Leaf anatomy of the mosaic <Emphasis Type="Italic">Ficus benjamina</Emphasis> cv. Starlight and interaction of source and sink chimera components

Leaf anatomy was studied in the mosaic Ficus benjamina cv. Starlight and non-chimeric Ficus benjamina cv. Daniel. The number of chloroplasts in a white, chlorophyll-deficient tissue declines as compared to the green tissue. However, their functional activity is retained. The leaf of the mosaic F. benjamina contains two or, sometimes, three subepidermal layers. Mesophyll forms one layer in the green and white parts of leaf palisade and one white and one green layer in the transitional zone (edge). In the transitional zone, green spongy mesophyll is located between two white spongy layers and the proportion of photosynthesizing cells varies. In cv. Daniel, there are two subepidermal layers and one layer of columnar mesophyll cells. According to the morphometry data, the proportion of white zone in the leaf correlates with the leaf position in the whole shoot: the higher the branch order, the larger the proportion of white zone. The total leaf area depends also on its position in the shoot. No such correlation was found in non-chimeric F. benjamina cv. Daniel. In the mosaic chimera, the source-sink status appears to depend on the leaf position in the shoot. Experiments with individual shoots of the same order and elimination of all lateral shoots have shown that the proportion of white zone in new leaves on the shoot increases with the total area of green zone. Thus, the area of assimilating shoot surface affects the formation of leaves in the meristem. A hypothesis was put forward that the source-sink state affects the ratio of green and white parts in the leaf primordium. Products of photosynthesis (carbohydrates) are a possible metabolic signal affecting the meristem. It cannot be excluded as well that the hormonal state undergoes changes in the chimeric plant.     

Marking cell layers with spectinomycin provides a new tool for monitoring cell fate during leaf development

Spectinomycin, an inhibitor of plastid protein synthesis, can be used to mark specific cell layers in the shoot meristem of Brassica napus. Pale yellow-green (YG) plants resulting from spectinomycin-treatment can be propagated indefinitely in vitro. Microscopic examination showed that YG-plants result from inactivation of plastids in the L2 and L3 layers and are composed of a pale green epidermis covering a white mesophyll layer. Epidermal cells of YG and normal green plants are similar and contain 10-20 small pale green plastids. YG plants are equivalent to periclinal chimeras with the important distinction that there is no genotypic difference between the white and green cell layers. Periclinal divisions of epidermal cells take place at all stages of leaf development to produce invaginations of green mesophyll located in sectors of widely varying sizes. A periclinal division rate of 1 in 3000-4000 anticlinal divisions for the adaxial epidermis, was 2-3-fold higher than that estimated for the abaxial epidermis. Analysis of white and green mesophyll showed that chloroplasts are essential for palisade cell differentiation and this requirement is cell-autonomous. Stable marking of cell lineages with spectinomycin is simple, rapid and reveals the requirement for functional plastids in cellular differentiation.     

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.     

Leaf biomechanics, morphology, and anatomy of the deciduous mesophyte Prunus serrulata (Rosaceae) and the evergreen sclerophyllous shrub Heteromeles arbutifolia (Rosaceae)

Leaf tensile properties were compared between the mesic deciduous tree Prunus serrulata (var. "Kwanzan") and the xeric and sclerophyllous chaparral evergreen shrub Heteromeles arbutifolia (M. Roem). All values for biomechanical parameters for H. arbutifolia were significantly greater than those of P. serrulata. The fracture planes also differed between the two species with P. serrulata fracturing along the secondary veins, while H. arbutifolia most often fractured across the leaf irrespective of the vein or mesophyll position, thus yielding qualitative differences in the stress-strain curves of the two species. Anatomically, P. serrulata exhibits features typical for a deciduous mesophytic leaf such as a thin cuticle, a single layer of palisade mesophyll, isodiametric spongy mesophyll, and extensive reticulation of the laminar veins. Heteromeles arbutifolia leaves, however, are typically two- to three-fold thicker with a 35% higher dry mass/fresh mass ratio. The vascular tissue is restricted to the interface of the palisade and spongy mesophyll near the center of the leaf. Both epidermal layers have a thick cuticle. The palisade mesophyll is tightly packed and two to three layers thick. The spongy mesophyll cells are ameboid in shape and tightly interlinked both to other spongy cells as well as to the overlying palisade layer. We conclude that the qualitative and quantitative biomechanical differences between the leaves of these two species are likely due to a complex interaction of internal architectural arrangement and the physical/chemical differences in the properties of their respective cell walls. These studies illustrate the importance that morphological and anatomical correlates play with mechanical behavior in plant material and ultimately reflect adaptations present in the leaves of chaparral shrubs that are conducive to surviving in arid environments.     

Herbivory could unlock mutations sequestered in stratified shoot apices of genetic mosaics

Many higher plants have shoot apical meristems that possess discrete cell layers, only one of which normally gives rise to gametes following the transition from vegetative meristem to floral meristem. Consequently, when mutations occur in the meristems of sexually reproducing plants, they may or may not have an evolutionary impact, depending on the apical layer in which they reside. In order to determine whether developmentally sequestered mutations could be released by herbivory (i.e., meristem destruction), a characterized genetic mosaic was subjected to simulated herbivory. Many plants develop two shoot meristems in the leaf axils of some nodes, here referred to as the primary and secondary axillary meristems. Destruction of the terminal and primary axillary meristems led to the outgrowth of secondary axillary meristems. Seed derived from secondary axillary meristems was not always descended from the second apical cell layer of the terminal shoot meristem as is expected for terminal and primary shoot meristems. Vegetative and reproductive analysis indicated that secondary meristems did not maintain the same order of cell layers present in the terminal shoot meristem. In secondary meristems reproductively sequestered cell layers possessing mutant cells can be repositioned into gamete-forming cell layers, thereby adding mutant genes into the gene pool. Herbivores feeding on shoot tips may influence plant evolution by causing the outgrowth of secondary axillary meristems.     

盆栽榕树蓟马种类及优势种榕管蓟马对寄主植物的致害性

为明确盆栽榕树蓟马的种类, 了解蓟马优势种对在同一温室内混合种植的榕属及非榕属盆栽植物的致害性差异, 以福建漳州、 福州和泉州等地的盆栽榕树种植基地为观测点, 采集榕树叶片, 调查蓟马种类, 确定优势种蓟马; 以天南星科喜林芋属、 紫葳科菜豆树属、 木棉科瓜栗属和桑科榕属等不同科属盆栽植物为试验材料, 测试榕管蓟马Gynaikothrips uzeli Zimmerman对寄主植物的致害性。结果表明： 盆栽榕树蓟马种类有2亚目, 2科, 8属, 9种, 优势种为榕管蓟马, 常见种为棘腿管蓟马Androthrips ramachandrai Karny和榕腿管蓟马Mesothrips jordani Zimmermann, 其他6种蓟马均为偶见种。榕管蓟马对不同寄主植物的致害性差异显著, 以对桑科榕属植物致害性为最强, 而对天南星科喜林芋属、 紫葳科菜豆树属和木棉科瓜栗属等其他植物的致害性较弱。在6种榕属植物中, 榕管蓟马对垂叶榕Ficus benjamina Linn.、 榕树F. microcarpa Linn. f.、 花叶垂叶榕F. benjamina cv. Golden Princess等3种榕属植物的为害等级均达3级以上, 以垂叶榕最重, 榕树次之, 花叶垂叶榕略轻; 对金叶榕F. microcarpa cv. Golden Leaves、 黑叶橡胶榕F. elastica cv. Deocora Burgundy、 斑叶橡胶榕F. elastica var. variegata等3种榕属植物的为害很轻, 为害等级均仅为1级; 同时, 榕管蓟马在金叶榕、 黑叶橡胶榕和斑叶橡胶榕上繁殖力弱、 无法完成世代, 而在榕树、 垂叶榕和花叶垂叶榕上繁殖力强、 能完成世代, 但以在垂叶榕上的发育情况最好。研究可为选择利用寄主植物抗虫性来有效防控盆栽榕树蓟马提供技术支撑。     

Peltate Leaf Development in Brasenta schreberi Gruel

The present investigation is a report with a detailed account of peltate leaf development in Brasenia schreberi. The preliminary indication of leaf initiation is seen in periclinal divisions of the subepidrmal cells on the flank of the shoot apex. By the time a leaf primordium becomes 73 μm high, the apical growth is present, and it has undergone repeated periclinal and anticlinal divisions and introduces aew cells into the body of the primordium. The procambial strand is evident very early in ontogeny. Vacuolation of cells proceeds acropetally along the primordium. At 109 μm longitudinal sections reveal a ventral outgrowth. This ventral growth, termed a lateral zone or Querzone, is initiated by subepidermal cells on the ventral (adaxial) side of primordium. The Querzone is considered to represent the congenital fused laminar margins of the leaf. Transection analysis of a primordium of 160 μm indicates that the Querzone growth is initiated on the midbasal portion of primordium. Below the midbasal portion of primordittm which later forms the petiole of the leaf. The marginal 'growth occurs at a time when the primordinm is approximately 160 μm high. Initiation of marginal growth takes place in 42 μm from the base of a primordium. Marginal growth at first can be seen while the primordium exhibits unilateral. By anticlinal divisions, the marginal initials produce the upper and lower protoderm, which give rise to the upper and lower epidermis respectively, and submarginal initiates divide in anticlinal plane, giving rise to the adaxial and abaxial layers. Subsequent divisions of the adaxial layer are anticlinal only so that it forms a single layer which later develops as the palisade parenchyma. The cells of the abaxial layer, by divisions in all planes, form the tissues of the spongy parenchyma and all of the lateral venation system. At maturity, the mesophyll is much less compact and there are mumerous large intercellular spaces in the spongy region and between the palisade cells. The veins are collateral: There is a reduction in the amount of xylem and the ultimate veinlets terminate as single spiral tracheids. The glandular bairs are mumerous on the lower epidermis and are epidermal in origin, each consisting two basel cells and one termined cell. On the basis of morphological examination we suggest that the peltate leaf of Brasenia schreberi is clearly distinct from the foliage leaf in the development of adaxial meristem and marginal growth. We found the primordimn of Brasenia schreberi as an erect organ and arises.by monopodial growth. In the development of leaf and the form of venation the Brasenia schreberi shows marked resemblance and relationship to the Nelumbo nucifera.     

EARLY HISTOGENESIS AND SEMIQUANTITATIVE HISTOCHEMISTRY OF LEAF INITIATION IN TRITICUM AESTIVUM

The shoot apex of Triticum aestivum cv. Ramona 50 was investigated histologically to describe cell lineages and events during leaf initiation. During histogenesis three periclinal divisions occurred in the first apical layer, with one or two divisions in the second apical layer. This sequence of cell divisions initially occurred in one region and spread laterally in both directions to encircle the meristem. Cells of the third apical layer were not involved in leaf histogenesis. Initially, young leaf primordia were produced from daughter cells of periclinal divisions in the two outer apical layers. Nuclear contents of protein, histone, and RNA in the shoot apex were evaluated as ratios to DNA by means of semiquantitative histochemistry. Daughter cells of periclinal divisions in the outer apical layer which produced the leaf primordia had higher histone/DNA ratios than cells of the remaining meristem. However, protein/DNA and RNA/DNA ratios were similar in both regions. Leaf initial cells had a higher ³H-thymidine labeling index, a higher RNA synthesis rate, and smaller nuclear volumes than cells of the residual apical meristem.     

Cell lineage analysis of maize bundle sheath and mesophyll cells

Maize leaves are divided into repeated longitudinal units consisting of vascular tissue, bundle sheath (BS), and mesophyll (M) cells. We have carried out a cell lineage analysis of these cell types using six spontaneous striping mutants of maize. We show that certain cell division patterns are preferentially utilized, but not required, to form the characteristic arrangement of cell types. Our data suggest that early in development a central cell layer is formed, most frequently by periclinal divisions in the adaxial subepidermal layer of the leaf primordium. Lateral and intermediate veins are initiated in this central layer, most often by divisions which contribute daughter cells to both the procambium and the ground meristem. These divisions generate "half vein" units which comprise half of the bundle sheath cells around a vein and a single adjacent M cell. We show that intermediate veins are multiclonal both in this transverse direction and along their lengths. BS cells are more closely related to M cells in the middle layer of the leaf than to those in the upper and lower subepidermal layers. An examination of sector boundaries has shown that photosynthetic differentiation in M cells is affected by the phenotype of neighboring BS cells.     

Differential effect of short-term cold stress on growth, anatomy, and hormone levels in cold-sensitive versus -resistant cultivars of Digitaria eriantha

Two cultivars of Digitaria eriantha (cold-sensitive cv. Sudafricana and cold-resistant cv. Mejorada INTA) were exposed to cold stress (5?°C) for 0, 6, 24, or 72?h, and compared in terms of leaf and root growth, recovery period, shoot and leaf anatomy, and levels of chlorophyll, auxin (indole-3-acetic acid, IAA) and cytokinins (CKs). In Sudafricana, cold treatment caused reduced growth, slight changes in chlorophyll level, reduced levels of IAA and CK iso-pentenyladenine (iP), and reduced leaf dry weight (DW) and fresh weight (FW) during the recovery period. Anatomical damage was observed in chloroplasts, main stem, and axillary buds. Ultrastructural study showed reduced numbers of starch grains in chloroplasts of the bundle sheath and mesophyll. In Mejorada, cold treatment had no significant effect on growth or chlorophyll level. Leaf DW and FW quickly returned to normal levels during the recovery period. Anatomy of ground meristem was affected, but ultrastructure of bundle sheath and mesophyll chloroplasts was not. The cold tolerance of cv. Mejorada appears to be related to the stability of chlorophyll and CK levels, increase of IAA, and maintenance of normal shoot and leaf anatomy and ultrastructure.     

The OKRA leaf shape mutation in cotton is active in all cell layers of the leaf

Okra (L2O) is a semidominant mutation of cotton (Gossypium barbadense) that alters leaf shape by increasing the length of lobes and decreasing lamina expansion. Chimeras containing L2O and wild-type tissue were generated using Semigamy (Se), a mutation that blocks syngamy during fertilization and produces haploid maternal/paternal chimeral progeny at low frequency. In sectorial chimeras, changes in leaf morphology coincide with the boundary between mutant and wild-type tissues, suggesting that L2O does not regulate a laterally diffusible factor within the leaf. However, in mericlinal or periclinal chimeras, the presence of L2O in tissue derived from any of the three histogenic layers (L1, L2, or L3) of the shoot apical meristem produced leaves with a partial mutant phenotype. The presence of L2O in the epidermis (an L1 derivative), or in the subepidermal mesophyll of the leaf (L2 derivatives) reduced the growth of the lamina and thus increased the depth of leaf lobes. The presence of L2O in the middle mesophyll of the lamina and the vasculature of major lateral veins (L3 derivatives) had no local effect on the expansion of the lamina, but significantly increased lobe length. These results demonstrate that L2O is active in every tissue layer of the leaf.     

Tissue layer specific regulation of leaf length and width in Arabidopsis as revealed by the cell autonomous action of ANGUSTIFOLIA

In vascular plants the shoot apical meristem consists of three tissue layers, L1, L2 and the L3, that are kept separate during organ formation and give rise to the epidermis (L1) and the subepidermal tissues (L2, L3). For proper organ development these different tissue layers must interact with each other, though their relative contributions are a matter of debate. Here we use ANGUSTIFOLIA (AN), which controls cell polarity and leaf shape, to study its morphogenetic function in the epidermis and the subepidermis of Arabidopsis thaliana. We show that ANGUSTIFOLIA expression in the subepidermis cannot rescue epidermal cell polarity defects, indicating a cell‐autonomous molecular function. We demonstrate that leaf width is only rescued by subepidermal AN expression, whereas leaf length is also rescued by epidermal expression. Strikingly, subepidermal rescue of leaf width is accompanied by increased cell number in the epidermis, indicating that AN can trigger cell divisions in a non‐autonomous manner.     

The paraveinal mesophyll of soybean leaves in relation to assimilate transfer and compartmentation

Nitrogen and carbohydrate assimilates were temporally and spatially compartmented among various cell types in soybean (Glycine max L., Merr.) leaves during seed filling. The paraveinal mesophyll (PVM), a unique cell layer found in soybean, was demonstrated to function in the synthesis, compartmentation and remobilization of nitrogen reserves prior to and during the seed-filling stages. At anthesis, the PVM vacuoles contain substantial protein which completely disappears by two weeks into the seed filling. Distinct changes in the PVM cytoplasm, tonoplast and organelles were correlated with the presence or absence of the vacuolar material. Microautoradiography following the accumulation of several radiolabeled sugars and amino acids demonstrated the glycoprotein nature of the vacuolar material. Incorporation of methionine, leucine, glucose, and glucosamine resulted in heavy labelling of the PVM vacuole, in contrast to galactose, proline, and mannose which resulted in a much reduced labelling pattern. In addition, starch is unequally compartmented and degraded among the various leaf cells during seed filling. At the end of the photoperiod at the flowering stage, the highest starch accumulation was in the second palisade layer followed by the spongy mesophyll and the first (uppermost) palisade layer. Starch in the first palisade layer was completely degraded during the dark whereas the starch in the second palisade and spongy mesophyll was not remobilized to any appreciable extent. By mid-podfilling (approximately five weeks postanthesis) starch was absent in the first palisade layer at the end of the photoperiod while the second palisade and spongy mesophyll layers contained substantial starch. Starch was remobilized from these latter cells during the remainder of seed filling when current photosynthetic production is low. Structural changes associated with cell senescence first appear in the upper palisade layer and then progress (excluding the PVM) to the second palisade and spongy mesophyll layer. The PVM and phloem appear to retain their structural integrity into the leaf yellowing stage. Reducing sink capacity by pod removal resulted in a continued accumulation of vacuolar protein, an increase in cytoplasmic volume, and fragmentation of the vacuole in the PVM. Pod removal also resulted in an increased amount of accumulated starch (which did not turn over) in all mesophyll layers, and an increase in cell size and cell-wall thickness.     

Epidermal focussing and effects upon photosynthetic light-harvesting in leaves of Oxalis

Abstract. In Oxalis , epidermal cells on both the adaxial and abaxial surface of the leaf concentrated light within the leaf by a lens mechanism. Focal lengths of epidermal cells were estimated using two methods: they were calculated from radius of curvature measurements taken from individual epidermal cells, and were measured directly in agarose replicas of the leaf surface. In the three species of Oxalis examined, light that was incident upon the adaxial leaf surface was concentrated within the palisade, whereas light that was incident upon the abaxial leaf surface was concentrated within the spongy mesophyll. Using sensiometric analysis, theoretically maximal focal intesifications were measured in leaf replicas at the focal maximum and at intermediate positions corresponding to the mid-region of the palisade and spongy mesophyll tissues. Focal intensifications ranged from 2.2 to 10.4 times incident light at the focal maximum, and 1.3 to 4.5 in the palisade or spongy mesophyll layers. Elimination of epidermal focussing, by covering the leaf surface with a thin layer of mineral oil, strongly affected chlorophyll fluorescence induction curves resulting in a decrease of 10–40% in the initial (F₀) and variable fluorescence (F_v). These results are consistent with the interpretation that the chloroplasts were adapted to their light microenvironment within the leaf and that focussing by the epidermis channelled light to a population of chloroplasts that were adapted to high light.     

STABILITY OF LEAF VARIEGATION IN SAINTPAULIA IONANTHA DURING IN VITRO PROPAGATION AND DURING CHIMERAL SEPARATION OF A PINWHEEL FLOWERING FORM

Plants of the foliarly variegated cultivar Saintpaulia ionantha Tommie Lou and the florally variegated cultivar Candy Lou were regenerated through tissue culture from leaf sections, petal sections, and subepidermal tissue. This provided explants with derivatives of all histogen layers of the shoot apex, layers I and II only, and layers II and III only. Over 1,000 plants of Tommie Lou and Candy Lou were grown to flowering. A low level of phenotypic variation was observed, but in no case could this be attributed to the separation of genotypically distinct cell lines. The foliar variegation pattern of both cultivars was stable through in vitro propagation. In contrast, the chimeral components of the flower color pattern in Candy Lou separated during regeneration. These data demonstrate that Tommie Lou-type foliar variegation is not caused by periclinal chimerism and that all leaf cell layers possess the genetic information necessary to produce variegated foliage. The production of all green and all white plants from a radiation-induced periclinal chimera demonstrated that the system used could detect chimeral separation. These results support the contention that adventitious shoots in Saintpaulia almost always differentiate in vitro from a derivative(s) of a single histogen layer, and this layer is usually the LI.     

Development of white spruce somatic embryos: II. Continual shoot meristem development during germination

Summary This study compares the development of shoot apical meristems of white spruce somatic and zygotic embryos during germination. In mature somatic embryos, the functional part of the shoot apical meristem was bi-layered. After partial drying, a normal shoot meristem was formed from these two cell layers during germination. Other cells within the meristem were vacuolated and separated by intercellular air spaces. In the absence of the partial drying treatment, somatic embryos enlarged in size primarily due to vacuolation of cells and the formation of large intercellular air spaces. A majority of these somatic embryos failed to form a functional shoot apical meristem. Compared with somatic embryos, the shoot apical meristem of a mature zygotic embryo was well organized with a densely cytoplasmic apical layer. The cells within the meristem were tightly packed. Judging from the cell profiles during germination, all cells within the meristem of the zygotic embryo took part in the formation of the vegetative shoot apical meristem.     

Structural Organization of the Shoot Apex and Axillary Bud in Slipper Spurge (Pedilanthus tithymaloides Poit.) I

The slipper spurge (Pedilanthus tithymaloides) is a small cactus-likeherbaceous plant. The shoot apex has a single tunica layer andsometimes the second layer also simulates it. There is a centralmeristem zone whose significance could not be determined. Thefirst bud meristem differentiates at the second node. The earliestbud meristem has a procambium but no shell zone was observed.The node is trilacunar. There are three bud traces and threeprophyll traces. The single prophyll is situated at right anglesto the subtending leaf.     

Transient expression of visible marker genes in meristem cells of wheat embryos after ballistic micro-targeting

Seven days after anthesis, the shoot apical meristem of immature embryos of wheat (Triticum aestivum L.) is not yet covered by the coleoptile or leaf primordia and provides an optimal target for ballistic micro-targeting. Gold particles 1.2 μm in diameter at a concentration of 5·10⁵ particles per μl and propelled by 110-bar nitrogen penetrated up to four cell layers into embryo apical meristems but produced no deleterious effects on germination. The use of diaphragms with internal diameters of 100 or 200 μm restricted bombardment to meristem cells or also included surrounding tissues, respectively. The results of transient-expression experiments indicated successful delivery of foreign DNA into meristem cells. Cells of the central zone of the meristem or pro-meristem transiently expressed foreign genes driven by the Cauliflower mosaic virus (CaMV) 35S and rice actin1-D constitutive promoters. Partial plasmolysis before bombardment and slow recovery of normal turgor pressure increased transient-expression frequencies. Meristem cells transiently expressed foreign genes at frequencies 10-fold less than surrounding tissues under identical conditions. Transgenic sectors were observed in both coleoptiles and leaf primordia.     

豆蔻属(姜科)植物叶的比较解剖学研究

采用石蜡切片法对豆蔻属12个种的叶片横切面结构进行比较解剖学研究。结果显示:豆蔻属植物叶片表皮层由1层表皮细胞组成,在无下皮层的种中,近轴面的表皮细胞通常体积较大,而在有下皮层的种中,表皮层通常较薄,细胞壁增厚;下皮层的结构具有多样性;叶肉中栅栏组织通常1~2层,海绵组织2~6层细胞,常含丹宁,所观察的大部分种含有方晶或砂晶;中脉韧皮部极端维管束形态多样,维管束系统II通常缺失,未发现同时具有4个系统的种。此外,对叶缘的形态特点进行了概括性描述,并结合前人的研究资料讨论了叶解剖结构的系统学意义。     

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.