Effect of α-amanitine on puffing and intranuclear RNA synthesis in Chironomus salivary glands

Incubation of Chironomus salivary glands with -amanitine in concentrations from 1 to 10 /ml results in the suppression of puffing and chromosomal ³H-uridine incorporation after 30 to 60 min in 80% of the cells. Nucleolar ³H-uridine incorporation remains completely unaffected. Even 4 h after the injection of high doses of -amanitine into living larvae, nucleolar incorporation is still pronounced. The distribution of resistant cells within the salivary glands suggests that the uptake of -amanitine is subject to physiological restrictions.—A puff typically induced during in vitro incubation of salivary glands was found to be less sensitive to -amanitine than the Balbiani rings.     

Phytochrome dependent decrease of gibberellin-sensitivity

Exogenous gibberellin removes the genetical suppression of mesocotyl elongation in dark-grown seedlings of the rice cultivar Nihon Masari (japonica type). This gibberellin effect can be cancelled by light. All light effects can be accounted for by phytochrome. Dose-response and fluence-response studies show that phytochrome induces a reduction of the sensitivity to exogenous gibberellins. A cytological analysis of cell elongation and cortical microtubules led to a model where gibberellin and red light regulate mesocotyl elongation by controlling microtubule orientation in the epidermis of the mesocotyl. This causes corresponding changes of cellular extension growth, which can account for a large part of the observed growth responses. Comparative studies involving antimicrotubular drugs and gibberellin-synthesis inhibitors in the rice cultivar Kasarath (indica type) and a hybrid cultivar suggest that some of the differences between the cultivars are due to differences in gibberellin-sensitivity.     

Functional analysis of a complex oncogene arrangement in biotype III Agrobacterium tumefaciens strains

The ubiquitous grapevine-associated octopine/cucumopine Ti plasmids of biotype III Agrobacterium tumefaciens strains carry two T regions, TA and TB, with a complex oncogene arrangement. Within the octopine/cucumopine group, two main strain types were identified: large TA strains with a TA region resembling the TL region of the biotype I octopine strain Ach5 and small TA strains with a similar T region organization as the large TA strains but with a large internal TA deletion. Structural and functional studies of the representative large TA strain Tm4 revealed six oncogenes. Each oncogene was inserted in a disarmed vector and tested for biological activity using the corresponding oncogenes of Ach5 as standards. Five Tm4 oncogenes, TA-iaaM, T-ipt, T-6b, TB-iaaH and TB-iaaM, were shown to be active, the IS-interrupted TA-iaaH gene was inactive. To study the role of each gene in the pTiTm4 context, several single and multiple pTiTm4 mutations were constructed. It was shown that whereas TA-iaaM and TB-iaaH are essential for tumour formation on grapevine, T-ipt, T-6b and TB-iaaM are not. The avirulence of the TA-iaaM ^- mutant was shown to be due to an inhibitory effect of the T-ipt gene, since a TA-iaaM ^- /T-ipt ^- double mutant was fully virulent. We conclude that the TA-iaaM gene of large TA strains is specifically required to counteract the tumour growth inhibiting activity of the T-ipt gene. Both TA-iaaM and T-ipt are absent from the small TA strains. A model on the roles and interactions of the different oncogenes in large TA and small TA strains is presented.     

Blastomycosis: Report of the first case from Alberta,Canada

The first known case of laboratory confirmed blastomycosis in Alberta occurred in 1970. The patient, who is believed never to have left Alberta, presented with of headaches, sore neck and impaired intellect. Initially, tuberculous or cryptococcal meningitis was suspected, but laboratory findings did not support the diagnosis. A fungus resembling Blastomyces dermatitidis was isolated from the venticular cerebrospinal fluid and lung at autopsy. A few yeast cells suggestive of B. dermatitidis were seen in lung and brain tissue sections. Initial attempts at in vitro conversion of the mycelial form of the isolate into yeast form on several enriched media were unsuccessful. The fungus gave ± to ++ reactions with B. dermatitidis specific conjugate by the direct fluorescent antibody technique, it was not pathogenic for mice and guinea pigs, and no asexual spores were produced in slide cultures. Further investigation indicated that the mycelial form of the fungus converted into its yeast form when an actively growing inoculum was used, although the yeast cells varied considerably in size. The yeast form produced disseminated infection in mice within 10 days. Exoantigenic analysis demonstrated an A antigen specific for B. dermatitidis, which revealed the identity of this organism as an atypical strain of B. dermatitidis.

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Zusammenfassung Der erste Fall in Blastomycosis von einem Laboratorium wurde 1970 in Alberta bestätigt. Der Patient — der wahrscheinlich Alberta nie verlassen hat — klagte über Kopfschmerzen, Genickschmerzen und zeigte beeinträchtigte Verstand. Anfänglich wurde TBC — oder cryptococcal meningitis vermutet, laborfunde unterstutzten jedoch nicht die Diagnose. Ein Fungus — ahnlich zum Blastomyces dermatitidis wurde von venticular cerebrospinal Flüssigkeit und von der Lunge nach der Autopsie isoliert. Wenige Hefezellen hinweisend auf B. dermatitidis wurden gewebschnitten von Lunge und Gehirn festgestellt. Anfängliche Versuche die isolierten mycel Form in die Hefe Form in vitro mit Hilfe verschiedener angereicherter Nahrboden was erfolglos. Der Fungus ergab in der Direct Fluorescent Antibody Technik. ± zu ++ Reaktion mit dem B. dermatitidis specifische Konjugate; es war nicht pathogen fur Mause und Meerschweinchen, asexual Sporen wurden in der objecttrage Kultur produziert. Weitere Untersuchungen zeigten, dass sich die mycel Form des Fungus in die Hefeform umwandelte wenn ein gut wachsendes Inoculum gebraucht wurde. Die Hefezellen zeigten jedoch beträchtliche Grossenunterschiede. Die Hefeform verursachte in Mauseneine generallisierte Infektion in inerhalb von 10 Tagen. Exoantigenik Analyse zeigte ein A Antigen, specifisch für B. dermatitidis, welches die Identität des Organismus als atypischen Stamm des B. dermatitidis aufwies.

     

Evaluation of an exotic maize population adapted to a locality

Summary An exotic Zea mays L. population (Tuxpeno) was adapted to North Carolina conditions by first introducing genes for adaptability from two North Carolina varieties ([(Jarvis X Indian Chief)Tuxpeno]Tuxpeno) including four generations of intermating, and then selecting for adaptability using maturity as the primary measure. The study evaluated selection for adaptability and the diversity available between adapted Tuxpeno and the local varieties, Jarvis and Indian Chief. Analytical procedures were developed to quantify the diversity between populations and the complementation of local varieties by introduced germ plasms. The analyses utilized the specific effects available from the diallel mating design.Three replicate selections responded similarly under simple recurrent mass selection (1/10) for the earliest disease-free plants initially and additionally for plant types (primarily height) in the final generation. The 1/4 local germ plasm permitted rapid adaptation of Tuxpeno gene pool to local conditions. The adapted Tuxpeno populations yielded similarly to the local populations with an average heterosis for grain yield of 28% when crossed to the local populations used as source of genes for adaptability. The diversity found between adapted Tuxpeno lines and these local varieties based on genes affecting grain yield was 1.5 to 2.5 times that measured between the local varieties (Jarvis and Indian Chief). Diversity lost through intergradation with local material was a reasonable investment. Yield genes introduced from Tuxpeno complemented local gene pools through nonadditive, primarily dominance-associated, gene effects. Reassortment of major gene blocks apparently occurred leading to significant divergence among replicate selections involving both additive-associated and dominance-associated gene effects.Paper No. 6355 of the North Carolina Agri. Res. Ser., Raleigh, NC. Research supported in collaboration with the Rockefeller Foundation and CIMMYT, D.F. (Mexico)     

Regional differences in the distribution of golgi cells in the cerebellar cortex of man and some other mammals

Summary The number of Golgi cells per unit volume was determined in different regions of the cerebellar cortex of man and of ten other mammals. Despite the general belief in the uniform architecture of the cerebellar cortex, regional differences in the distribution of Golgi cells were found. In the inferior parts of the vermis, the number of Golgi cells per unit volume is twice that in the corresponding hemispheres. In addition, there are differences between the anterior and inferior parts of the vermis. These differences are a feature of the cytoarchitecture of the cerebellum in man and all the investigated mammals. The ratio of Purkinje cells to Golgi cells was also determined and found to differ in different species. In man, this ratio is 11.5, while in the monkey and cat it is almost 11.9 and in the rat 13.3. These differences in the ratio of Purkinje cells to Golgi cells are discussed from the point of view of cerebellar evolution.Supported by the Deutsche Forschungsgemeinschaft.     

Phenotypic analyses of lymphokine-activated killer cells that release interferon γ and tumor necrosis factor α

Summary We recently reported that interleukin-2(IL-2)-activated peripheral blood lymphocytes and CD3⁺, lymphokine-activated killer (LAK) cell clones release tumor necrosis factor (TNF) and interferon (IFN) when stimulated with K562 erythroleukemia cells. We examined the phenotype of IL-2-activated peripheral blood leukocytes that secrete TNF and IFN when stimulated with K562 cells and demonstrated that TNF secretion is not due to the presence of contaminating mononuclear phagocytes. Further, we demonstrate that IL-2-activated natural killer (NK) cells release only IFN when stimulated with K562 cells while T lymphocytes exposed to monoclonal anti-CD3 and K562 cells secrete both TNF and IFN. However, T cells stimulated only with K562 cells did not release IFN or TNF while the admixture of these T cells with NK cells, when stimulated with K562 cells, released levels of TNF comparable to those produced by the unseparated cells. At present it is unclear whether only one or both effector cell types respond to K562 by releasing TNF or why the presence both cell types is needed.This work was supported by grants from the national Institutes of Health (CA 23074 and CA 17094) and the Arizona Disease Commission (8277-000000-1-0-YR-9301)     

Adoptions expérimentales de larves entre des fourmis de genres différents (II):Myrmica laevinodis Nylander etAnergates atratulus Schenck

Résumé Nous avons fait élever des larves d'Anergates atratulus par des ouvrières deMyrmica laevinodis à 22°C. Pour y parvenir, il n'est pas utile de faire hivernerensemble les larves d'Anergates et les ouvrières deMyrmica. La présence de larves autochtones n'empêche pas lesMyrmica d'élever des larves d'Anergates. Dans toutes les expériences lesMyrmica ont été soumises au fridavant de recevoir des larves d'Anergates. Aucune reine deMyrmica n'a été utilisée dans ces expériences.Sur les 64 larves d'Anergates que nous avons utilisées, 38 se sont transformées en imagos. C'est au début de l'adoption et au moment des métamorphoses que périrent la plupart des 26Anergates perdus. Les femelles vécurent en général 2 ou 3 jours et cherchèrent très tôt à quitter le nid natal. Les mâles vécurent 2 à 3 semaines.

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Summary Larvae ofAnergates atratulus were experimentally reared by workers ofMyrmica laevinodis, at 22°C. An overwintering of both larvae ofAnergates and workers ofMyrmica is not necessary for the success of that experiment. The presence of larvae ofMyrmica does not keep theMyrmica from rearing larvae ofAnergates. The workers ofMyrmica have been cooled, in all the experiments, before receiving larvae ofAnergates. No queen ofMyrmica have been used in that experiments.38 of the 64 larvae ofAnergates used became imagos. Most of the 26 lostAnergates died at the beginning of the adoption and during the metamorphosis. The females lived generally 2 or 3 days and tried, very early, to leave their native nest. The males lived 2 or 3 weeks.

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Anergates atratulus Myrmica laevinodis, 22 . bmecme Anergates Myrmica. Myrmica Anergates. Myrmica Anergates. Myrmica . 64 Anergates , 38 . 26 Anergates 2 3 . 2 3 .

     

Life cycle of Calanus chilensis Brodsky in Bay of San Jorge,Antofagasta, Chile

The copepod Calanus chilensis is an endemic component of the zooplankton community in northern Chile. Size distributions of adult females, relative frequency of copepodid stages and relative numbers of adult males and nauplii, suggest the presence of at least 6 generations during the year, although the species seems to continuously reproduce through all seasons. Temperature profiles from 0 to 175 m indicated the presence of the El Niño current during March and April. Surface temperature ranged between 21.1 and 13.1 °C. Warm waters during the El Niño event seemed to affect the body size of adult females and the normal course of cohort development, although the population tended to recover rapidly through the subsequent months. We discuss the role of oceanographic conditions in controlling the life cycle of this species, as well as its continuous growth through the year compared to other Calanus species.     

Chromosomal loci of genes controlling site-specific restriction endonucleases of Bacillus subtilis

Summary In Saccharomyces cerevisiae, diploid strains which are respiratory deficient (e.g., rho^–) or are homozygous for the mating-type locus (i.e., either a/a or /) are unable to sporulate. In order to induce sporulation in these nonsporulating strains, the technique of protoplast fusion mediated by polyethylene glycol was adopted. In this study, the products of protoplast fusion were induced to sporulate without reversion to normal cells.Protoplasts from a respiratory-deficient diploid strain were mixed with those from a respiratory-competent haploid one carrying mitochondrial drug resistance markers, treated with 30% polyethylene glycol-4000 and 25 mM CaCl₂, and incubated in 0.1 M potassium acetate containing 0.8 M sorbitol as an osmotic stabilizer. After two days' incubation, asci with three to eight spores were formed at a frequency of 1×10^–3 to 2×10^–4. Sporulation was also observed in products of fusion between an a/a diploid and haploid strains and between an / diploid and a haploid strains. The analysis of the genotypes of spores revealed that when fusion products were cultured under conditions for sporulation, karyogamy did not take place, diploid nuclei underwent meiosis, and both diploid and haploid nuclei were able to develop into spores.     

The assignment of a Thinopyrum distichum (Thunb.) Löve-derived translocation to the long arm of wheat chromosome 7D using endopeptidase polymorphisms

Summary Endopeptidase zymograms of the translocation line Indis revealed the presence of several major and minor bands that had differential expression in coleoptile and seed tissues. While Indis lacks Ep-D1a, which is present in the parental cultivar Inia 66, it also may not express any of the Th. distichum bands. The Indis zymogram was found to be identical to that of an isogenic line of Inia 66 possessing Lr19. Since the absence of an Ep-D1a product appears to be linked to the 7DL translocation, it is possible to use the null condition as a marker for both the Lr19 or Indis translocations. The Indis translocation also did not show recombination with the cn-D1 chlorophyl mutant on 7DL, confirming that a part of 7D was involved. The results of a telocentric mapping experiment involving the 7D telosomes indicated that in Indis a chromosome segment from Th. distichum replaced a large section of 7DL of Inia 66.     

Observations on the reduction of non-activated carboxylates by Clostridium formicoaceticum with carbon monoxide or formate and the influence of various viologens

Crude extracts or supernatants of broken cells of Clostridium formicoaceticum reduce unbranched, branched, saturated and unsaturated carboxylates at the expense of carbon monoxide to the corresponding alcohols. The presence of viologens with redox potentials varying from E ₀=-295 to-650 mV decreased the rate of propionate reduction. The more the propionate reduction was diminished the more formate was formed from carbon monoxide. The lowest propionate reduction and highest formate formation was observed with methylviologen. The carbon-carbon double bond of E-2-methyl-butenoate was only hydrogenated when a viologen was present. Formate as electron donor led only in the presence of viologens to the formation of propanol from propionate. The reduction of propionate at the expense of a reduced viologen can be followed in cuvettes. With respect to propionate Michaelis Menten behavior was observed. Experiments are described which lead to the assumption that the carboxylates are reduced in a non-activated form. That would be new type of biological reduction.Non-standard abbreviations glc Gas liquid chromatography - HPLC high performance liquid chromatography - RP reverse phase; Mediators (the figures in parenthesis of the mediators are redox potentials E ₀ in mV) - CAV²⁺ carbamoylmethylviologen, 1,1-carbamoyl-4,4-dipyridinium dication (E ₀=-296 mV) - BV²⁺ benzylviologen, 1,1-dibenzyl-4,4-dipyridinium dication (E ₀=-360 mV) - MV methylviologen, 1,1-dimethyl-4,4-dipyridinium-dication (E ₀=-444 mV) - DMDQ²⁺ dimethyldiquat, 4,4-dimethyl-2,2-dipyridino-1,1-ethylendication (E ₀=-514 mV) - TMV²⁺ tetramethylviologen, 1,1,4,4-tetramethyl-4,4-dipyridinium dication (E ₀=-550 mV) - PDQ²⁺ propyldiquat, 2,2-dipyridino-1,1-propenyl dication (E ₀=-550 mV) - DMPDQ²⁺ dimethylpropyldiquat, 4,4-dimethyl-2,2-dipyridino-1,1-propenyl dication (E ₀=-656 mV) - PN productivity number=mmol product (obtained by the uptake of one pair of electrons) x (biocatalyst (dry weight) kg)^-1×h^-1     

Metabotropic Glutamate Receptors Stimulate Phospholipase D via Different Pathways in the Adult and Neonate Rat Hippocampus

In order to characterize the ontogenetic profile of metabotropic glutamate (mGlu) receptors coupled to phospholipase D (PLD) we examined the effects of selected mGlu agents on PLD activity in immature and adult rat hippocampus. The group I mGlu receptor agonist 3,5-dihydroxyphenylglycine stimulated PLD in immature tissue, but reduced the PLD response evoked by the nonselective mGlu receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate [(1S,3R)-ACPD] in adult hippocampus. (2R,1S,2R,3S)-2-(2-Carboxy-3-phenylcyclopropyl)glycine (PCCG-13), a recently characterized selective antagonist of PLD-coupled mGlu receptors, displayed a much greater activity in reducing the PLD response to (1S,3R)-ACPD in adult than in neonate hippocampus. Our results lend support to the hypothesis that glutamatergic activation of PLD in the rat hippocampus is developmentally regulated.     

Effect of phosphorus supply on phosphate uptake and alkaline phosphatase activity in Rhizobia

The effect of P nutrition on phosphate uptake and alkaline phosphatase activity was studied in chemostat culture for four rhizobial and three bradyrhizobial species. Phosphate-limited cells took up phosphate 10- to 180-fold faster than phosphate-rich cells. The four fast-growing rhizobial strains contained high levels of alkaline phosphatase activity under P-limited conditions compared to the repressed levels found in P-rich cells; alkaline phosphatase activity could not be detected in three slow-growing rhizobial strains, regardless of their P-status.Glycerol 1-phosphate-uptake in the cowpea Rhizobium NGR234 was derepressed over 50-fold under P-limited conditions, and appeared to be co-regulated with phosphate uptake.The phosphate-uptake system appeared similar in all strains with apparent K _m values ranging from 1.6 M to 6.0 M phosphate and maximum activities from 17.2 to 126 nmol · min^-1 · (mg dry weight of cells)^-1. Carbonyl cyanide m-chlorophenyl hydrazone strongly inhibited phosphate uptake in all strains and a number of other metabolic inhibitors also decreased phosphate uptake in the cowpea Rhizobium NGR234. The phosphate uptake system in all strains failed to catalyse exchange of ³²P label in preloaded cells or efflux of phosphate. The results suggest a single, repressible, unidirectional and energy-dependent system for the transport of phosphate into rhizobia.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - DCCD N,N-dicyclohexylcarbodiimide - HEPES N-2-hydroxyethyl-piperazine-N-2-ethanesulphonic acid     

Molecular mapping of a new gene Rrs4 CI 11549 for resistance to barley scald (Rhynchosporium secalis)

Doubled haploid (DH) progeny from a cross between the scald susceptible barley (Hordeum vulgare L.) cultivar Ingrid and the resistant accession CI 11549 (Nigrinudum) was evaluated for resistance in the pathogen Rhynchosporium secalis (Oudem) J.J. Davis. Two linked and incompletely dominant loci confer resistance CI 11549 against isolate 4004. One is an allele at the complex Rrs1 locus on chromosome 3H close to the centromere; the other is located 22 cM distally on the long arm. The latter locus is designated Rrs4. In BC₃-lines into Ingrid from CI 2222 (another Nigrinudum) resistance seems governed by one locus close to the telomeric region of chromosome 7H, probably allelic to Rrs2. In neither case did we find any trace of the recessive gene rh8 reported to be present in Nigrinudum. Various resistance donors of Ethiopian origin designated as Nigrinudum, Jet or Abyssinian were identical to a great extent with respect to markers, but differed in resistance to different isolates of scald or in barley yellow dwarf virus (BYDV) resistance. The implications for their use as differentials in scald tests and screening of germplasm collections are discussed.     

A novel wheat alpha-amylase gene (alpha-Amy3)

Summary A genomic clone of a wheat -amylase gene (Amy3/33) was identified, on the basis of hybridisation properties, as different from -Amy1 and -Amy2 genes which had been characterised previously. The nucleotide sequence revealed that this gene has the normal sequence motifs of an active gene and an open reading frame interrupted by two introns. The protein sequence encoded by this open reading frame is recognisably similar to that of -amylase from the -Amy1 and -Amy2 genes and there is high sequence homology in all three proteins at the putative active sites and Ca⁺⁺ binding region. In addition, the introns are at positions equivalent to the position of introns in the -Amy1 and -Amy2 genes. However, the sequence was less similar to -Amy1 and -Amy2 than these are to each other. Southern blot analysis showed that the Amy3/33 DNA is one of a small multigene family carried on a different chromosome (group 5) from either the -Amy1 or -Amy2 genes. A further difference from the -Amy1 and -Amy2 genes was the pattern of expression. Amy3/33 was expressed only in immature grains and, unlike the -Amy1 and -Amy2 genes, not at all in germinating aleurones. These data suggested therefore that this gene represents a third type of -amylase gene, not described before, which shares a common evolutionary ancestor with the -Amy1 and -Amy2 genes.     

Characterization of phosphoinositide hydrolysis products induced by hexachlorocyclohexane isomers in rat brain cortex

Water-soluble inositol metabolites were separated by anion-exchange chromatogrphy in order to determine whether or not -hexachlorocyclohexane (-HCH, lindane) and related compounds affect phosphatidylinositol hydrolysis in rat brain cortex slices. Hydrolysis was increased by -and -HCH, while - and -HCH were inactive. Muscarinic receptor stimulation of rat cortical slices with carbachol increases inositol phosphates formation. The combined effect of carbachol and the hexachlorocyclohexane isomers together were approximately equal to the sum of the effect of each one separately. The results suggest that lindane stimulates phosphoinositide phospholipase C and/or inhibits the phosphases implicated in dephosphorylation of inositol phosphates.     

Oxygen and carbon isotope composition of parasitic plants and their hosts in southwestern Australia

We measured leaf dry matter ¹⁸O and ¹³C in parasitic plants and their hosts growing in southwestern Australia. Parasite/host pairs included two mistletoe species, three species of holoparasites, and five species of root hemiparasites. Among these parasite functional types, significant variation was observed in parasite/host isotopic differences for both ¹⁸O (P<0.0001, n=65) and ¹³C (P<0.0001, n=64). Mistletoes were depleted in both ¹⁸O and ¹³C compared to their hosts; parasite/host differences were –4.0 for ¹⁸O (P<0.0001) and –1.9 for ¹³C (P<0.0001). The lower ¹⁸O in mistletoe leaf dry matter compared to their hosts is consistent with the frequently observed high transpiration rates of these parasites. Root hemiparasites were also depleted in ¹⁸O and ¹³C compared to their hosts, but not to the same extent as mistletoes; parasite/host differences were –1.0 for ¹⁸O (P=0.04) and –1.2 for ¹³C (P=0.0006). In contrast to mistletoes and root hemiparasites, holoparasites were enriched in both ¹⁸O and ¹³C compared to their hosts; parasite/host differences were +3.0 for ¹⁸O (P<0.0001) and +1.5 for ¹³C (P=0.02). The enrichment in ¹⁸O for holoparasite dry matter did not result from more enriched tissue water; holoparasite tissue water ¹⁸O was less than host leaf water ¹⁸O by a difference of –3.8 when sampled at midday (P=0.0003). Enrichment of holoparasites in ¹³C compared to their hosts is consistent with a generally observed pattern of enrichment in heterotrophic plant tissues. Results provide insights into the ecology of parasitic plants in southwestern Australia; additionally, they provide a context for the formulation of specific hypotheses aimed at elucidating mechanisms underlying isotopic variations among plants.     

Depth distribution of Campostoma grazing scars in an Ozark stream

Synopsis Campostoma spp., widespread and abundant herbivorous minnows of eastern North America, produce distinctive grazing scars when feeding on algae attached to natural substrates in streams. These scars are particularly prominent upon the low growth forms of blue-green algae that dominate the attached algal flora of many upland streams. In one stream pool in the Ozark uplands of Oklahoma, numbers and sizes of grazing scars coincided with numbers and sizes of individual Campostoma that occurred across a depth gradient, demonstrating that the information contained in the scars can provide quantification of microhabitat use and grazing intensity of these important herbivores. The results also support the hypothesis that in environments free of aquatic predators, larger fish use deeper parts of available stream habitats, particularly if threats from terrestrial or avian predators exist.     

Tolerance to a whitefly-transmitted virus causing muskmelon yellows disease in Spain

Summary Muskmelon yellowing disease was one of the most serious problems affecting muskmelon crops along the south-east coast of Spain throughout the 1980s. The causal agent of this disease is a virus that we call muskmelon yellows virus (MYV); MYV is transmitted by the greenhouse whitefly Trialeurodes vaporariorum Westwood. It has proven impossible to find sources of resistance to MYV within a wide collection of Spanish muskmelon landraces and exotic varieties. However, Nagata Kin Makuwa and PI 161375, lines of Asiatic origin, show tolerance to this disease. These two lines were studied together with two others (Galia and Piel de Sapo type) that are very susceptible to MYV. The crosses between them (susceptible x tolerant) and the segregant generations derived from these crosses were also investigated. The studies were carried out in two different places and years. The expression of tolerance is influenced by the environment. A parabolic type relationship exists between the average value of percentage of tolerant plants and their variation. This allowed us to quantify the expected response in the segregant generations. The results observed in these generations agreed with a simple genetic control of tolerance. This tolerance, combined with protective measures which delay the infection, can contribute notably to mitigating the effects of MYV.