Ethylene Evolution from Bracts and Leaves of Poinsettia, Euphorbia pulcherrima Willd

Woodrow, L. and Grodzinski, B. 1987. Ethylene evolution trombracts and leaves ol Poinsettia, Euphorbia pulcherrima Willd.—J.exp. Bot. 38: 2024–2032. Ethylene release from fully expanded, red and white bracts andleaves of poinsettia, Euphorbia pulcherrima Willd., was compared.On a laminar (area) basis leaves contained about 50 times morechlorophyll and demonstrated 10 times the photosynthetic rateof the bracts. Both tissues contained starch, however, solublecarbohydrate in the bracts consisted primarily of reducing hexoseswhile the leaves contained mainly sucrose for translocation.The total free alpha-amino nitrogen content of the bract tissuewas twice that of the leaf tissue. The leaves contained moreACC (1-aminocyclopropane-1-carboxylic acid) and produced proportionallymore endogenous C²H⁴ than either the red or white bracts. ACC-stimulated₂H₄ release was also greatest from the green tissue indicatingthat the EFE (ethylene forming enzyme) was most active in theleaves. The specific activity of the ¹⁴C₂H₄/¹²C₂H₄ releasedfrom [2,3-¹⁴C]ACC confirmed ACC as the primary precursor ofC₂H₄ in this tissue. Ethylene release from the non-photosynthetic,bract tissue was not markedly affected by alterations in CO₂or light conditions. In green leaf tissue endogeneous ethylenerelease increased from 1·5 to 6·0 pmol C₂H₄ cm^–2h^–1 while ACC-stimulated ethylene release increased from10 to 35 pmol C₂H₄ cm^2– h^1– as the CO₂ partial pressureincreased from 100 to 1 200 µbar. Key words: Poinsettia, ethylene, bracts     

Turnover of labile and recalcitrant soil carbon differ in response to nitrate and ammonium deposition in an ombrotrophic peatland

The effects of 4 years of simulated nitrogen deposition, as nitrate (NO₃^?) and ammonium (NH₄⁺), on microbial carbon turnover were studied in an ombrotrophic peatland. We investigated the mineralization of simple forms of carbon using MicroResp^? measurements (a multiple substrate induced respiration technique) and the activities of four soil enzymes involved in the decomposition of more complex forms of carbon or in nutrient acquisition: N‐acetyl‐glucosaminidase (NAG), cellobiohydrolase (CBH), acid phosphatase (AP), and phenol oxidase (PO). The potential mineralization of labile forms of carbon was significantly enhanced at the higher N additions, especially with NH₄⁺ amendments, while potential enzyme activities involved in breakdown of more complex forms of carbon or nutrient acquisition decreased slightly (NAG and CBH) or remained unchanged (AP and PO) with N amendments. This study also showed the importance of distinguishing between NO₃^? and NH₄⁺ amendments, as their impact often differed. It is possible that the limited response on potential extracellular enzyme activity is due to other factors, such as limited exposure to the added N in the deeper soil or continued suboptimal functioning of the enzymes due to the low pH, possibly via the inhibitory effect of low phenol oxidase activity.     

Ethylene Exchange in Lycopersicon esculentum Mill. Leaves During Short- and Long-Term Exposures to CO2

The effects of long-term and transient exposure to elevatedCO₂ concentrations on photosynthetic gas exchange and ethylenerelease by tomato leaves were investigated. The net CO₂ assimilationrate was enhanced when leaf tissue grown at ambient (35 Pa CO₂)levels was assayed at 100 Pa CO₂. Leaf tissue grown at high(130 Pa) CO₂ exhibited a lower net CO₂ assimilation rate athigh CO₂ levels than leaf tissue grown at ambient (35 Pa) CO₂.This decrease in CO₂ exchange rate in response to growth athigh CO₂ is typical of C₃ species. Rates of endogenous and 1-aminocyclopropane-l-carboxylicacid (ACC)-stimulated ethylene release from leaf tissue wereenhanced by exposure to elevated CO₂ levels whether the leaftissue had been grown at ambient or enriched CO₂ levels. Thedata demonstrate that CO₂ enhanced C₂H₄ release from leaf tissuein response to both short-term perturbations in CO₂ concentrationand long-term growth and development under high CO₂. Prolongedgrowth at elevated CO₂ concentrations induced a higher endogenousrate of C₂H₄ release relative to that of leaf tissue grown atlower CO₂ levels. Leaf tissue from all leaf positions of plantsgrown at high CO₂ consistently evolved more C₂H₄ than correspondingtissue from ambient-grown plants when assayed under standardizedconditions. Endogenous (ACC) tissue contents and rates of ACC-stimulatedethylene release were also higher at all leaf positions in CO₂-enrichedtissue. Thus the higher rates appeared to be due to both higherendogenous precursor (ACC) levels in the tissue and greaterACC to C₂H₄ conversion capacity. Growth at elevated CO₂ levelsresulted in a persistent increase in the rate of endogenousC₂H₄ release in leaf tissue. The capacity for increased ethylenerelease in response to CO2 did not decline after prolonged growthat high CO₂. Key words: CO₂enrichment, ethylene, leaves, tomato     

Challenging Nature: Local Knowledge, Agroscience, and Food Security in Tanga Region, Tanzania

Challenging Nature: Local Knowledge, Agroscience, and Food Security in Tanga Region, Tanzania . Philip W. Porter. Chicago: University of Chicago Press, 2006. 318 pp.     

Effects of Ethylene on Photosynthesis and Partitioning in Tomato, Lycopersicon esculentum Mill

The extended period of ethylene release from ethephon (2-chloroethylphosphonicacid) after application to intact tomato plants has provideda model system in which the effects of ethylene on photosyntheticmetabolism and carbon partitioning has been studied. Ethylenerelease from leaf tissue after ethephon treatment was 10 timesgreater than that from untreated control leaves. The specificactivity of 14C2H4 released from [14C] ethephon remained constantover several days demonstrating that the ethylene was derivedfrom the applied ethephon. The ethephon-treated plants exhibitedextreme epinasty of the leaves and 24 h after application theflower buds in the first visible cluster had abscised, leafexpansion at the apex had ceased and developing adventitiousroots were visible on the lower stem. Rates of steady-state photosynthesis, respiration, photorespirationand transpiration were the same in treated and control leaves24 h after ethephon application. Both treated and control leavespartitioned similar proportions of newly-fixed 14C from 14CO²into neutral (46.4%), acidic (14.0%), basic (5.0%) and insoluble(34.0%) leaf fractions under steady-state conditions. The speedof 11C-assimilate movement in the stems of control plants (3.62±0.42cm min-1 towards the apex and 4.03±0.15 cm min-1 towardsthe roots) was more rapid than in the ethephon-treated plants(2.90±0.31 cm min-1 upwards and 2.59±0.22 cm min-1downwards). Furthermore, in the control plants 20.0±5.4%of the 14C exported to the plant from the source leaf was transportedtowards the developing flower cluster and young leaves. Twenty-fourhours after ethephon application only 6.5 ±1.7% of theexported 14C was translocated towards the shoot. Contrary tosome reports ethylene did not affect steady-state gas exchangeprocesses while carbon partitioning was significantly alteredindicating that ethylene effects on photosynthetic carbon metabolismare indirect and not due to direct effects on photosyntheticprocesses per se. Key words: Ethylene, photosynthesis, partitioning     

Studies of halo-blight seed infection and disease transmission in dwarf beans

The transmission of Pseudomonas phaseolicola from plant to seed was mainly by the penetration of bacteria from external pod lesions to the underlying seeds. There was no evidence for translocation of bacteria from other parts of the plant to the seed, and symptomless pods contained only healthy seeds. Although a small proportion of infected seeds showed obvious symptoms of infection, the majority showed either slight symptoms, which could be detected only by careful observation, or were symptomless. In tests of disease transmission from seed to seedling, seeds with slight symptoms, or those which were symptomless were responsible for 35% and 52% respectively of the total disease transmission compared to 13% for obviously infected seeds. The viability of bacteria in seed stored under relatively uncontrolled conditions (10–27 C) declined by a factor of 250 per annum over the first 3 yr with extrapolation predicting effective extinction after c . 5 yr. The pathogen survived longer under controlled conditions (7–10 C and 45–50% r.h.) but no viable bacteria were detected in seed stocks which were 10-yr-old and with one exception 6-yr-old stocks were also free of the pathogen.     

An Evaluation of the Effects of Ethylene on Carbon Assimilation in Lycopersicon esculentum Mill

Leaf and whole plant gas exchange rates of Lycopersicon esculentumMill, were studied during several days of continuous exposureto ethylene. Steady-state photosynthesis and transpiration ratesof control and ethylene-treated individual leaves were equivalent.However, the photosynthesis and transpiration rates of treatedleaves required at least five times longer to reach 50% of thesteady-state rate. This induction lag was attributed to ethylene—inducedleaf epinasty and temporary acclimation to lower incident lightlevels immediately prior to measurement of gas exchange. Thewhole plant net carbon exchange rate (NCER) of a representativetreated plant was also reduced by 51% after 24 h exposure toethylene relative to both its pre-treatment rate and that ofthe control. Ethylene exposure reduced the growth rate of thetreated plant by 50% when expressed as carbon (C) gain. Theinhibition of NCER and growth rate associated with epinastywas completely reversed when the epinastic leaves were returnedto their original positions and light interception was re-established.The results demonstrate that the inhibition of whole plant CO₂assimilation is indirect and due to reduced light interceptionby epinastic leaves. Morphological changes caused by environmentalethylene are thus shown to reduce plant C accumulation withoutinhibiting leaf photosynthesis processes per se. Key words: Ethylene, carbon assimilation, growth     

TACKLING SOCIALLY DETERMINED DENTAL INEQUALITIES: ETHICAL ASPECTS OF CHILDSMILE, THE NATIONAL CHILD ORAL HEALTH DEMONSTRATION PROGRAMME IN SCOTLAND

Many ethical issues are posed by public health interventions. Although abstract theorizing about these issues can be useful, it is the application of ethical theory to real cases which will ultimately be of benefit in decision-making. To this end, this paper will analyse the ethical issues involved in Childsmile, a national oral health demonstration programme in Scotland that aims to improve the oral health of the nation's children and reduce dental inequalities through a combination of targeted and universal interventions. With Scotland's level of dental caries among the worst in Europe, Childsmile represents one of the largest programmes of work aimed at combating oral health inequalities in the UK. The areas of ethical interest include several contrasting themes: reducing health inequalities and improving health; universal and targeted interventions; political values and evidence base; prevention and treatment; and underlying all of these, justice and utility.     

A new arthropod resting trace and associated suite of trace fossils from the Lower Jurassic of Warwickshire, England

Abstract:  A new suite of arthropod trace fossils, attributed to a decapod crustacean, is described from the Lower Jurassic Saltford Shale Member of the Blue Lias Formation of Southam Cement Works Quarry, eastern Warwickshire, England. Solusichnium southamensis igen. et isp. nov. consists of small, isolated, bilaterally symmetrical, suboval hypichnia, comprising three regions. The concave anterior region contains imprints of chelate appendages, antennae and antennules. The elongate middle region contains abdominal appendage imprints that extend laterally, separated by a bifurcated medial imprint. The convex posterior region terminates in a globular V-shaped telson imprint. The large sample size and range of trace morphologies allows identification of five morphotypes within a taphoseries. S. southamensis is found on the base of siltstone lenses in what is otherwise a dysaerobic laminated mudstone unit, associated with epichnial Rusophycus , and the suite of trace fossils is interpreted as the resting traces (Cubichnia) and escape reactions (Fugichnia) of small decapods that were trapped below a distal storm deposit. The producer of S. southamensis was possibly an Eryon -like decapod, similar to those known from the slightly older Wilmcote Limestone Member of southwestern Warwickshire.     

THE GROWTH OF LACTIC ACID STREPTOCOCCI IN MIXED STARTER CULTURES

SUMMARY: An attempt has been made so to combine rapid acid-producing streptococci that on daily subculture the individual components in the mixture will remain present in even proportions. Some such combinations have been made, but frequently the proportions of the components alter until one culture becomes dominant. When one culture dominates rapidly this is due to the production of antibiotic factors.