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Individual Leaves (individual + leaf)
Terms modified by Individual Leaves Selected AbstractsA dynamic simulation model for powdery mildew epidemics on winter wheat,EPPO BULLETIN, Issue 3 2003V. Rossi A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991,98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics. [source] Ecophysiological significance of leaf size variation in Proteaceae from the Cape Floristic RegionFUNCTIONAL ECOLOGY, Issue 3 2010Megan J. Yates Summary 1.,Small leaves of species endemic to Mediterranean-type climate areas have been associated with both low rainfall and nutrient availability, but the physiological reasons for this association remain unknown. 2.,We postulated that small leaves have thin boundary layers that facilitate transpiration in winter and sensible heat loss in summer. High transpiration rates when water is available may facilitate nutrient acquisition in winter, whereas efficient sensible heat loss reduces the requirement for transpirational leaf cooling in summer. 3.,The consequences of varying leaf sizes for water and heat loss in Cape Proteaceae were examined at two scales. At the leaf level, gas exchange and thermoregulatory capacities of 15 Proteaceae species with varying leaf size were assessed under controlled conditions using phylogenetically independent contrasts. At an environmental level, leaf attributes of Proteaceae occurring in the winter-rainfall area of the Cape Floristic Region were correlated with climatic environments derived from distribution data for each species. 4.,Leaf temperature was positively correlated with leaf size when wind speed was negligible. However, transpiration decreased significantly with increasing leaf size when measured on individual leaves, detached branches and when expressed on a per stoma basis. 5.,From multiple stepwise regression analysis of climatic variables obtained from distribution data, leaf size was negatively correlated with A-Pan evaporation, mean annual temperatures and water stress in January. We conclude that leaf size is conservative for survival over relatively rare periods of hot dry conditions with low wind speeds. 6.,Narrow leaves enable plants to shed heat through sensible heat loss during summer droughts, without the need for transpirational cooling. Additionally, small leaf dimensions confer a capacity for high transpiration when evaporative demand is low and water is abundant (i.e. winter). This may be a particularly important strategy for driving nutrient mass-flow to the roots of plants that take up most of their nutrients in the wet winter/spring months from nutrient-poor soils. [source] Using classification tree analysis to reveal causes of mortality in an insect populationAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2010Chris J. K. MacQuarrie 1Invasive species pose significant threats to native and managed ecosystems. However, it may not always be possible to perform rigorous, long-term studies on invaders to determine the factors that influence their population dynamics, particularly when time and resources are limited. We applied a novel approach to determine factors associated with mortality in larvae of the sawfly Profenusa thomsoni Konow, a leafminer of birch, and a relatively recent invader of urban and rural birch forests in Alaska. Classification tree analysis was applied to reveal relationships between qualitative and quantitative predictor variables and categorical response variables in a large data set of larval mortality observations. 2We determined the state (living or dead) of sawfly larvae in samples of individual leaves. Each leaf was scored for variables reflecting the intensity of intra-specific competition and leaf quality for leafminers, year of collection and degree-days accumulated were recorded for each sample. We explored the association of these variables with larval state using classification tree analysis. 3Leafminer mortality was best explained by a combination of competition and resource exhaustion and our analysis revealed a possible advantage to group feeding in young larvae that may explain previously observed patterns of resource overexploitation in this species. Dead larvae were disproportionately found in smaller leaves, which highlights the potential effect of competition on mortality and suggests that smaller-leaved species of birch will better able to resist leafminer damage. 4We show that classification tree analysis may be useful in situations where urgency and/or limited resources prohibit traditional life-table studies. [source] Is heterosis in maize mediated through better water use?NEW PHYTOLOGIST, Issue 2 2010José Luis Araus Summary ,Heterosis increases yield potential and improves adaptation to stress in maize (Zea mays); however, the underlying mechanisms remain elusive. ,A set of tropical inbred lines and their hybrids were grown in the field for 2 yr under three different water regimes. First-year plant water use was evaluated by measuring instantaneous traits (stomatal conductance (gs) and steady-state chlorophyll fluorescence (Fs)) in individual leaves together with time-integrative traits, which included mineral accumulation in the whole leaves of plants and oxygen isotope enrichment above source water (,18O) and carbon isotope discrimination (,13C) in the same pooled leaves and in mature kernels. Second-year water use was evaluated by measuring leaf temperature, gs and relative water content (RWC). ,Within each growing condition, hybrids showed higher Fs, mineral accumulation, RWC, and lower leaf temperature, ,18O and ,13C than inbred lines. Therefore, hybrids had a better water status than inbred lines, regardless of the water conditions. Differences in grain yield across growing conditions were explained by differences in water-use traits, with hybrids and inbred lines following a common pattern. Within each growing condition, most variations in grain yield, between hybrids and inbred lines, were also explained by differences in plant water-use traits. ,Heterosis in tropical maize seems to be mediated by improved water use, irrespective of the water conditions during growth. [source] Allocation of resources within mountain birch canopy after simulated winter browsingOIKOS, Issue 1 2000Kari Lehtilä As a response to browsing, birches are known to produce fewer but larger, more nutritious leaves, with enhanced palatability for herbivores. We simulated winter browsing in ramets of mountain birch (Betula pubescens ssp. czerepanovii) to find out whether it decreases subsequent foliage biomass and alters the number and type of shoots. After removal of a considerable proportion of buds (up to 35%) in late winter, the birches were able to compensate for the lost leaf biomass in the following summer; there were no differences in total leaf biomass between winter-clipped and control ramets. This indicates that foliage growth was limited by the total amount of stored resources, not by the number of buds. Depending on the position of the buds removed, different mechanisms were responsible for the compensation. After removal of apical buds, the number of leaves decreased significantly but leaves were larger than in control ramets. Removal of the same mass of basal buds , containing similar amount of carbohydrates and proteins as in the treatment removing apical buds , activated dormant buds, especially in apical locations, so that leaf number was similar as in the controls; consequently, size of individual leaves increased only slightly. Thus, while the total leaf biomass in a tree seems to be limited by resources from source organs, the distribution of resources among different canopy sections is controlled by their relative sink strengths. In terms of leaf biomass, apical parts are able to compensate for bud loss by increasing shoot number, basal parts only by increasing leaf size. [source] Spatial association of photosynthesis and chemical defense in Arabidopsis thaliana following herbivory by Trichoplusia niPHYSIOLOGIA PLANTARUM, Issue 2 2009Jennie Tang Because they share common precursors and require significant amounts of energy, photosynthesis and defense against herbivores and pathogens may be inversely related. This relationship was examined in Arabidopsis thaliana exposed to herbivory by Trichoplusia ni neonates. The spatial pattern of photosynthesis was compared statistically with that of induction of the defense-related cinnamate-4-hydroxylase (C4H) gene across individual leaves exposed to herbivory in transgenic plants harboring a C4H:GUS gene fusion. In portions of the leaf where C4H:GUS expression was upregulated, photosynthesis was depressed, while non-photochemical quenching was increased, suggesting a trade-off between these two processes. However, photosynthetic damage spread further into surrounding areas than the induction of C4H:GUS expression. Photosynthetic depression was observed up to 1 mm from the edges of holes, whereas C4H:GUS induction typically was limited to about 0.5 mm or less from edges. Other mechanisms may be responsible for the spread of photosynthetic damage beyond where C4H-related defense was induced. Alternatively, C4H induction may reflect a subset of defensive responses more limited in their spatial distribution than the downregulation of photosynthesis. The suppression of photosynthesis in remaining leaf tissue represents a ,hidden cost' of herbivore damage. [source] Seasonal, populational and ontogenic variation in the volatile oil content and composition of individuals of Origanum vulgare subsp.PHYTOCHEMICAL ANALYSIS, Issue 5 2004Hirtum, assessed by GC headspace analysis, by SPME sampling of individual oil glands Abstract Small-scale GC headspace analyses combined with SPME sampling of individual oil glands have been used to measure the variation in volatile content and composition in and within different oregano plants as affected by age, season and developmental state. The main monoterpenes found were p -cymene, carvacrol and their precursor , -terpinene. The early season preponderance of p -cymene over carvacrol was reversed as the season progressed and this pattern could also be seen at any time within the plant, from the latest leaves to be produced (low in cymene) to the earliest (high in cymene). Seedlings from the same mother plant developed this pattern at different rates. Within individual leaves the pattern was not observed, even within the youngest developing leaves. However it was found that the oil composition of individual glands within a single leaf varied considerably, most notably in respect of the production of carvacrol and its isomer thymol. Copyright © 2004 John Wiley & Sons, Ltd. [source] Adjustment of leaf photosynthesis to shade in a natural canopy: rate parametersPLANT CELL & ENVIRONMENT, Issue 3 2005A. LAISK ABSTRACT The present study was performed to investigate the adjustment of the rate parameters of the light and dark reactions of photosynthesis to the natural growth light in leaves of an overstorey species, Betula pendula Roth, a subcanopy species, Tilia cordata P. Mill., and a herb, Solidago virgaurea L., growing in a natural plant community in Järvselja, Estonia. Shoots were collected from the site and individual leaves were measured in a laboratory applying a standardized routine of kinetic gas exchange, Chl fluorescence and 820 nm transmittance measurements. These measurements enabled the calculations of the quantum yield of photosynthesis and rate constants of excitation capture by photochemical and non-photochemical quenchers, rate constant for P700+ reduction via the cytochrome b6f complex with and without photosynthetic control, actual maximum and potential (uncoupled) electron transport rate, stomatal and mesophyll resistances for CO2 transport, Km(CO2) and Vm of ribulose-bisphosphate carboxylase-oxygenase (Rubisco) in vivo. In parallel, N, Chl and Rubisco contents were measured from the same leaves. No adjustment toward higher quantum yield in shade compared with sun leaves was observed, although relatively more N was partitioned to the light-harvesting machinery in shade leaves (H. Eichelmann et al., 2004). The electron transport rate through the Cyt b6f complex was strongly down-regulated under saturating light compared with darkness, and this was observed under atmospheric, as well as saturating CO2 concentration. In vivo Vm measurements of Rubisco were lower than corresponding reported measurements in vitro, and the kcat per reaction site varied widely between leaves and growth sites. The correlation between Rubisco Vm and the photosystem I density was stronger than between Vm and the density of Rubisco active sites. The results showed that the capacity of the photosynthetic machinery decreases in shade-adjusted leaves, but it still remains in excess of the actual photosynthetic rate. The photosynthetic control systems that are targeted to adjust the photosynthetic rate to meet the plant's needs and to balance the partial reactions of photosynthesis, down-regulate partial processes of photosynthesis: excess harvested light is quenched non-photochemically; excess electron transport capacity of Cyt b6f is down-regulated by ,pH-dependent photosynthetic control; Rubisco is synthesized in excess, and the number of activated Rubisco molecules is controlled by photosystem I-related processes. Consequently, the nitrogen contained in the components of the photosynthetic machinery is not used at full efficiency. The strong correlation between leaf nitrogen and photosynthetic performance is not due to the nitrogen requirements of the photosynthetic apparatus, but because a certain amount of energy must be captured through photosynthesis to maintain this nitrogen within a leaf. [source] Adjustment of leaf photosynthesis to shade in a natural canopy: reallocation of nitrogenPLANT CELL & ENVIRONMENT, Issue 3 2005H. EICHELMANN ABSTRACT The present study was performed to investigate the adjustment of the constituents of the light and dark reactions of photosynthesis to the natural growth irradiance in the leaves of an overstorey species, Betula pendula Roth, a subcanopy species Tilia cordata P. Mill., and a herb Solidago virgaurea L. growing in a natural plant community in Järvselja, Estonia. Shoots were collected from the site and properties of individual leaves were measured in a laboratory, by applying a routine of kinetic gas exchange and optical measurements that revealed photosystem II (PSII), photosystem I (PSI), and cytochrome b6f densities per leaf area and the distribution of excitation (or chlorophyll, Chl) between the two photosystems. In parallel, N, Chl and ribulose-bisphosphate carboxylase-oxygenase (Rubisco) content was measured from the same leaves. The amount of N in photosynthetic proteins was calculated from the measured contents of the components of the photosynthetic machinery. Non-photosynthetic N was found as the residual of the budget. Growth in shade resulted in the decrease of leaf dry mass to a half of the DW in sun leaves in each species, but the total variation, from the top to the bottom of the canopy, was larger. Through the whole cross-section of the canopy, leaf dry weight (DW) and Rubisco content per area decreased by a factor of four, N content by a factor of three, but Chl content only by a factor of 1.7. PSII density decreased by a factor of 1.9, but PSI density by a factor of 3.2. The density of PSI adjusted to shade to a greater extent than the density of PSII. In shade, the distribution of N between the components of the photosynthetic machinery was shifted toward light-harvesting proteins at the expense of Rubisco. Non-photosynthetic N decreased the most substantially, from 54% in the sun leaves of B. pendula to 11% in the shade leaves of T. cordata. It is concluded that the redistribution of N toward light-harvesting Chl proteins in shade is not sufficient to keep the excitation rate of a PSII centre invariant. Contrary to PSII, the density of PSI , the photosystem that is in immediate contact with the carbon assimilation system , shade-adjusts almost proportionally with the latter, whereas its Chl antenna correspondingly increases. Even under N deficiency, a likely condition in the natural plant community, a substantial part of N is stored in non-photosynthetic proteins under abundant irradiation, but much less under limiting irradiation. At least in trees the general sequence of down-regulation due to shade adjustment is the following: (1) non-protein cell structures and non-photosynthetic proteins; (2) carbon assimilation proteins; (3) light reaction centre proteins, first PSI; and (4) chlorophyll-binding proteins. [source] Variations in leaf stomatal density and distribution of 53 vine species in JapanPLANT SPECIES BIOLOGY, Issue 1 2008AI-CHEN TAY Abstract To determine variations in stomatal density and distribution in individual leaves of vine species with different growth/life forms and different habitat types, we quantified and compared leaf-area-based stomatal density, epidermal cell density and stomatal index (percentage of stoma on the epidermis to the total cell number, including epidermal and stomatal cells on the epidermis) of 53 species comprising 19 woody species (lianas) and 34 herbaceous vines growing in Japan. We counted the numbers of stomata on both the adaxial and abaxial leaf surfaces using a light microscope. Stomatal density and distribution on the leaf surfaces varied greatly among species. Most of the creeping herbaceous species had stomata on both the adaxial and abaxial leaf surfaces (amphistomatous); however, lianas had no stomata on the adaxial leaf surface. Species from coastal (probably drier) habitats had greater adaxial to abaxial ratios of stomatal density and stomatal indices compared with species from inland habitats. A positive correlation between stomatal density and epidermal cell density was found on the abaxial/adaxial leaf surfaces of the examined species. This suggests that there is a developmental similarity among vine species in which stomata are developed with differentiation of epidermal cells on the leaf surface. Thus, leaf stomatal density and distribution appear to vary among species with different growth/life forms from different habitats under a developmental constraint of leaf surface in vine plants in Japan. [source] Developmental and light effects on the accumulation of FtsH protease in Arabidopsis chloroplasts , implications for thylakoid formation and photosystem II maintenanceTHE PLANT JOURNAL, Issue 5 2005Adi Zaltsman Summary The chloroplast ATP-dependent metalloprotease FtsH is involved in the degradation of unassembled proteins, the repair of photosystem II (PSII) from photoinhibition, and, apparently, the formation of thylakoids. In Arabidopsis, it is encoded by a family of 12 genes. However, the products of only four of them, FtsH1, 2, 5 and 8, have been found in chloroplasts to date. Mutations in two of these, FtsH2 and 5, demonstrate a visible phenotype of variegated leaves, with the phenotype of the FtsH2 mutant being more pronounced. Moreover, the degree of variegation appears to be dependent on developmental stage and environmental factors, suggesting an intricate relationship between the different gene products. To explore this, developmental and light effects on the accumulation of FtsH protease were studied in wild-type (WT) and FtsH2-mutant plants. Whereas cotyledons of the mutant were indistinguishable from those of the WT, the first true leaves were almost completely white. Subsequent leaves contained increasing proportions of green sectors. Analysis of the mRNA of the four FtsH genes, in cotyledons, first and second leaves of WT and mutant plants, revealed that: (i) transcript level increases during development, and (ii) transcript level in the mutant is higher than in the WT. FtsH protein level in the mutant was ca. 50% of that found in the WT, whereas the levels of other thylakoid proteins were the same. In individual leaves, the level of FtsH protein increased during development as well. Exposure of seedlings to different light intensities did not affect the degree of variegation, suggesting that it is due to a defect in chloroplast development rather than photobleaching. Examination of FtsH protein during exposure to high light revealed a decrease in its level, concomitant with a decrease in PSII potential, suggesting that the kinetics of photoinhibition reflects not only photodamage to PSII and induction of protective mechanisms, but also a decrease in repair capacity due to a reduction in the level of FtsH protease. [source] Salinity-induced changes in essential oil, pigments and salts accumulation in sweet basil (Ocimum basilicum) in relation to alterations of morphological developmentANNALS OF APPLIED BIOLOGY, Issue 2 2010N. Bernstein The objective of the project was to study salinity-induced effects on essential oil, pigments and salts accumulation in sweet basil (Ocimum basilicum, the cultivar Perrie) in relation to the alteration of plant morphological development and yield production. Hydroponically grown plants were exposed to one of six NaCl concentrations (1, 25, 50, 75, 100 and 130 mM NaCl). Inhibitory effects of salinity on biomass production of the shoot and the root, and area of individual leaves were apparent already under cultivation with 25 mM NaCl. Elevation of salinity from 1 to 100 mM NaCl induced 63% and 61% reductions in fresh and dry herb biomass production, respectively. The stress-induced reduction of foliage biomass sourced mainly from inhibition of leaf area development rather than reduction of internode and leaf number. Cl and Na concentrations in the leaves, stems and roots increased with elevation of NaCl concentration in the cultivation solution. While the extent of Cl accumulation was leaves>stems>roots, Na was largely excluded from the leaves and was preferentially accumulated in roots and the stems, potentially accounting for the moderate sensitivity of the leaf tissue to salinity. Salt stress increased the contents of essential oil and carotenoids in the leaves that may further account for the moderate sensitivity of sweet basil to salinity and suggest a potential for agro-industrial production. A twofold increase in both carotenoid concentration and the percent of essential oil in the fresh tissue was observed by elevation of the salinity from 1 to 130 mM NaCl. Overall, the stress induced increase of the percent of essential oil in the tissue in the salinity range 1,75 mM NaCl was about 50%, and thereby compensated for the similar reduction of biomass production in this salinity range, so that oil production on per plant basis was not reduced by salinity. [source] | ||||||||||||||||||||||