Ricerche Sull'ultrastruttura della Parete Cellulare

Abstract

A study about the cell wall of AVENA coleoptile epidermis cells. — A new type of lamellae structures embedded in the outer periclinal wall of oat coleoptile epidermis cells has been observed. These structures are present more frequently in the inner non-cutinized portion of the cell wall; their orientation, most often parallel to the cell surface, follows a regular pattern. They are formed by alternate layers of electrontransparent and electron-dense bands. The thickness of these lamellar bodies is about 200–300 Å; their length is rather difficult to determinate. They are bounded by a 30–40 Å thick membrane; the inner compartment is formed by a central highly manganophilic zone 50–70 Å thick where several thin lamellae can be seen and by two lateral zones about 40–50 Å in thickness.

Embedded in the cutinized portion of the wall some elliptical bodies have also been observed, surroundedd by a single membrane, 20 Å in thickness. The interior of these bodies shows thin lamellae enclosed in an electron-transparent stroma.

In experimental conditions unfavourable to growth, the frequency of these structures falls greatly. When the cell distension comes to end, their aspect undergoes deep changes. It is proposed in this paper that these new structures are involved in cell wall growth and development.     

ABSORBING TRICHOMES IN THE PLEUROTHALLIDINAE (ORCHIDACEAE)

Glandular trichomes occur on both surfaces of leaves of all examined genera and species of the subtribe Pleurothallidinae (Orchidaceae). Trichome initiation is effected by one periclinal division of a protodermal cell, producing a thin-walled, globose apical cell with a relatively large nucleus and a subapical stalk cell with heavily cutinized lateral walls. In some species a second periclinal division produces a third small basal cell also having thick lateral walls but thin transverse walls. As leaf development proceeds, the trichome apparatus assumes a sunken position due to continued anticlinal divisions of protoderm. Prior to laminar expansion and guard-mother-cell division on the abaxial surface, the wall of the apical cell ruptures and is replaced by a brown opaque residue. Finally, after vascular tissue differentiation and the cessation of meristematic activity, two or more pitted foot cells develop at the base of the trichome and adjacent to the water-storing hypodermal layers. Preliminary investigations indicate that the trichome apparatus is absorptive throughout its development and similar in function to tillandsioid scales in Bromeliaceae.     

Plant cells which aid in pollen digestion within a beetle's gut

Summary The peach palm, Bactris gasipaes H.B.K., in Costa Rica, possesses unusual trichomes on the inflorescence epidermal surface. Certain cells of the trichome possess a thick, highly lignified cell wall and are consumed by the beetle Cyclocephala amazona L. before it ingests pollen from the same inflorescence. Chemical analyses show the trichome to possess no nutritive value. The thick-walled trichome cells pass intact through the beetle's digestive system, while ingested pollen is crushed. We suggest that the specialized plant cells function as gastroliths in the beetle's digestive tract.     

Pro‐inflammation and pro‐fibrosis factors were highly induction in heart tissues of carotid arteries balloon‐injured animal model

To investigate the changes of cardiomyocyte inflammation and fibrosis factors in heart of carotid artery balloon injury inflammatory rat model. Using rat carotid artery balloon injury model to detect left ventricular characteristics at 2 h, 2 days and 14 days after surgery using hematoxylin‐eosin (H&E) gross stain, Masson's trichome stain and Western blot analysis for inflammatory and fibrosis‐induced factors, tumour necrosis factor α (TNFα), JNK1, P38α, connective tissue growth factor (CTGF), SP1 and transforming growth factor β (TGFβ) protein expressions. The rat carotid arteries were injured after 2 h, 2 days and 14 days. Balloon‐angioplasty to H&E stain results showed the increasing trend of left ventricular wall at 2 h and 2 days; then, the left ventricular wall became thinner, and the left ventricular chamber became enlarged and dilated after 14 days of carotid artery balloon injury. In addition, the Masson's trichome stain results showed that the left ventricular section has fibrosis‐related blue staining (collagen) at 2 and 14 days after rat carotid artery balloon injury, and became even more severe at 14 days. Furthermore, we observed the protein expression level changs, which include TNFα, JNK1, P38α, CTGF, SP1 and TGFβ using Western blotting assay. All proteins were induced at 2 h, 2 days and then reached the maximal level at 14 days. The vessel inflammation was associated with cardiac inflammatory and fibrosis effects during or after carotid artery balloon injury. Copyright © 2012 John Wiley & Sons, Ltd.     

THE CELL WALL OF COSMARIUM BOTRYTIS12

The cell wall of Cosmarium botrytis was studied through the use of the freeze-etch technique. The cell wall consists of many thin layers. Fracturing along one layer reveals the positioning of the wall sculpturing, wall pores, and wall microfibrils. The individual microfibrils are grouped together in bands of parallel oriented fibrils. The different bands of parallel microfibrils were apparently arranged at random angles with regard to each other. Small particles may also be present in the cell walls. The cell wall pore unit of Cosmarium botrytis was studied through the use of scanning, freeze-etching, and thin sectioning techniques. The pore sheaths, on the outside of the cell wall, form a collar around the mouth of each pore. The pore sheath is composed of needle-like fibrils radiating outward from the pore. A pore channel traverses the cell wall and leads to a complex pore bulb region between the cell wall and the plasmalemma. The pore bulb contains many small fibrils which radiate toward the plasmalemma from a number of net-like fibril layers which in turn merge into a very electron dense region near the base of the pore.     

Taxonomic and functional implications of stigma morphology in species ofCassia,Chamaecrista, andSenna (Leguminosae:Caesalpinioideae)

Two stigma forms occur inChamaecrista andSenna, but only one inCassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.     

Direct evidence for pressure-generated closure of plasmodesmata

Pressure differentials were generated between adjacent leaf trichome cells of Nicotiana clevelandii using a modified micropressure probe/injection system. The location of the pressure differentials was altered using two main treatments: (a) puncturing one of the cells in the trichome to induce a large differential at its junction with the next basal cell, or (b) raising the pressure of the impaled cell and ‘clamping’ it at a higher value, thus creating a differential at its upper, as well as lower, wall. In both treatments basipetal intercellular transport of Lucifer yellow was impeded exactly at the sites predicted by the generated pressure differentials; at the base of punctured cells and at the top of clamped cells. In flaccid trichomes puncturing was without effect because the turgor of all the cells in the trichome was too low (<50 kPa) to generate a sufficiently large pressure differential between the punctured cell and its neighbours. Elevations of cell turgor (ΔP) in excess of 200 kPa or more were required to impede intercellular transport When cells were clamped at a high pressure and then subsequently allowed to lose their turgor by withdrawal of the probe the effects of the original pressure clamp were partially retained, indicating an inability to resume intercellular transport.     

Cost of trichome production and resistance to a specialist insect herbivore in <Emphasis Type="Italic">Arabidopsis lyrata</Emphasis>

Theory predicts that trade-offs between resistance to herbivory and other traits positively affecting fitness can maintain genetic variation in resistance within plant populations. In the perennial herb Arabidopsis lyrata, trichome production is a resistance trait that exhibits both qualitative and quantitative variation. Using a paternal half-sib design, we conducted two greenhouse experiments to ask whether trichomes confer resistance to oviposition and leaf herbivory by the specialist moth Plutella xylostella, and to examine potential genetic constraints on evolution of increased resistance and trichome density. In addition, we examined whether trichome production is induced by insect herbivory. We found strong positive genetic and phenotypic correlations between leaf trichome density and resistance to leaf herbivory, demonstrating that the production of leaf trichomes increases resistance to leaf damage by P. xylostella. Also resistance to oviposition tended to increase with increasing leaf trichome density, but genetic and phenotypic correlations were not statistically significant. Trichome density and resistance to leaf herbivory were negatively correlated genetically with plant size in the absence of herbivores, but not in the presence of herbivores. There was no evidence of increased trichome production after leaf damage by P. xylostella. The results suggest that trichome production and resistance to leaf herbivory are associated with a cost and that the direction of selection on resistance and trichome density depends on the intensity of herbivory.     

Sacrificial cell death and trichome breakage in an oscillatoriacean blue-green alga: the role of murein

Summary Trichomes of Microcoleus vaginatus, a motile blue-green alga of the family Oscillatoriaceae, were studied by light and electron microscopy in an effort to determine the sites of trichome breakage during production of hormogonia.According to the evidence presented herein, transcellular breakage of trichomes is the only mechanism of hormogonium production in M. vaginatus. Tearing of the murein sacculus appears to be necessary and sufficient for transcellular breakage to ensue. As Fuhs and earlier investigators have correctly claimed, this process always involves the death of the cell whose wall is torn.When trichomes of M. vaginatus break across cells to produce hormogonia, the murein sacculus usually tears along a circumferential set of junctional pores. This particular mechanism of trichome breakage is not universal among members of the family Oscillatoriaceae.This report is based on a thesis submitted in partial fulfillment of the requirements for a Ph. D. degree in Biology at Harvard University.     

Zur Epidermisaußenwand der Fühlborsten von Dionaea muscipula

Summary The outer epidermal wall of the podium of the trigger hair of Dionaea muscipula reveals an unusual ultrastructure under the electron microscope. The cuticular layer is penetrated by numerous radially arranged fibrils of about 2 nm in diameter inserting in a fibrillar network beneath the cutinized part of the wall. Both the fibrils and the fibrillar network are heavily stained after treatment with lead citrate. Possibly these specific wall structures make the podium elastic and enable it to undergo repeated bendings.     

Evolution of trichome types and its systematic significance in the genus Phlomoides (Lamioideae–Lamiaceae)

Despite a number of recent molecular phylogenetic studies on Phlomoides, in terms of trichome morphology the genus is still among the most poorly studied taxa in the family Lamiaceae. In order to test the utility of trichome characters for delimitation of sections, subsection and species of Phlomoides, we examined trichomes of 64 species representing all recognized sections and subsections using stereomicroscopy and scaning electron microscopy. Two basic types of trichomes could be identified: non‐glandular and glandular. Both trichome types can be simple or branched. The glandular trichomes were sessile, short stalked or long stalked. Different kinds of branched trichomes were observed in most species of P. sect. Phlomoides, i.e. symmetrically stellate, stellate with a central long branch, bi‐ or trifurcate. The species of P. sect. Filipendula were mostly covered by simple trichomes. Moreover, variation in trichome characters appears to have particular value, not only for the classification at sectional or subsectional rank, but also for delimitation of species within each section. For example, all studied species of P. subsect. Fulgentes are characterized by various kinds of stellate trichomes, while the trichome variability in P. subsect. Tetragonae was sufficiently high for species discrimination. An ancestral character state reconstruction was performed in order to investigate the evolution of trichome types and it revealed the following evolutionary trends in trichome characters of Phlomoides: 1) branched trichomes are primitive in Phlomoides as compared to simple ones, 2) long simple non‐glandular trichomes are derived as compared to short simple ones and 3) the presence of stalked glandular trichomes is advanced as compared to subsessile or sessile ones.     

TOMATO TRICHOMES AND MUTATIONS AFFECTING THEIR DEVELOPMENT

A new trichome type for the genus Lycopersicon is described in L. esculentum Mill. It is a short (0.03–0.08 mm), pendant, glandular hair with a club-shaped head consisting of 8–12 cells. Two previously described “hairless” mutations were examined microscopically. One, hl, does not affect the frequency of hairs nor the number of cells per hair, but causes abnormal enlargement of the stalk cells of all hair types, and thus produces shortened, extremely bent and twisted hairs. Observations on the time of action of this gene indicate that in trichome development two to four cell divisions occur prior to any appreciable cell enlargement. The second mutation, h, affects only the large type of trichome. This mutation effects a developmental shift from trichome to stomatal apparatus at the apex of the multicellular base normally supporting the large trichomes.     

Fine structure of antheridia and oogonia of Phytophthora macrospora,the downy mildew fungus of rice plants

In the present paper fine structure of antheridium and oogonium ofPhytophthora macrospora (Sacc.)S. Ito etI. Tanaka, the downy mildew fungus of rice plants was discussed.Before the fertilization some nuclei and a large number of mitochondria were scattered in the cytoplasm of the antheridium. Many lipid granules were observed in the peripheral region, but vacuoles did not appear at this stage of antheridium. Many mitochondria were associated in the neighborhood of the fertilization pore. The wall at the pore was very thin, but the wall surrounding the pore was slightly swollen towards the inside.In the oogonium, many nuclei, mitochondria and cytoplasmic matrix were observed at the peripheral part. A large number of lipid granules was found in the oogonium, but they were more numerous in the peripheral region. The vacuoles developed as the oogonium matured. They were enveloped by tonoplast and contained vacuolar matrix. Many electron dense granules were in contact with the tonoplast or free in the vacuoles, and they were larger in the central part. As stated above, wall at the fertilization pore was thin. However, the oogonial wall surrounding the pore swelled protruding into the oogonium. An electron-dense layer was recognized between the antheridial and oogonial wall, and the walls of both the organs were closely in contact with each other.Contribution No. 252.     

Geometry and mechanics of the morphogenesis of active membranes on the example of plant trichome cells of the genus <Emphasis Type="Italic">Draba</Emphasis> L.

The stages of the early morphogenesis of simple (unbranched) and complex (branched) unicellular trichomes are studied in two species of the genus Draba—D. sibirica (Pall.) Thell. and D. daurica DC. The geometry of morphogenesis is estimated by analyzing intraindividual variation of quantitative morphological characteristics of the developing leaf blade and peduncle trichomes. The surface of all types of trichome cells first acquires a spherical shape, followed by a U-shaped configuration with cylindrical proximal and spherical distal regions. In the development of complex trichomes, the area of the distal zone grows at a higher rate, which leads to separation of its volume into individual spherical regions, the morphogenesis of which repeats the early morphogenetic stages of the overall trichome cell, forming simple (unbranched) or complex (branched) trichome rays. As a rule, the lateral polarity of a trichome cell coincides with the proximodistal polarity of the leaf. Quantitative morphological data make it possible to infer an algorithm of the changes in shape common for all trichome cells, namely, the growth cycle comprising alternation of the phases of increase and decrease in the curvature of the outer cell surface. This surface is an active membrane expanded by the internal pressure and concurrently capable of actively increasing its area by incorporation of new structural elements. A distinctive feature of the proposed model is the geometrical inhomogeneity of the surface movement, changing the radius of curvature and creating internal (active) mechanical stresses in this membrane. A decrease in the ratio of the membrane surface area to the volume deprives the spatially homogeneous shape of its stability; correspondingly, the transition from elastic resistance to internal pressure to active resistance with the help of curvature differentiation becomes more energetically favorable. The source for growth and morphogenesis of the active membrane is alternation of the phases of local curvature leveling, which “charges” the membrane with active mechanical stresses and “discharge” of these stresses, leading to differentiation of the membrane’s local curvatures.     

Lima bean–lady beetle interactions: hooked trichomes affect survival of <Emphasis Type="Italic">Stethorus punctillum</Emphasis> larvae

We tested the hypothesis that Lima bean Phaseolus lunatus L. (Henderson cultivar) trichome density affects the survival of the acariphagous lady beetle Stethorus punctillum Weise. When isolated throughout larval development, 10% or less of S. punctillum larvae reared on two-spotted spider mite Tetranychus urticae Koch on small (rather than large) P. lunatus leaves survived until pupation. Although other factors might have contributed to larval mortality, we demonstrated that survival rate was related to trichome density (i.e., number of hooked trichomes per cm on the underside of leaves). Trichome density was greatest on the underside of small leaves and least on large leaves, indicating that survival rate increased as trichome density decreased. Hooked trichomes impaled S. punctillum larvae more often at the apex of the abdomen than at any other body part. Hooked trichomes also trapped S. punctillum adults, but they always managed to free themselves. This study highlights the negative effect of Lima bean hooked trichomes on a predacious lady beetle that attacks the two-spotted spider mite.     

中国薯蓣属植物叶表皮微形态特征及其分类学意义

利用扫描电子显微镜(SEM)对中国薯蓣科薯蓣属7组31种1亚种2变种植物的叶表皮细胞、叶表皮毛、气孔器类型、气孔大小、气孔纹饰等叶表皮微形态特征进行了观察和比较研究,为薯蓣属内种间的分类界定及系统发育研究提供证据。结果表明:中国薯蓣属各组之间在叶表皮毛、叶表皮细胞和气孔等微形态特征存在较大的差异,但也呈现出一定的组间特异性规律,如:四至六边形的叶表皮细胞、气孔周围平直的垂周壁式样为根茎组植物所特有;丁字型毛组叶脉和叶肉细胞上覆盖大量特有的2叉T型表皮毛;复叶组的叶脉和叶肉细胞具相当密集的表皮毛;基生翅组和周生翅组的气孔器类型衍生出了三胞型;气孔旋转方向在各组中明显分化,在丁字型毛组、白薯莨组和周生翅组(多毛叶薯蓣除外)中为左旋,而顶生翅组、基生翅组和复叶组表现为右旋。研究表明,叶表皮微形态特征在薯蓣属植物中是较为稳定的演化特征,可以作为中国薯蓣属分类与鉴定的依据;据此推断薯蓣属中顶生翅组和周生翅组较为进化,根茎组是薯蓣属的分化中心;对薯蓣属中存在争议的种:盾叶薯蓣和小花盾叶薯蓣、穿龙薯蓣和柴黄姜、马肠薯蓣、多毛叶薯蓣以及白薯莨等进行了分类界定。     

A landscape of hairy and twisted: hunting for new trichome mutants in the Saskatoon Arabidopsis T‐DNA population

A total of 88 new Arabidopsis lines with trichome variation were recovered by screening 49,200 single‐seed descent T₃ lines from the SK activation‐tagged population and from a new 20,000‐line T‐DNA insertion population (called pAG). Trichome variant lines were classified into 12 distinct phenotype categories. Single or multiple T‐DNA insertion sites were identified for 89% of these mutant lines. Alleles of the well‐known trichome genes TRY, GL2 and TTG1 were recovered with atypical phenotype variation not reported previously. Moreover, atypical gene expression profiles were documented for two additional mutants specifying TRY and GL2 disruptions. In remaining mutants, ten lines were disrupted in genes coding for proteins not implicated in trichome development, five were disrupted in hypothetical proteins and 11 were disrupted in proteins with unknown function. The collection represents new opportunities for the plant biology community to define trichome development more precisely and to refine the function of individual trichome genes.     

TheAnabaena-Azolla symbiosis: Diversity and relatedness of neotropical host taxa

TheAnabaena-Azolla association has proved to be an effective biofertilizer in tropical regions of wetland rice production. Three neotropical host species,A. microphylla, A. caroliniana, andA. mexicana, are similar in vegetative morphology (growth habits, frond dimensions, trichome cell number) and ecophysiology (relative heat tolerance). They were observed during our investigation to also be genetically alike and distinct from other taxa.