Radial leaves of the maize mutant ragged seedling2 retain dorsiventral anatomy

ragged seedling2 (rgd2) is a novel, recessive mutation affecting lateral organ development in maize. The mutant phenotype of homozygous rgd2-R leaves is variable. Mild leaf phenotypes have a reduced midrib and may be moderately narrow and furcated; severe Rgd2-R(-) leaves are filamentous or even radial. Despite their radial morphology, severe Rgd2-R(-) mutant leaves develop distinct adaxial and abaxial anatomical features. Although Rgd2-R(-) mutants exhibit no reduction in adaxial or abaxial cell types, areas of epidermal cell swapping may occur that are associated with misaligned vascular bundles and outgrowths of ectopic margins. Scanning electron microscopy of young primordia and analyses of leaf developmental-marker gene expression in mutant apices reveal that RGD2 functions during recruitment of leaf founder cells and during expansive growth of leaf primordia. Overall, these phenotypes suggest that development is uncoordinated in Rgd2-R(-) mutant leaves, so that leaf components and tissues may develop quasi-independently. Models whereby RGD2 is required for developmental signaling during the initiation, anatomical patterning, and lateral expansion of maize leaves are discussed.     

Ontogenetic differences in mesophyll structure and chlorophyll distribution in Eucalyptus globulus ssp. globulus

Mesophyll structure has been associated with the photosynthetic performance of leaves via the regulation of internal light and CO(2) profiles. Differences in mesophyll structure and chlorophyll distribution within three ontogenetically different leaf types of Eucalyptus globulus ssp. globulus were investigated. Juvenile leaves are blue-grey in color, dorsiventral (adaxial palisade layer only), hypostomatous, and approximately horizontal in orientation. In contrast, adult leaves are dark green in color, isobilateral (adaxial and abaxial palisade), amphistomatous, and nearly vertical in orientation. The transitional leaf type has structural features that appear intermediate between the juvenile and adult leaves. The ratio of mesophyll cell surface area per unit leaf surface area (A(mes)/A) of juvenile leaves was maximum at the base of a single, adaxial palisade layer and declined through the spongy mesophyll. Chlorophyll a + b content showed a coincident pattern, while the chlorophyll a:b ratio declined linearly from the adaxial to abaxial epidermis. In comparison, the mesophyll of adult leaves had a bimodal distribution of A(mes)/A, with maxima occurring beneath both the adaxial and abaxial surfaces within the first layer of multiple palisade layers. The distribution of chlorophyll a + b content had a similar pattern, although the maximum ratio of chlorophyll a:b occurred immediately beneath the adaxial and abaxial epidermis. The matching distributions of A(mes)/A and chlorophyll provide further evidence that mesophyll structure may act to influence photosynthetic performance. These changes in internal leaf structure at different life stages of E. globulus may be an adaptation for increased xeromorphy under increasing light exposure experienced from the seedling to adult tree, similar to the characteristics reported for different species according to sunlight exposure and water availability within their native habitats.     

Leaf anatomy of the Pittosporaceae R. Br.

WILKINSON, H. P., 1992. Leaf anatomy of the Pittosporaceae R. Br. An anatomical study of the leaves of 58 species representing all nine genera has been made. The anatomical characters found to be of most use in distinguishing taxa are: in surface view-cuticular architecture as seen with the SEM, stomatal outline, occasionally stomatal density, presence/absence of hairs, hair type in adult leaves; in transverse section-petiole/midrib outline, midrib number of vascular bundles and number of secretory ducts, adaxial epidermis in 1/2 layers, dimensions of adaxial epidermal cells, thickness of outer wall of adaxial epidermis, occasionally chlorenchyma interrupted/not interrupted above the midrib vascular tissue in Pittosporum species; leaf margin.     

Leaf and twig anatomy of Eriope, a xeromorphic genus of Labiatae

The leaf and twig anatomy of 25 species of the genus Eriope were studied. The twig anatomy is very uniform apart from the level of formation of early layers of cork. Leaf anatomy shows considerable variation between the species, and this is correlated to some extent with the extreme habit range from trees to woody herbs. Characters of the lamina that show variation are: trichome type and frequency, cuticular markings, leaf dorsiventral or isobilateral, presence of adaxial stomata, presence of a hypodermis, number of layers of adaxial palisade mesophyll cells, occurrence of large bundles of phloem fibres at main veins, type of areolation and marginal venation. Petiole vasculature is simple and generally with either four distinct vascular bundles or two vascular arcs. The most xeromorphic species are usually woody herbs or sub-shrubs, and tend to have thick, isobilateral leaves with large bundles of phloem fibres and few hairs, or strongly dorsiventral leaves with a hypodermis and stomata in deep abaxial hair-lined depressions. The correlation of xeromorphic characters with environmental conditions is discussed. Leaf anatomy is of limited value in elucidating relationships within the genus.     

Anatomically preserved leaves of the conifer Notophytum krauselii (Podocarpaceae) from the Triassic of Antarctica

Permineralized leaves of the Triassic podocarpaceous conifer Notophytum krauselii are described from the Fremouw Formation of Antarctica. The leaves are elongate and apetiolate with 8-12 parallel veins. The adaxial epidermis consists of rows of rectangular to pentagonal cells; the abaxial epidermis is papillate. Longitudinally oriented stomata occur on both surfaces. An adaxial palisade layer is present and auxiliary sclereids are common in the mesophyll. The vascular bundles have a weakly defined sheath and are flanked by transfusion tracheids. Bundles in the basipetal area of the leaf are capped by sclerotic tissue and subtended by resin canals. These leaves are superficially similar to those of the extant podocarp genus Nageia, but probably represent a distinct acquisition of this leaf type within the Podocarpaceae. Notophytum leaves are similar to the common compression fossil Heidiphyllum elongatum and may be closely related or even conspecific. Evidence from Antarctica suggests that Heidiphyllum and the seed cone Telemachus were produced by the same plant, and may be closely related to several other early Mesozoic conifers with multiveined leaves.     

Ficus rubiginosa 'variegata', a chlorophyll-deficient chimera with mosaic patterns created by cell divisions from the outer meristematic layer

BACKGROUND AND AIMS: Sections leaves of Ficus rubiginosa 'Variegata' show that it is a chimera with a chlorophyll deficiency in the second layer of the leaf meristem (GWG structure). Like other Ficus species, it has a multiseriate epidermis on the adaxial and abaxial sides of the leaf, formed by periclinal cell divisions as well as anticlinal divisions. The upper and lower laminae of the leaf often exhibit small dark and light green patches of tissue overlying internal leaf tissue. METHODS: The distribution of chlorophyll in transverse sections of typical leaves was determined by fluorescence microscopy. KEY RESULTS: Patches of dark and light green tissue which arise in the otherwise colourless palisade and spongy mesophyll tissue in the entire leaf are due to further cell divisions arising from the bundle sheath which is associated with major vascular bundles or from the green multiseriate epidermis. Leaves produced in winter exhibit more patches of green tissue than leaves which expand in mid-summer. Many leaves produced in summer have no spotting and appear like a typical GWG chimera. There is a strong relationship between the number of patches on the adaxial side of leaves and the number on the abaxial side, showing that the cell division in upper and lower layers of leaves is strongly coordinated. In both winter and summer, there are fewer patches on the abaxial side of leaves compared with the adaxial side, indicating that periclinal and anticlinal cell divisions from the outer meristematic layer are less frequent in the lower layers of leaf tissue. Most of the patches are small (<1 mm in longest dimension) and thus the cell divisions which form them occur late in leaf development. Leaves which exhibit large patches generally have them on both sides of the leaves. CONCLUSION: In this cultivar, the outer meristematic layer appears to form vascular bundle sheaths and associated internal leaf tissue in the entire leaf lamina.     

EARLY HISTOGENESIS OF THE ADULT LEAVES OF DARLINGTONIA CALIFORNICA (SARRACENIACEAE) AND ITS BEARING ON THE NATURE OF EPIASCIDIATE FOLIAR APPENDAGES

In order to assess the validity of various interpretations of tubular leaves of angiosperms, a histogenetic study of the ontogeny of adult leaves of Darlingtonia californica was undertaken. The adult leaf of Darlingtonia is characterized by a sheathing leaf base, an elongate ascidium, an overarching hood, and two “fishtail” appendages which arise near the leaf apex. A keellike growth, with two rows of alternate vascular bundles, traverses the tube from base to mouth. Ontogenetic studies show that the primordium arises by a monopodial rather than a sympodial mode of growth as previously reported. After the formation of a small, erect primordium, a restricted adaxial meristem is initiated that expands both adaxially and upwards. This “querzone” serves, in effect, to congenitally combine the two primordial margins during its extension. Growth and maturation of the subjacent portions cause tubular elongation in the leaf. Primordial apical divisions are later replaced by more general intercalary growth with acropetal and centrifugal maturation. The hood and fishtails are established early in ontogeny by adaxial growth of the primordial apex and subsequent activation of juxtaposed localized meristems. Comparative morphology has established that the epiascidiate leaf is a foliar appendage that undergoes certain specific morphogenetic modifications. It has a structural relationship to ensiform appendages of Acacia and Acorus as well as to peltate foliar organs. The early ontogeny of Darlingtonia leaves is considered to be homologous with other epiascidiate foliar organs, including some supposedly primitive carpels.     

ADAPTIVE LEAF ARCHITECTURE IN EMERGENT AND FLOATING SPARGANIUM

The robust emergent leaves of Sparganium eurycarpum and S. americanum are supported by corner fiber masses and large bundle sheaths, but the thin floating leaves of S. fluctuans and S. minimum have only moderate bundle sheaths. In emergent types heavily photosynthetic diaphragms bearing vascular bundles are separated from each other in the leaf compartments by three lightly photosynthetic diaphragms without bundles, but in floating types only every other heavily photosynthetic diaphragm has a bundle. Palisade chlorenchyma occurs only at aerial surfaces—abaxial and adaxial in emergent leaves, but only adaxial in floating leaves. Extra photosynthetic areas are provided in emergent leaves by concentrations of chlorenchyma in limited areas on interior partitioning walls, while the remainder of the walls is translucent. Since only 25 % of the diaphragms are heavily photosynthetic, and the others essentially transparent because of their diffusely distributed chloroplasts and large intercellular spaces, a sieve effect exists which allows even the interior parts of thick emergent leaves to photosynthesize.     

LEAF DEVELOPMENT IN SENECIO ROWLEYANUS (COMPOSITAE)

Prolonged apical growth of the leaf primordium and the presence of distinct marginal meristems do not occur in Senecio rowleyanus. Intercalary cell divisions accompanied by radial expansion of derivatives from an adaxial meristem account for the spherical shape of the leaf. The “window” in the lamina marks the position of the adaxial meristem and precludes interpretation of the leaf as being unifacial. Stomata are mesoperigenous and anomocytic in type. Schizogenous secretory canals occur in both the leaf and the stem, and their association with vascular bundles is discussed. The anatomy of the leaf is interpreted in terms of xeromorphy.     

STRUCTURE AND DEVELOPMENT OF LEAVES IN CARLUDOVICA PALMATA (CYCLANTHACEAE) WITH REFERENCE TO OTHER CYCLANTHACEAE AND PALMAE

The adult leaf of Carludovica palmata consists of a plicate lamina, adaxial hastula, petiole, and sheath. The leaf is unusual in the angiosperms because about two-thirds of the apical meristem is utilized in its initiation. The adult leaf requires about 4–5 plastochrons to mature. Shortly after its initiation the adult leaf and apical meristem collectively appear pyramid-shaped and various parts of the mature adult leaf may be traced back to particular portions of the pyramid. Plications develop by differential growth within the lamina, not by splitting of leaf tissue. Quantitative studies indicate that certain regions of the developing adult leaf elongate more rapidly or slowly than other regions depending upon the stage of leaf development. The adult leaf of C. palmata develops differently from those of previously studied palms in various ways. It therefore appears less justifiable to consider the superficial similarity between the adult leaves of various Cyclanthaceae (particularly those of Carludovica sensu strictu) and those of fan palms as evidence of especial affinity between the Cyclanthaceae and Palmae. Juvenile leaves of C. palmata differ from adult leaves both in their mode of origin and appearance at maturity. The juvenile leaf appears homologous to the entire adult leaf.     

Integrated control of water hyacinth with a mycoherbicide and a phenylpropanoid pathway inhibitor

The fungus Alternaria eichhorniae isolate 5 (Ae5) is being developed as an effective mycoherbicide against water hyacinth in Egypt. To improve its pathogenicity, integration with 3,4-methylenedioxy trans-cinnamic acid (MDCA), a phenylpropanoid pathway inhibitor that weakens the plant's defense system, was explored. The severity of the disease induced by Ae5 increased when applied to water hyacinth plants pretreated with MDCA. Infection with Ae5 amplified the total phenol concentration in diseased water hyacinth leaves, whereas MDCA reduced it. Plants treated with both Ae5 and MDCA contained a comparable level of total phenols to that in the untreated control plants. Phenol-storing cells were located at three sites in the leaf, within the adaxial palisade tissue, above the abaxial epidermis and in the vicinity of the vascular bundles. Dimensions of these three cell types were increased by infection with Ae5, decreased by MDCA treatment and, in the combined treatment, were similar to those in control leaves. Increased numbers of phenol-storing cells were found only in the region near vascular bundles of plants treated with either Ae5 or MDCA.     

THE RELATIONSHIPS BETWEEN THE PRIMARY VASCULAR SYSTEM AND PHYLLOTACTIC PATTERNS OF ANAGALLIS ARVENSIS (PRIMULACEAE)

The various primary vascular systems of shoots of Anagallis arvensis L. (Primulaceae) can be distinguished in relation to the number of leaves (two, three, or four) at each node. In this study, shoot segments (single intemodes and the nodes above them) were examined. The arrangement of segments within shoots was also recorded. The vasculature forms a closed system with the number of sets of bundles usually equal to twice the number of leaves. Irregularities are found in the following features of the system: the number of bundles composing leaf half-traces; occurrence of anastomosing bundles; the number of intemodes through which bundles extend; levels of leaf attachment to the stem at the node; and distribution of parenchyma within the vascular cylinder, which determines the number of bundles in sets and the number of bundle sets. The irregularities occur with different frequencies for segments exhibiting different phyllotactic patterns. Comparison of these frequencies leads to the following conclusions: anastomosing bundles occur only in decussate or trimerous shoot segments, whereas sets of bundles united within intemodes and displaced leaves occur only in tetramerous or trimerous ones; decrease of the number of bundles per leaf and displacement of leaves at the nodal level are correlated; variation between segments exhibiting the same phyllotactic pattern is greatest for trimerous, less for tetramerous, and least for decussate segments; the vascular system of decussate shoot segments is more stable than that of the other systems; and trimerous segments seem to be intermediate between the other two segment types.     

ESTABLISHMENT OF THE VASCULAR SYSTEM IN SEEDLINGS OF POPULUS DELTOIDES BARTR.

Seven seedlings ranging from 1 to 25 days old were embedded in Spurr's resin and serially sectioned at 1–2 μm. Sectioning extended from well above the apex downward to the hypocotyl base in the 1–day seedlings and to varying levels in the hypocotyl in the older seedlings. Procambial development was analyzed in its entirety for each seedling, and a composite two-dimensional diagram representing the procambial system of a 25-day-old seedling was prepared. Each cotyledon was served by a double-trace, one-half of which was derived from each of two embryonic bundles. The central traces serving the four primary leaves were in turn derived from the four cotyledonary bundles comprising the double traces. The procambial system serving the cotyledons and the four primary leaves approximated a decussate phyllotaxy. The central traces serving the secondary leaves were arranged in a helix that conformed at first to a 1/3 and then to a 2/5 phyllotaxy. Transitions to higher phyllotactic orders were systematic and reproducible, and they occurred in an orderly sequence in both the central and lateral leaf traces. The manner in which leaf traces diverged from parent traces to serve new leaf primordia provided for vascular redundancy. Thus, the entire vascular system was integrated into a highly functional whole.     

Comparative anatomy of the young stem,node, and leaf of Bonnetiaceae,including observations on a foliar endodermis

A comprehensive study of the nodal and leaf anatomy of Bonnetiaceae was completed in order to provide evidence for evaluation in relation to systematics. Nodal anatomy is trilacunar, three-trace or unilacunar, one-trace. Basic leaf anatomical features of the family include: complete or incomplete medullated vascular cylinder in petiole; paracytic mature stomata with encircling ridges; large mucilaginous cells in the adaxial surface of mesophyll; periclinal divisions in upper surface layers; and discrete patches of phloem within the vascular bundles. Especially noteworthy is the presence in some genera of foliar vascular bundles enveloped by a sheath composed of two concentric regions, i.e., an inner region consisting of multiple layers of fibers and an outer specialized endodermis composed of thin-walled cells with Casparian strips. Leaves are variable with respect to lamina and cuticle thickness, relative amount and number of palisade and spongy layers, venation of lamina, and the presence or absence of sclereids and crystals in the mesophyll. A major feature in the evolution of Bonnetiaceae is development of a highly divergent, essentially parallel, leaf venation that is superficially similar to that of some monocotyledons and apparently unique among dicotyledons. Foliar anatomy provides important characters for the recognition of subgroups within Bonnetiaceae and is consistent with the segregation of Bonnetiaceae from Theaceae.     

VASCULARIZATION OF A MULTILACUNAR SPECIES: POLYSCIAS QUILFOYLEI (ARALIACEAE) I. THE STEM

The odd-pinnate leaves of Polyscias quilfoylei have a sheathing leaf base that completely encircles the stem. At each node, many traces depart the vascular cylinder and traverse an obliquely upward course through the leaf base before aggregating in the rachis. Lateral traces diverge from parent traces in the stem vasculature at variable times relative to the leaf they serve, from variable positions in the vascular cylinder and from parent traces of variable ages. The stem vasculature is formed by the coalescing of leaf traces from as many as five leaves. All bundles departing the vascular cylinder at a node to serve a leaf are true leaf traces originating independently in the stem. Leaf traces develop acropetally from their positions of origin on parent traces. Primordial leaves are first served by the median trace and later by lateral traces. Many traces were recognized in the internodes subtending embryonic leaves, but they could not be related either to a specific leaf or to a specific position within a leaf. Because these traces had not yet achieved contact with a primordial leaf site, they were assumed to be in the process of developing acropetally at the time of sampling. Observations suggest that the multiple traces in this species might perform a similar function of integrating the vascular cylinder that subsidiary bundles perform in certain uni- and trilacunar species.     

Physical features of grass leaves influence the placement of eggs within the plant by the Hessian fly

Hessian fly eggs are more likely to be found on adaxial rather than abaxial surfaces of wheat leaves. These leaf surfaces differ in their physical features: the adaxial side of the leaf has parallel grooves and ridges while the abaxial side is relatively smooth. We used leaf models to investigate the relationship between Hessian fly egglaying and these physical features. When both sides of a green paper leaf model were treated with a wheat leaf extract, but only one side of the model was scored with parallel grooves, the grooved side received more eggs than the smooth side. As the number of grooves per surface increased from 0 to 10, eggs per model increased. When grooves and the wheat leaf extract were tested together and separately, the grooves significantly increased egg numbers in the presence, but not the absence, of wheat extract. In contrast, wheat extract increased egg numbers both in the absence and presence of grooves. Molding techniques were used to recreate the physical features of the adaxial and abaxial leaf surfaces of five grasses. For four of the grass genotypes (a triticale, two common wheats, and a durum wheat), patterns of egglaying on real leaves and molded models were similar, i.e., adaxial leaf surfaces and adaxial molded models were preferred over abaxial leaf surfaces and abaxial models. On the fifth grass, oat, preferences for the adaxial side of real leaves and for adaxial models were not as obvious. We conclude that the adult female Hessian fly obtains information about the leaf surface through her tactile and/or kinesthetic senses and uses this information when making egglaying decisions.     

Anatomical structure and distribution of secondary metabolites as a peripheral defence strategy in Aloe hereroensis leaves

Eight leaves from four different plants of Aloe hereroensis and 18 leaf parts of each leaf were tested by anatomic, fluorescence microscopy and TLC methods. Four phenolic secondary metabolites, homonataloin and three isomers of aloeresin, were found in the leaves. The highest content of these metabolites was found in the top third of a leaf and along the leaf margins. In the margins, the content of the four secondary metabolites in the adaxial was higher than in the abaxial direction. In the centre parts of the leaves, the metabolic content of the abaxial parts was higher than in the adaxial parts. The results indicate that homonataloin mainly accumulates in the inner bundle sheath cells (IBSC). The three isomers of aloeresin appear in the outer bundle sheath and in the boundary cells between the chlorenchyma and water-storage tissues. The density of the vascular bundles, the area ratio of the chlorenchyma to the tested counterpart, and the area ratio of the IBSC to a whole bundle are important structural factors to determine the differences in the content of these four secondary metabolites in all the leaf parts. The distribution according to the rosette leaf arrangement and the existence of the 'cocktail' of four phenolic secondary metabolites indicate a peripheral defence strategy of this plant. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 138 , 107–116.