cultures, supplemented with 2% sterile NNN overlay, or from NNN cultures.
The numbers of extracellular parasites, proportions of infected cells, and percentage distribution of infected cells relative to the number of intracellular leishmanial bodies were determined on days 2 or 3 and 5 of parasite cultivation in many experiments. Analyses of the data gave the following results. Extracellular parasites increased 2- to 14-fold during the first 2 or 3 days, depending upon the source and size of the inocula, and 10- to 20-fold during the last 2 or 3 days. Cell infection continued throughout incubation at daily rates of 1.4-4.5%; 8-22% of the cells became infected during the 5 days of incubation. Intracellular growth was reflected most clearly by increases in the proportion of cells having >10 leishmanial bodies. This increase was about 5% daily during the last 2 or 3 days of incubation.
A useful test procedure for assessing the antiparasitic action and chick embryo cell toxicity of drugs is illustrated by data obtained with furazolidone and tris ( p -aminophenyl)carbonium chloride.     

The effect of genetic transformations for pest resistance on foliar solanidine-based glycoalkaloids of potato (Solatium tuberosuni)

Foliage of potato cv. Desiree was harvested from glasshouse‐cultivated plants of five experimental transgenic lines expressing three different insecticidal proteins (snowdrop lectin, Galanthus nivalis agglutinin (GNA); jackbean lectin, Concanavalin A (Con A), cowpea trypsin inhibitor; (CpTi)), tissue‐cultured control plants and standard control (non‐tissue cultured) plants. The foliage was subdivided into stems, upper, middle and lower leaves and analysed separately by HPLC for the solanidine‐based glycoalkaloids a‐solanine and a‐chaconine. The results demonstrate that one or more stages in the plant transformation process (i.e. insecticidal‐ and marker‐gene insertions, gene expression and tissue culture) resulted in a lower level of leaf glycoalkaloids than that found in either the tissue‐cultured controls or standard controls, based on the selected potato lines transformed for insecticidal protein expression. However, the distribution of glycoalkaloids throughout the plant foliage was unaffected by genetic transformation and tissue culture, with the highest glycoalkaloid levels being observed in the top third of the plant. The importance of investigating unexpected effects of genetic engineering on plant secondary metabolism is discussed from an ecological viewpoint.     

Language, Ideology, and Political Economy

After sharply defining and contrasting an "analytic-scientific" and an "emotional-ethical" approach and their interrelations, this article goes on to explore some possible interconnections among the three main phenomena, before discussing each in more detail. The first is political economy in several important senses; germane problems are noted that deal with (ethno) quantification and the innovative individual. The second phenomenon is ideology, in three senses: (1) notional ideology, (2) ideology for maintaining or changing a sociopolitical order, and (3) ideology for masking a structure of domination. The third phenomenon is language, again in various senses, but particularly as (1) a symbolism with a structure analogous in some ways to that of economics, and (2) a mediator between ideology and political economy; considerable attention is given to the political-economic functions of language figures such as irony and synecdoche. A fourth, analytically crucial kind of ideology, "linguacultural ideology," fills in the foregoing structure. Alternative logics, alternative combinations of variables, and alternative complementary theories are suggested throughout, particularly in the final section.     

Temporal variation in temperature and rainfall differentially affects ectomycorrhizal colonization at two contrasting sites

We examined the roles that seasonal shifts in precipitation and temperature played in the ectomycorrhizal (ECM) colonization of pinyon pine ( Pinus edulis Engelm.) at two contrasting sites in northern Arizona. Pinyons growing in ash and cinder soils experienced much greater water and nutrient stress than pinyons growing nearby in sandy-loam soils. Over a one year period, we obtained monthly measurements of ECM colonization, root zone soil moisture and temperature, and air temperature and precipitation. Four major patterns emerged. Firstly, although climate as measured by ambient temperature and precipitation did not vary between the two sites, soil temperature was significantly higher and soil moisture significantly lower at the cinder site than at the sandy-loam site. Secondly, ECM colonization was significantly higher at the cinder site for 5 of 12 months. Thirdly, although nearly 70% of the variation in ECM colonization of pinyons growing in cinder soil was predicted by a combination of soil moisture and soil temperature, these same variables had little predictive power for pinyons growing in sandy-loam soils. Air temperature and precipitation were also significantly correlated with ECM colonization at the cinder site but not the sandy-loam site. Fourthly, a watering experiment showed that ECM colonization significantly increased with supplemental water at the cinder site, but not at the sandy-loam site. Thus, in two sites that did not differ in plant community or climate, ectomycorrhizas in cinder soils were far more sensitive to changes in moisture and temperature than ectomycorrhizas in sandy-loam soils.     

The self-incompatibility phenotype in brassica is altered by the transformation of a mutant S locus receptor kinase

The self-incompatible (SI) Brassica napus line W1, which carries the 910 S allele, was transformed with an inactive copy of the 910 S locus receptor kinase (SRK) gene. Two transformed lines were analyzed based on their heritable ability to set self-seed. The first line was virtually completely self-compatible (SC), and reciprocal pollinations with the original W1 line demonstrated that only the stigma side of the SI phenotype was altered. An analysis of the expression of endogenous SRK-910 demonstrated that the mechanism of transgene action is via gene suppression. Furthermore, the expression of the S locus glycoprotein gene present in the 910 allele (SLG-910), SLG-A10, which is derived from a nonfunctional S allele, and an S locus-related gene were also suppressed. When the transgene was crossed into another SI line carrying the A14 S allele, it was also capable of suppressing the expression of the endogenous genes and of making this line SC. The second transgenic line studied was only partly SC. In this case as well, only the stigma phenotype was affected, although no gene suppression was detected for endogenous SRK-910 or SLG-910. In this line, the expression of the transgene most likely was causing the change in phenotype, and no effect was observed when this transgene was crossed into the other SI line. Therefore, this work reinforces the hypothesis that the SRK gene is required, but only for the stigma side of the SI phenotype, and that a single transgene can alter the SI phenotype of more than one S allele.     

Evolution of Hoxa-11 Expression in Amphibians: Is the Urodele Autopodium an Innovation?

In this paper we present preliminary results on the expressionof Hoxa-11 in the frog Xenopus laevis and the newt Notophthalmusviridescens. In amniote limbs, Hoxa-11 is expressed exclusivelyin the prospective zeugopodium and is involved in the developmentof zeugopodial character identity. While the Hoxa-11 expressionpattern in Xenopus is similar to those described in mice andchick, the newt Notophthalmus has a phase of autopodial Hoxa-11expression starting with the development of digit III. Expressionis particularly strong in the buds of the postaxial digits.This Hoxa-11 expression pattern is unique among tetrapods andadds to the list of developmental peculiarities of urodele limbdevelopment, which also include an anterior to posterior polarityof digit development. We propose a scenario to explain the evolutionaryorigin of urodele limb development. We assume that recent urodelesare derived from a lineage of amphibians which underwent partialdigit reduction, leaving only two digits intact, most likelydigits III and IV according to Morse's law. This implies thaturodele digits I and II are homologous to amniote digits IIIand IV, and that the postaxial digits of urodeles are an evolutionaryinnovation (re-invention). Supporting evidence for this homologyhypothesis is found in the developmental connections betweenthe basale commune and the postaxial zeugopodial element.     

A giant Upper Jurassic turtle revealed by its trackways

Exceptional fossilization of large tetrapod swimming traces occurs in the Cerin Lagerstätte (Jura Mountains, France). These trackways are imprinted in Jurassic (Late Kimmeridgian) lagoonal fine-grained limestones and are attributed to giant turtles, which swam with a simultaneous movement of their forelimbs like the modern ones. These turtles swam in very shallow waters close to land, perhaps near a nesting area. As a major consequence, these new ichnologic data place the origin of true large marine turtles during the Jurassic period and not during the Cretaceous period as previously considered on the basis of skeletal remains.