Palisade Cell Layers Research Articles

Leaf anatomy and chlorophyll content of 12 woody species in contrasting light conditions in a Bornean heath forest

This paper reports the anatomy, chlorophyll content, and some optical properties of leaves of 12 tree species in sun and shade conditions in a tropical heath forest in Brunei (northern Borneo). These plants displayed some xeromorphic leaf features, e.g., relatively low stomata density compared with lowland rain forest plants and sun leaves usually with two or more layers of palisade cells. Most species displayed substantial plasticity in leaf structure and chlorophyll concentration in response to different light conditions. Dipterocarp leaves had thinner palisade mesophyll and greater spongy to palisade thickness ratios than non-dipterocarp leaves. The chlorophyll content per unit leaf area of the species studied was within the range quoted for American tropical rainforest trees. Their chlorophyll a : chlorophyll b ratios, however, were much lower than those for forest plants in humid temperate and subtropical regions. This could be attributed to the regular soil water deficits of this forest. Despite large variation in leaf structure and chlorophyll concentration among species and within species on the two distinct conditions, their absorptance of photosynthetic active light was similar. Chlorophyll concentration per unit weight was adversely and nonlinearly related to leaf thickness for the data pooled from all species in both light conditions (R2 = 0.49, P < 0.001).Key words: chlorophyll concentration, leaf anatomy, kerangas, light acclimation, leaf plasticity, tropical heath forest.

Leaf anatomy and chlorophyll content of 12 woody species in contrasting light conditions in a Bornean heath forest

This paper reports the anatomy, chlorophyll content, and some optical properties of leaves of 12 tree species in sun and shade conditions in a tropical heath forest in Brunei (northern Borneo). These plants displayed some xeromorphic leaf features, e.g., relatively low stomata density compared with lowland rain forest plants and sun leaves usually with two or more layers of palisade cells. Most species displayed substantial plasticity in leaf structure and chlorophyll concentration in response to different light conditions. Dipterocarp leaves had thinner palisade mesophyll and greater spongy to palisade thickness ratios than non-dipterocarp leaves. The chlorophyll content per unit leaf area of the species studied was within the range quoted for American tropical rainforest trees. Their chlorophyll a : chlorophyll b ratios, however, were much lower than those for forest plants in humid temperate and subtropical regions. This could be attributed to the regular soil water deficits of this forest. Despite lar...

Anatomy, chloroplast structure and compartmentation of enzymes relative to photosynthetic mechanisms in leaves and cotyledons of species in the tribe Salsoleae (Chenopodiaceae)

Certain members of the family Chenopodiaceae are the dominant species of the deserts of Central Asia; many of them are succulent halophytes which exhibit C 4 -type CO 2 fixation of the NAD- or NADP-ME (malic enzyme) subgroup. In four C 4 species of the tribe Salsoleae, the Salsoloid-type Kranz anatomy in leaves or stems was studied in relation to the diversity in anatomy which was found in cotyledons. Halocharis gossypina, has C 4 NAD-ME Salsoloid-type photosynthesis in leaves and C 3 photosynthesis in dorsoventral non-Kranz cotyledons; Salsola laricina has C 4 NAD-ME Salsoloid-type leaves and C 4 NAD-ME Atriplicoid-type cotyledons; Haloxylon persicum, has C 4 NADP-ME Salsoloid-type green stems and C 3 isopalisade non-Kranz cotyledons; and S. richteri has C 4 NADP-ME Salsoloid-type leaves and cotyledons. Immunolocalization studies on Rubisco showed strong labelling in bundle sheath cells of leaves and cotyledons of organs having Kranz anatomy. The C 4 pathway enzyme phosphoenolpyruvate carboxylase was localized in mesophyll cells, while the malic enzymes were localized in bundle sheath cells of Kranz-type tissue. Immunolocalization by electron microscopy showed NAD-ME is in mitochondria while NADP-ME is in chloroplasts of bundle sheath cells in the respective C 4 types. In some C 4 organs, it was apparent that subepidermal cells and water storage cells also contain some chloroplasts which have Rubisco, store starch, and thus perform C 3 photosynthesis. In non-Kranz cotyledons of Halocharis gossypina and Haloxylon persicum, Rubisco was found in chloroplasts of both palisade and spongy mesophyll cells with the heaviest labelling in the layers of palisade cells, whereas C 4 pathway proteins were low or undetectable. The pattern of starch accumulation correlated with the localization of Rubisco, being highest in the bundle sheath cells and lowest in the mesophyll cells of organs having Kranz anatomy. In NAD-ME-type Kranz organs (leaves and cotyledons of S. laricina and leaves of H. gossypina) the granal index (length of appressed membranes as a percentage of total length of all membranes) of bundle sheath chloroplasts is 1.5 to 2.5 times higher than that of mesophyll chloroplasts. In contrast, in the NADP-ME-type Kranz organs (S. richteri leaves and cotyledons and H. persicum stems) the granal index of mesophyll chloroplasts is 1.5 to 2.2 times that of the bundle sheath chloroplasts. The mechanism of photosynthesis in these species is discussed in relation to structural differences.

An Arabidopsis gene encoding a chloroplast‐targeted β‐amylase

beta-Amylase is one of the most abundant starch degrading activities found in leaves and other plant organs. Despite its abundance, most if not all of this activity has been reported to be extrachloroplastic and for this reason, it has been assumed that beta-amylases are not involved in the metabolism of chloroplast-localized transitory leaf starch. However, we have identified a novel beta-amylase gene, designated ct-Bmy, which is located on chromosome IV of Arabidopsis thaliana. Ct-Bmy encodes a precursor protein which contains a typical N-terminal chloroplast import signal and is highly similar at the amino acid level to extrachloroplastic beta-amylases of higher plants. Expression of the ct-Bmy cDNA in E. coli confirmed that the encoded protein possesses beta-amylase activity. CT-BMY protein, synthesized in vitro, was efficiently imported by isolated pea chloroplasts and shown to be located in the stroma. In addition, fusions between the predicted CT-BMY transit peptide and jellyfish green fluorescent protein (GFP) or the entire CT-BMY protein and GFP showed accumulation in vivo in chloroplasts of Arabidopsis. Expression of the GUS gene fused to ct-Bmy promoter sequences was investigated in transgenic tobacco plants. GUS activity was most strongly expressed in the palisade cell layer in the leaf blade and in chlorenchyma cells associated with the vascular strands in petioles and stems. Histochemical staining of whole seedlings showed that GUS activity was largely confined to the cotyledons during the first 2 weeks of growth and appeared in the first true leaves at approximately 4 weeks.

Comparative Anatomical, Morphological, and Physiological Parameters Controlling Photosynthesis in Two Populusxeuramericana Clones During Short-Term Osmotic Treatment

The relationships between drought response and anatomical/physiological properties were assessed in two poplar clones belonging to the Aigeros section: Populusxeuramericana clone Dorskamp (drought-tolerant) and clone Luisa Avanzo (drought-sensitive). Cuttings of both clones were exposed for 12 h to 0 mM (control). 50 mM (osmotic potential −0.112 MPa), and 150 mM (−0.336 MPa) mannitol. In control, Dorskamp had smaller stomata than Luisa Avanzo, one or two layers of palisade cells, a spongy mesophyll, and high concentrations of antioxidative compounds (ascorbate, glutathione). After exposure to 50 or 150 mM mannitol, both clones closed their stomata: leaf conductance and opening of stomata decreased. When exposed to 50 mM mannitol, net photosynthetic rate (P N) and chlorophyll (Chl) and total solute contents remained stable; ribulose-1,5-bisphosphate carboxylase/-oxygenase activity, Chl synthesis and turn-over, ascorbate peroxidase and glutathione reductase activities were less affected in Dorskamp than in Luisa Avanzo. Following an exposure to 150 mM mannitol, Dorskamp exhibited higher P N and higher contents of antioxidants (ascorbate, glutathione) and antioxidative enzymes (ascorbate peroxidase, glutathione reductase) than Luisa Avanzo. Hence the drought-tolerant poplar was able to better avoid and tolerate osmotic stress.

Structural characteristics of stored black beans (Phaseolus vulgaris L.)

AbstractScanning electron microscopy (SEM) was used to study and compare the structural characteristics of black beans after 2 years of storage under ambient conditions (AC) and refrigerated hypobaric conditions (RHC). The exterior surface of the seed coats of the black beans were covered with small flake‐like materials randomly clustered together. The hilar regions of black beans stored under either AC or RHC were similar, and the “linea lucida” exhibited well defined double palisade cell layers in both bean treatments. Cross sections of the seed coats revealed that the parenchymal cell layers of the beans stored under AC were disrupted and frequently exhibited large intercellular spaces between the cell layers. The parenchymal cell layers of the beans stored under RHC demonstrated little disruption of the cell layers, with only occasional intercellular spaces between the cell layers. Cotyledon cross sections of blackbeans showed that the cotyledon cells of the beans stored under RHC exhibited many large intercellular spaces characteristic of normal beans. Conversely, cotyledon cross sections of the beans stored under AC exhibited cotyledon cells with few small intercellular spaces characteristic of hard‐to‐cook beans.

Histochemical and Immunocytochemical Localization of Tropane Alkaloids in Erythroxylum coca var. coca and E. novogranatense var. novogranatense

The tropane alkaloids of Erythroxylum coca var. coca and Erythroxylum novogranatense var. novogranatense were localized using histochemical, cytochemical, and immunocytochemical probes. At the tissue level, these alkaloids were localized in leaves, stems, and fruits with Dragendorff's reagent. Alkaloids were found in the mesophyll, including palisade, spongy, and vascular parenchyma cell layers, and in some cells of the collenchyma. No alkaloids were detected in the epidermis of either Erythroxylum species. Alkaloids were also detected in the endosperm and embryos of orange and mature red fruits but not in tissues of immature green fruits. Quantitative HPLC reveals that embryos had 2.5-5 times more cocaine (w/w%) than endosperms, but 40 times less than leaves. In contrast to leaves, cocaine was a minor alkaloid present in fruits. Dragendorff's reagent was used to develop thin-layer chromatography plates and specifically stained the alkaloids extracted from leaves of both species. Complexing of alkaloids with tannins resulted in aggregates in the vacuole of E. coca leaf cells as visualized by transmission electron microscopy. Immunocytochemical localization, using anticocaine polyclonal antibodies on leaf tissues, proved that these compounds are localized in vacuoles of both photosynthetic and vascular parenchyma, as demonstrated by the use of Dragendorff's reagent. The alkaloids were associated with intravacuolar globules and appear to be aggregates with a core formed by phenolic compounds and a periphery enriched in alkaloids. The vacuolar localization of the cocaine alkaloids indicate that they may be complexed with phenols in vivo, thereby rendering them relatively immobile. The implications of the cellular and tissue localization of tropane alkaloids in Erythroxylum are discussed.

Associations between leaf structure, orientation, and sunlight exposure in five Western Australian communities

Five plant communities in Western Australia, as well as selected desert and Rocky Mountain species of the western USA, were surveyed to evaluate associations among leaf structure, orientational properties, and the sunlight exposure and precipitation characteristic of each community. Selected leaf structural features have been associated previously with photosynthetic function and included shape, thickness, the ratio of thickness to width, stomatal distribution, leaf surface coloration, and the number and distribution of palisade cell layers. Decreases in annual precipitation (<4 to over 15 cm/yr) and increases in total daily sunlight (4.2 to 29.2 mol photons/m1) corresponded strongly to an increase in the percentage of species in a given community with more inclined (more inclined than +/- 45 degrees from horizontal) or thicker leaf mesophyll (>0.4 mm) leaves. Also, the percentage of species with a leaf thickness to width ratio >0.1, which were amphistomatous, or which had palisade cell layers beneath both leaf surfaces, increased from >20% in the highest rainfall and lowest sunlight community to >80% in the community with least rainfall but greatest sunlight exposure. Over 70% of the species in the most mesic, shaded community had lighter abaxial than adaxial leaf surfaces (leaf bicoloration). All of the above structural features were positively associated with a more inclined leaf orientation (r1 = 0.79), except for leaf bicoloration, which was negatively associated (r1 = 0.75). The ratio of adaxial to abaxial light was more strongly associated with leaf bicoloration (r1 = 0.83) and the presence of multiple adaxial and isobilateral palisade cell layers(r1 = 0.80) than with total incident sunlight on just the adaxial leaf surface (r1 = 0.69 and 0.73, respectively). These results provide field evidence that leaf orientation and structure may have evolved in concert to produce a photosynthetic symmetry in leaf structure in response to the amount of sunlight and other limiting factors of the community. This structural symmetry may serve fundamentally to regulate the distribution of both light and CO2 levels inside the leaf and, thus, increase photosynthetic CO2 uptake per unit leaf biomass.

Role of Saliva in the Highly Destructive Fourlined Plant Bug (Hemiptera: Miridae: Mirinae)

The fourlined plant bug, Poecilocapsus lineatus (F.), is among the more damaging hemipterans, causing immediate and conspicuous lesions at feeding sites on leaves. The damage appears histologically to involve complete loss of cellular integrity and removal of the palisade cell layer. The ability of P. lineatus to cause such remarkable damage appears to reside in the chemical nature of its salivary products; however, among tests of the salivary enzymes that included assays for pectinase, cellulase, proteinase, polyphenol oxidase, lipase, and amylase, only an exopectinase was found. The size of the salivary gland complex in later instars and adults (≈14–21% of total body mass) was proportionately far greater than that found in other Heteroptera, such as in another mirid, Lygus hesperus Knight (where salivary gland complexes were only 4–7% of total body mass). Ultrastructure analysis of the salivary glands revealed that the vast majority of the cellular make-up of the glands is rough endoplasmic reticulum. A complex of proteins was present in salivary gland extracts with molecular weights of 87, 79, 42, 33, 30, and 21 kDa. Gel filtration chromatography revealed a major peak of exopectinase activity corresponding to a molecular weight of ≈30–35 kDa; and ion exchange chromatography revealed 2 peaks of exopectinase activity eluting with an ion strength of ≈0.4 and 0.5 M NaCl.

Ecophysiological attributes of the native Acer saccharum and the exotic Acer platanoides in urban oak forests in Pennsylvania, USA.

When the exotic Acer platanoides L. (Norway maple) and the native A. saccharum Marsh. (sugar maple) grow together in the understories of urban Quercus forests in the eastern USA, average annual height growth increments are nearly twice as large in A. platanoides as in A. saccharum, 19.26 +/- 3.22 versus 10.01 +/- 1.69 cm. We examined several ecophysiological mechanisms that might be associated with the superior invasive ability and growth of A. platanoides in two urban oak forests in Pennsylvania. Leaf longevity was 12 days greater in A. platanoides than in A. saccharum. In addition, leaf mass/leaf area ratio was greater in A. platanoides than in A. saccharum (2.67 +/- 0.03 versus 2.32 +/- 0.02 mg cm(-2)); however, leaf thickness was significantly lower in A. platanoides than in A. saccharum suggesting that A. platanoides contains more dense palisade and mesophyll cell layers than A. saccharum. Field net photosynthesis (mass basis) and photosynthetic light response curves (area basis) indicated significantly greater carbon assimilation, and nitrogen and phosphorus use efficiencies in A. platanoides than in A. saccharum. Acer platanoides also exhibited higher water use efficiency than A. saccharum (0.88 +/- 0.12 versus 0.32 +/- 0.09 mmol CO(2) mol(-1) H(2)O). Acer platanoides exhibited significantly lower osmotic potentials than A. saccharum, but a similar relative water content at zero turgor. We conclude that A. platanoides utilizes light, water and nutrients more efficiently than A. saccharum.

Development of the strophiole in seeds of white clover (Trifolium repens L.)

AbstractThe seed coat of Trifolium repens L. was studied with special emphasis on the development of the strophiole, which is the site for water entry during imbibition in leguminous seeds. The epidermal cells of the strophiole are longer than the cells in the remainder of the seed epidermis in the mature ovule. During seed development the median cells of the strophiolar epidermis divide periclinally into an outer layer of palisade cells and an inner layer of isodiametric cells. Prior to maturity a fissure is formed between some of the palisade cells in the centre of the strophiole. It is suggested that tension develops between the palisade cells and the iso-diametrical cells during later maturation stages causing the formation of the fissure which it is believed functions in water uptake. It is indicated that the ‘light line’ is caused by alteration of cellulose microfibrillar orientation in palisade cell walls. It is confirmed that removal of the epicuticular wax from hard seeds by rinsing in absolute alcohol or hexane does not induce water imbibition. Only when seed coats are mechanically abraded do hard seeds germinate.

Morphology and Anatomy of Leaves of Eucalyptus camaldulensis Clones: Variation Between Geographically Separated Locations

Leaves of six clonal individuals of Eucalyptus camaldulensis Dehnh. from five Australian locations were compared. Two clones were from Wooramel, WA while single clonal lines were from Dongara, WA, Erudina, SA, Murray Bridge, SA and Silverton, NSW. Principal component analysis of climatic factors for the five locations, derived by BIOCLIM, provided patterns of temperature, radiation and atmospheric moisture, which might be expected to influence the morphological and anatomical features of the leaves. Isozyme analysis indicated that the two Wooramel clones were closely related, but comparable similarity in isozyme pattern was also found between a Wooramel clone and the representative from Murray Bridge. Leaf morphological and anatomical features showed patterns related to the habitat climate of the parent plants, but considerable genetic variation was observable even within a single location. Leaf thickness was generally greatest for clones from the more arid locations and least for clones from the most mesic of locations, but leaf length and width were not associated with any of the climatic factors considered. Thin leaf cuticles were associated with thin leaves. Leaf thickness was determined by the thickness of the internal cell layers, as all clones contained an epidermal and three palisade parenchyma cell layers on both adaxial and abaxial sides. Adaxial palisade layers were thicker than abaxial palisade layers. Stomatal density was not related to leaf dimensions, but clones with the greatest stomatal density tended to have the smallest stomatal pore dimensions. Oil gland density was greatest for leaves of Western Australian clones. Clones from the more arid locations displayed larger chloroplasts. In general, there was a lack of correlation between leaf characteristics and climatic data. Ground water availability, root structure and internal transport of water may have a greater influence on leaf structure than atmospheric demand.

Alterations in Leaf Morphology of Two Landscape Shrubs in Response to Disparate Climate and Paclobutrazol

Paclobutrazol at 0 and 750 μl·liter–1 was sprayed on shoots of Feijoa sellowiana O. Berg. and Ligustrum japonicum Thunb. grown under similar production regimes in central Arizona (subtropical desert) and southern Georgia (humid temperate). Five months after application, Feijoa and Ligustrum leaves were generally smaller and thicker in Arizona than in Georgia. Arizona leaves were thicker than those in Georgia because of more layers of palisade and spongy mesophyll cells. Compared with leaves from control plants, paclobutrazol 1) increased Feijoa leaf area in Georgia, 2) decreased Ligustrum leaf area at both locations by ≈50%, and 3) decreased leaf thickness of both species in Arizona. Arizona Feijoa leaves had trichomes on adaxial and abaxial surfaces, whereas Georgia Feijoa leaves had trichomes on abaxial surfaces only. Paclobutrazol increased trichome frequency on adaxial surfaces of Arizona Feijoa leaves. Stomatal frequency of Georgia Feijoa leaves was about doubled by paclobutrazol. Reflectance of near-infrared radiation by paclobutrazol-treated Feijoa leaves was 1.4 times higher than that of nontreated leaves in Georgia and 1.9 times in Arizona. Near-infrared reflectance by Georgia Ligustrum leaves was 1.3 times higher than by Arizona Ligustrum leaves and was not affected by paclobutrazol. Leaf reflectance of photosynthetically active radiation (PAR) by Arizona Feijoa was higher than by Georgia Feijoa. Paclobutrazol increased PAR reflectance by Arizona Feijoa leaves. In contrast, Georgia Feijoa PAR reflectance was decreased by paclobutrazol. Paclobutrazol or location did not affect Ligustrum PAR reflectance. Chemical name used: (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol).

Stomata and Structure of Tetraploid Apple Leaves cultured in Vitro

Leaves of anther-derived tetraploid apple (Malus pumila Mill.) shoots were examined by low-temperature scanning electron microscopy (LT-SEM). Leaves were serrate and wide with an undulating adaxial surface due to convex epidermal cells, apparently without crystalline epicuticular wax. Stomata were absent from the adaxial surface, except for the marginal teeth which exhibited 40-60 stomata per leaf; they probably originated from residual mitotic activity. One third of abaxial stomata was occluded by the residual cuticle of the mother guard cell across the stomatal pore which ruptured when the stomata became functional. The stomatal index was 7·2 (± 1·6) with 60-75 stomata mm-2, i.e. abaxial stomata of tetraploid leaves expanded in vitro were less frequent than those in triploid leaves either cultured in vitro (475-575 stomata mm-2) or grown on the tree (320-390 stomata mm-2) where the stomatal index was 21 (± 4). Freeze-fracture transsections showed that the tetraploid in vitro leaves were composed of a layer of adaxial epidermal cells, followed by a single layer of palisade cells and four to five layers of spongy mesophyll cells and the abaxial layer of epidermal cells, in contrast to juvenile seedling-grown apple leaves in which the two layers of palisade cells comprised the majority (52-60%) of the leaf volume. The same morphological features, such as wide and less pointed leaves, reduced stomatal density and stomatal index, and increased stomatal size that were previously reported for tree-grown tetraploid leaves were also expressed in vitro. Thus, causes of the stomatal deformation in tissue-cultured Rosaceae are interpreted to be in part genetic and not purely environmental.

Foliar sclereids of Olea europaea may function as optical fibres

Adaxial epidermises that contained an intact "subepidermal" "T"-shaped sclereid network, were isolated from olive tree leaves using a new method of enzymatic maceration. In the leaf, the sclereid network was anchored on the adaxial epidermis. The basal parts of the T-shaped sclereids penetrate the palisade cell layers into the underlying spongy parenchyma cells. In paradermal sections, the basal parts of the sclereids appeared as light-emitting sources or spots among the dark-green background of the palisade layers. The light spots almost disappeared when the intercellular air spaces were filled with immersion oil that had a similar refractive index to that of cell walls. It is plausible that light is propagated through multiple reflections between the thick cell wall of sclereids and the air filling the intercellular spaces, the former having a significantly higher refractive index. Sclereids act like synthetic optical fibres and, besides other functions, they may contribute to the improvement of the light microenvironment within the mesophyll of the thick and compact sclerophyllous leaves of Olea. Key words: foliar sclereids, optical fibres, light guiding, Olea europaea.

621 (PS 3) EFFECT OF CONTRASTING PRODUCTION LOCATION ON LEAF MORPHOLOGY OF TWO LANDSCAPE SHRUBS

Same-source rooted cuttings of Feijoa Sellowiana Hort. and Ligustrum japonicum L. were grown under identical production systems in Tempe, AZ, USA or Tifton, GA, USA during the Spring and Summer 1992. Leaf area was largest and specific leaf weight was lowest for all Georgia-grown plants. Scanning electron microscopy revealed that Arizona Feijoa leaves had trichomes on both the abaxial and adaxial leaf surfaces, whereas, leaves of Georgia Feijoa had trichomes on the abaxial surface only. Arizona Feijoa leaves also had increased abaxial surface pubescence compared to leaves of Georgia Feijoa. Both Feijoa and Ligustrum grown in Arizona had a higher density of palisade and spongy mesophyll cell layers compared to their Georgia counterparts. When placed under the same irradiance source, adaxial leaf surface temperatures of Georgia-grown Ligustrum and Feijoa were approximately 4.2 and 0.2C, respectively, higher than for those grown in Arizona. Higher leaf temperatures of Georgia-grown plants were correlated with darker leaf color compared to the Arizona-grown plants.

Characteristics of leaf structure and photosynthetic apparatus within the crown of systematically shadedQuercus petraea andNothofagus procera seedlings

Four-year-old seedlings ofQuercus petraea (Matt.) Liebl. andNothofagus procera (Poepp. et Endl.) Querst were grown outdoors in pots while subjected to full, medium and low irradiances. Shading and decrease in height of leaf attachment generally increased specific leaf area, the diameters of chloroplasts and of palisade and spongy mesophyll cells, but decreased leaf thickness, number of palisade cell layers, length of palisade and spongy mesophyll cells, number of chloroplasts per mesophyll cell and epidermal cell and cuticle thickness, stomata and hair densities per unit leaf area, hair length, maximum hair breath and cell wall thickness in the two species. However, inN. procera grown under full irradiance, leaves at the upper and middle positions had hairs on both upper and lower epidermes, whereas those in other treatments and all leaves in all treatments inQ. petraea, had theirs only on the upper epidermis.

Abundance and mortality of a specialist leafminer in response to experimental shading and fertilization of American holly.

Phytomyza ilicicola (Diptera: Agromyzidae), a univoltine specialist leafminer, typically reaches higher population densities on cultivated host planted in sunny, urban sites than it does on native trees in the forest understory. I tested the hypothesis that environmental factors, more specifically differences in light intensity and soil fertility, are responsible for this observed pattern, either by affecting leaf morphology or nutritional quality, or indirectly through early leaf abscission. Clonal trees were planted at a common site and experimentally shaded and fertilized for 14 months before being exposed to oviposition by adult flies. Differences in leaf thickness, nitrogen and water status, and in the abundance, developmental rate, survival, pupal weights and abscission-related mortality of leafminers were compared among trees. Leaves from experimentally shaded trees were larger and thinner, with only two palisade cell layers as compared to three to four layers in leaves from unshaded trees. Crystals, probably of calcium oxalate, are abundant in the abaxial cell layer, and it was hypothesized that these might set mechanical constraints on larvae feeding within shaded leaves. However, there was little or no difference in leafminer abundance, developmental rate, survival to pupation, area of finished mines, or pupal weight between shaded and unshaded trees. Leafminers compensated for feeding within thinner, shaded leaves by consuming portions of the abaxial and adaxial palisade layers and leaving a thinner roof on the mine. Furthermore, there was no difference in thickness between leaves with successful or aborted mines in either shade or sun. Leaves from fertilized trees contained 37% higher total nitrogen than those from unfertilized control trees. Fertilization did not significantly affect leafminer abundance, developmental rate, mine area or pupal weight, but survival to pupation was slightly lower on fertilized trees. Abscission-related mortality of P. ilicicola was much higher in full sun than for shaded trees, opposite of what would be predicted if early abscission per se were a primary determinant of relative abundance between habitats. These results indicate that structural constraints on leafminer larvae within shaded leaves, differences in leaf nitrogen related to soil fertility, and/or differential mortality resulting from early leaf abscission are probably not the proximate causes of density variation of this leafminer between woods and urban habitats.

Fruits from the mid-cretaceous of north america with pollen grains of theclavatipollenitestype

Abstract Small fruits with clumps of monocolpate, reticulate pollen grains of the Clavatipollenites type adhering to the stigmatic surface have been recovered from mid-Cretaceous (early Cenomanian) Potomac Group sediments of eastern North America. They provide the first megafossil evidence of this important early angiosperm pollen genus. The fruits are described as Couperites mauldinensis gen.et sp. nov. They are unicarpellate and unilocular containing a single, anatropous and pendulous seed. The fruit wall is thin with distinct, tubercular protrusions enclosing spherical resin bodies. The seed wall is apparently composed of two distinct tissues, indicating that the seed was probably derived from a bitegmic ovule. The outer tissue consists of one layer of cuboid palisade cells, the inner tissue consists of longitudinally elongated cells. Fruit and seed characters indicate that Couperites is more closely related to Chloranthaceae than to any other magnoliid family, and support the systematic affinity suggested for most dispersed Clavatipollenites taxa. However, the anatropous seeds place Couperites outside the current circumscription of the family and imply a more basal phylogenetic position.

The Morphology and Anatomy of the Leaf of Moricandia arvensis (L.) DC. (Brassicaceae)

Mature leaves of Moricandia arvensis (L.) DC. were examined with the light microscope to determine their vasculature and the spatial relationships of vascular bundles to the mesophyll. One median and two lateral leaf traces enter the sessile lamina at the node. Upon entering the lamina, the continuations of both lateral traces bifurcate unevenly. The outer, smaller branches divide further to innervate the basal portion of the lamina, while the inner, larger branches and the continuation of the median trace constitute the primary bundles of the midvein. As the midvein progresses acropetally in a prominent midrib, branches from the lateral primaries diverge outward and continue as secondary veins toward the margins. By the median level of the lamina, the lateral primaries themselves diverge outward as secondary veins. Above the divergence of the lateral primaries the midvein is represented solely by the median bundle. Tertiary veins arise from both secondaries and the midvein; other higher-order minor veins arise from all orders of veins. All major veins-primaries and secondaries-are associated with rib tissue. All minor veins are completely surrounded by a chlorenchymatous bundle sheath. The mesophyll of the typically bifacial leaf is composed of poorly defined layers of palisade and spongy parenchyma cells. In addition, two poorly defined layers of mesophyll occur in the plane of the minor venation. Extensive lateral contact exists between contiguous mesophyll cells at all levels of the lamina.