Deterrent effect of carboxylic acids on cabbage root fly oviposition

In laboratory experiments, 11 selected carboxylic acids were tested to determine which part of the sinapic acid molecule is responsible for deterring cabbage root fly from laying its eggs on otherwise-acceptable cauliflower host-plants. The deterrent effect was only obtained with compounds containing at least one carboxylic group in the molecule. Hence, the aliphatic acids were as deterrent as the aromatic acids to the fly and all the carboxylic acids were as deterrent as sinapic acid, reducing oviposition by > 50%. The inclusion of two carboxylic groups in the molecule, (e.g. phthalic acid and oxalic acid) did not increase the deterrent effect observed with sinapic acid. Some of the long chain fatty acids, with low volatility, low water solubility and thus greater persistence, offer practical opportunities for deterring Delia radicurn from laying its eggs on plants in the field.     

Relationships between Acetylene Reduction Activity, Hydrogen Evolution and Nitrogen Fixation in Nodules of Acacia spp.: Experimental Background to Assaying Fixation by Acetylene Reduction under Field Conditions

Hansen, A. P., Pate, J. S. and Atkins, C. A. 1987. Relationshipsbetween acetylene reduction activity, hydrogen evolution andnitrogen fixation in nodules of Acacia spp.: Experimental backgroundto assaying fixation by acetylene reduction under field conditions.—J.exp. Bot. 38: 1–12 Glasshouse grown, symbiotically-dependent seedlings of Acaciaalata R.Br., .A. extensa Lindl., and A. pulchella R.Br. wereexamined for acetylene reduction in closed assay systems usingundisturbed potted plants, excavated whole plants, nodulatedroots or detached nodules. Nitrogenase activity declined sharplyover the first hour after exposure of detached nodules to acetylene(10% v/v in air), less steeply or not at all over a 3 h periodin assays involving attached nodules. Using detached nodules,rates of acetylene reduction, nitrogen (¹⁵N₂) fixation, andhydrogen evolution in air (¹⁵N₂) and acetylene-containing atmosphereswere measured in comparable 30 min assays. Total electron flowthrough nitrogenase in air was determined from rates of nitrogen(¹⁵N₂) fixation ( ? 3) plus hydrogen evolution, that in thepresence of acetylene from rates of acetylene reduction andhydrogen evolution in air: acetylene. Values for the ratio ofelectron flow in air: acetylene to that in air ranged from 0?43to 0?83 in A. pulcheila, from 0?44 to 0?66 in A. alala and from0?37 to 0?70 in A. extensa, indicating substantial inhibitionof electron flow through nitrogenase of detached nodules byacetylene. Relative efficiencies of nitrogenase functioningbased on hydrogen evolution and acetylene reduction were from0?15 to 0?79, those based on nitrogen (¹⁵N₂) fixation and hydrogenevolution from 0?53 to 0?87. Molar ratios of acetylene reducedto nitrogen (¹⁵N₂) fixed were 2?82 ? 0?24, 201 ? 0?15, and 1?91? 0?11 (?s.e.; n = 7) for A. pulcheila,A. extensa and A. alata respectively A standard 5–10 min acetylene reduction assay, conductedon freshly detached unwashed nodules in daytime (12.00–14.00h), was calibrated for field use by comparing total N accumulationof seedlings with estimated cumulative acetylene reduction overa 7-week period of glasshouse culture. Molar ratios for acetylenereduced: nitrogen fixed using this arbitrary method were 3?58for A. alata, 4?82 for A. extensa and 1?60 for A. pulchella.The significance of the data is discussed. Key words: Acacia spp, nitrogenase functioning     

Relationship between Photosynthesis and Plasmalemma Transport

Hansen, U.-P., Kolbowski, J. and Dau, H. 1987. Relationshipbetween photosynthesis and plasmalemma transport.—J. exp.Bot. 38: 1965–1981. The yield of chlorophyll-fluorescence (F), of oxygen evolution(PAS, photo-acoustic signal) and the light-induced changes ofplasmalemma potential (V) were measured in the presence of red(633 nm) background light with blue or far-red (720 nm) sinusoidallymodulated actinic light. The kinetic study based on curve-fittingof the measured frequency responses led to the following: theresponse of chlorophyll-fluorescence (F) to blue actinic lightcomprises four time-constants located at 2·7,50,400 and4000 s. Membrane potential (V) displays five time-constants:2· 50, 160±330, —1, 4000 s. These time-constantswere assigned to the reactions involved as follows: from thecomparison of the effects of blue and far-red actinic lightthe time-constants of 2·7 s and 400 s were related tothe plastoquinone pool and to the state-transition controller.The time-constant of 4000 s was not investigated. The complextime-constants of V are known to be related to the controllerof cytoplasmic pH from previous studies. The time-constant of50 s was common to V, F, and PAS. From the sign of the 50 scomponent in F and in PAS (q_E-component), the following modelof the light action on membrane transport was developed: theuptake of protons into the inner space of the thylakoids causesan alkalinization of the cytoplasm which slows down the plasmalemmaH₊-pump via a substrate effect. Key words: Chlorophyll-fluorescence, frequency responses, kinetic analysis, plasmalemma potential, photo-acoustic effect, proton flux, spinach, state-transitions, thylakoid membrane, time-constants     

Further studies relating chlorogenic acid concentration in carrots to carrot fly damage

The effects of first generation carrot fly larval damage on chlorogenic acid concentration in carrots was investigated in a field experiment at Wellesbourne in 1985. In a separate experiment carrots grown in the absence of a resident population of carrot fly were also analysed for chlorogenic acid; these carrots maintained low concentrations of chlorogenic acid through the summer and autumn until low ground temperatures occurred from November to January. The relationship between chlorogenic acid concentration and damage by the first generation of carrot fly was described by a similar model to the one derived previously for late-generation damage but without the cultivar dependence. This may have been because first generation damage takes place in mid-summer when soil temperature is not sufficiently low for differential chlorogenic acid production by carrot cultivars. The model supports the hypothesis that carrot fly damage increases chlorogenic acid production which subsequently encourages further attack. The increase in acid production due to the low winter temperature may be the mechanism which, in turn, induced a differential cultivar response in carrots harvested during the winter.     

Powdery mildew of tobacco (Erysiphe cichoracearum DC)

A Hirst volumetric spore trap, at a height of 30 cm., was used to assess the diurnal distribution of Erysiphe conidia in the air in tobacco crops infected with E. cichoracearum in Rhodesia. Air temperature and humidity, and the length of time leaves were wet each day, were also recorded at the same height, amongst the plants. In four seasons, most conidia were caught between 13.00 and 15.00 hr. There were close positive correlations in 1962 between numbers of conidia per m.3 of air per hour and saturation deficit and air temperature during the same hours (10.00–18.00 hr.) Correlations of total Erysiphe conidia per day with temperature and humidity were very variable; temperature had no apparent effect during three seasons, but in one (1961)there was a highly significant positive correlation between numbers of conidia and the daily duration of temperatures > 25d? C. More conidia were also caught when the air was dry for long periods that season, though temperature probably had the greater effect. In 1962, more conidia were caught per day the longer the air was humid (s.D. 0–1 mb.) In 1961, the amount of rain per day had no apparent effect on numbers of conidia, but in 1962 more were caught the greater the daily rainfall. However, rain, which nearly always fell in the afternoon, also removed most conidia from the air that afternoon. Neither windspeed nor duration of leaf wetness appeared to affect spore dispersion.     

Variation in Outcrossing Rates in Eichhornia paniculata: Temporal Changes in Populations of Contrasting Style Morph Structure

Abstract Surveys of mating-system parameters in populations of the annual, self-compatible, tristylous, emergent aquatic, Eichhornia paniculata (Pontederiaceae) from N.E. Brazil and Jamaica have indicated that the species exhibits a wide range of outcrossing rates. To investigate whether temporal variation in outcrossing rate was also a feature of populations, open-pollinated families were sampled from five populations of contrasting style morph structure from N.E. Brazil over three consecutive years (1987–1989). Multilocus estimates of outcrossing rate ( t ) were obtained from assays of isozyme polymorphisms using starch gel electrophoresis. There was significant variation both among populations and between years in the frequency of outcrossing. Outcrossing in three tristylous populations was high ( t > 0.80), with relatively small fluctuations occurring over the three-year sampling period. In contrast, in a dimorphic and monomorphic population considerable self-fertilization occurred and the frequency of outcrossing declined significantly from 1987 to 1989 in both populations. In the dimorphic population, increased selfing was associated with a marked reduction in population size and an increase in the frequency of selfing variants of the mid-styled morph. The significance of temporal variation in outcrossing frequency in plant populations is discussed in relation to its effect on population genetic structure and recent models of mating-system evolution.     

Short-Term Nitrate Effects on Hydroponically-Grown Soybean cv. Bragg and its Supernodulating Mutant: II. DISTRIBUTION AND RESPIRATION OF RECENTLY-FIXED 13C-LABELLED PHOTOSYNTHATE

Fully symbiotic or nitrate treated (3 d, 4·0 mol m^–3)soybean (Glycine max [L.] Merr.) cv. Bragg and a nitrate tolerantsupernodulating soybean mutant nts 1007 were exposed to ¹³Cenriched CO₂ for a period of 10 h. During this period and forthe subsequent 24 h, continuous measurements of ¹³CO₂ and ¹²CO₂evolution of their root systems were undertaken. Three harvestsduring the experiment allowed determinations of the distributionof recently fixed carbon in different plant organs. These measurementsindicated higher dependence of N₂ fixation in nts 1007 on recentlyfixed carbon (RFC) by showing elevated RFC concentrations innodules as well as their augmented respiration. Root respirationof both genotypes was generally more reliant on stored carbon. Nitrate induced in all measured parameters a clear responsein the mutant analogous to the wild type, but quantitative differencesremained throughout. Nodule respiratory activity, the relativespecific activity (RSA), and the utilization of RFC were substantiallyreduced, but remained higher in nts 1007 than in Bragg, whilethe demand of roots for RFC increased in Bragg more than inthe supernodulator. The elevated carbon requirement of the nodulecomplement of the mutant and a high dependence on recently fixedcarbon could be attributed to higher nodule growth and maintenancecosts of the supernodulating genotype and were not associatedwith augmented nitrogen fixation activity. This less efficientutilization of carbon and the associated almost parasitic characterof the nodule complement of nts 1007 is considered to be thecause of reduced growth of the mutant. No evidence was foundfor a physiologically based nitrate tolerance in terms of nitrogenfixation. Key words: Glycine max, nitrate, N₂fixation, respiration, carbon partitioning, steady-state labelling     

Influence of Nitrogen Form and Nitrogen Absence on Utilization of Assimilates for Growth and Maintenance in Tops and Roots of Lolium multiflorum

Utilization of assimilates for growth and maintenance of tops and roots of Lolium multiflorum was determined for plants supplied with either nitrate or ammonium. Carbon dioxide exchange rates were measured continuously for tops and roots separately. Three-day periods were applied for two irradiation levels. On the last day of each three-day period no nitrogen was supplied to the two treatments. In the nitrate treatment, the coefficient of utilization for converting assimilates into constructive growth (Y_G) remained unaffected in absence of nitrate. However, in absence of nitrate the maintenance respiration (M) for both tops and roots was only one third of that in presence of nitrate. In the treatment with ammonium the maintenance respiration of the plants was not influenced by the absence of ammonium. However, especially for the tops Y_G increased in absence of ammonium. In both the treatments, growth respiration of the roots was inefficient compared to that of the tops. Only in the case of absence of nitrate, maintenance respiration of the roots was similar to that of the tops.