Processes modulating calcium distribution in citrus leaves. An investigation using x-ray microanalysis with strontium as a tracer

Citrus leaves accumulate large amounts of calcium that must be compartmented effectively to prevent stomatal closure by extracellular Ca2+ and interference with Ca(2+)-based cell signaling pathways. Using x-ray microanalysis, the distribution of calcium between vacuoles in different cell types of leaves of rough lemon (Citrus jambhiri Lush.) was investigated. Calcium was accumulated principally in palisade, spongy mesophyll, and crystal-containing idioblast cells. It was low in epidermal and bundle sheath cells. Potassium showed the reverse distribution. Rubidium and strontium were used as tracers to examine the pathways by which potassium and calcium reached these cells. Comparisons of strontium and calcium distribution indicated that strontium is a good tracer for calcium, but rubidium did not mirror the potassium distribution pattern. The amount of strontium accumulated was highest in palisade cells, lowest in bundle sheath and epidermal cells, and intermediate in the spongy mesophyll. Accumulation of strontium in palisade and spongy mesophyll was accompanied by loss of potassium from these cells and its accumulation in the bundle sheath. Strontium moved apoplastically from the xylem to all cell types, and manipulation of water loss from the adaxial leaf surface suggested that diffusion is responsible for strontium movement to this side of the leaf. The results highlight the importance of palisade and spongy mesophyll as repositories for calcium and suggest that calcium distribution between different cell types is the result of differential rates of uptake. This tracer technique can provide important information about the ion uptake and accumulation properties of cells in intact leaves.     

石蒜属12 种植物叶片比较解剖学研究

 对石蒜属( Lycoris Herb. ) 12 种植物叶片的比较解剖学研究表明: (1) 石蒜属植物叶片横切面的端部、中部及基部的轮廓基本呈浅“W”或“V”字型, 有些种的表皮细胞上具有明显的尖刺状乳突; ( 2)石蒜属植物均为异面叶, 叶肉组织有一定的栅栏组织和海绵组织分化, 但二者的厚度、叶肉中所占比例及栅栏组织的细胞层数在种间有一定的差异; (3) 海绵组织发达、具有大而明显的薄壁细胞或细胞裂溶后形成空腔(分泌腔或气腔); (4) 叶片中维管束数目大多为奇数, 叶脉维管束鞘由薄壁细胞组成; (5) 石蒜属植物横切面上叶缘的形状分为圆弧形和楔形两种类型。石蒜属植物叶的解剖结构具有许多相似特征; 同时又具有一定的种间差异, 可为石蒜属植物的种间关系和开发利用提供有价值的信息。     

Leafminers help us understand leaf hydraulic design

Leaf hydraulics of Aesculus hippocastanum L. were measured over the growing season and during extensive leaf mining by the larvae of an invasive moth (Cameraria ohridella Deschka et Dimic) that specifically destroy the palisade tissue. Leaves showed seasonal changes in hydraulic resistance (R_lamina) which were related to ontogeny. After leaf expansion was complete, the hydraulic resistance of leaves and the partitioning of resistances between vascular and extra‐vascular compartments remained unchanged despite extensive disruption of the palisade by leafminers (up to 50%). This finding suggests that water flow from the petiole to the evaporation sites might not directly involve the palisade cells. The analysis of the temperature dependence of R_lamina in terms of Q₁₀ revealed that at least one transmembrane step was involved in water transport outside the leaf vasculature. Anatomical analysis suggested that this symplastic step may be located at the bundle sheath where the apoplast is interrupted by hydrophobic thickening of cell walls. Our findings offer some support to the view of a compartmentalization of leaves into well‐organized water pools so that the transpiration stream would involve veins, bundle sheath and spongy parenchyma, while the palisade tissue would be largely by‐passed with the possible advantage of protecting cells from short‐term fluctuations in water status.     

Effects of nitrogen deprivation on cell division and expansion in leaves of Ricinus communis L.

The effects of nitrogen deprivation on leaf extension, cell numbers and epidermal cell size were followed in leaves of Ricinus communis L. The extent to which reductions in final cell number or final epidermal cell size contributed to the reduction in final leaf size depended on the developmental stage of the leaf at the time of N deprivation. In leaves which already had their full complement of cells (leaf 2), the reduction in final leaf size following nitrogen deprivation was associated with a reduction in final cell size. In leaves that were at earlier stages of development at the onset of N deprivation (leaves 3 and 4), the reduction in final leaf size was greater than in leaf 2. In these younger leaves, the final cell size was even smaller than in leaf 2, but the greatest contribution to reduced final leaf size was a reduction in the number of cells produced. This accounted for approximately 80% of the reduction in final leaf size in leaf 4. During leaf development, the contribution from different tissue layers to the total cell number changed. In the smallest leaf sizes, the contribution from upper and lower epidermis and spongy parenchyma was greater than that from palisade parenchyma. As the leaf size increased, cells in the palisade parenchyma continued to divide for longer than in the other layers. At final leaf size, the contribution from the different tissue layers to total cell number was the same for leaves 2, 3 and 4, irrespective of N treatment. In these final leaf structures, palisade parenchyma contributed 60% of the total cell number. Thus, although nitrogen deprivation affected leaf size variously through cell division and cell expansion, depending on leaf developmental stage at the time of nitrogen deprivation, the ratio of cell numbers and sizes in different tissue layers, at final leaf size, was unaffected.     

中国芸香科植物叶分泌囊比较解剖学研究

利用整体透明、石腊和薄切片方法对芸香科22属,40种和2变种植物叶分泌囊的形态结构和分 布进行了比较研究。成熟分泌囊都由鞘细胞和一层上皮细胞围绕圆形腔隙构成,上皮细胞扁平,细胞壁 薄、完整,故分泌囊属裂生方式发生。鞘细胞1～5层,不同种类的层数有变化,个别种缺乏。内层鞘细 胞为扁平的薄壁细胞,外层的细胞壁较厚。分泌囊的形态结构、着生位置和分布密度等在不同属或不同 种间存在一定差异。根据分泌囊在叶中的分布位置和形态结构特点,可将其划分为:叶缘齿缝分泌囊, 叶肉分泌囊和两者混合型。叶肉分泌囊又可分海绵组织分泌囊和栅栏组织分泌囊。在此基础上对该科各类型分泌囊的形态演化关系以及各亚科或各属间的亲缘关系进行了探讨。     

沉香叶解剖结构的研究

通过石蜡切片法,光学显微镜观察,研究了沉香叶的解剖结构。结果表明,沉香叶为典型的异面叶,但具有许多旱生特征。表皮由一层排列紧密的形状不规则的表皮细胞组成,细胞外壁角质膜较厚,上表皮角质膜较下表皮的厚3.48μm,下表皮上零星分布着单细胞表皮毛,气孔类型为无规则型,仅分布在下表皮上,微下陷;叶肉组织发达,其间分布着较多的长方晶体,其长轴与表皮垂直;栅栏组织由1～2层圆柱形细胞组成,其外层细胞转化为异细胞,栅栏组织∶海面组织为1∶3.5,下表皮内具有1～2层由异细胞组成的下皮层;主脉发达,有异细胞组成的维管束鞘,具内生韧皮部;叶内具有发达的木质部外纤维。以上特征反映出植物结构与环境的统一性。     

DEVELOPMENT OF THE DIMORPHIC CHLOROPLASTS OF SUGAR CANE

The vascular bundle sheath cells of sugar cane contain starch-storing chloroplasts lacking grana, whereas the adjacent mesophyll cells contain chloroplasts which store very little starch and possess abundant grana. This study was undertaken to determine the ontogeny of these dimorphic chloroplasts. Proplastids in the two cell types in the meristematic region of light-grown leaves cannot be distinguished morphologically. Bundle sheath cell chloroplasts in tissue with 50% of its future chlorophyll possess grana consisting of 2-8 thylakoids/granum. Mesophyll cell chloroplasts of the same age have better developed grana and large, well structured prolamellar bodies. A few grana are still present in bundle sheath cell chloroplasts when the leaf tissue has 75% of its eventual chlorophyll, and prolamellar bodies are also found in mesophyll cell chloroplasts at this stage. The two cell layers in mature dark-grown leaves contain morphologically distinct etio-plasts. The response of these two plastids to light treatment also differs. Plastids in tissue treated with light for short periods exhibit protrusions resembling mitochondria. Plastids in bundle sheath cells of dark-grown leaves do not go through a grana-forming stage. It is concluded that the structure of the specialized chloroplasts in bundle sheath cells of sugar cane is a result of reduction, and that the development of chloroplast dimorphism is related in some way to leaf cell differentiation.     

LEAF ANATOMY OF TISSUE-CULTURED LIQUIDAMBAR STYRACIFLUA (HAMAMELIDACEAE) DURING ACCLIMATIZATION

Structural changes accompanying the acclimation process were observed in leaves of sweetgum, Liquidambar styraciflua, using light and transmission electron microscopy (TEM). Comparisons were made of leaves obtained from tissue culture, plantlets acclimated after transfer from the in vitro environment to soil, and field grown trees. Leaves of cultured plantlets lacked a differentiated palisade parenchyma and had spongy parenchyma interspersed with large air spaces. Field grown leaves showed distinct palisade and spongy tissues and a high cell density. New leaves from acclimated plantlets showed an elongation of the upper mesophyll with fewer intercellular spaces than cultured plants. Cells from leaves from in vitro plantlets had large vacuoles, limited cytoplasmic content and flattened chloroplast with an irregularly arranged internal membrane system. Acclimated and field leaf cells had a greater cytoplasmic content than cultured leaves, with the former having more dominate vacuoles. Chloroplasts had evident grana. Acclimated and field leaves had a well developed cuticle unlike leaves from culture.     

Field studies of leaf development and expansion in the leek (Allium porrum)

An analysis of leek leaf development and expansion was carried out over three seasons using field-grown plants of three varieties which were directly sown at different dates or transplanted from controlled conditions. In all cases, successive leaves appeared (tip visible) at equal intervals of accumulated temperature. Detailed analysis of a single sowing in 1985 showed that the regularity of leaf appearance was a consequence of the coordinated response to accumulated temperature of leaf initiation (plastochron 100°C days > 0°C) and leaf blade and sheath extension. For each successive leaf, an additional 32°C days were required between initiation and appearance to allow for the linear increase in ‘sheath’ height, giving a phyllochron of 132°C days. Direct measurement of leaf extension before and after leaf appearance, and of the length of the leaf extension zone, confirmed that the rate of leaf extension, in terms of accumulated tempeature, was constant, and independent of leaf number. However, there were differences between seasons and between varieties in the responses of leaf appearance, leaf extension and ‘sheath’ length to accumulated temperature. It was concluded that the simple ontogenetic increase in leaf dimensions, which was a feature of all the crops studied, was a consequence of the progressive increase in the duration of leaf expansion.     

中华芦荟叶的解剖学、组织化学和植物化学研究

用解剖学,组织化学和植物化学方法研究了中华芦荟（Aloe vera L.var.chinensis(Haw.)Berg.)叶的结构,芦荟素的含量及其可能的储藏和合成场所,解剖学研究结果表明,中华芦荟叶的结构由表皮,同化薄壁组织,维管束和储水组织组成,其旱生结构特征比较明显,表皮具厚的角质层,外切向壁次生加厚,气孔下陷,中央储水组织发达,绿色组织没有明显的分化,其中,5个细胞环绕的气孔器和叶基出现的第二轮维管束在芦荟属中首次报道,具有种的特征,中华芦荟叶中所含的蒽醌类次生代谢物主要是芦荟素（barbaloin or aloin),其含量和叶位及同一叶的不同部位有关,植株上剖嫩叶及每一叶的上部含量高于下部老叶和叶的中部,叶基部含量最低,比较被测的解剖学指标和植物化学分析的结果发现,叶中维管束的密度和芦荟素的含量呈明显的正相关,用5％Pb(CH3COOH)2沉淀处理及5％NaOHR颜色反应检测芦荟素的储藏物合成部位,初步结果表明,位于韧皮部端的数个发达大型薄壁细胞是芦荟素的储藏场所,而绿色组织和维管束鞘是可能的合成场所。     

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.     

Structure of Crystal Cells and Influences of Leaf Development on Crystal Cell Development and Vice Versa in Phaseolus vulgaris (Leguminosae)

The structure of cells with calcium oxalate crystals and their nelghbouring cells has been studied by light and transmission electron microscopy at different stages of bean leaf development. Plants were grown with varying calcium supply to identify a possible influence of calcium nutrition on cell structure. Crystals are formed inside the vacuole of already highly vacuolated cells of bundle sheath extensions. The membrane around the crystal vacuole is continuous with the plasmalemma. The crystal vacuole contains membraneous structures. In the fully expanded leaf the crystal becomes ensheathed by wall material. Chloroplasts of bundle sheath extension cells, with or without crystals, are smaller, with fewer membranes, and with much narrower stroma regions than those of the palisade parenchyma. There is a stage in the young leaf when only the bundle sheath extension cells without crystals have starch grains in their chloroplasts. As their number is lower in plants grown with high calcium supply this means that, in this case, less cells are competent for photosynthesis.     

Anatomy,Histochemistry and Phytochemistry of Leaves inAloe vera var. chinensis

A multidisciplinary approach—anatomy, histochemistry and phytochemistry—was used to investigate the leaf structure, the content and the storage location of barbaloin in the leaves of Aloe vera L. var. chinensis (Haw.) Berg. Xeromorphic characteristics including secondary thickened epidermal cell walls, thicker cuticle, ambiguous differentiation of spongy and palisade tissues in the chlorenchyma, and well-developed aquiferous tissue could be seen in the leaves. Several large parenchymatous cells were observed at the phloem pole of the first ring of vascular bundles. The secondary ring of vascular bundles in the leaf base and the stomata, which are surrounded by five cells, have some classification significance in this species. The density of vascular bundles, the content of barbaloin and the intensity of histochemical reaction differed among leaf numbers L1 (annual leaf), L2 (biennial leaf), L3 (triennial leaf) and L4 (quadrennial leaf), and in different parts of the leaf. These three factors were highest in the youngest leaf, L1, and top parts of all the leaves and lowest in the basal parts and the oldest leaf, L4. The density of vascular bundles had a positive correlation to the content of barbaloin. The histochemical results revealed that the small sheath cells that surrounded the bundles might be the location of barbaloin synthesis and the large parenchymatous cells beneath the sheath might be the storage places of this metabolite.     

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 C4-type CO2 fixation of the NAD- or NADP-ME (malic enzyme) subgroup. In four C4 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 C4 NAD-ME Salsoloid-type photosynthesis in leaves and C3 photosynthesis in dorsoventral non-Kranz cotyledons; Salsola laricina has C4 NAD-ME Salsoloid-type leaves and C4 NAD-ME Atriplicoid-type cotyledons; Haloxylon persicum, has C4 NADP-ME Salsoloid-type green stems and C3 isopalisade non-Kranz cotyledons; and S. richteri has C4 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 C4 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 C4 types. In some C4 organs, it was apparent that subepidermal cells and water storage cells also contain some chloroplasts which have Rubisco, store starch, and thus perform C3 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 C4 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.     

Observation of Apparently Unchanging Mesophyll Cell Diameters Throughout Leaf Ontogeny in Woody Species

The expansion of plant leaves usually lasts 3–6 weeks and it is widely believed that most cell types (epidermal and mesophyll) continue to expand in unison over a similar time period. The evidence supporting this account was derived from studies of herb leaves. We observed in woody species, however, that the diameter of mesophyll cells (spongy and palisade) changed little during leaf expansion from about 5 to 100 % maximum size. To keep pace with epidermal cell enlargement and leaf area expansion, mesophyll cells divided but palisade cell length expanded as leaves grew thicker. The prolonged division of mesophyll and apparently unchanging mesophyll cell diameters constitute a novel pattern of leaf cell development, different from that previously described for herbs. Possible mechanisms that attribute the varied expansion direction and speed to the different cellulose distributions in woody and herbaceous species are suggested. This finding could contribute to an enhanced understanding of the overall mechanism of leaf development.     

Changes in chloroplast morphology of different parenchyma cells in leaves of Haberlea rhodopensis Friv. during desiccation and following rehydration

The size, shape, and number of chloroplasts in the palisade and spongy parenchyma layers of Haberlea rhodopensis leaves changed significantly during desiccation and following rehydration. The chloroplasts became smaller and more rounded during desiccation, and aggregated in the middle of the cell. The size and number of chloroplasts in the palisade parenchyma cells were higher than in spongy parenchyma. The good correlation observed between the size or number of chloroplasts and the cross-sectional area of mesophyll cells, the cross-sectional width of the leaf and its water content suggested that the palisade cells were more responsive to water availability than the spongy cells. Changes in chloroplast number during desiccation and rehydration process are characteristic features for desiccation-tolerant plants (especially in homoiochlorophyllous strategy).     

MORPHOLOGY AND ANATOMY OF THE LEAF OF COLEUS BLUMEI (LAMIACEAE)

Leaves of the Princeton and a variegated clone of Coleus blumei Benth. were examined with the light microscope to determine the course of their vasculature and the spatial relationship between the mesophyll, bundle sheath, and vascular tissues. In Princeton clone leaves two leaf traces enter the petiole at the node and quickly branch to form an arc of bundles which undergo further divisions as well as fusions in the distal half of the petiole. The anastomosing arc of bundles reaches its greatest complexity in the base of the midvein, where its lateral-most bundles unite and diverge outward to form secondary veins. As the midvein bundles continue acropetally, they gradually fuse more and divide less until only a single bundle remains, from which secondaries and smaller veins branch. Major (ribbed) veins include not only the midvein and secondaries but also tertiary and quaternary veins. Decreasing vein size is accompanied by increasing direct contact between vascular and photosynthetic tissues. Minor veins, which make up 86% of the total vein length, are completely surrounded by photosynthetic bundle sheaths and mesophyll consisting of palisade and spongy parenchyma. Statoliths occur in a layer of cells just outside the phloem of the petiole-midrib axis and secondary veins. Functional hydathodes are present at the apices of the marginal teeth. The overall organization of tissues in variegated leaves differs little in either the green or albuminous areas from corresponding (but always green) regions of Princeton leaves. Chloroplasts are lacking in mesophyll, bundle-sheath, and most guard cells of the albuminous region but are present in guard cells which are within 1 mm of green areas.     

白蜡虫7种寄主植物叶片解剖结构与寄主选择性的关系

用石蜡切片法在显微镜下观察白蜡虫[Ericerus pela(Chavannes)]7种寄主植物叶的解剖结构。结果表明,寄主植物的叶脉、表皮、栅栏组织、海绵组织、维管束解剖结构及数量性状特征在属、种间存在显著差异。7种寄主植物中,华南小蜡(Ligustrum calleryanum Decne.)和白蜡树(Fraxinus chinensis Roxb.)表皮被毛,华南小蜡表皮毛浓密,白蜡树表皮毛稀疏,其它寄主植物表皮无毛;女贞树(Ligustrum lucidum Ait.)栅栏组织、海绵组织和叶脉的厚度最厚、维管束直径最大,其它寄主植物相对较小。因此,叶片表面光滑、叶脉发达、叶片肥厚是白蜡虫优良寄主植物的重要解剖学特征。7种寄主植物中脉和侧脉发达,近轴面凹陷,远轴面突起,肉脉包埋在叶肉中,推测叶脉突起和凹槽可能是白蜡虫固定位点选择的关键线索。     

刺槐叶的亚显微结构与耐旱性的关系

刺槐（RobiniapseudoacaciaLinn．）虽然引自北美,但现在已成为西北干旱半干旱地区的主要造林树种。叶片形状为羽状复叶,小叶呈椭圆形,叶面积与体积之比为5．6。叶表面具蜡质壳状、管状毛和鳞片状纹饰。叶片与叶柄被以毛状体;叶背面有浅内陷气孔,具大孔下室。上下表皮细胞外壁具明显的角质层加厚;上表皮细胞呈椭圆形,下表皮细胞呈乳头状;栅栏组织与海绵组织之间界限不明显,栅栏组织较为发达,排列紧密,约2—3层细胞,海绵组织有退化的趋势;中脉和叶柄维管束均有厚壁组织细胞组成的维管束鞘;薄壁组织细胞中含有大量的晶体和淀粉粒,叶片已具有许多旱生特征。     

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.