Soybean Leaf Urease: A Seed Enzyme?

The soybean (Glycine max L. [Merrill]) var Itachi has 0.2 to 0.3% the urease activity found in developing embryos of a normal line, Prize. The hydroxyurea sensitivity and pH preference of this basal seed urease indicate that it represents a unique enzyme rather than an unusually low level of the normal seed urease. Itachi's seed urease is less sensitive to hydroxyurea inhibition (65-80% inhibition) than Prize seed urease (85-95% inhibition) and is more active at pH 6.1 and 8.8 than at 7.4, whereas the normal seed urease is least active at pH 8.8. Both properties of the basal seed urease are in agreement with the behavior of the leaf urease in extracts of Prize and Itachi leaves.

Neither the leaf urease nor the Itachi seed urease is immuneprecipitated by affinity-purified seed urease antibodies. However, when antibody is in excess, Staphylococcus aureus (Cowan) cell walls containing protein A can precipitate soluble antibody-urease complexes (47-68% of total enzyme) from both leaf (Itachi and Prize) and Itachi seed extracts. Under identical conditions, greater than 90% of Prize seed urease is precipitated. At a 100-fold dilution of antibody, 60% of Prize seed urease is still antibody-complexed while the antibody recognition of the leaf or Itachi seed urease is reduced to 2 to 24%.

The cell culture urease also resembles leaf urease by the criteria of pH preference, hydroxyurea sensitivity, and recognition by seed urease antibodies. In the presence of cycloheximide, nickel stimulates cell culture urease levels (14- or 35-fold depending on assay pH) indicating that cell cultures make a preponderance of apourease under nickel-limiting conditions.

Inasmuch as the ureases of leaf, cell culture, and Itachi seeds are more closely related to each other than they are to the abundant (Prize) seed urease, suggests that the three tissues either contain an identical urease or related tissue-specific isozymes. This second form of urease may have an assimilatory role since it is found in both leaf and seed sink tissues and is required for urea assimilation in cell culture (Polacco 1977 Plant Physiol 59: 827-830).

     

Leaf Epidermal Cells： A Trap for Lipophilic Xenobiotics

Plant surfaces are covered by a layer of cuticle, which functions as a natural barrier to protect plants from mechanical damage, desiccation, and microbial invasion. Results presented in this report show that the epicuticular wax and the cuticle of plant leaves also play an important role in resisting xenobiotic invasion. Although the epicuticular wax is impermeable to hydrophilic xenobiotics, the cuticle not only restricts the penetration of hydrophilic compounds into leaf cells, but also traps lipophilic ones. The role of the epidermal cells of plant leaves in resisting xenobiotic invasion has been neglected until now. The present study shows, for the first time, that the epidermal cells may reduce or retard the transport of lipophilic xenobiotics into the internal tissues through vacuolar sequestration. Although the guard cells appear to be an easy point of entry for xenobiotics, only a very small proportion of xenobiotics present on the leaf surface actually moves into leaf tissues via the guard cells .     

Latitudinal Patterns and Climatic Drivers of Leaf Litter Multiple Nutrients in Chinese Broad-Leaved Tree Species: Does Leaf Habit Matter?

Leaf litter nutrients play a key role in nutrient cycling in forest ecosystems, yet our current knowledge of the ways in which climate controls leaf litter nutrients remains uncertain, especially for broad-leaved tree species in China. We performed a meta-analysis of geographic patterns of leaf litter nutrients of Chinese broad-leaved tree species in relation to climatic variables and leaf habit (as a discrete classification of tree species). We found that mean leaf litter carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were 458.36, 10.11, 0.72, 6.37, 14.22 and 2.59 mg^?1 g, respectively. Leaf litter nutrients did not diverge between leaf habits where they coexisted. These leaf litter nutrients displayed significant latitudinal trends, partly driven by climatic factors and a shift in leaf habit. Mean annual precipitation explained the largest amount of total variation in leaf litter C, N, P and K, and mean annual temperature was the most important predictor for leaf litter Mg, whereas leaf habit was the largest contributor to total variation in leaf litter Ca. We further found that the relationships between climate and leaf litter nutrients were distinguishable for evergreen and deciduous broad-leaved tree species. Collectively, our study differed from previous studies that evaluated leaf litter nutrients and only focused on N and P, and substantiated that leaf litter nutrients in forest ecosystems were affected by climate and leaf habit, but the strengths of the influences of these factors were strongly contingent on leaf litter nutrient identity. Therefore, alteration of climate would directly and indirectly (via a shift in species composition) affect latitudinal patterns of leaf litter nutrients and thus the associated nutrient flux and ecosystem functioning. Our study also underlined the need to include multiple nutrients to explore the influence of climate on leaf litter nutrient stoichiometry.     

Leaf phyllotaxis: Does it really affect light capture?

The intriguing mathematical properties of leaf phyllotaxis still attract scientific attention after centuries of research. Phyllotaxis, and in particular the divergence angle between successive leaves, have been frequently interpreted in terms of maximization of light capture, although certain model simulations of light capture by vertical shoots revealed minor effects of phyllotaxis in comparison with the effect of other morphological features of the plant. However, these simulations assumed a number of simplifications, did not take into account diffuse light, and were not based on real plants with their natural range of morphological variation. This study was aimed at filling these gaps by examining the influence on light harvesting of shoot architecture and divergence angle in four species with spiral phyllotaxis (Quercus ilex, Arbutus unedo, Heteromeles arbutifolia and Daphne gnidium) with a realistic 3-D model (Y-plant). A wide range of divergence angles (from 100° to 154°) was observed within each species, with 144° being the most frequent one. These different divergence angles rendered very different vertical projections of the shoot due to contrasting patterns of leaf overlap as seen from above, but they rendered indistinguishable light interception efficiencies (Ea). Setting the leaves with an opposite-decussate phyllotaxis led, however, to a 40–50% decrease of Ea. The interplay of internode length, leaf size and shape, and leaf elevation angle led to significant species differences in Ea. Thus, only particular phyllotaxis (e.g., decussate) might be functionally inefficient under certain combinations of the various morphological variables that influence light capture of a shoot. This revised version was published online in June 2006 with corrections to the Cover Date.     

Structural Response of Soybean Leaf to Elevated CO２ Concentration

The effects of CO2 concentration on the morphological and anatomical characters of soybean (Glycine max) leaf were investigated by means of light microscopy and SEM. It was noticed that exomorphology did not show dramatic change, while stomatal density decreased with increasing CO2 concentration. Under SEM, no epicuticular wax was observed on both abaxial and adaxial sides of the control group as well as on adaxial side of the treatment group. However, leaf surface of abaxial side was noticed to be densely covered with microasterisk epicuticular wax when they were exposed to CO2-enriched environment. The epicuticular wax deposition was present in equal abundance on both stomatal and nonstomatal areas. Furthermore, leaf thickness increased significantly due largely to the origin of an extra layer of palisade in the treatment group. The results confirmed that CO2 enrichment might enhance cell division and induce greater quantity of epicuticular wax.     

Leaf domatia: carbon‐limited indirect defence?

Plant‐based defence mutualisms utilize plant morphology to reduce the performance of plant parasites through their natural enemies. Leaf domatia primarily occur in the axials of secondary veins and are often inhabited by microbivorous and predaceous mites which often increase plant growth rates and reproductive success by controlling plant pests. Our study investigated if domatia investment is limited by plant primary productivity. To our knowledge no studies have tested if foliar domatia are resource‐limited. We tested our hypothesis using the genus Coprosma (Rubiaceae), conducting correlative field surveys and manipulative experiments measuring domatia production in new leaves along temperature, nutrient and irradiance gradients. Field surveys indicated a strong positive association between leaf area, the number of secondary veins, and domatia per leaf. The number of potential sites for domatia is underutilised, with leaves on selected Coprosma species having on average 47 to 72% of the ‘maximum’ number of available sites where domatia could occur. Foliar carbon was positively associated with domatia investment. Coprosma plants held under elevated night‐time temperatures showed a 34–91% decrease in daily carbon gain, a 38% decrease in domatia per leaf mass, and a positive relationship between domatia investment and integrated daily carbon gain. Under irradiance and nutrient stress, our data indicated evidence of a positive relationship between domatia investment and foliar carbon. We found a significant negative association between relative investment in domatia produced and investment in new leaf biomass. Our findings suggest investment in foliar domatia is limited by primary productivity. We propose that domatia are discretionary goods and not intrinsic structures produced automatically on leaves that mites utilize. We suggest that plants have the ability to regulate domatia formation during leaf ontogeny, with investment controlled by resource availability and some intrinsic allocation mechanism to defence.     

Do we Underestimate the Importance of Leaf Size in Plant Economics? Disproportional Scaling of Support Costs Within the Spectrum of Leaf Physiognomy

BACKGROUND: Broad scaling relationships between leaf size and function do not take into account that leaves of different size may contain different fractions of support in petiole and mid-rib. METHODS: The fractions of leaf biomass in petiole, mid-rib and lamina, and the differences in chemistry and structure among mid-ribs, petioles and laminas were investigated in 122 species of contrasting leaf size, life form and climatic distribution to determine the extent to which differences in support modify whole-lamina and whole-leaf structural and chemical characteristics, and the extent to which size-dependent support investments are affected by plant life form and site climate. KEY RESULTS: For the entire data set, leaf fresh mass varied over five orders of magnitude. The percentage of dry mass in mid-rib increased strongly with lamina size, reaching more than 40 % in the largest laminas. The whole-leaf percentage of mid-rib and petiole increased with leaf size, and the overall support investment was more than 60 % in the largest leaves. Fractional support investments were generally larger in herbaceous than in woody species and tended to be lower in Mediterranean than in cool temperate and tropical plants. Mid-ribs and petioles had lower N and C percentages, and lower dry to fresh mass ratio, but greater density (mass per unit volume) than laminas. N percentage of lamina without mid-rib was up to 40 % higher in the largest leaves than the total-lamina (lamina and mid-rib) N percentage, and up to 60 % higher than whole-leaf N percentage, while lamina density calculated without mid-rib was up to 80 % less than that with the mid-rib. For all leaf compartments, N percentage was negatively associated with density and dry to fresh mass ratio, while C percentage was positively linked to these characteristics, reflecting the overall inverse scaling between structural and physiological characteristics. However, the correlations between N and C percentages and structural characteristics differed among mid-ribs, petioles and laminas, implying that the mass-weighted average leaf N and C percentage, density, and dry to fresh mass ratio can have different functional values depending on the importance of within-leaf support investments. CONCLUSIONS: These data demonstrate that variation in leaf size is associated with major changes in within-leaf support investments and in large modifications in integrated leaf chemical and structural characteristics. These size-dependent alterations can importantly affect general leaf structure vs. function scaling relationships. These data further demonstrate important life-form effects on and climatic differentiation in foliage support costs.     

phenoVein—A Tool for Leaf Vein Segmentation and Analysis

Precise measurements of leaf vein traits are an important aspect of plant phenotyping for ecological and genetic research. Here, we present a powerful and user-friendly image analysis tool named phenoVein. It is dedicated to automated segmenting and analyzing of leaf veins in images acquired with different imaging modalities (microscope, macrophotography, etc.), including options for comfortable manual correction. Advanced image filtering emphasizes veins from the background and compensates for local brightness inhomogeneities. The most important traits being calculated are total vein length, vein density, piecewise vein lengths and widths, areole area, and skeleton graph statistics, like the number of branching or ending points. For the determination of vein widths, a model-based vein edge estimation approach has been implemented. Validation was performed for the measurement of vein length, vein width, and vein density of Arabidopsis (Arabidopsis thaliana), proving the reliability of phenoVein. We demonstrate the power of phenoVein on a set of previously described vein structure mutants of Arabidopsis (hemivenata, ondulata3, and asymmetric leaves2-101) compared with wild-type accessions Columbia-0 and Landsberg erecta-0. phenoVein is freely available as open-source software.Leaf veins are an important aspect of leaf structure and responsible for both the mechanical support of leaves and the long-distance transport of water, nutrients, and photoassimilates (Onoda et al., 2011; Malinowski, 2013). The molecular mechanisms by which vascular tissues acquire their identities are yet largely unknown (Roschzttardtz et al., 2014), and there is high interest in analyzing and evaluating traits of veins or leaf venation networks and their genetic regulation. The impact of vein density on photosynthesis is a major investigated topic (Sack and Scoffoni, 2013). During the last decade, a positive correlation between leaf venation and photosynthesis has been observed (Sack and Holbrook, 2006; Brodribb et al., 2007). An optimization of photosynthetic rates was shown to occur by spatial coordination between leaf vein and stomatal densities (Zhang et al., 2012; Carins Murphy et al., 2014; Fiorin et al., 2015). Additionally, there is interest in the impact of vein density on interveinal distances (Dengler et al., 1994; McKown and Dengler, 2009) and the effect of climate, habitat, or growth form on vein density (Sack and Scoffoni, 2013; Scoffoni et al., 2015) or vein width with respect to leaf hydraulic conductance (Feild and Brodribb, 2013; Xiong et al., 2015). Other researchers are particularly interested in the evolution from C3 to C4 plants, which requires higher vein density (Gowik and Westhoff, 2011) and led to selecting for variation of vein density within species (e.g. in a mutant collection by Feldman et al., 2014).Leaf venation studies analyzing traits of veins and venation networks are generally performed on microscopic images of leaves that are properly cleared after harvest. For very small leaves, e.g. the cotyledons or the first leaves (leaves 2–5) of Arabidopsis (Arabidopsis thaliana), basic traits, such as total vein length or vein density (vein length per leaf area), can be achieved manually. However, for larger leaves, manual vein segmentation may become tedious, and at least partially automated analysis is needed for studies on large series of leaf collections. Furthermore, the quantification of vein widths and in particular mean values of vein width of certain vein pieces of interest can hardly be achieved manually. Dedicated image processing tools are, therefore, needed to support researchers for fast and reliable data analysis.A number of software tools have been published that are either specifically made or adapted to analyze leaf veins. These programs have some common properties, like image processing functionalities for vein/areole segmentation and trait extraction. However, they differ in handling strategies or vein parameter analysis methods. A general overview on plant image analysis tools is collected in an online database at http://www.plant-image-analysis.org (Lobet et al., 2013). Programs allowing automated or semiautomated analysis of leaf venation parameters are, for example, a method to extract leaf venation patterns (Rolland-Lagan et al., 2009), the leaf extraction and analysis framework graphical user interface LeafGUI (Price et al., 2011), the leaf image analysis interface LIMANI (Dhondt et al., 2012), the user-interactive vessel generation analysis tool VESGEN (Vickerman et al., 2009; Parsons-Wingerter et al., 2014), and the software network extraction from images NEFI (Dirnberger et al., 2015). Nevertheless, for the analysis of large-scale leaf vein phenotyping experiments, there are certain needs that are only partly covered by each of the approaches and programs mentioned above. Specifically, the following properties are needed: (1) automated vein segmentation with optional manual correction; (2) invariance of the segmentation procedure to inhomogeneous illumination or brightness variations in the leaf image; (3) automated determination of total vein length and projected leaf area; (4) a well-defined and automated determination of vein widths, which is, as far as possible, independent of user chosen thresholds; (5) ability to process large high-resolution images of whole leafs; and (6) full transparency of the source code as well as offline availability of the tool. To provide these functionalities, we developed the user-friendly analysis tool phenoVein. It features automated leaf vein segmentation based on advanced image filtering techniques and includes determination of various vein traits, particularly a model-based vein width estimation. phenoVein allows easy and fast visual control and manual correction on the automatically achieved skeleton of the veins enabled by a real-time overlay of the segmented leaf vein structures on the original image. The length measurement algorithm of phenoVein was validated against complete manual segmentation. We evaluated the impact of image resolution on the results, which has recently been discussed (Price et al., 2014; Sack et al., 2014), and tested whether the orientation (angle) of a leaf on an image may affect the results as suspected from image analysis theory on binary skeleton length measurements (Russ, 2011). To show the powerful phenotyping capabilities of phenoVein, we analyzed the venation traits of leaves of Arabidopsis at different developmental stages (cotyledons, pooled leaves 1 + 2, and leaf 6) harvested from previously described venation mutants and corresponding wild-type lines: asymmetric leaves2-101 (as2-101), ondulata3 (ond3), and hemivenata2 (hve-2) versus Columbia-0 (Col-0) and Landsberg erecta-0 (Ler-0; Semiarti et al., 2001; Alonso-Peral et al., 2006; Robles et al., 2010; Pérez-Pérez et al., 2011). We offer the source code of phenoVein to the public as open-source software that can be further adapted or improved (for details, see “Materials and Methods”).     

Photosynthesis and Leaf Structure in Domesticated Cassava (Euphorbiaceae) and a Close Wild Relative: Have Leaf Photosynthetic Parameters Evolved Under Domestication?

Broad patterns across wild plant species show that leaf composition and morphology vary predictably among habitats, richer habitats favoring resource‐acquisition strategies and poorer habitats favoring resource‐conservation strategies. Domestication is often accompanied by a shift to richer habitats, and might thus be expected to lead to a shift in leaf composition and morphology and hence in photosynthetic parameters. We compared leaf photosynthetic parameters in domesticated cassava (Manihot esculenta) and a close wild relative, using greenhouse‐grown plants. In domesticated cassava, CO₂ exchange rate expressed per unit mass and specific leaf area (SLA, m²/kg dry mass) were greater than in the wild relative, whereas leaf dry matter content (LDMC, dry mass/fresh mass) was lower in the domesticate. These results suggest that SLA and net photosynthetic rates may both have increased in the evolution of cassava under domestication, enabling more rapid growth in relatively resource‐rich and protected agricultural habitats. Previous comparisons of photosynthetic rates in domesticated plants and wild relatives have usually considered only leaf area‐based measures. Here, we discuss the interest of using mass‐based rates to study the evolution of ecological strategies under domestication.     

Leaf structural modifications in Populus × euramericana subjected to Zn excess

In previous experiments elevated but sub-symptomatic applications of Zn (0.1 mM and 1 mM) caused impairments in growth parameters and photosynthetic performance of Populus × euramericana (Dode) Guinier clone I-214. The aim of this work was to evaluate leaf morphological and anatomical traits in this clone in response to the same Zn concentrations. The results showed that Zn treatments induced variations in leaf dry mass, area, mesophyll thickness, intercellular spaces, stomatal density and size. Stronger modifications, especially concerning stomata characteristics induced by 1 mM Zn, were consistent with physiological impairments while those induced by 0.1 mM Zn suggested a compensatory strategy for maintaining functional integrity.     

Cotton Leaf Curl Virus： Ionic Status of Leaves and Symptom Development

In the present study, the relationship between the nutritional status of leaves and the development of symptoms of cotton leaf curl virus （CLCuV） in two cotton （Gossypium hirsutum L.） cuItlvars （I.e. CIM-240 and S-12） was Investigated. The incidence of disease attack was found to be 100% In the S-12 cuItlvar and 16% in the CIM-240 cuItivar. Geminivirus particles in infected leaves were confirmed by transmission electron microscope examination of highly specific geminivirus coat protein antlsera-treated cell sap. The CLCuV Impaired the accumulation of different nutrients in both cuItivars. A marked decrease in the accumulation of Ca^2＋ and K^＋ was observed in infected leaves. However, the disease had no effect on leaf concentrations of Na^＋, N, and P. It was observed that the curling of leaf margins in CLCuV-Infected plants was associated with the leaf Ca^2＋ content; leaf curling was severe in plants with a significant reduction In Ca^2＋ content. Moreover, leaf K＆＋ content was found to be associated with resistance/susceptibility to CLCuV infection.     

Can Leaf Litter from Genetically Modified Trees Affect Aquatic Ecosystems?

In addition to potential benefits, biotechnology in silviculture may also be associated with environmental considerations, including effects on organisms associated with the living tree and on ecosystems and processes dependent on tree residue. We examined whether genetic modification of lignin characteristics (CAD and COMT) in Populus sp. affected leaf litter quality, the decomposition of leaf litter, and the assemblages of aquatic insects colonizing the litter in three natural streams. The decomposition of leaf litter from one of the genetically modified (GM) lines (CAD) was affected in ways that were comparable over streams and harvest dates. After 84 days in streams, CAD-litter had lost approximately 6.1% less mass than the non-GM litter. Genetic modification also affected the concentration of phenolics and carbon in the litter but this only partially explained the decomposition differences, suggesting that other factors were also involved. Insect community analyses comparing GM and non-GM litter showed no significant differences, and the two GM litters showed differences only in the 84-day litterbags. The total abundance and species richness of insects were also similar on GM and non-GM litter. The results presented here suggest that genetic modifications in trees can influence litter quality and thus have a potential to generate effects that can cross ecosystem boundaries and influence ecosystem processes not directly associated with the tree. Overall, the realized ecological effects of the GM tree varieties used here were nevertheless shown to be relatively small.     

Spring Wheat Leaf Appearance and Temperature: Extending the Paradigm?

Extensive research shows temperature to be the primary environmental factor controlling the phyllochron, or rate of leaf appearance, of wheat (Triticum aestivum L.). Experimental results suggest that soil temperature at crown depth, rather than air temperature above the canopy, would better predict wheat leaf appearance rates. To test this hypothesis, leaf appearance in spring wheat ('Nordic') was measured in a 2-year field experiment (Nunn clay loam soil; fine, smectitic, mesic Aridic, Argiustoll) with three planting dates and two soil temperature treatments. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3 degrees C above the ambient soil temperature (denoted +0C). Main stem cumulative leaf number was measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although there was a stronger linear relationship with soil GDD in the +0C plants than in +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found that heating the soil did not increase the rate of leaf appearance, as the paradigm would predict. To explain these results, we propose extending the paradigm in two ways. First, three processes are involved in leaf appearance: (1) cell division at the shoot apex forms the primordium; (2) cell division in the intercalary meristem forms the cells that then (3) expand to produce the leaf. Cell division is predominantly controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining the influence of other factors on the phyllochron. Secondly, the vertical distribution of the two meristems and region of cell expansion occur over a significant distance, where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for the entire temperature regime under which leaves are developing.     

Blue Light Induction of Barley Leaf Unfolding. A Phytochrome Reaction?

Low-energy blue light (450, 475 nm) has been found to induced unfolding of etiolated barley leaves (Hordeum rulgare cv. Ingrid). This induction can be reversed by far-red light. Barley leaf unfolding is normally stimulated by red light, reversed by far-red light, and can be considered to be a typical phytochrome controlled response. It is possible to explain the effects by red and blue light as mediated by the same photoreceptor. The phototransformation of this pigment results in two forms, P₂ and P₄, to which physiological activity can be ascribed. The red and blue light affect different steps in a cyclical photoconversion. Calculated theoretical dose response curves are presented for such a model in agreement with the experimental data.     

Leaf anatomy and water loss of in vitro PEG-treated ‘Valiant’ grape

Polyethylene glycol was used to induce water stress of micropropagated Valiant grape. Reduced growth and slow rooting were observed in treated plantlets with 2, 4 and 6% polyethylene glycol as compared to control plantlets with no polyethylene glycol in the rooting medium. At high concentrations of 4 and 6%, leaves exhibited wilting and necrosis. At the 2% level, plantlets recovered and grew satisfactorily. Detached leaves of treated plantlets with 2% polyethylene glycol lost less water than controls when exposed to low humidity for 4 hours. Leaf anatomy of plantlets treated with 2% polyethylene glycol, control (in vitro plantlets) and greenhouse-grown plants were compared under light microscopy. Leaves from control plantlets contained larger mesophyll cells, lacked normal palisade layer formation, had greater intercellular pore spaces and fewer chloroplasts. Leaves from polyethylene glycol-treated plantlets, however, had smaller mesophyll cells, a more defined palisade layer, reduced intercellular pore space and the greatest number of chloroplasts. These results suggest that an osmoticum such as polyethylene glycol may be used to induce more normal leaf anatomy and reduced water loss in micropropagated Valiant grapes.Abbreviations BA 6-benzylaminopurine - FAA formalin-acetol-alcohol - MS Murashige & Skoog (1962) medium - MW molecular weight - NAA napthaleneacetic acid - PEG polyethylene glycol - TBA tertiary butyl alcohol     

Leaf variegation in Caladium steudneriifolium (Araceae): a case of mimicry?

The leaves of Caladium steudneriifolium (Araceae) of the understorey of a submontane rainforest in the Podocarpus National Park (South East Ecuador, 1,060 m a.s.l.) are plain green or patterned with whitish variegation. Of the 3,413 individual leaves randomly chosen and examined in April 2003, two-thirds were plain green, whereas one third were variegated (i.e., whitish due to absence of chloroplasts). Leaves of both morphs are frequently attacked by mining moth caterpillars. Our BLAST analysis based on Cytochrome-c-Oxidase-subunit-1 sequences suggests that the moth is possibly a member of the Pyraloidea or another microlepidopteran group. It was observed that the variegated leaf zones strongly resemble recent damages caused by mining larvae and therefore may mimic an attack by moth larvae. Infestation was significantly 4–12 times higher for green leaves than for variegated leaves. To test the hypothesis that variegation can be interpreted as mimicry to deter ovipositing moths, we first ruled out the possibility that variegation is a function of canopy density (i.e., that the moths might be attracted or deterred by factors unrelated to the plant). Then plain green leaves were artificially variegated and the number of mining larvae counted after 3 months. The results on infestation rate (7.88% of green leaves, 1.61% of the variegated leaves, 0.41% of white manipulated leaves and 9.12% of uncoloured manipulated leaves) suggest that ovipositing moths are deterred by the miner-infestation mimicry. Thus, variegation might be beneficial for the plants despite the implicated loss of photosynthetically active surface.     

Modelling Plant Responses to Elevated CO2: How Important is Leaf Area Index?

BACKGROUND AND AIMS: The problem of increasing CO(2) concentration [CO(2)] and associated climate change has generated much interest in modelling effects of [CO(2)] on plants. While variation in growth and productivity is closely related to the amount of intercepted radiation, largely determined by leaf area index (LAI), effects of elevated [CO(2)] on growth are primarily via stimulation of leaf photosynthesis. Variability in LAI depends on climatic and growing conditions including [CO(2)] concentration and can be high, as is known for agricultural crops which are specifically emphasized in this report. However, modelling photosynthesis has received much attention and photosynthesis is often represented inadequately detailed in plant productivity models. Less emphasis has been placed on the modelling of leaf area dynamics, and relationships between plant growth, elevated [CO(2)] and LAI are not well understood. This Botanical Briefing aims at clarifying the relative importance of LAI for canopy assimilation and growth in biomass under conditions of rising [CO(2)] and discusses related implications for process-based modelling. MODEL: A simulation exercise performed for a wheat crop demonstrates recent experimental findings about canopy assimilation as affected by LAI and elevation of [CO(2)]. While canopy assimilation largely increases with LAI below canopy light saturation, effects on canopy assimilation of [CO(2)] elevation are less pronounced and tend to decline as LAI increases. Results from selected model-testing studies indicate that simulation of LAI is often critical and forms an important source of uncertainty in plant productivity models, particularly under conditions of limited resource supply. CONCLUSIONS: Progress in estimating plant growth and productivity under rising [CO(2)] is unlikely to be achieved without improving the modelling of LAI. This will depend on better understanding of the processes of substrate allocation, leaf area development and senescence, and the role of LAI in controlling plant adaptation to environmental changes.