The Effects of Shade Treatment and Light Intensity on Rihulose-1,5-Diphosphate Carboxylase Activity and Fraction I Protein Level in the First Leaf of Barley

It has been confirmed that shading leaves from day 5 onwardslowers the rate of CO₂ fixation when they are placed in saturatingirradiances. The reduction due to shade treatment is about 46per cent and a similar reduction in maximum chlorophyll contentof the leaf follows shading. Maximum amounts of total solubleprotein and of Fraction I protein are less in shaded leavesthan in control leaves and prolonged treatment leads to a declinein leaf protein content. The relative amounts of different proteinare also affected by treatment; in control leaves Fraction Iprotein accounts for about 45 per cent of the total but in shadedleaves the value is about 30 per cent. Increases and decreasesin leaf protein amount, with concomitant changes in the ratioof Fraction I to total protein can be brought about by removingshades and re-applying them. Such changes can be induced evenin fully expanded leaves in which net protein synthesis is notusually found. Maximal amounts of leaf protein are found in irradiances of60 W m^–2 or more, with lower values at lower light intensities.Where the first leaf is held in a stream of CO₂-free air a lowerlevel of protein is found. This, and the ratio of Fraction Ito total protein, are similar to values for shaded leaves, andsuggest the involvement of photosynthetic carbon fixation indetermining leaf protein amount. A 1:1 linear correlation between amount of Fraction I proteinand RuDP carboxylase activity is shown but the rate of CO₂ incorporationby leaf extracts is 2–3 times greater than that of theintact leaf. The significance of this and the effect of irradianceon leaf protein amount are discussed.     

Sensitivity Analyses of a Population Projection Model of Ring-Necked Pheasants

Abstract A large literature exists on population dynamics of ring-necked pheasant (Phasianus colchicus) in North America, but there has not been an attempt to formulate a matrix model nor a sensitivity analysis of the relationships between vital rates and population finite growth rate (Λ) that can be used to guide management. We summarized demographic data available from a 5-year field study in Iowa, USA, collected in Kossuth County (low composition of perennial habitat) and Palo Alto County (high composition of perennial habitat) into a 2-stage (young and adult) matrix projection model. We estimated Λ₁ (the dominant eigenvalue of the deterministic matrix), the stable age distribution (ω), relative reproductive value vector (n̈), other demographic parameters, and Λ_iid, a bootstrap estimate of growth that includes interannual variation in life history parameters. We analyzed the relative importance of vital rates on population growth rate using sensitivity and elasticity of both matrix elements and lower-level parameters such as winter survival and nest success. We first characterized general life history using averaged data from both areas and all years that yielded Λ₁ = 1.086, and a stable stage distribution of. Minimum success of the initial nesting attempt (H₁) that would maintain Λ ≥ 1 under average conditions was estimated to be 42%. Changes in Λ₁ were most sensitive to survival of chicks during brood rearing (S_B), followed in importance by survival during the subsequent winter (S_W), followed by H₁. We followed the general analyses with analyses that helped us to focus on the differences in the landscapes of northwest Iowa. Λ_iid was ≥1 in only 9% of simulations of data from Kossuth whereas estimated Λ_iid was ≥1 in 88% of simulations from Palo Alto. Our analyses of the relative importance and interactions between S_B, S_W, and total recruitment (M, including H₁ and renesting), if combined with data more specific to a local area, would guide management aimed at affecting multiple life history stages whose relative importance will vary across the landscape.     

Modelling animal populations in changing landscapes

Models of Mobile Animal Populations (MAP models) simulate long-term land use changes, population trends and patterns of biological diversity on landscapes of 10³-10⁵ ha. MAP models can incorporate information about past land-use patterns and management practices and can project future patterns based on management plans. We illustrate this approach with an example of how implementation of a U.S. Forest Service management plan at the Savannah River Site in South Carolina, U.S.A., might influence population trends of Bachman's Sparrow Aimophila aestivalis, a relatively rare and declining species in southeastern pine forests. In this case, a management plan, largely designed to improve conditions for an endangered species, Red-cockaded Woodpecker Picoides borealis, may have a negative impact, at least in the short term, on another species of management concern, Bachman's Sparrow.
In a parallel processing version of the MAP models, a single landscape that would ordinarily be too large or detailed to be simulated on a single computer is subdivided into a number of smaller landscapes, and each landscape is simulated in parallel, either on a single multi-tasking machine or on a group of networked machines. With this approach we are attempting to determine just how large a landscape must be before the dynamics of a population within it are more or less independent of factors beyond the landscape boundaries.     

Morphology,Ultrastructure, and Small Subunit rDNA Phylogeny of the Marine Heterotrophic Flagellate Goniomonas aff. amphinema

ABSTRACT. Marine goniomonads have a worldwide distribution but ultrastructural information has not been available so far. An isolate of the heterotrophic marine nanoflagellate Goniomonas (G. aff. amphinema) from North Wales (UK) has been studied, providing information on its morphology and cellular structure using video, electron, laser scanning confocal microscopy (LSCM), and atomic force microscopy. Here, we describe a new feature, a granular area, potentially involved in particle capture and feeding. The binding of the lectin wheat germ agglutinin to the granular area of cells with discharged ejectisomes indicates the adhesive nature of this novel feature. The presence of a microtubular intracellular cytopharynx, apparently also used for feeding, has been revealed by LSCM. The small subunit rRNA gene of the isolate has been sequenced (1,788 bp). Phylogenetic results corroborate significant genetic divergence within the marine members of Goniomonas. This work highlights the need for integrated morphological, ultrastructural, and molecular investigation when describing and studying heterotrophic nanoflagellates.     

Seasonal variation of tadpole spatial niches in permanent streams: The roles of predation risk and microhabitat availability

Phenotypic plasticity can improve fitness in unstable environments and can be expressed in many traits, such as life history attributes, growth and behavioural features. Microhabitat choice can have important consequences for development and survival of aquatic organisms and is expected to vary in response to stimuli, such as predation risk, food availability and temperature. At seasonal sites, microhabitat availability and associated benefits may change from season to season, which might lead to altered patterns of microhabitat use by tadpoles. We investigated this hypothesis in 17 streams from two localities in south‐eastern Brazil. We tested whether water level drops significantly during the dry season, whether lower water level results in altered microhabitat availability and whether predation risk changes between seasons, based on predator density. We then tested whether tadpoles change their pattern of microhabitat use, their spatial niche breadth (given by diversity of used microhabitats) and spatial niche overlap (in the case of co‐occurring species). We were able to include in our analyses tadpoles of four species of Hylidae, that occurred throughout both seasons. Stream depth decreased in the dry season, but microhabitat availability remained relatively stable in many streams, and predator density did not change significantly. Tadpoles of three out of the four species studied were more abundant during the dry season, which may be an adaptation to adjust time of metamorphosis to the rainy season. Tadpoles changed their patterns of microhabitat use between seasons, although the potential causing factors investigated did not seem to be responsible. Tadpole plasticity in microhabitat use may indicate the existence of selective pressures that vary through time and space and are still not well understood.     

Investigations into the Stomatal Physiology of Upland Cotton: 2. Calibration of the Infiltration Method against Leaf and Stomatal Resistances

Data are presented to show that reductions in leaf water contentof up to 12 per cent, are associated with increases of mesophyllresistance to viscous flow of air of from 50 to 130 per cent.This effect may explain the variation observed in the relationshipbetween Infiltration Score (I), and the logarithm of leaf resistance,measured porometrically, for leaves with different water contents. Highly significant linear correlations were obtained by plottingthe llogarithm of the resistance iof 10,000 stomata againstI for leaves from plants grown in the field (r = –0.92)kjor in the greenhouse (kr = –o.94). For the two se5tsof material the slopes of the loines were similar, but a differencein levels was highly significant. This is considered in relationto leaf and stomatal structure. The use of the infiltrationmethod for deriving estimates of stomatal resistance is discussed.     

An Analysis of the Response of Young Barley Seedlings to Time of Application of Nitrogen

The reasons for the sensitivity of young barley seedlings totime of application of nitrogen have been examined. It is shownthat the transfer of nitrogenous reserves from endosperm toembryo which begins at about 36 h from planting proceeds ata faster relative rate than that of dry matter as a whole. Inconsequence embryo and endosperm nitrogen contents become temporarilysimilar some 24–36 h earlier than is the case for dryweights. Addition of nitrate on day 2 does not affect ratesof transfer of endosperm reserves but leads to a significantlyhigher nitrogen content in the embryo of treated plants, particularlyin the shoots. This additional nitrogen is present as nitrateup to around day 5 when reduction of accumulated nitrate commencesin the first leaf in significant amounts. For plants up to 14 days old delay in application of nitrateleads to a lowering of total nitrogen level which is proportionalto the delay in treatment. This is so for all parts of the plantexcept the first leaf for which the evidence indicates thatlevels of total and organic nitrogen and of accumulated nitrateare much lower when treatment is made late. It is argued thatnitrate accumulation by the leaf becomes progressively lessas it reaches full expansion, but irrespective of time of nitrateapplication about 95 per cent of the additional nitrogen presentin the leaf is in organic form Significant increases in organic nitrogen are found from day6 for plants supplied with nitrate up to day 4; for plants suppliedon day 6, or day 8nitrateand nitrate reductase activity in leafextracts are found within 6 h of treatment. Peak levels of nitratereductase activity are found for all treatments around days8–10 when the first leaf is fully expanded and when photosyntheticactivity is maximal. However, late supply of nitrate leads toa lower level of enzyme activity. Nitrate reduction in the rootsystem is undetectably low, and it is concluded that a substantialamount of carbon translocated from leaf to roots is in the formof nitrogenous compounds. The effects of time of application are also found when ammoniumnitrogen is substituted for nitrate indicating that the responseis independent of effects on the nitrate reducing system inthe leaf. Some inhibition of growth, particularly of the roots,is found due to ammonium toxicity. Why plants supplied early with nitrate show superior growthand enhanced photosynthetic activity in the first leaves isexplained in terms of treatment alleviating the restrictiveeffects of declining endosperm reserves. This is only possibleif nitrogen is supplied while the first leaf is expanding andable to accumulateand utilise the available nitrogen. Late supplyis associated with failure to use the nitrogen provided leadingto a lower protein level in the leaf; this can be correlatedwith the smaller size of leaf and the lower rates of carbonfixation occurring there.     

The tolerance of black currant flowers to induced frosts

Flower buds on potted plants of 17 varieties of black currant were frosted to -3.3, -4.5 and -5.2 °C between the grape stage and full flower in 1979 and 1980. In all varieties more flower buds died after the -5.2 °C frosts and at full flower, and less after the -3.3 °C frosts and at the grape stage. Varieties related to Ben More and Ojebyn tolerated the -4.5 °C frosts until after first flower while Baldwin and Magnus became susceptible at the grape stage. Seabrooks Black, Greens Black and Ben Lomond and its relatives were intermediate. In both years flower buds tolerated frosts to similar growth stages but in 1980 the varieties flowered about 2 wk earlier than in 1979 and suffered more frost damage at full flower. The frosted plants had slightly larger fruits than the unfrosted ones in 1979. The immature fruit drop was similar in frosted and unfrosted plants in both years except when it was increased after -5.2 °C in 1980. It is pointed out that for reliable cropping, varieties should flower late as well as tolerate spring frosts and that tests of frost tolerance should be done for at least three growth stages.     

Glycoalkaloid increase in Solarium tuberosum on exposure to light

Tubers of six commercially available potato cultivars were placed in bright light (140 jUmol“¹ m”²), approximately equivalent to dull daylight, for a continuous period of up to seven days. The tubers were sampled at intervals, scored for degree of greening, freeze-dried and subsequently assessed for glycoalkaloid and chlorophyll content. There were significant differences between the cultivars in their rates of greening and increase in glycoalkaloid content. There was an apparent relationship between the two characters. Increases in the individual glycoalkaloids a–chaconine and a-solanine were also assessed. The results are discussed in terms of the implications for the potato industry.