Suppression of Stomatal Opening in Leaves Treated with Abscisic Acid

Small doses of abscisic acid (approximately 0.02 µg cm^-2of leaf) applied to the leaf surface as a 10^-4 M solution causedmarked stomatal closure in Xanthium pennsylvanicum, and theeffect persisted for up to 9 days after application. Similareffects were found when 10^-4 M abscisic acid was supplied todetached tobacco leaves via their petioles. CO²-free air didnot cause a reversal of the closure, and it was therefore concludedthat the effect was not due simply to an increase in the intercellularCO²concentration; a more direct effect on the stomatal apparatusis suggested. It is considered that abscisic acid could playan endogenous role in the control of stomatal aperture, andthat this, and/or related substances, might be more useful as‘anti-transpirants’ than the phytotoxic substancescurrently employed for this purpose.     

THE FUNGICIDAL CONTROL OF LETTUCE DOWNY MILDEW, CAUSED BY BREMIA LACTUCAE

Protection experiments carried out in the greenhouse showed that preparations of thiram, zineb, ferbam and ziram were superior to cuprous oxide and copper oxy-chloride preparations, in controlling downy mildew of lettuce and in lack of phytotoxic effect.
Tests made in winter on lettuce seedlings grown in Dutch lights, showed that Bremia lactucae attack reduced the stand of seedlings, diminished their size and weight, and, when the crop was planted out into the open ground, reduced survival in the field and slightly delayed the date of reaching maturity. The best overall results in protecting foliage against downy mildew were given by thiram and zineb preparations.     

Browsed twig environmental DNA: diagnostic PCR to identify ungulate species

Ungulate browsing can have a strong effect on ecological processes by affecting plant community structure and composition, with cascading effects on nutrient cycling and animal communities. However, in the absence of direct observations of foraging, species‐specific foraging behaviours are difficult to quantify. We therefore know relatively little about foraging competition and species‐specific browsing patterns in systems with several browsers. However, during browsing, a small amount of saliva containing buccal cells is deposited at the bite site, providing a source of environmental DNA (eDNA) that can be used for species identification. Here, we describe extraction and PCR protocols for a browser species diagnostic kit. Species‐specific primers for mitochondrial DNA were optimized and validated using twigs browsed by captive animals. A time series showed that about 50% of the samples will amplify up to 12 weeks after the browsing event and that some samples amplify up to 24 weeks after browsing (12.5%). Applied to samples of natural browsing from an area where moose (Alces alces), roe deer (Capreolus capreolus), fallow deer (Cervus dama) and red deer (Cervus elaphus) are sympatric, amplification success reached 75%. This method promises to greatly improve our understanding of multispecies browsing systems without the need for direct observations.     

Nerium oleander as an alternative host plant for south Florida milkweed bugs, Oncopeltus fasciatus

Abstract.

• 1 Life history data were gathered for south Florida Oncopeltus fasciatus reared from eggs on Nerium oleander seeds and milkweed seeds in the laboratory.
• 2 Milkweed seeds were found to be a superior food source since O.fasciatus grew faster, laid more clutches, and has a higher total fecundity on milkweed seeds.
• 3 Fruiting N.oleander was found to be a better food source than nonfruiting milkweeds in a summer field study in south Florida since no nymphs survived to the adult stage on nonfruiting milkweeds but some did on N.oleander.
• 4 O.fasciatus adults and nymphs are abundant on N.oleander in the summer in south Florida when N.oleander is fruiting; no O.fasciatus nymphs are found in the summer on the milkweeds which are not fruiting.
• 5 O.fasciatus leave N.oleander in the autumn when milkweeds start to fruit and can then be found on fruiting milkweeds.

     

Biotic and abiotic constraints to a plant invasion in vegetation communities of Tierra del Fuego

The biotic resistance theory relates invader success to species richness, and predicts that, as species richness increases, invasibility decreases. The relationship between invader success and richness, however, seems to be positive at large scales of analysis, determined by abiotic constraints, and it is to be expected that it is negative at small scales, because of biotic interactions. Moreover, the negative relationship at small scales would be stronger within species of the same functional group, because of having similar resource exploitation mechanisms. We studied the relationship between the cover of a worldwide invader of grasslands, Hieracium pilosella L., and species richness, species diversity and the cover of different growth forms at two different levels of analysis in 128 sites during the initial invasion process in the Fuegian steppe, Southern Patagonia, Argentina. At regional level, the invader was positively correlated to total (r = 0.28, P = 0.003), exotic (r = 0.273, P = 0.004), and native species richness (r = 0.210, P = 0.026), and to species diversity (r = 0.193, P = 0.041). At community level, we found only a weak negative correlation between H. pilosella and total richness (r = ?0.426, P = 0.079) and diversity (r = ?0.658, P = 0.063). The relationship between the invader and other species of the same growth form was positive both at regional (r = 0.484, P < 0.001) and community (r = 0.593, P = 0.012) levels. Consequently, in the period of establishment and initial expansion of this exotic species, our results support the idea that invader success is related to abiotic factors at large scales of analysis. Also, we observed a possible sign of biotic constraint at community level, although this was not related to the abundance of species of the same growth form.     

A comparison of spike and spikelet survival in mainstem and tillers of barley

Initiation and abortion of spikelet primordia on primary tillers and mainstem were compared for plants of spring barley, Maris Mink, sown on two sowing dates during 1983, in plots at the Scottish Crop Research Institute (SCRI) and at Long Ashton Research Station (LARS). Sowing date had no effect on the number of spikelets initiated on either mainstem or surviving tillers and many more spikelets were initiated on equivalent stems at LARS than at SCRI but more spikelets aborted at the former site. The final number of spikelets produced was eventually similar. Spikelet abortion was complete by anthesis and coincided with the period of rapid stem and rachis elongation and with the time over which tiller death occurred. Despite the fact that plants at SCRI produced fewer fertile tillers they outyielded those at LARS because much heavier grains were produced on the mainstem and tiller 1 of plants at the Scottish site. An interval of 2 wk between sowing had only small effects on the components of yield.     

Cytotaxonomic observations in tropical Vaccinieae (Ericaceae)

Chromosome numbers are reported for 36 accessions representing 31 species from nine genera of the tribe Vaccinieae, family Ericaceae. The plants are tropical and come from Southeast Asia and Central and South America. The taxonomy of the tribe is outlined in these regions. Genera are often poorly defined and taxa were chosen to reflect the range of variation of the Vaccinieae. Most Southeast Asian Vaccinium species were diploid (2n= 24) as were those of Agapetes subgenus Agapetes (apart from the Himalayan A. flava), Agapetes scortechinii and Costera endertii. All other accessions were found to be polyploid. The correlation between polyploidy, geographical distribution and the possession of an ‘anatomical complex’ of the leaf and stem in Vaccinieae of New Guinea and the neotropics is discussed.     

Sporozoites of Rodent and Simian Malaria, Purified by Anion Exchangers, Retain their Immunogenicity and Infectivity

SYNOPSIS. Sporozoites of rodent malaria, Plasmodium berghei , and simian malaria, Plasmodium knowlesi and Plasmodium cynomolgi , were partially separated from mosquito debris and microbial contaminants by passage of Anopheles material through a DEAE-cellulcse column. In addition to eliminating most of the contaminants (80–90%), this simple technic has made it possible to recover rapidly large numbers of viable sporozoites (55–75% yield), which have retained their infectivity, immunogenicity, and capacity to react with known antisera. Mice injected with varying doses of column-purified sporozoites (CS) of P. berghei produced infections which paralleled those seen in the controls. Total protection against challenge with a potentially lethal dose of viable sporozoites was acquired by mice inoculated twice with irradiated CS of P. berghei. CS of P. berghei and P. cynomolgi gave positive circumsporozoite precipitation (CSP) reactions, upon inoculation with the respective immune sera. The preservation of the surface antigens of CS was documented by immunofluorescence.
It was shown that differences in elution behavior exist among sporozoites of certain species of Plasmodium as well as among sporozoites of the same species derived from different organs of the mosquito. These results may be attributed to differences in the surface charge of the sporozoites or conditions in sample media.
Purified sporozoites obtained by the method described in this report provide an adequate source of parasites for a variety of in vitro studies.     

Monocaryotization of Cultures of Lenzites trabea (Pers.) Fr. and other Wood-destroying Basidiomycetes

Cultures of Lenzites trabea and some other basidiomycetes grownon nutrient agar containing high concentrations of sodium arsenateconsistently reverted from the dicaryotic to the monocaryoticcondition. This effect could also be induced by a wide varietyof other toxicants, including copper sulphate, zinc sulphate,sodium dichromate, sodium pentachlorophenate, creosote, crystalviolet, boric acid, and sodium taurocholate, but sodium arsenatewas the most reliable monocaryotizing agent, being effectivewith eight of the fourteen basidio-mycete species tested withit. The neohaplonts formed by sodium arsenate and other toxicantsmate normally with each other and with compatible monosporeisolates. The value of chemical monocaryotization as a techniquein fungal genetics and experimental taxonomy is discussed. Byusing the mating factor alleles as genetic markers, it was demonstratedthat when L. trabea is monocaryo-tized by sodium arsenate orcopper sulphate, only one of the two nuclei in the dicaryoncan be recovered in the neohaplonts, the direction of this completenuclear selection depending on the toxicant and the dicaryonconcerned. It was shown to occur in treated wood blocks duringroutine soil-block decay tests of inorganic wood preservativesand it is probably a frequent, though hitherto unrecognized,occurrence in the laboratory testing of wood preservatives andother fungicides against basidiomycetes.