Erythronium dens-canis L. (Liliaceae): An unusual case of change of leaf mottling

ArticleinPlant Physiology and Biochemistry 74C:108-117 · November 2013with 240 Reads
Cite this publication
Abstract
Erythronium dens-canis is an early-flowering understory lily of southern Europe with two leaves and a single flower, although a number of plants have only one leaf and do not flower. The leaves are mottled with silvery flecks and brown patches, that gradually vanish turning to a lively green color. The nature and function of this striking variegation pattern were investigated in differently colored leaf parts following the springtime color change. Tissue organization was examined by light and electron microscopy; photosynthetic pigments were analyzed by spectrophotometry and HPLC; chlorophyll fluorescence parameters were evaluated by MINI-PAM. The results showed that brown patches originated in vacuolar anthocyanins in the subepidermal cell layer while air spaces between the upper epidermis and underlying chlorenchyma resulted in silvery flecks. The two leaf areas did not differ in photosynthetic pigments, chloroplast organization and photosynthetic parameters (Fv/Fm, NPQ, rETR). Greening of brown patches due to anthocyanin resorption was faster in non-flowering plants than in flowering ones, occurring only when young fruits were developing. Anthocyanin disappearance did not change the structural-functional features of photosynthetic tissues. As a whole the results suggest that the anthocyanin pigmentation of E. dens-canis leaves does not affect the photosynthetic light use and has no photoprotective function. It is proposed that the complex leaf color pattern may act as a camouflage to escape herbivores, while the reflective silvery spots may have a role in attracting pollinators of this early-flowering species.

Do you want to read the rest of this article?

Request full-text
Request Full-text Paper PDF
  • Article
    Full-text available
    Relationships between age, time of emergence, and leaf traits of individuals were investigated in a population of Erythronium dens-canis L. in a hilly woodland area named Farneto-C, near Bologna, Italy. In 2015, 591 individuals were counted, 19 of which were flowering (FLO), 442 were mature non-flowering (MNF) and 130 were juveniles (JUV). FLO emerged at the end of February, whereas most MNF and JUV appeared at the middle and end of March, respectively. The mean aboveground survivorship of MNF was 24 days. Most MNF had large, oval to shield-shaped leaves with red-brown mottling, whereas most JUV leaves were smaller, usually oblong or lanceolate with a rough maculation or none. These results suggest that both timing of emergence and leaf shape are related to the age of the bulb. Based on leaf background, plants were classified into three major types with a likely genetic basis in the 2015 and 2016 surveys (the latter limited to FLO): a dominant silvery type (SLV, 62–74%), silvery-and-green type (S&G, 23–32%), and a less frequent vivid-green type (GRN, 3–5%). Several subtypes were also identified, but only one was dominant within each type. The three basic patterns appear to be phenotypically stable and no differences between MNF and FLO were found; once the juvenile stage has passed, each plant produces the same leaf type year after year. In addition, our results on the discoloration time-course of red-brown spots suggest that the functional role of leaf mottling is not related to pollinator attraction. Instead, leaf mottling could play a role in camouflage against herbivores.The observed massive grazing on flowers, more than leaves, could explain why the frequency of mature individuals was biased towards the non-flowering ones.
  • Article
    Since spring ephemerals are credited to be all “sun” species with unusually elevate photosynthesis, in contrast to shade-tolerant trees and understory geophytes with a long aboveground cycle, we examined the photosynthetic efficiency of 6 woody species, 9 long-cycle geophytes, and 8 spring ephemeral geophytes using blue flashes of increasing energy with the Imaging PAM fluorometer. Several parameters were obtained: quantum yield of electron transport (ΦETR) or of PSII (ΦPSII), maximum measured photosynthesis rate (ETRhv), maximum extrapolated rate of photosynthesis (ETRem), half-saturating photon flux density (KPAR), and in some cases photochemical (qP) and non-photochemical quenching (NPQ). Results confirm the ecological consistency of the three plant groups, with internal differences. Woody species have low ETRem and KPAR values with good ΦETR; long-cycle herbs have low ETRem and ΦETR and moderate KPAR values; spring ephemerals have elevate ΦETR, ETRem and KPAR values. The mean ETRem of ephemerals of 91 μmol m⁻² s⁻¹ exceeds that of long-cycle herbs 2.9-fold and woody species 4.8-fold, and corresponds to 19 μmol CO2 m⁻² s⁻¹ by assuming an ETR/ΦCO2 ratio of 4.7. Highest photosynthesis rates and KPAR were exhibited by five ephemerals (Eranthis, Erythronium, Narcissus, Scilla, Tulipa) with peak ETRem values equivalent to ∼40 μmol CO2 m⁻² s⁻¹ or ∼60 μmol CO2 (g Chl)⁻¹ s⁻¹ (“sun” species). According to a new, fluorescence based heliophily index, all trees and five long-cycle herbs were definitely “shade” species, while four long-cycle herbs and three ephemerals were intermediate shade-tolerant.
  • Article
    Relationships between age, time of emergence, and leaf traits of individuals were investigated in a population of Erythroniumdens-canis L. in a hilly woodland area named Farneto-C , near Bologna, Italy. In 2015, 591 individuals were counted, 19 of which were flowering (FLO), 442 were mature non-flowering (MNF) and 130 were juveniles (JUV). FLO emerged at the end of February, whereas most MNF and JUV appeared at the middle and end of March, respectively. The mean aboveground survivorship of MNF was 24 days. Most MNF had large, oval to shield-shaped leaves with red-brown mottling, whereas most JUV leaves were smaller, usually oblong or lanceolate with a rough maculation or none. These results suggest that both timing of emergence and leaf shape are related to the age of the bulb. Based on leaf background, plants were classified into three major types with a likely genetic basis in the 2015 and 2016 surveys (the latter limited to FLO): a dominant silvery type (SLV, 62–74%), silvery-and-green type (S&G, 23–32%), and a less frequent vivid-green type (GRN, 3–5%). Several subtypes were also identified, but only one was dominant within each type. The three basic patterns appear to be phenotypically stable and no differences between MNF and FLO were found; once the juvenile stage has passed, each plant produces the same leaf type year after year. In addition, our results on the discoloration time-course of red-brown spots suggest that the functional role of leaf mottling is not related to pollinator attraction. Instead, leaf mottling could play a role in camouflage against herbivores.The observed massive grazing on flowers, more than leaves, could explain why the frequency of mature individuals was biased towards the non-flowering ones.
  • Article
    Full-text available
    Cyclamen purpurascens originates from the forest understorey and has variegated leaves and red abaxial epidermis. We measured the morphological and biochemical traits, and reflectance and transmittance spectra of leaves of C. purpurascens sampled through the growing season. We determined the optical properties and differences between the light-green and dark-green sections of the variegated leaves, and investigated the role of the red abaxial epidermis. The light-green leaf sections contained lower contents of chlorophyll a and b, carotenoids (in all samples) and anthocyanins (in April only) per leaf area, compared to the dark-green leaf sections, although the ratios of chlorophyll a to b and carotenoids to total chlorophyll were the same, except in April. During the closing of the canopy, chlorophyll a and b contents increased, while contents of carotenoids and anthocyanins decreased, as did the chlorophyll a/b and carotenoid/total chlorophyll ratios. The optical properties of the leaves in February showed high reflectance for UV and violet radiation, and low reflectance for near infrared radiation, for both types of leaf sections. The transmittance spectra for leaves without the red anthocyanic epidermis showed a pronounced peak from 520 nm to 625 nm, and enhancement in the near infrared region. The relative reflectance spectra of the red and colourless abaxial epidermis alone differed only in the green and yellow range. The relative transmittance of the red abaxial epidermis was significantly lower than for the colourless epidermis over the entire spectral range. Decreased transmittance in the green and yellow was obtained only for the red coloured abaxial epidermis. The variability of transmittance spectra during the season is best explained by the levels of chlorophyll b, carotenoids and anthocyanins. Our data reveal the importance of these pigments in leaf variegation, and particularly of the red abaxial anthocyanic epidermis for absorbing light in the green, yellow and near infrared.
  • Chapter
    Full-text available
    It has been suggested that white variegation, the outcome of various developmental, genetic, and physiological processes, may defend leaves and other plant organs from herbivory by several proposed mechanisms: camouflage, aposematism (including Müllerian and Batesian mimicry), mimicry of insect damage and fungal attacks, dazzle effects that make it hard for large herbivores to decide where to bite the leaves and for insects to land on them, and by visual repellence of insects from landing as well as by unknown mechanisms. Very few cases of these suggested leaf defenses by variegation have been examined in depth. Some such studied cases were indeed found to actually operate as defense from herbivory either in nature or in experiments, suggesting the potential defensive function of others. However, the specific operating defensive mechanism by white variegation was not always identified or even proposed, even when variegation was found to be associated with reduced herbivory. Studying white variegation has a significant advantage over studying other types of plant defensive coloration because even bi-chromatic vision is sufficient to see these patterns. Moreover, white variegation is probably visible under most types of natural light conditions, including strong moonlight. While in this essay I wish to stimulate an effort for a broader and deeper understanding of the defensive roles of white variegation, the possible simultaneous physiological roles of white leaf variegation that will not be reviewed here should not be ignored.
  • Article
    Cryptic colouration is a common predation-avoidance strategy in animals that is postulated to occur in plants, but few experimental studies have rigorously tested this hypothesis.We investigated the colouration of Corydalis benecincta, an alpine plant with remarkably dimorphic leaf colours (grey and green), based on a cost–benefit analysis. First we tested the premise that herbivores (Parnassius butterflies) cannot distinguish grey leaves from a scree background by spectrographic measurements and by estimating discriminability between leaves and scree using a butterfly colour vision model. Then we estimated the potential costs of inconspicuousness by comparing the photosynthetic performance and visual attractiveness to flower visitors of the two colour morphs. Finally, we examined the potential benefits of inconspicuousness by comparing damage, survivorship and female reproductive success.It is difficult for herbivores to distinguish grey-coloured morphs against the background. This grey colour originates in a combination of anthocyanins and chlorophylls. The two colour morphs had similar photosynthetic performance, visual attractiveness and female reproductive success. However, grey morphs had significantly lower herbivore damage and higher survivorship.Grey leaves benefit C. benecincta by reducing herbivory with low investment in anthocyanin synthesis, and little cost on photosynthesis and mating opportunity. This cryptic colouration may have evolved through selection pressure imposed by visually foraging herbivores.
  • Article
    Full-text available
    Populations of Pulmonaria with unique features and associated with shady and dry conditions were found in high beech woods on the west side of Mt. Marzola and in other dolomitic sites of Trentino (southern Alps). Morpho-statistical and karyological analyses suggest that these populations represent a new subspecies of P. officinalis, Pulmonaria officinalis subsp. marzolae. The change of the basal leaves shape during the year, the peculiar traits of foliar spots and hairs as well as a divergence of the karyotype asymmetry indices are distinct from the typical form of P. officinalis, whereas the general form, the major hair types, inflorescence morphology and the chromosome number 2n = 16 reveal their affinity to this species.
  • Article
    Full-text available
    Studies of species' range limits focus most often on abiotic factors, although the strength of biotic interactions might also vary along environmental gradients and have strong demographic effects. For example, pollinator abundance might decrease at range limits due to harsh environmental conditions, and reduced plant density can reduce attractiveness to pollinators and increase or decrease herbivory. We tested for variation in the strength of pollen limitation and herbivory by ungulates along a gradient leading to the upper elevational range limits of Trillium erectum (Melanthiaceae) and Erythronium americanum (Liliaceae) in Mont Mégantic National Park, Québec, Canada. In T. erectum, pollen limitation was higher at the range limit, but seed set decreased only slightly with elevation and only in one of two years. In contrast, herbivory of T. erectum increased from <10% at low elevations to >60% at the upper elevational range limit. In E. americanum, we found no evidence of pollen limitation despite a significant decrease in seed set with elevation, and herbivory was low across the entire gradient. Overall, our results demonstrate the potential for relatively strong negative interactions (herbivory) and weak positive interactions (pollination) at plant range edges, although this was clearly species specific. To the extent that these interactions have important demographic consequences—highly likely for herbivory on Trillium, based on previous studies—such interactions might play a role in determining plant species' range limits along putatively climatic gradients.
  • Article
    Background and aims – Sedum hispanicum acts as a pioneer species on the gypsum outcrops of Emilia Romagna region (Northern Italy). The species was studied in two Sites of Community Importance through a comparative phenological and genetic diversity analysis to provide insights into strategies adopted by the species for successful reproduction in the harsh conditions of these rocky outcrops. Methods – Phenology was examined in individuals from four sampling sites chosen in one study area (Gessi Bolognesi e Calanchi dell’Abbadessa, GB) from March to June in two years (2013 and 2015) with different spring temperatures. Reproductive and vegetative phenophases were compared among sites and over years. ISSR-based molecular analysis was performed to obtain genetic diversity measures on individuals collected at the same four GB sites and, for comparison, in a second area (Gessi di Monte Rocca, Monte Capra e Tizzano). Key results – Individuals at the four GB sites showed inter-annual differences in full flowering and leaf senescence, but intra-annual synchrony of all monitored phenophases. Moderate amounts of genetic diversity were observed in the two areas (P% = 79.67, 67.48; I = 0.209, 0.205; He = 0.118, 0.122). Low genetic structure (Φst = 0.05; Gst = 0.06) and high gene flow (Nm = 3.92) resulted within the GB area. Genetic differentiation was higher between the two areas (Φst = 0.37, Gst = 0.22). Evidence of inbreeding (s = 0.61) was found in the GB area. Conclusions – Inter-annual differences in timing of full flowering phenophase seem to be related chiefly to spring temperatures. The estimates of genetic diversity in S. hispanicum are comparable to those of autogamous and clonal species, while the partitioning of genetic diversity reflects the low structure typical of outcrossing species. Intra-annual flowering synchrony is likely to promote sexual reproduction. Sedum hispanicum seems to adopt multiple reproductive modes to overcome environmental extremes of gypsum outcrops. © 2017 Botanic Garden Meise and Royal Botanical Society of Belgium.
  • Article
    Full-text available
    The small genus Pisum is composed of two annual species, P. fulvum and the domesticated pea P. sativum. The domesticated pea has two main wild-type taxa: P. elatius and P. humile. Members of the genus Pisum are not well defended from herbivory by high levels of toxins like the seeds of many other legume species. We studied the color patterns in the pods and seeds of these three wild taxa (P. fulvum, P. elatius and P. humile) in order to examine their potential for defensive coloration (camouflage and Batesian mimicry). All three taxa are polymorphic concerning pod and seed coloration. The mature pods of many individuals of P. humile and P. elatius mimic aposematic caterpillars, but some are plain green. The pods of some individuals of P. elatius have a zigzag or straight red marking along them that resembles the conspicuous dorsal markings of the local common venomous viper, potentially mimicking it. The pods of many individuals of P. fulvum have dark blotches that when compared to such patterns in animals, potentially function as camouflage. The seeds of all three species are camouflaged by either: (1) color matching with that of soil (especially P. fulvum and P. elatius), (2) disruptive coloration (especially P. humile), (3) variability in seed-coat color that may undermine the use of search images by visually oriented granivores that look for cryptic seeds (all taxa). The mature pods of P. fulvum are also defended in many inflorescences by degenerated flowers that develop into sharp thorns. It seems that this species is still in the process of evolving this mechanical defense as the response to millennia of strong grazing pressure.
  • Article
    Full-text available
    The fdl1-1 mutation, caused by an Enhancer/Suppressor mutator (En/Spm) element insertion located in the third exon of the gene, identifies a novel gene encoding ZmMYB94, a transcription factor of the R2R3-MYB subfamily. The fdl1 gene was isolated through co-segregation analysis, whereas proof of gene identity was obtained using an RNAi strategy that conferred less severe, but clearly recognizable specific mutant traits on seedlings. Fdl1 is involved in the regulation of cuticle deposition in young seedlings as well as in the establishment of a regular pattern of epicuticular wax deposition on the epidermis of young leaves. Lack of Fdl1 action also correlates with developmental defects, such as delayed germination and seedling growth, abnormal coleoptile opening and presence of curly leaves showing areas of fusion between the coleoptile and the first leaf or between the first and the second leaf. The expression profile of ZmMYB94 mRNA-determined by quantitative RT-PCR-overlaps the pattern of mutant phenotypic expression and is confined to a narrow developmental window. High expression was observed in the embryo, in the seedling coleoptile and in the first two leaves, whereas RNA level, as well as phenotypic defects, decreases at the third leaf stage. Interestingly several of the Arabidopsis MYB genes most closely related to ZmMYB94 are also involved in the activation of cuticular wax biosynthesis, suggesting deep conservation of regulatory processes related to cuticular wax deposition between monocots and dicots. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.
  • Article
    Full-text available
    Drought is one of the most damaging types of abiotic stresses that causes significant annual yield losses, and poses a serious threat to sustainable agriculture. However, like other stressors, the drought triggers in plants a wide range of responses that are implemented at the molecular, cellular and organism level and aimed at reducing the damaging effects and formation of plant tolerance to water deficit. The study of plant adaptive responses to drought and interpretation of mechanisms to enhance drought tolerance requires adequate and reliable methods of experimentation and objective methods for assessment of research results. The review examined three types of current models that are used in experiments on the effect of drought on plants, namely, soil, water, and agar models. The main advantages and disadvantages of each model are discussed including models with drought conditions simulation by providing PEG in the root medium but the choice of optimal model should be determined depending on the specific problems solved by the experimenter. Currently, researchers have a wide range of methodological approaches and tools for objective assessment of changes in physiological and biochemical parameters of plants in response to the drought. Among the most common are methods associated with the assessment of such parameters as stomatal conductance, photosystem II efficiency using PAM fluorometry, accumulation of osmotically active substances. Special attention is given to methods of assessing the activity of the antioxidant systems in plants, primarily of ascorbate-glutathione cycle as one of the most efficient methods in screening species and varieties of plants on drought tolerance. It should concluded that for the successful development of new strategies aimed at the improvement of drought resistance of plants the acquisition of knowledge is required with the use of current molecular biological methods based on the application of metabolomics and proteomic analyses of plants.
  • Article
    Macaranga bancana is considered as a successful pioneer plant species. Usually found in disturbed and open areas, most of the current research focused on its relations with ants. One of the unique feature of the plants is that the seedling leaves are red, resembling and almost matching the background. Using a portable spectrometer, we measured the color reflectance of M. bancana seedlings (less than 20 cm in height). We also measured the leaf litter reflectance, adult M. bancana leaves and also seedlings of several other species found in the vicinity of M. bancana seedlings. The reflectances of M. bancana seedlings are very similar to that of the leaf litter background. We suggest that this cryptic coloration is crucial during the early stages of the plant when it still cannot rely on the protection of ants.
  • Chapter
    Concerning defensive signaling by white marking, two evolutionary issues should be specifically mentioned: first, the significance of white marking in contrast to colorful marking and second, the probable convergence of this character as expressed by geography and taxonomy. When a certain herbivore is color-blind to a certain sector of the spectrum or is color-blind altogether; or when illumination is not strong or it has an altered color temperature for some meteorological, ecological, or daytime related reason, then white marking increases the possibility that a signal will still be visible. As will be discussed below in several chapters, defensive white marking seems to be common in many plant species originating in various taxa, continents, ecologies, life forms and in many plant organs (see Lev-Yadun 2001, 2003a, 2014a, b, c, d).
  • Article
    Full-text available
    There is strong empirical evidence that foliar anthocyanins assist in protecting chloroplasts from potentially damaging effects of supernumerary photons. Nevertheless, around 30% of published reports failed to uncover any photoprotective advantage of red pigmentation. To understand why anthocyanins are evidently more useful in some situations than in others, we compared the stress responses of wild type (Col-0) Arabidopsis thaliana, which had only trace amounts of foliar anthocyanins, with those of the anthocyanin-rich pap1-D mutant, and, in some experiments, the anthocyanin-deficient ttg1-1. We recorded effects of light quality, light intensity, air temperature, and duration of exposure on quantum yields of photosystem II (ΦPSII) in leaves of different ages, and compared pigment profiles before and after treatment. Although similar in anatomy, chlorophyll content, and xanthophyll cycle activity, pap1-D was photoinactivated less than Col-0, but only when given at least 2 h exposure to saturating light at 10 °C. Differences between the responses of red and green leaves were greatest in older plants that were given protracted exposures to high fluxes of cool-white light (5600 K) at chilling temperatures, the decline in ΦPSII being inversely proportional to foliar anthocyanin concentration. Anthocyanins were more abundant in Col-0 and pap1-D after treatment, especially acylated forms for which the absorption spectrum matched the action spectrum for photoinhibition. The quality, intensity and duration of light stress profoundly influence the degree of photoprotection afforded by foliar anthocyanins. Photoabatement by anthocyanins provides a functional advantage only when the capacity for thermal energy dissipation is exceeded by the need to quench excess light.
  • Chapter
    Camouflage is the most common visual defense in the animal kingdom (Stevens and Merilaita 2011) and potentially the best of all defenses. If an organism is well camouflaged its enemies do not see or sense it via other modalities and do not even consider an attack. Camouflage, when functioning well, is therefore the ultimate way to avoid attack.
  • Article
    Plant cuticles are covered by waxes with considerable ultrastructural and chemical diversity. Many of them are of great systematic significance. Waxes are an essential structural element of the surface and of fundamental functional and ecological importance for the interaction between plants and their environment. An extensive literature has been published since the introduction of scanning electron microscopy (SEM). Hitherto, the area has lacked a complete classification and terminology necessary as a standard for comparative descriptions. A refined classification and terminology of epicuticular waxes is therefore proposed based on high-resolution SEM analysis of at least 13 000 species, representing all major groups of seed plants. In total 23 wax types are classified. Thin wax films appear to be ubiquitous, while thicker layers or crusts are rare. The most prominent structures are local wax projections, which most probably result from self-assembly of wax molecules. These projections are supposed to be mainly of a crystalline nature and are termed crystalloids here. Among these, platelets and tubules are the most prominent types, while platelets arranged in parallel rows and stomatal wax chimneys are the most striking orientation and aggregation patterns. In addition, a comprehensive overview on the correlation between wax ultrastructure and chemical composition is given.
  • Phylogeny and biogeography of Erythronium (Liliaceae) inferred from chloroplast matK and nuclear rDNA ITS sequences Classification and terminology of plant epicuticular waxes Photon yield of O 2 -evolution and chloroplast fluorescence characteristics at 77 K among vascular plants of diverse origins
    • G A Allen
    • D E Soltis
    • P S W M Soltis
    • C Neinhuis
    • D Cutler
    • F Ditsch
    • I Meusel
    • I Theisen
    • H Wilhelmi
    Allen, G.A., Soltis, D.E., Soltis, P.S., 2003. Phylogeny and biogeography of Erythronium (Liliaceae) inferred from chloroplast matK and nuclear rDNA ITS sequences. Syst. Bot. 28, 512e523. Barthlott, W.M., Neinhuis, C., Cutler, D., Ditsch, F., Meusel, I., Theisen, I., Wilhelmi, H., 1998. Classification and terminology of plant epicuticular waxes. Bot. J. Linn. Soc. 126, 237e260. Björkman, O., Demmig, B., 1987. Photon yield of O 2 -evolution and chloroplast fluorescence characteristics at 77 K among vascular plants of diverse origins. Planta 170, 489e504. www.eFloras.org (Flora of North America, FNA vol. 26).
  • Article
    The Argenteum (Arg) mutant of pea is characterized by a gray-green, silvery cast of the leaves and stipules. Light and electron microscopy showed that the nature of the silvery cast was due to extensive intercellular air space between the epidermis and palisade parenchyma. Adaxial epidermal strips from mutant leaves were free of palisade cell wall fragments, whereas similar strips from normal leaves had remnants of the torn palisade cells attached to the epidermal cell walls. The periphery of the epidermal-palisade cell wall interfaces showed a more electron-opaque middle lamella in the normal leaves than in the Arg mutant leaves.
  • Article
    The thermal conductivity (TC) of the sand, clay and rock is measured by QTM-D2. And the effects of different experiment sizes and different conditions of saturated samples are discussed. The size error of TC among different samples is found out through experimental results and numerical simulation, which offers a solution to the measurement of TC of the geotechnical materials in site. During the measurement of TC by use of the heat line, the effect of sample size is limited, and the measured results of samples with different geometric sizes are similar. According to the domestic and international studies on empirical relation between TC and temperature, the empirical relation between the temperature and TC at the condition of normal temperature is obtained, and the thermal variance coefficient β is also obtained, based on a large number of measured data and numerical calculations. The values of β of geotechnical materials are small, mostly with magnitude 10-3, and the curves of TC and temperature is approximately linear. These coefficients and the experimental relationships are important to the understanding on the TC of the geotechnical materials in north China and to the temperature simulation programming as well.
  • Article
    Plant cuticles are covered by waxes with considerable ultrastructural and chemical diversity. Many of them are of great systematic significance. Waxes are an essential structural element of the surface and of fundamental functional and ecological importance for the interaction between plants and their environment. An extensive literature has been published since the introduction of scanning electron microscopy (SEM). Hitherto, the area has lacked a complete classification and terminology necessary as a standard for comparative descriptions. A refined classification and terminology of epicuticular waxes is therefore proposed based on high-resolution SEM analysis of at least 13 000 species, representing all major groups of seed plants. In total 23 wax types are classified. Thin wax films appear to be ubiquitous, while thicker layers or crusts are rare. The most prominent structures are local wax projections, which most probably result from self-assembly of wax molecules. These projections are supposed to be mainly of a crystalline nature and are termed crystalloids here. Among these, platelets and tubules are the most prominent types, while platelets arranged in parallel rows and stomatal wax chimneys are the most striking orientation and aggregation patterns. In addition, a comprehensive overview on the correlation between wax ultrastructure and chemical composition is given.
  • Article
    The maximum quantum yield for photosynthetic O2 evolution in red leaf coleus varieties having anthocyanin in their upper epidermis is much lower in green light and slightly lower in white light than in a green leaf variety lacking anthocyanin. A similar degree of photoinhibition occurred under excess visible light in the red versus green varieties; whereas, the red leaf varieties were less damaged by UV-B and UV-C radiation suggesting protection by anthocyanin in their epidermal tissue.
  • Article
    Full-text available
    Trichomes are known to have many functions, including protecting plants from excess sunlight, improving water economy, salt secretion, defense from herbivores, and signaling to animals. Additional anti-herbivore functions of trichomes, especially in coastal and desert habitats, are reviewed and proposed. Many sand-dune and sandy shore plants are white, whitish, or silver-colored because of white trichomes, because of sticky glandular trichomes to which sand grains and clay adhere, or because of light-colored waxes. The common explanation for this coloration is that it protects from irradiation, and that in addition, the glued sand defends them from abrasion by moving sand. This coloration was also proposed to camouflage the plants from herbivores. Similar coloration in animals that live in white, snow-covered habitats or light-colored sand or other soil substrates is commonly referred to as camouflage, and the same logic may also apply to plants. It has also been proposed that white plant surfaces undermine the camouflage of herbivorous insects that have other colors and expose them to predation. Three novel defensive mechanisms are proposed here: (1) because dust is a strong insect repellent and is lethal to insects, attached soil particles (especially clays) may defend plants with sticky glandular trichomes from insect herbivory; (2) in dicotyledonous plants that have sticky glandular trichomes, the attached sand may defend from herbivory by mammals by causing teeth wear as do phytoliths (silica bodies) of grasses; and (3) white coloration of leaves and branches may mimic fungal infestation. Direct experimental data for the functionality of these defensive mechanisms are missing for many of the old and all new hypotheses, but there are many indirect supporting indications.
  • Article
    The mechanism of sparkling metallic lustre formation in leaves of Begonia rex Putz. was investigated. On the metallic lustre and normal green areas of one leaf, we observed two light reflection patterns, one a spotted pattern (SP) composed of white spots formed on the centre of epidermal cells and the other a polygonal pattern (PP) composed of white polygons formed around the epidermal cell edges. The SP was observed both in metallic lustre and normal green areas, and the intensity did not differ significantly, but the PP was much stronger in the metallic lustre area. Different reflection of the PP in metallic lustre and normal green areas indicated that metallic lustre formation was attributable to the PP. Light reflection of the PP was mainly derived from interior light reflection because the PP became very weak after air removal from leaf. The formation of the PP is associated with the interior structure of the leaf, such as chlorophyll density, cell arrangement and air space. The experimental results indicated that interior air space is an important factor in forming the polygonal pattern.
  • Article
    Photon yields of oxygen evolution at saturating CO2 were determined for 44 species of vascular plants, representing widely diverse taxa, habitats, life forms and growth conditions. The photonyield values on the basis of absorbed light (fa) were remarkably constant among plants possessing the same pathway of photosynthetic CO2 fixation, provided the plants had not been subjected to environmental stress. The mean fa value ±SE for 37 C3 species was 0.106±0.001 O2·photon-1. The five C4 species exhibited lower photon yields and greater variation than the C3 species (fa=0.0692±0.004). The fa values for the two Crassulaceanacid-metabolism species were similar to those of C3 species. Leaf chlorophyll content had little influence on fa over the range found in normal, healthy leaves. Chlorophyll fluorescence characteristics at 77 K were determined for the same leaves as used for the photon-yield measurements. Considerable variation in fluorescence emission both at 692 nm and at 734 nm, was found 1) among the different species; 2) between the upper and lower surfaces of the same leaves; and 3) between sun and shade leaves of the same species. By contrast, the ratio of variable to maximum fluorescence emission at 692 nm (Fv/FM, 692) remained remarkably constant (The mean value for the C3 species was 0.832±0.004). High-light treatments of shade leaves resulted in a reduction in both fa and the Fv/FM, 692 ratio. The extent of the reductions increased with time of exposure to bright light. A linear relationship was obtained when fa was plotted against Fv/FM, 692. The results show that determinations of the photon yield of O2 evolution and the Fv/FM, 692 ratio can serve as excellent quantitative measures of photoinhibition of overall photosynthetic energy-conversion system and of photochemistry of photosystem II, respectively. This is especially valuable in field work where it is often impossible to obtain appropriate controls.
  • Article
    Proposes that mottling may serve to camouflage the foliage of certain groups of short-statured forest herbs, by disrupting their outline as perceived by colour-blind vertebrate herbivores in sun-dappled understoreys. Certain phenological groups are likely to be particularly vulnerable to herbivores, based on their high leaf N content (spring ephemerals, spring leaves of summer-active species), leaf activity when few other species possess foliage (evergreen species, wintergreen species, winter leaves of dimorphic species) and/or relative cost of replacing consumed foliage (evergreen species on sterile soils). These groups are also exposed to relatively high irradiance and so are less likely to suffer photosynthetic losses as a result of the reduced leaf absorptance that accompanies mottling. A survey of the incidence of leaf mottling in the native flora of the NE USA supports these ideas: mottled leaves occur almost exclusively among forest herbs and are substantially over-represented among evergreen, wintergreen, and spring ephemeral species, and among the winter leaves of dimorphic species and the spring leaves of summer-active species. -from Author
  • Article
    This study investigates the role played by showy structures in the reproduction of Lavandula stoechas L. (Lamiaceae), a self-compatible Mediterranean shrub with compact, head-like inflorescences that are terminated by a tuft of conspicuous pink bracts. Pollinator visitation rates to plants with bracts correlated positively with that of paired, treated shrubs with all their bracts removed and, overall, bractless and control plants had equivalent visitation rates. In experimentally split shrubs, however, a strong effect on pollinator choice was evident, and distant visitor approaches were most often to that side keeping the attractive organs. Fecundity was not depressed in plants with reduced visual displays, and neither was the amount of pollen dispersed per flower or the size of stigmatic loads. There were, however, more pollen tubes, on average, at the lowermost part of the style in controls (10.8 tubes/style) than in bractless shrubs (8.3 tubes/style). Small, non-significant declines in average seed size, germinability, and seedling mass were detected following bract removal. Data support the notion that bracts are not essential to seed production in mature, relatively dense Lavandula populations where bee pollinators are often in good supply, but may be all-important f plant density is extremely low, or during population establishment. The roe of an amplified display in increasing average pollination distance and progeny quality in this species is discussed.
  • Article
    Full-text available
    Twenty-one wild spiny or thorny plant species growing in Israel have been found so far that are conspicuous because of white stripes and spots found on their leaves. Twenty of these species occupy open habitats, and only one is a climber (Smilax aspera) that is found in both shady and open habitats. I propose that these spiny, thorny, or prickly conspicuous plants form a defensive Müllerian mimicry ring. The genus Launaea (Asteraceae) includes several species that are both white variegated and spiny or thorny (a defended Müllerian mimicry ring), and four non-thorny but variegated plants (a Batesian mimicry ring). I propose that these four species that form a non-defended Batesian mimicry ring enjoy the indirect protection of both their co-generic spiny and thorny species and also of defended plants from other taxa. The long history of the considerable impact of grazing in this arid region seems to have selected for this character.
  • Article
    Leaf-mining insects produce conspicuous and distinct leaf mines on various types of plant leaves. The diversity of leaf-mine morphology has typically been explained by several factors, such as selective feeding on plant tissues, improvement of microclimate, faecal disposal, reduction in the efficiency of parasitoid search behaviour and leafminer phylogeny. Although these factors are certainly associated with mining patterns, masking the mines, rather than making them conspicuous, appears to be more advantageous for deterring parasitoids and predators of leafminers. However, here, I propose that prominent leaf mines may serve to signal or cue herbivores to avoid feeding on the mined leaves. Because most leafminers are sessile and complete their development within a single leaf, herbivory of mined leaves is detrimental to leafminer survival. Other herbivores appear to avoid consuming mined leaves for a variety of reasons: leaf mines mimic leaf variegation or mottling; mined leaves induce chemical and physical defences against herbivores; and leaf mines mimic fungal infection, animal excrement, and necrosed plant tissues. Hence, natural selection may have favoured leafminers that produce conspicuous mines because of the increased survival and fecundity of thereby reducing herbivory on mined leaves.
  • Article
    Full-text available
    This study investigated the extent to which the reproductive success of plants of Erythronium dens-canis (Liliaceae), a spring herb of mountain habitats, is dependent on floral morphology. To this end, a series of studies was performed in an area in northwest Spain. The results show that E. dens-canis plants in this area a) are self-compatible, b) need pollinator visits (largely Bombus terrestris and Andrena spp.) to produce seed, and c) show high fruit set under natural conditions. Only 20% of among-plant variance in floral morphology variables was explained by variation in plant size. Floral morphology variables (outer tepal length, stamen length, style length and ovule number) tend to vary in parallel, indicating the existence of an “integrated floral phenotype”. Two floral morphology variables (initial number of ovules and outer tepal length) had statistically significant or near-significant effects on seed production. A more detailed experimental analysis indicated that small-flowered plants produce fewer seeds than large-flowered plants, and that this is attributable to less efficient pollination of small flowers. The results of this study thus suggest that among-plant variation in floral morphology in E. dens-canis has implications for reproductive success.
  • Article
    Full-text available
    The color of many animals matches that of their preferred habitats, making them difficult for predators to locate. However, quantitative examples of crypsis in plants are comparatively rare. We conducted morphometric and spectrographic analyses of a heteroblastic tree species that is endemic to New Zealand (Elaeocarpus hookerianus Raoul) to test whether it is cryptic in appearance from the perspective of birds, who were once dominant browsers in New Zealand. The leaves of smaller, juvenile plants are highly variable in size and shape and are mottled brown in color from the perspective of birds, which would make them difficult for herbivorous birds to locate against a background of leaf litter. However, once plants grow to above 3 m in height, beyond the reach of the largest herbivorous bird known to inhabit New Zealand, plants suddenly produce leaves that are ordinary in size, shape, and color. Results provide quantitative support for the hypothesis that E. hookerianus is cryptically colored when within reach of flightless browsing birds.
  • Article
    Full-text available
    Leaf variegation refers to local regions of the upper surface of a leaf having reduced or obstructed chlorophyll, which results in whitish spots. These lighter spots may compromise the photosynthetic efficiency of a leaf, and many competing hypotheses have been put forward to explain why this patterning may be adaptive. It has been suggested that variegation is either an adaptive response to environmental conditions or a defence mechanism against herbivore damage. To test whether leaf variegation reduces herbivore damage, we first assessed the frequency of variegated and nonvariegated leaves in natural populations of the plant Hydrophyllum virginianum L., and second, measured herbivore damage to both variegated and nonvariegated leaves. We found that variegated leaves were present at high frequencies within natural populations (6%-31%) and that nonvariegated leaves sustained nearly twice the amount of damage by comparison with variegated leaves. Therefore, leaf variegation appears to be beneficial by reducing herbivore damage to leaves. These data are consistent with the fundamental prediction of the herbivory hypothesis for the benefits of leaf variegation.
  • Article
    Full-text available
    We investigated phylogenetic relationships within Erythronium using DNA sequences from the chloroplast gene matK and the internal transcribed spacer (ITS) of nuclear ribosomal DNA. Erythronium, Amana, and Tulipa form a strongly supported clade that appears to be of Asian origin. Erythronium is widely distributed in the Northern Hemisphere, and consists of three well supported and geographically distinct clades occurring in western North America, eastern North America, and Eurasia. ITS analyses suggest that the Eurasian and eastern North American clades form a monophyletic group that separated into two lineages following divergence from the western North American clade. Although the three clades are each characterized by distinct morphological features, convergence both among and within geographic areas is seen in several characters. The western North American clade exhibits greater morphological and molecular diversity than either of the other two clades, and many of its species hybridize, suggesting both recent and ongoing speciation. The geographic distribution of Erythronium suggests initial diversification in Tertiary mixed mesophytic forest, followed by fragmentation of the range during the late Tertiary or early Pleistocene and subsequent radiation in western North America.
  • Article
    Leaf hydraulic conductance (K(leaf) ) and vulnerability constrain plant productivity, but no clear trade-off between these fundamental functional traits has emerged in previous studies. We measured K(leaf) on a leaf area (K(leaf_area) ) and mass basis (K(leaf_mass) ) in six woody angiosperms, and compared these values with species' distribution and leaf tolerance to dehydration in terms of P(50) , that is, the leaf water potential inducing 50% loss of K(leaf) . We also measured several morphological and anatomical traits associated with carbon investment in leaf construction and water transport efficiency. Clear relationships emerged between K(leaf_mass) , P(50) , and leaf mass per unit area (LMA), suggesting that increased tolerance to hydraulic dysfunction implies increased carbon costs for leaf construction and water use. Low P(50) values were associated with narrower and denser vein conduits, increased thickness of conduit walls, and increased vein density. This, in turn, was associated with reduced leaf surface area. Leaf P(50) was closely associated with plants' distribution over a narrow geographical range, suggesting that this parameter contributes to shaping vegetation features. Our data also highlight the carbon costs likely to be associated with increased leaf tolerance to hydraulic dysfunction, which confers on some species the ability to thrive under reduced water availability but decreases their competitiveness in high-resource habitats.
  • Article
    MATHEW, B., 1992. A review of Erythronium L. (Liliaceae). The morphology, distribution and horticultural value of the genus is reviewed and a tentative key to the identification of the species is provided.
  • Article
    In the present study we explored the possibility of assessing the allocation of photons absorbed by photosystem II (PSII) antennae to thermal energy dissipation and photosynthetic electron transport in leaves of several plant species under field conditions. Changes in chlorophyll fluorescence parameters were determined in situ over the course of an entire day in the field in sun-exposed leaves of two species with different maximal rates of photosynthesis, Helianthus annuus (sunflower) and Vinca major. Leaves of Vinca minor (periwinkle) growing in a deeply shaded location were also monitored. We propose using diurnal changes in the efficiency of open PSII centers (F′v/F′m) in these sun and shade leaves to (a) assess diurnal changes in the allocation of absorbed light to photochemistry and thermal energy dissipation and, furthermore, (b) make an estimate of changes in the rate of thermal energy dissipation, an analogous expression to the rate of photochemistry. The fraction of light absorbed in PSII antennae that is dissipated thermally (D) is proposed to be estimated from D = 1-F′v/F′m, in analogy to the widely used estimation of the fraction of light absorbed in PSII antennae (P) that is utilized in PSII photochemistry from P = F′v/F′m× qP (where qP is the coefficient for photochemical quenching; Genty, B., Briantais, J.-M. & Baker, N. R. 1989. Biochim. Biophys. Acta 990: 87-92). The rate of thermal dissipation is consequently given by D × PFD (photon flux density), again in analogy to the rate of photochemistry P × PFD, both assuming a matching behavior of photosystems I and II. Characterization of energy dissipation from the efficiency of open PSII centers allows an assessment from a single set of measurements at any time of day; this is particularly useful under field conditions where the fully relaxed reference values of variable or maximal fluorescence needed for the computation of nonphotochemical quenching may not be available. The usefulness of the assessment described above is compared with other currently used parameters to quantify nonphotochemical and photochemical chlorophyll fluorescence quenching.
  • Butterfly pollination and high-contrast visual signals in a low-density distylous plant Photosynthetic efficiency, and photodamage by UV and visible radiation, in red versus green leaf Coleus varieties Leaf variegation is associated with reduced herbivore damage in Hydrophyllum virginianum
    • R M Borges
    • V Gowda
    • M Zacharias
    • e
    • J Burger
    • G E Edwards
    Borges, R.M., Gowda, V., Zacharias, M., 2003. Butterfly pollination and high-contrast visual signals in a low-density distylous plant. Oecologia 136, 571e573. Burger, J., Edwards, G.E., 1996. Photosynthetic efficiency, and photodamage by UV and visible radiation, in red versus green leaf Coleus varieties. Plant Cell Physiol. 37, 395e399. Campitelli, B.E., Steglik, I., Stinchcombe, J.R., 2008. Leaf variegation is associated with reduced herbivore damage in Hydrophyllum virginianum. Botany 86, 306e 313. Demmig-Adams, B., Adams, W.W., Barker, D.H., Logan, B.A., Bowling, D.R., Verhoeven, A.S., 1996. Using chlorophyll fluorescence to assess the fraction of absorbed light allocated to thermal dissipation of excess excitation. Physiol. Plant 98, 253e264.
  • Article
    Full-text available
    This study explored reflectance indices sampled with a ‘leaf reflectometer’ as measures of pigment content for leaves of contrasting light history, developmental stage and functional type (herbaceous annual versus sclerophyllous evergreen). We employed three reflectance indices: a modified normalized difference vegetation index (NDVI), an index of chlorophyll content; the red/green reflectance ratio (RRED∶RGREEN), an index of anthocyanin content; and the change in photochemical reflectance index upon dark–light conversions (ΔPRI), an index of xanthophyll cycle pigment activity. In Helianthus annuus (sunflower), xanthophyll cycle pigment amounts were linearly related to growth light environment; leaves in full sun contained approximately twice the amount of xanthophyll cycle pigments as leaves in deep shade, and at midday a larger proportion of these pigments were in the photoprotective, de-epoxidized forms relative to shade leaves. Reflectance indices also revealed contrasting patterns of pigment development in leaves of contrasting structural types (annual versus evergreen). In H. annuus sun leaves, there was a remarkably rapid increase in amounts of both chlorophyll and xanthophyll cycle pigments along a leaf developmental sequence. This pattern contrasted with that of Quercus agrifolia (coast live oak, a sclerophyllous evergreen), which exhibited a gradual development of both chlorophyll and xanthophyll cycle pigments along with a pronounced peak of anthocyanin pigment content in newly expanding leaves. These temporal patterns of pigment development in Q. agrifolia leaves suggest that anthocyanins and xanthophyll cycle pigments serve complementary photoprotective roles during early leaf development. The results illustrate the use of reflectance indices for distinguishing divergent patterns of pigment activity in leaves of contrasting light history and functional type.
  • Article
    The function of anthocyanins in green, vegetative tissues has always been a contentious issue. Here we evaluate their proposed photoprotective function since recent findings have shown that anthocyanins reduce photoinhibition and photobleaching of chlorophyll under light stress conditions. Anthocyanins generally accumulate in peripheral tissues exposed to high irradiance, although there are some exceptions (e.g. accumulation in abaxial leaf tissues and in obligatory shade plants) and accumulation is usually transient. Anthocyanin accumulation requires light and generally coincides with periods of high excitation pressure and increased potential for photo-oxidative damage due to an imbalance between light capture, CO2 assimilation and carbohydrate utilization (e.g. greening of developing tissues, senescence and adverse environmental conditions). Light attenuation by anthocyanin may help to re-establish this balance and so reduce the risk of photo-oxidative damage. Although it has been suggested that anthocyanins may act as antioxidants, the association between anthocyanins and oxidative stress appears to relate to the ability of anthocyanins to reduce excitation pressure and, hence, the potential for oxidative damage. The various aspects of anthocyanin induction and pigmentation presented here are compatible with, and support, the proposed general role of anthocyanins as photoprotective light screens in vegetative tissues.
  • Chapter
    Full-text available
    In addition to their well-documented beneficial effects on plant physiological processes, anthocyanins have also been proposed to function in a diverse array of plant/animal interactions. These include the attraction of pollinators and frugivores, as well as the repellence of herbivores and parasites. The optical properties of anthocyanins may serve as visual signals to potential herbivores, indicating a strong metabolic investment in toxic or unpalatable chemicals. Anthocyanins have also been implicated in the camouflage of plant parts against their backgrounds, in the undermining of insect crypsis, and in the mimicry of defensive structures. These hypotheses have in recent years attracted strong theoretical support and increasing experimental evidence. We emphasize that both the defensive and the physiological functions of anthocyanins may operate in plants simultaneously.
  • Article
    The leaves of Caladium steudneriifolium (Araceae) of the understorey of a submontane rainforest in the Podocarpus National Park (South East Ecuador, 1,060m 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 3months. 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.
  • Article
    The extinction coefficients for chlorophylls a and b in diethylether (Smith, J.H.C. and Benitez, A. (1955) in Modern Methods of Plant Analysis (Paech, K. and Tracey, M.V., eds.), Vol. 4, pp. 143–196, Springer-Verlag, Berlin), used in this paper as primary standards, were verified, to within an error of less than 1%, by magnesium determination using atomic absorbance spectrophotometry. We also report the determination of accurate extinction coefficients for chlorophylls a and b in N,N′-dimethylformamide, methanol or buffered 80% aqueous acetone. Highly purified chlorophylls were used and methods were employed which not only minimize errors due to evaporation of the volatile solvents employed in their estimation but also eliminate variable micro-contamination by chlorophyll degradation products, a potential source of inconsistency between the extinction coefficients obtained in each of these three solvents. Using these new coefficients, expressed as both millimolar and specific coefficients, we have derived new simultaneous equations to obtain chlorophyll concentrations as nmol/ml and μg/ml, respectively. These equations were applied to data obtained with leaf discs from spinach and Flindersia brayleyana extracted with the three specified solvents and to a concentrated solution (in N,N′ -dimethylformamide) of a chlorophyll a + b mixture added to the threesolvent systems. The validity of these equations is proven by the consistency of the chlorophyll determinations and of the chlorophyll a/b ratios. New simultaneous equations, compatible with the equations derived for the threesolvents, are presented for the assay of chlorophylls a and b converted to their cyclic hydroxylactone derivatives by extraction with alkaline pyridine reagent (2.1 M pyridine in 0.35 M NaOH). Most chlorophyll analyses in higher plants, including the chlorophyll content and chlorophyll a/b ratios of plant thylakoids and chlorophyll-protein complexes, have been obtained in 80% aqueous acetone with the much used simultaneous equations of Arnon (Arnon, D.I. (1949) Plant Physiol. 24, 1–15). For this reason we include conversion factors whichcorrect these earlier data and make it compatible with data calculated with the simultaneous equations presented in this paper. The importance of these corrections to the formulation of meaningful models of the photosynthetic apparatus is demonstrated. Our results also indicate that grinding leaf discs with N,N′-dimethylformamide is a more reliable method for extracting all chlorophylls than shaking with this solvent for 24 h.
  • Article
    The leaves of some plants display an optical patchiness on their upper side, displaying light- and dark-green areas with high and low reflectance, respectively. In this investigation, we studied the fine structure of the corresponding sectors and we asked whether the lost reflected light entails a photosynthetic cost to these leaves. Four species, i.e. Arum italicum, Ranunculus ficaria, Cyclamen hederifolium and Cyclamen persicum were investigated. Scanning electron microscope examination revealed that epidermal cells of light-green sectors of all species are more bulgy than corresponding cells of neighboring dark-green leaf sectors. The comparative anatomical study revealed that (i) epidermis thickness of the light-green areas and the number of mesophyll cell layers does not differ from those of the adjacent dark-green leaf sectors and (ii) palisade cells of light-green sectors are slightly larger and more loosely arranged, allowing a much higher percentage of intercellular air spaces. The latter histological feature seems to provide the structural basis for the different optical properties between the two leaf sectors. Contrary to expectations, net photosynthetic rates (expressed on a leaf area basis) were similar in the light-green and the dark-green areas of the two cyclamen species. Yet, in C. persicum net photosynthesis was higher in the light-green areas, if expressed on a dry mass basis. The small size of the light-green spots in the rest of the test plants precluded CO2 assimilation measurements, yet maximum linear photosynthetic electron transport rates displayed no differences between the two sectors in all plants. Thus, the assumption of a photosynthetic cost in the light-green areas was not confirmed. On the contrary, a higher construction cost was evident in the dark-green areas of three species, displaying a significantly higher specific leaf mass, without any photosynthetic benefit. The results on net photosynthesis were compatible with leaf optical properties and pigment levels. Thus, in spite of the considerably higher reflectance of the light-green areas and their lower (yet normal for a green leaf) chlorophyll levels, corresponding differences in absorptance were slight. In addition, dry mass-based pigment contents in dark-green areas were higher, while chlorophyll a/b (in two species) and carotenoid/chlorophyll ratios (in three species) were lower, pointing to a shade adaptation in these sectors. We conclude that in variegated leaves of this kind, dark-green areas are more costly to build and probably less photosynthetically active. We argue that the high pigment contents of dark-green areas establish steep light gradients in the corresponding mesophyll, rendering deeper chloroplast layers more shade adapted.
  • Article
    The adaptive significance of leaf reddening, as it occurs during specific developmental stages or after stress, has puzzled biologists for more than a century. Theoretically, the accumulation of a non-photosynthetic pigment competing with chlorophylls for photon capture would impose a photosynthetic cost, which should be paid off by the benefits afforded by anthocyanins under some circumstances. Hence, the proposed hypotheses presume protective functions against excess light, UV-B radiation, reactive oxygen species, water stress (osmoregulation) and herbivory. The existing arguments in favor of an anti-oxidant, anti-UV-B and osmoregulatory role are confounded by the co-occurrence in leaves of other compounds having the same properties, not absorbing visible light, attaining much higher concentrations and, in some cases, having a more appropriate location to fulfill the ascribed functions. Moreover, the excess light hypothesis should take into account that anthocyanins mainly absorb green photons, which are used photosynthetically in deeper cell layers needing less photoprotection. The more ecological, anti-herbivore hypotheses, consider red leaf color as a signal denoting high defensive commitment, as a camouflage obscuring the green reflectance indicative of a healthy leaf and/or as a device undermining the folivorous insects camouflage. The anti-herbivore hypotheses have not been thoroughly tested, yet they are compatible with the known optical preferences of insects and their underlying physiology. Overall, although a multiplicity of potential roles can be argued, the primary role may depend on the reference system, i.e. species, developmental stage or specific biotic and abiotic stressors.
  • Article
    The leaves from many of New Zealand's native species are remarkably polymorphic for anthocyanin expression. Red coloration varies not only as a function of seasonal and developmental factors, but can also differ among individuals of a population, among leaves within a canopy, and even among tissues within a leaf. Moreover, the biosynthesis of anthocyanin in these leaves can be induced by a host of disparate environmental and biotic stimuli. Any unified explanation for the presence of anthocyanins in leaves must accommodate both the variability in pigmentation patterns over time and space, and the diverse range of triggers. Our data indicate that anthocyanins confer a phytoprotective role, rather than being the default end-product of a saturated flavonoid metabolism. Anthocyanins are primarily associated with chlorophyllous tissues, and significantly modify both the quantity and the quality of light incident on a chloroplast. Red leaves photosynthesise less than green leaves, but are also photoinhibited less and recover sooner following exposure to high light fluxes. Photoabatement also reduces the generation of free radicals and reactive oxygen species from photooxidation, photorespiration, and Mehler reaction activities. Anthocyanins inhibit Fenton hydroxyl radical generation by chelating to ferrous ions, and effectively scavenge superoxide and hydrogen peroxide generated by mechanical injury, sudden temperature changes, and exposures to high light. Anthocyanins are evidently versatile and highly effective phytoprotectants. However, there is probably no unified explanation for their presence in leaves. Common among the first land plants, anthocyanins have probably been hijacked over the course of evolution to perform an array of tasks.
  • Article
    Full-text available
    Foliar variegation is recognized as arising from two major mechanisms: leaf structure and pigment-related variegation. Begonia has species with a variety of natural foliar variegation patterns, providing diverse examples of this phenomenon. The aims of this work are to elucidate the mechanisms underlying different foliar variegation patterns in Begonia and to determine their physiological consequences. Six species and one cultivar of Begonia were investigated. Light and electron microscopy revealed the leaf structure and ultrastructure of chloroplasts in green and light areas of variegated leaves. Maximum quantum yields of photosystem II were measured by chlorophyll fluorescence. Comparison with a cultivar of Ficus revealed key features distinguishing variegation mechanisms. Intercellular space above the chlorenchyma is the mechanism of variegation in these Begonia. This intercellular space can be located (a) below the adaxial epidermis or (b) below the adaxial water storage tissue (the first report for any taxa), creating light areas on a leaf. In addition, chlorenchyma cell shape and chloroplast distribution within chlorenchyma cells differ between light and green areas. Chloroplasts from both areas showed dense stacking of grana and stroma thylakoid membranes. The maximum quantum yield did not differ significantly between these areas, suggesting minimal loss of function with variegation. However, the absence of chloroplasts in light areas of leaves in the Ficus cultivar led to an extremely low quantum yield. Variegation in these Begonia is structural, where light areas are created by internal reflection between air spaces and cells in a leaf. Two forms of air space structural variegation occur, distinguished by the location of the air spaces. Both forms may have a common origin in development where dermal tissue becomes loosely connected to mesophyll. Photosynthetic functioning is retained in light areas, and these areas do not include primary veins, potentially limiting the costs of variegation.
  • Article
    The presence of pale-green flecks on leaves (speckling) is a frequent character among herbaceous species from shady places and is usually due to local loosening of palisade tissue (air space type of variegation). In the winter-green Arum italicum L. (Araceae), dark-green areas of variegated leaf blades are ca. 400 μm thick with a chlorophyll content of 1080 mg m⁻² and a palisade parenchyma consisting of a double layer of oblong cells. Pale-green areas are 25% thinner, have 26% less chlorophyll and contain a single, loose layer of short palisade cells. Full-green leaves generally present only one compact layer of cylindrical palisade cells and the same pigment content as dark-green sectors, but the leaf blade is 13% thinner. A spongy parenchyma with extensive air space is present in all leaf types. Green cells of all tissues have normal chloroplasts. Assays of photosynthetic activities by chlorophyll fluorescence imaging and O₂ exchange measurements showed that variegated pale-green and dark-green sectors as well as full-green leaves have comparable photosynthetic activities on a leaf area basis at saturating illumination. However, full-green leaves require a higher saturating light with respect to variegated sectors, and pale-green sectors support relatively higher photosynthesis rates on a chlorophyll basis. We conclude that i) variegation in this species depends on number and organization of palisade cell layers and can be defined as a "variable palisade" type, and ii) the variegated habit has no limiting effects on the photosynthetic energy budget of A. italicum, consistent with the presence of variegated plants side by side to full-green ones in natural populations.
  • Article
    Full-text available
    Erythronium japonicum (Liliaceae) (Japanese name, katakuri) is indigenous to Japan and adjacent Far East regions. We examined their embryo elongation, germination, and seedling emergence in relationship to the temperature. In incubators, seeds did not germinate at 20°/10° (light 12 h/dark 12 h alternating temperature), 20°, 15°, 5°, or 0°C with a 12-h light photoperiod for 200 d. They germinated at 15°/5° or 10°C, starting on day 135. If seeds were kept at 20° or at 25°/15°C before being exposed to 5°C, the seeds germinated, but if kept at 25° or 30°C they did not. Embryos at 25°/15°C grew to half the seed length without germinating; at 0° or 5°C, embryos elongated little. Embryos grew and seeds germinated when kept at 25°/15°C for 90 d and then at 5°C. In the field, seeds are dispersed in mid-June in Hokkaido and in Honshu, mid-May to mid-June. Seeds do not germinate immediately after dispersal because the embryo is underdeveloped. Embryos elongated at medium temperatures in autumn after summer heat, and germination ends in November at 8°/0°C. After germination, seedling emergence was delayed, and most seedlings were observed in early April around the snowmelt when soil cover was 2-3 mm.
  • Article
    Full-text available
    Plant coloration, shown to play a dynamic role in animal attraction, has been proposed as a means of defense, although these reports lack experimental evidence. This study empirically assesses defensive coloration in the mycoheterotrophic plant, Monotropsis odorata, which produces stems and flowers covered by dried vegetative bracts. Field studies were conducted using an experimental group of plants with bracts removed and a control group to evaluate the frequency of and fitness impacts associated with herbivory. Additionally, we quantitatively assessed the reflectance spectra of bracts, stems, and flowers of M. odorata relative to an ambient leaf litter substrate. Across the 2-yr study, the experimental group experienced a 20-27% higher mean herbivory rate and 7-20% lower mean fruit production relative to the control group. Bracts were shown to strongly resemble ambient leaf litter in spectral analyses, with stems and flowers having more conspicuous coloration. Results show that the presence of dried bracts effectively camouflages conspicuous stem and floral tissues, significantly reducing the frequency of floral and stem herbivory, and thereby increasing fruit set, a component of plant fitness. This study supports the principal hypothesis that coloration can play a fundamental role in plant defense.
  • Article
    Full-text available
    • Premise of the study: Climate change has affected species worldwide, including alterations in phenology, migration patterns, distribution, and survival. Because Erythronium grandiflorum is an early-season bloomer, alterations in its phenology may have serious implications for many North American Rocky Mountain communities, including changes in resource availability for pollinators and herbivores. • Methods: We investigated whether changes in the snowmelt date, summer temperature, and summer precipitation have altered the timing and abundance of flowering in E. grandiflorum by collecting long-term data on floral abundance from 1975-2008 in a series of 2 × 2 m plots at the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado in the United States. • Key results: Snowmelt date and mean summer temperature were negatively correlated. Over the 30-yr study, the snowmelt date advanced by 4.14 d/decade, and mean summer temperature increased by 0.38°C/decade. Summer precipitation was variable, showing no change. The first, peak, and last flowering dates of E. grandiflorum advanced an average of 3.2 d/decade. Furthermore, earlier snowmelt and greater summer precipitation in the previous year led to earlier flowering in E. grandiflorum. There was no change in flowering abundance in this species, indicating it may be controlled by a complex set of abiotic and biotic variables. • Conclusions: Our study indicates that snowmelt is arriving earlier at the RMBL, which has caused earlier flowering in E. grandiflorum. Because alterations in phenology can disrupt important ecological interactions, information on potential phenological shifts in species that interact with E. grandiflorum is essential in determining the net effect of climate-driven alterations in phenology.
  • Article
    Full-text available
    Charles Darwin was fascinated by the orchid-pollinator interactions, but he did not realize that many orchid species are pollinated by deceit. Cypripedium, a model lineage of nonrewarding orchid flowers, is pollinated primarily by bees. Here we present both an example of floral mimesis of fungus-infected foliage in orchids and an example of flat-footed flies (Agathomyia sp.; Platypezidae) as pollen vectors for angiosperms. Cypripedium fargesii is a nectarless, terrestrial, endangered orchid from southwestern China that requires cross-pollination to produce the maximum number of viable embryos. All insects caught entering or leaving the labellum sac were Agathomyia sp. carrying conidia of Cladosporium sp. on their mouthparts and legs, suggesting mycophagy. Blackish hairy spots on the upper surface of foliage may imitate black mold spots, serving as short-term visual lures. Some odor molecules also associated with Cladosporium cultures were isolated in the floral scent. Mimesis of fungus-infected foliage probably represents an overlooked but important option in angiosperm diversification, because there are three to five more Cypripedium spp. in southwestern China with the same mode of floral presentation and black-spotted hairy leaves.
  • Article
    Full-text available
    Spring geophytes produce larger storage organs and present delayed leaf senescence under lower growth temperature. Bulb and leaf carbon metabolism were investigated in Erythronium americanum to identify some of the mechanisms that permit this improved growth at low temperature. Plants were grown under three day/night temperature regimes: 18/14 °C, 12/8 °C, and 8/6 °C. Starch accumulated more slowly in the bulb at lower temperatures probably due to the combination of lower net photosynthetic rate and activation of a ‘futile cycle’ of sucrose synthesis and degradation. Furthermore, bulb cell maturation was delayed at lower temperatures, potentially due to the delayed activation of sucrose synthase leading to a greater sink capacity. Faster starch accumulation and the smaller sink capacity that developed at higher temperatures led to early starch saturation of the bulb. Thereafter, soluble sugars started to accumulate in both leaf and bulb, most probably inducing decreases in fructose-1,6-bisphosphatase activity, triose-phosphate utilization in the leaf, and the induction of leaf senescence. Longer leaf life span and larger bulbs at lower temperature appear to be due to an improved equilibrium between carbon fixation capacity and sink strength, thereby allowing the plant to sustain growth for a longer period of time before feedback inhibition induces leaf senescence.
  • Article
    Full-text available
    Spatio-temporal patterns of snowmelt and flowering times affect fruiting success in Erythronium grandiflorum Pursh (Liliaceae) in subalpine western Colorado, USA. From 1990 to 1995, I measured the consistency across years of snowmelt patterns and flowering times along a permanent transect. In most years since 1993, I have monitored fruit set in temporal cohorts (early- to late-flowering groups of plants) at one site. To assess 'pollination limitation', I have also conducted supplemental hand-pollination experiments at various times through the blooming season. The onset of blooming is determined by snowmelt, with the earliest years starting a month before the latest years owing to variation in winter snowpack accumulation. Fruit set is diminished or prevented entirely by killing frosts in some years, most frequently but not exclusively for the earlier cohorts. When frosts do not limit fruit set, pollination limitation is frequent, especially in the earlier cohorts. Pollination limitation is strongest for middle cohorts: it tends to be negated by frost in early cohorts and ameliorated by continuing emergence of bumble-bee queens in later cohorts. This lily appears to be poorly synchronized with its pollinators. Across the years of the study, pollination limitation appears to be increasing, perhaps because the synchronization is getting worse.
  • Article
    * Animals often use colours to hide from predators (crypsis) or advertise defences (aposematism), but there is little evidence for colour-based defence in plants. * Here, we test whether ontogenetic changes in leaf colour of lancewood (Pseudopanax crassifolius) may have been part of a defensive strategy against flightless browsing birds called moa, which were once the only large herbivores in New Zealand. We tested this hypothesis by conducting spectrographic measurements on different-sized plants grown in a common garden. We also compared these results with observations on a closely related, derived species that evolved in the absence of moa on the Chatham Islands. * Spectrographic analyses showed that birds would have difficulty distinguishing seedling leaves against a background of leaf litter. Conversely, brightly coloured tissues flanking spines on sapling leaves are highly conspicuous to birds. Once above the reach of the tallest known moa, adults produce leaves that are typical in appearance to adult leaves. The Chatham Island species lacks ontogenetic colour changes entirely. * Overall, the results indicate that P. crassifolius goes through a remarkable series of colour changes during development, from cryptically coloured seedlings to aposematically coloured saplings, which may have formed a defensive strategy to protect against giant browsing birds.
  • Article
    Full-text available
    In low-density butterfly-pollinated Mussaenda frondosa (Rubiaceae), flowers attract pollinators at short distances while conspicuous, non-rewarding accessory bracts are detectable at long distances by long-ranging pollinators such as the birdwing butterfly Troides minos that did not detect flower-bearing plants in the absence of these bracts. However, even in the absence of flowers, the white, ultraviolet-absorbing bracts attracted butterflies that visited flowerless plants. Although flower visits by short-ranging territorial butterflies declined significantly on removal of bracts, they did not cease completely. Nectar-robbing carpenter bees and birds did not change their behaviour following bract removal. Bract removal caused a significant decline in fruit set, indicating their importance as visual signals to pollinators.
  • Article
    The rosette and cauline leaves of the highly thorny winter annual plant species of the Asteraceae in Israel (Silybum marianum) resemble green zebras. The widths of typical variegation bands were measured and found to be highly correlated with leaf length, length of the longest spines at leaf margins and the number of spines along leaf circumference. Thus, there is a significant correlation between the spinyness and strength of variegation. I propose that this is a special case of aposematic (warning) coloration.
  • Article
    The surface of the primary aerial parts of terrestrial plants is covered by a cuticle, which has crucial autecological functions, but also serves as an important interface in trophic interactions. The chemical and physical properties of this layer contribute to these functions. The cuticle is composed of the cuticular layer and the cuticle proper, which is covered by epicuticular waxes. Whereas the cutin fraction is a polyester-type biopolymer composed of hydroxyl and hydroxyepoxy fatty acids, the cuticular waxes are a complex mixture of long-chain aliphatic and cyclic compounds. These highly lipophilic compounds determine the hydrophobic quality of the plant surface and, together with the microstructure of the waxes, vary in a species-specific manner. The physicochemical characteristics contribute to certain optical features, limit transpiration, and influence adhesion of particles and organisms. In chemical ecology, where interactions between organisms and the underlying (allelo-) chemical principles are studied, it is important to determine what is present at this interface between the plant and the environment. Several useful equations can allow estimation of the dissolution of a given organic molecule in the cuticle and its transport properties. The implementation of these equations is exemplified by examining glucosinolates, which play an important role in interactions of plants with other organisms. An accurate characterization of physicochemical properties of the plant surface is needed to understand its ecological significance. Here, we summarize current knowledge about the physical and chemical properties of plant cuticles and their role in interactions with microorganisms, phytophagous insects, and their antagonists.
  • Article
    Full-text available
    Juvenile phase English ivy (Hedera helix L.) plants accumulate anthocyanin pigment in the hypodermis of stems and petioles, whereas genetically identical plants of the mature phase do not. The objective of this work was to assess which enzyme(s) might limit anthocyanin accumulation in mature phase ivy. Leaf discs of both juvenile and mature phase ivy accumulated comparable levels of the flavonols kaempferol and quercetin, whereas only juvenile phase discs accumulated anthocyanin. The accumulation of quercetin, but lack of accumulation of leucocyanidin or anthocyanin in mature phase discs, suggested that mature discs lacked dihydroflavonol reductase activity. There was no detectable dihydroflavonol reductase activity in mature phase discs, whereas there was an induction of activity in juvenile phase discs in response to sucrose, or photosynthetically fixed carbon, and light as a photomorphogenic signal. Phenylalanine ammonia-lyase, an enzyme early in the anthocyanin biosynthetic pathway, was induced above its basal level by sucrose and light in discs of both phases of ivy, with greater activity in mature phase discs. Phenylpropanoids, a class of compounds that are precursors to flavonoids, accumulated in leaf discs of both phases, with greater levels in mature phase discs. These results indicate that the lack of dihydroflavonol reductase activity limits the accumulation of anthocyanin in mature phase tissue.
  • Article
    Full-text available
    Free porphyrins and their magnesium complexes, including chlorophylls, are potent photo-sensitizers. Plants usually accumulate these compounds bound to proteins together with protective compounds like carotenoids. Besides their protective role, carotenoids can play a structural role in these complexes. To analyze the effect of impaired carotenogenesis on plastid membranes we applied to barley seedlings the bleaching herbicide 2-(4-chlorophenylthio)triethylamine (CPTA) as a specific inhibitor for the cyclization of lycopene. To avoid interference with photo-oxidation, the essential experiments were performed on seedlings grown in darkness. While the amount of total carotenoids decreased, we found accumulation of more 6-carotene than lycopene in darkness clearly showing that CPTA inhibits the lycopene beta-cyclase more effectively than the lycopene epsilon-cyclase. The CPTA treatment resulted in accumulation of non-photoactive protochlorophyllide a; the amount of photoactive protochlorophyllide and NADPH:protochlorophyllide oxidoreductase remained constant. Further, the level of Mg protophorphyrin and its monomethyl ester increased to an extent similar to that obtained by application of 5-aminolevulinic acid (ALA). The perturbation of the ultrastructure of etioplast inner membranes, observed after CPTA-treatment, was not found after ALA-treatment; this excluded the accumulated tetrapyrroles as responsible for the perturbation. By contrast, the down-regulation of Lhcb and RbcS genes found after CPTA-treatment was compatible with the presumed role of Mg protophorphyrin as "plastid signal" for regulation of nuclear gene expression. Possible mechanisms for enhancement of tetrapyrrole accumulation by non-cyclic carotenoids are discussed.
  • Article
    Variegated leaves occur rarely in nature, but there are some species, primarily in the forest understory, that possess this characteristic. We recently studied two variegated plants: Erytronium dens-canis L., which is characterised by a pattern of red patches and Pulmonaria officinalis L., with light green spots. These non-green areas could attenuate light reaching mesophyll cells with respect to green sections. The aim of the study was to verify whether such red and light green parts are more photoprotected than green ones and if this trait could be of adaptive value. Red patches in E. dens-canis were due to a single layer of red cells in the upper parenchyma, which accumulated anthocyanins. Light green spots in P. officinalis were caused by the presence of loosely arranged cells instead of a well-established layer of packed cells in the palisade parenchyma. Chlorophyll fluorescence imaging was performed under light treatment, showing a greater decrease of photochemical efficiency in red and light green patches than in green sections. Differences in the extent of photochemical efficiency among patches were not attributable to different activation of the xanthophyll cycle. These observations failed to confirm our initial hypothesis, but they questioned the physiological reason for this higher sensitivity in red and light green patches of photosynthetic tissues. Chlorophyll fluorescence imaging was therefore performed in the field. The same pattern of photochemical efficiency was maintained only in E. dens-canis. The current results demonstrate that in both species the benefits of variegation, if any, are different from enhanced photosynthetic performance.