Chloroplast and cytoplasmic low-molecular-weight ribonucleic acid components of the leaf of Vicia faba L

1. A method for the extraction of plant nucleic acids and their separation on methylated-serum-albumin-kieselguhr columns is described. It is demonstrated that the characteristics of the elution profiles of material from the same source are consistently reproducible. 2. Major dissimilarities were found in the elution profiles of nucleic acids from root and from leaves of Vicia faba L. These dissimilarities were confirmed by polyacrylamide-gel electrophoresis. 3. Four distinct types of low-molecular-weight RNA were demonstrated to be present in leaves, clearly distinguished by their behaviour when chromatographed on methylated-serum-albumin-kieselguhr columns. (a) Both cytoplasmic and chloroplast ribosomes contained a low-molecular-weight RNA, and these components were distinct from each other. (b) The chloroplast possessed a unique ;soluble' RNA (i.e. RNA that is not precipitated by centrifugal forces that sediment ribosomes) which was not present in the rest of the cell. (c) A soluble component, probably transfer RNA, was found in both the chloroplasts and in the cytoplasm. 4. The components distinguishable by methylated-serum-albumin-kieselguhr column chromatography could not be distinguished by sucrose-density-gradient centrifugation.     

Evidence for histidine in the active site of papain

Papain was irreversibly inhibited by 1,3-dibromoacetone, a reagent designed to react first with the active-site cysteine residue and subsequently with a second nucleophile. The molecular weight of the inhibited enzyme was indistinguishable from that of papain itself, and no evidence of dimeric or oligomeric species was found. The optical-rotatory-dispersion curves of chloroacetone-inhibited papain and 1,3-dibromoacetone-inhibited papain were essentially similar. Amino acid analysis of the 1,3-dibromo[2-¹⁴C]acetone-inhibited enzyme and the performic acid-oxidized material clearly showed that a cysteine and histidine residue had been alkylated through the thiol and N-1 of the imidazole group respectively. These groups must therefore be within 5å of each other in the tertiary structure of papain. Possible mechanistic implications are briefly discussed.     

Interspecific differences in the biology of aphids (homoptera: Aphididae) on leaves of Vicia faba I. Feeding behaviour

Aphids of six species settled on the undersurface of bean leaves in characteristic patterns. Some species, e.g. Aphis fabae, settled wholly on veins. In others, e.g. Myzus spp. a considerable proportion settled away from veins, especially on the leaf margin. Microscopic studies showed that the probes of A. fabae were directed to the phloem in the veins as were those probes of Myzus spp. which entered the veins. Many probes of Myzus passed into spongy mesophyll alone. This apparently offered an alternative food source to them. The interspecific differences, which were matched by differences between age groups within species, are explained in terms of the differing proportions of the aphid populations exploiting the alternative food sources and of preferences for veins of a particular size.

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Zusammenfassung Blattläuse sechs verschiedener Arten, die sich ungehindert auf reifen Blättern von Vicia faba ansiedeln konnten, bildeten arttypische Verteilungen. Auf diese Weise wurde eine Übergangsreihe von Arteigentümlichkeiten deutlich zwischen Aphis fabae und Megoura viciae, die sich an den großen Adern ansiedelten, und Myzus ornatus, welche sich auf den Blatträndern außerhalb der Adern häufte. Die Ernährungsweise von A. fabae, Myzus persicae und M. ornatus wurde durch mikroskopische Suche nach Speichelscheiden in ganzen, aufgehellten Blättern sowie an Schnittserien untersucht. A. fabae saugt am Phloem der Blattadern, M. persicae jedoch zum Teil und M. ornatus fast völlig am Schwammparenchym.Es wird angenommen, daß dieses Gewebe neben dem Phloem eine weitere Nahrungsquelle darstellte welche von gewissen Blattläusen in unterschiedlichem Ausmaße ausgenutzt zu werden vermag. Unterschiede sowohl im Anteil der am Mesophyll saugenden Population wie in dem bevorzugten Gefäßdurchmesser der von den Blattläusen besogenen Adern sind ursächlich mit den artcharakteristischen Ansiedlungsweisen verbunden. Unterschiede in beiden Richtunger werden zwischen den Arten deutlich, und ähnliche Unterschiede treten zwischen den Alters-gruppen einiger Aphidenarten häufig auf. Dem Auftreten wechselweise nutzbarer Nahrungsquellen, die in etwas verschiedener Weise ausgebeutet werden können, wird potentielle Bedeutung im Hinblick auf die Virusübertragung sowie auf die Wirksamkeit systemischer Insektizide beigemessen.

     

A serological comparison of the three morphological phases of Coccidioides immitis; complement fixation tests with anti-Histoplasma capsulatum serum

Summary The results of this study indicated that antigens prepared from the three morphological phases ofCoccidioides immitis differed in their complement fixing activity with anti-Histoplasma capsulatum pooled serum. Spherule antigens were serologically less active in tests with the anti-H. capsulatum pooled serum than antigens prepared from arthrospores and from mycelium.Antigenic determinants which are common toC. immitis andH. capsulatum appeared to be located on the intact arthrospore cellular surface but not on the surface of spherule cells.Part of a dissertation submitted to the Graduate School of Duke University in partial fulfillment of requirements for the Ph. D. degree.This work was supported by contract with the Department of the Army, Fort Detrick, Frederick, Maryland.In conducting the research reported herein, the investigators adhered to Guide for Laboratory Animal Facilities and Care established by the Committee on the Guide for Laboratory Animal Facilities and Care of the Institute of Laboratory Animal Resources, NAS-NRC.     

Measures of geographic range size: the effects of sample size

A number of methods have been used for quantifying the sizes of the geographic ranges of species. The consequences of different levels of sampling (the proportion of actual spatial occurrences) are explored for eight of these, using data on the occurrences of butterfly species on a 10 × 10 km grid across Britain. For all methods, the percentage error of estimation (PEE) decreases with the number of 10 × 10 km squares which a species occupies, most rapidly for extent measures, and more rapidly for area measures than for measures of numbers of units occupied. The rate of decline in PEE itself falls as sampling effort increases. At a given sampling level, rank correlations between range sizes measured by different methods are generally high, but there is no consistent change in the magnitude of these correlations as the level of sampling increases. The composition of the set of species with the smallest range sizes changes with the level of sampling.     

The control of respiration in wheat (Triticum aestivum L.) leaves

The aim of this work was to discover whether the respiration of wheat (Triticum aestivum L. cv. Huntsman) leaves, transferred to darkness after 7 h photosynthesis, showed an initial period of wasteful respiration. For young and old leaves, CO₂ production and O₂ uptake after 7 h photosynthesis were up to 56% higher than at the end of an 8-h night. The maximum catalytic activities of citrate synthase (EC 4.1.3.7), aconitase (EC 4.2.1.3), fumarase (EC 4.2.1.2) and cytochrome-c oxidase (EC 1.9.3.1) at the end of the day did not differ from those at the end of the night. Changes in the contents of glucose 6-phosphate, fructose-1,6-bisphosphate, dihydroxyacetone phosphate, and -ketoglutarate did not as a group parallel the changes in the rate of respiration. The detailed distribution of label from [U-¹⁴C] sucrose supplied to leaves in the dark was similar at the end of the day and the end of the night. No correlation was observed between the rates of leaf respiration and extension growth. It is argued that the higher rate of respiration at the beginning of the night cannot be attributed to wasteful respiration.Abbreviation RQ respiratory quotient We thank Dr H. Thomas and Professor C.J. Pollock, Institute for Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, UK for their generous help in measuring leaf extension. R.H.A. thanks the Science and Engineering Research Council for a studentship.