Xylem perfusion of tap root segments of Plantago maritima: the physiological significance of electrogenic xylem pumps

Abstract A method is described for perfusing xylem vessels in tap root segments of the halophyte P. maritima. Use of excised segments allowed recording of the trans-root potential (TRP) at both ends of a segment. It was shown that there can be a spatial variation of electrogenic ion pump activity along the xylem in one root segment. The pH of perfusion solutions, differing in buffering capacity, was adjusted by the root segment to pH 5.1–5.6 during How through the xylem. This pH range was similar to that of sap produced by root pressure. The K⁺ activity in the outflow solution (K⁺_out) was rather constant at 12–13 mol m^?l3 despite input K⁺ activities ranging from 8 to 20 mol m^?l3. Addition of fusicoccin (10^?l2 mol m^?l3) to the perfusion solution induced a strong acidification of the xylem sap, a decrease in K⁺_out and an increase in Na⁺_out. Inhibition of aerobic respiration through anoxia inhibited electrogenic proton pumping into the xylem and led to an increase in K⁺_out and a decrease in Na⁺_out. It is suggested that transport of K⁺ and Na⁺ to the shoot of the halophyte P. maritima is regulated in the tap root by means of ion exchange between xylem vessels and xylem parenchyma and that this exchange is energized by proton translocating ATPases.     

绒毛膜促性腺激素及其α、β亚单位抗体的抗生育作用

本文研究结果证明给小白鼠子宫分别注射特异的抗hCG及其α、β亚单位血清后,唯有抗hCG及β亚单位血清能表现出显著的抗生育作用。这一结果在经纯化过的hCG及卢亚单位免疫球蛋白G的相同实验中也得到了验证。从而证实着床前的小白鼠胚泡中存在hCG样糖蛋白物质。 特别使人感兴趣的是这类抗体只对妊娠第三天的小白鼠胚泡的着床有明显的抑制效应,这是一个前所未曾遇见的问题。     

Photo-oxidative Degradation of Chlorophyll-a and Unsaturated Lipids in Liposomal Dispersions at Low-Temperature

Liposomal dispersions in water were used as a tool to study photo-oxidation of chlorophyll-a and photo-oxidation of unsaturated lipids at 1 or 4°C. The presence of monogalactosyl diglyceride stimulated chlorophyll-a degradation. In addition the level of linolenic acid was decreased in liposomal dispersions containing chlorophyll-a, dipalmitoyl phosphatidyl choline, and monogalactosyl diglyceride, indicating that monogalactosyl diglyceride and chlorophyll-a were coupled in the preparations. In liposomal dispersions containing equal (molar) quantities of a-tocopherol, monogalactosyl diglyceride, and chlorophyll-a, a-tocopherol fully protected linolenic acid against photo-oxidative degradation, while chlorophyll-a degradation was only slightly reduced. In liposomal preparations containing a-tocopherol, chlorophyll-a and phosphatidyl choline, a-tocopherol catalyzed degradation of chlorophyll-a. Absorption spectra of the liposomal dispersions showed that the presence of a-tocopherol caused increased absorption in red light, which was attributed to structural changes in the liposomal preparations and thus could explain the noted effects. Tocopherol itself was rapidly degraded in chlorophyll-a containing liposomal preparations. Complex formation between chlorophyll-a and monogalactosyl diglyceride in chloroplasts is suggested and protection by a-tocopherol against photo-oxidation in chilling-sensitive plants; a suggestion which is founded on the similarities that exist between chloroplast preparations and liposomal preparations containing chlorophyll-a and monogalactosyl diglyceride as regards photo-oxidative degradation of chlorophyll-a, a-tocopherol and linolenic acid.     

Effect of α-Tocopherol, β-Carotene, Monogalactosyldiglyceride and Phosphatidylcholine on Light-Induced Degradation of Chlorophyll a in Acetone

The effect of α-tocopherol, β-carotene, monogalactosyldi-glyceride and phosphatidylcholine on red light induced degradation of chlorophyll a was studied in acetone at 4°C. Monogalaclosyldi-glyceride was ineffective up to a molar ratio of monogalactosyldi glyceride to chlorophyll of 1:10. α-Tocopherol, β-carotene and phosphatidylcholine inhibited chlorophyll degradation. Maximal protection by α tocopherol and β-carotene was similar (76%) but on a molar basis a tocopherol was less effective. Protection by phosphatidylcholine was less than by a tocopherol and α-carotene but the lipid was effective at a lower ratio of chlorophyll to protectant. Inhibition by phosphatidylcholine was independent of the degree of unsaturation of the fatty acids. Effects of β-carotene and α-tocopherol were additive at suboptimal concentrations, but addition did not increase the maximal protection of 76% by these substances alone. Phosphatidylcholine increased the effectiveness of α-tocopherol and β-carotene independent of their concentrations. It is suggested that interactions between lipids participate in the mechanism protecting chlorophyll a against photooxidation in the chloroplast membrane.     

Influence of ecdysterone, precocene and compounds with juvenile hormone activity on induction, termination and maintenance of diapause in the parasitoid wasp, Nasonia vitripennis

ABSTRACT. Using the Galleria bioassay, no difference could be found between the JH titre of diapausing and developing Nasonia larvae. Compared to the values found in some Lepidoptera, the JH titres in Nasonia larvae are low, c. 14 Galleria units/g live weight. Induction of diapause could not be brought about by topical application of JH I, JH analogues, precocene, or ecdysterone to the maternal generation, nor by treating eggs or larvae with compounds with JH activity. Diapause was easily terminated by topical application of ecdysterone, however. If ecdysterone treatment was preceded by JH-treatment, the percentage of larvae terminating diapause was reduced: JH II seems to be more potent than JH I or JH III in this effect if the interval between JH and ecdysterone treatment is 72 h.     

A Comparison of Methods and the Validity of Deoxyribonuclease Tests for the Characterization of Staphylococci Isolated from Animals

Strains isolated from pigeons belonging to the coagulase-positive species Staphylococcus intermedius , coagulase-negative Staph. hyicus subsp. chromogenes strains from cattle and pigs, and Staph. aureus strains from poultry, gave weakly positive reactions in DNase plate culture tests and heat-resistant DNase tests. Staph. aureus and Staph. intermedius strains from other sources and coagulase-negative and coagulase-positive Staph. hyicus subsp. hyicus strains reacted strongly in these tests. A standardized plate culture test procedure is proposed and the use of DNase tests in the identification of staphylococci isolated from animals is discussed.     

The evolution of the phenotypic covariance matrix: evidence for selection and drift in Melanoplus

Phenotypic variation in trait means is a common observation for geographically separated populations. Such variation is typically retained under common garden conditions, indicating that there has been evolutionary change in the populations, as a result of selection and/or drift. Much less frequently studied is variation in the phenotypic covariance matrix (hereafter, P matrix), although this is an important component of evolutionary change. In this paper, we examine variation in the phenotypic means and P matrices in two species of grasshopper, Melanoplus sanguinipes and M. devastator. Using the P matrices estimated for 14 populations of M. sanguinipes and three populations of M. devastator we find that (1) significant differences between the sexes can be attributed to scaling effects; (2) there is no significant difference between the two species; (3) there are highly significant differences among populations that cannot be accounted for by scaling effects; (4) these differences are a consequence of statistically significant patterns of covariation with geographic and environmental factors, phenotypic variances and covariances increasing with increased temperature but decreasing with increased latitude and altitude. This covariation suggests that selection has been important in the evolution of the P matrix in these populations Finally, we find a significant positive correlation between the average difference between matrices and the genetic distance between the populations, indicating that drift has caused some of the variation in the P matrices.     

Aminoacylation and conformational properties of yeast mitochondrial tRNA mutants with respiratory deficiency

We report the identification and characterization of eight yeast mitochondrial tRNA mutants, located in mitochondrial tRNA(Gln), tRNA(Arg2), tRNA(Ile), tRNA(His), and tRNA(Cys), the respiratory phenotypes of which exhibit various degrees of deficiency. The mutations consist in single-base substitutions, insertions, or deletions, and are distributed all over the tRNA sequence and structure. To identify the features responsible for the defective phenotypes, we analyzed the effect of the different mutations on the electrophoretic mobility and efficiency of acylation of the mutated tRNAs in comparison with the respective wild-type molecules. Five of the studied mutations determine both conformational changes and defective acylation, while two have neither or limited effect. However, variations in structure and acylation are not necessarily correlated; the remaining mutation affects the tRNA conformation, but not its acylation properties. Analysis of tRNA structures and of mitochondrial and cytoplasmic yeast tRNA sequences allowed us to propose explanations for the observed defects, which can be ascribed to either the loss of identity nucleotides or, more often, of specific secondary and/or tertiary interactions that are largely conserved in native mitochondrial and cytoplasmic tRNAs.