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1.
Phellogen Regeneration in Injured Peach Tree Bark 总被引:1,自引:0,他引:1
Injury to peach bark phellogen leads to the generation of newtissues and the re-establishment of meristematic continuity.Two types of tissue changes after wounding were identified andquantified in bark of seven peach clones: (1) cell wall modifications(lignification and suberization) of tissues present at the timeof wounding, and (2) generation of the new phellogen and itsderivatives. Tissue responses were quantified with a microscopephotometer using selective histochemistry and autofluorescenceto detect lignin and suberin deposition over time. Suberin continuitywas re-established via suberin deposition in a layer of cells,present at the time of wounding, approximately 800 µminternal to the wound surface. Phellogen continuity was re-establishedimmediately internal to and abutting the suberized tissue. Thenew phellogen gave rise to suberized phellem which, in its outwardexpansion, crushed the suberized boundary zone tissue formedearlier. All injured peach clones produced the same sequenceof tissue changes, although timing and degree of response variedwith clone and time of year. Differentiation, impervious tissue, lignin, Prunus persica (L.) Batsch, suberin, wounding 相似文献
2.
Following artificial inoculation of nonhost Populus balsamifera with Ophiostoma ulmi, structural defensive tissues were formed in the xylem. Among these tissues there was a perimedullary sheath of cells, located
adjacent to the invaded xylem, that originated from the dedifferentiation of perimedullary and xylem parenchyma cells. Histochemical
tests revealed that this sheath was intensively suberized. A band of lignified cells was frequently detected on both sides
of this suberized tissue. The formation of such a tissue at the pith margin represents a new type of anatomical barrier in
relation to compartmentalization processes described for trees. Ultrastructural examination showed that the wall of cells
forming this zone was generally composed of a compound middle lamella, a suberized secondary wall and a tertiary wall layer.
Using colloidal gold conjugated to monoclonal antibodies against pectin and to an exoglucanase for cellulose, only limited
labelling was obtained for pectin whereas labelling for cellulose was abundant in the compound middle lamella and the tertiary
wall layer. In a few fibres close to this suberized zone, the latter probe also made it possible to distinguish the occasional
presence of several alternating wall layers mainly composed of either suberin or cellulose. In Salix sp., another tree species belonging to the Salicaceae, this type of suberized reaction zone was also observed. The new reaction
zone is similar in structure and location to a suberized barrier formed in nonwoody carnation (Dianthus caryophyllus) plants in the defense against vascular fungi.
Received: 30 July 1996 / Accepted: 7 January 1997 相似文献
3.
Matts Lindbladh Mats Niklasson Matts Karlsson Leif Björkman Marcin Churski 《Journal of Biogeography》2008,35(4):682-697
Aim The dominant forces behind the expansion of Fagus sylvatica (beech) in northern Europe during the late Holocene have been much debated. Palaeoecological analyses were performed for a biodiversity hotspot reserve in order to study the processes behind the local establishment of Fagus, as well as the historical vegetational development in relation to present‐day biodiversity and conservation. Location Biskopstorp Forest Reserve in south‐west Sweden. Methods Pollen and charcoal were analysed from three small‐hollow sites in the reserve. Two of the investigated wetlands were located adjacent to old‐growth stands of Fagus, and the third was located near a stand of old Quercus. Results The 2500‐year record shows that Fagus was first established around the two Fagus old‐growth sites, c. ad 900 and 1200, respectively, and that this was followed by an expansion around ad 1600. During the establishment phase, and more so in the expansion phase, there were simultaneous increases in types of pollen indicative of human activity. These indicators are also frequent throughout the record from the Quercus site, but here Fagus never became common. Main conclusions The dynamics behind the establishment and expansion of Fagus in the reserve seems to have been influenced to a large degree by human activity, for example selective cutting, human‐induced fires, and agriculture. Fagus became established in the reserve more than 1000 years after it became established regionally, making climate less probable as the dominant force behind the species’ stand‐scale establishment. The spreading of Fagus across southern Scandinavia has previously been shown to be a patchy process in time and space. Our study suggests that this patchiness is evident also at a small spatial scale (a few kilometres). At the Quercus site, relatively high amounts of pollen from the field layer throughout the record indicate open conditions that probably favoured Quercus. The degree of human impact at this site was probably too high to allow the expansion of Fagus. With the long‐term perspective provided by our study it was possible to identify the last 200–300 years as an unrepresentative period with respect to tree species composition and forest dynamics. The large increase of Picea locally and regionally over the last several hundred years, combined with dramatic levels of human impact, have altered the tree composition and forest dynamics to such an extent that active management is necessary in order to maintain biodiversity in the reserve. 相似文献
4.
Abscisic Acid stimulation of suberization : induction of enzymes and deposition of polymeric components and associated waxes in tissue cultures of potato tuber 总被引:3,自引:6,他引:3
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Effect of abscisic acid (ABA) on suberization of potato (Solanum tuberosum var. Russet-Burbank) tuber tissue culture was studied by measuring deposition of suberin components and the level of certain key enzymes postulated to be involved in suberization. ABA treatment resulted in a 3-fold increase in the polymeric aliphatic components of suberin and a 4-fold increase in the polymeric aromatic components. Hydrocarbons and fatty alcohols, two components characteristic of waxes associated with potato suberin, increased 9- and 5-fold, respectively, as a result of ABA treatment. Thus, the deposition of the polymeric aliphatics and aromatics as well as waxes, all of which have been postulated to be components of suberized cell walls, was markedly stimulated by ABA. ω-Hydroxy-fatty acid dehydrogenase which showed a rather high initial level of activity increased only 60% due to ABA treatment. Phenylalanine ammonia-lyase activity reached a maximum at a 5-fold level after 4 days in the ABA medium, whereas the control showed only a 3-fold increase. ABA treatment also resulted in a dramatic (7-fold) increase in an isozyme of peroxidase which has been specifically associated with suberization. Thus, ABA appears to induce certain key enzymes which are most probably involved in suberization. 相似文献
5.
Katsuhiro Shiono Miho Ando Shunsaku Nishiuchi Hirokazu Takahashi Kohtaro Watanabe Motoaki Nakamura Yuichi Matsuo Naoko Yasuno Utako Yamanouchi Masaru Fujimoto Hideki Takanashi Kosala Ranathunge Rochus B. Franke Nobukazu Shitan Naoko K. Nishizawa Itsuro Takamure Masahiro Yano Nobuhiro Tsutsumi Lukas Schreiber Kazufumi Yazaki Mikio Nakazono Kiyoaki Kato 《The Plant journal : for cell and molecular biology》2014,80(1):40-51
Suberin is a complex polymer composed of aliphatic and phenolic compounds. It is a constituent of apoplastic plant interfaces. In many plant species, including rice (Oryza sativa), the hypodermis in the outer part of roots forms a suberized cell wall (the Casparian strip and/or suberin lamellae), which inhibits the flow of water and ions and protects against pathogens. To date, there is no genetic evidence that suberin forms an apoplastic transport barrier in the hypodermis. We discovered that a rice reduced culm number1 (rcn1) mutant could not develop roots longer than 100 mm in waterlogged soil. The mutated gene encoded an ATP‐binding cassette (ABC) transporter named RCN1/OsABCG5. RCN1/OsABCG5 gene expression in the wild type was increased in most hypodermal and some endodermal roots cells under stagnant deoxygenated conditions. A GFP‐RCN1/OsABCG5 fusion protein localized at the plasma membrane of the wild type. Under stagnant deoxygenated conditions, well suberized hypodermis developed in wild types but not in rcn1 mutants. Under stagnant deoxygenated conditions, apoplastic tracers (periodic acid and berberine) were blocked at the hypodermis in the wild type but not in rcn1, indicating that the apoplastic barrier in the mutant was impaired. The amount of the major aliphatic suberin monomers originating from C28 and C30 fatty acids or ω‐OH fatty acids was much lower in rcn1 than in the wild type. These findings suggest that RCN1/OsABCG5 has a role in the suberization of the hypodermis of rice roots, which contributes to formation of the apoplastic barrier. 相似文献
6.
Ulrich Ryser 《American journal of botany》1992,79(1):14-22
The basal part of cotton fibers (Gossypium arboreum and G. hirsutum) was studied with light and electron microscopy in order to improve the understanding of assimilate transport into the fibers during the deposition of the cellulosic secondary wall. Although the distal parts of white cotton fibers are not suberized, a variable amount of suberin was found at the fiber base. This suberin is typically deposited in concentric layers, alternating with polysaccharides. Numerous pits occur in the base of cotton fibers and in ordinary epidermal cells in the periclinal and anticlinal walls. About 25% of the length of periclinal walls is occupied by pits, but only 2% of the anticlinal walls, being pitted mainly in their proximal part. In suberized walls the deposition of suberin is not reduced in the pit region. The pits, whether or not suberized, contain plasmodesmata (22 ± 2.3 and 27 ± 3.3 · μm−-2 in the periclinal and anticlinal walls of the white lint cultivar of G. hirsutum). Transport of assimilates into the fibers through the symplast is therefore possible. This transport may occur directly from mesophyll cells to fibers, or indirectly via ordinary epidermal cells. The minimum amount of assimilates transported into individual fibers during the phase of secondary wall deposition could be estimated (1.3 pg · fiber−-1 · sec−-1), as well as the corresponding symplastic flux of assimilates through the periclinal cell wall, neglecting a possible transport through the anticlinal walls (10−-3 pg · μm−-2 · sec−-1). It is postulated that in the green lint genotype of G. hirsutum and in wild cotton species (not studied in this paper), the uptake of assimilates into the fibers occurs through the symplast, the apoplastic pathway being excluded by the suberization of the fibers during secondary wall formation. Although cultivated, white-linted cotton species may use the same pathway, loading of assimilates from the apoplast is theoretically also possible, and the relative contribution of both pathways has to be determined experimentally. 相似文献
7.
Summary The cell wall in laticifers of theConvolvulaceae, Calystegia silvatica, C. soldanella, C. tuguriorum, Convolvulus cneorum, C. verecundus, C. sabaticus subsp.mauritanicus, andIpomoea indica, contains an impregnated layer that surrounds the cells. The impregnated layer lies inside the primary wall of the laticifer, separated from the protoplast by a third (tertiary) layer of variable thickness. Histochemical and cytochemical staining give a positive reaction for suberin. The layer is often differentiated into dark and translucent regions, the latter frequently being composed of lamellae. The ultrastructure of this layer and its position within the cell wall of the laticifer is comparable to the condition found in oil cells where the walls contain a suberized layer. A suberized layer within the wall is unique for a laticifer system. 相似文献
8.
Yanni Zhang Alexandra Kachura Anica Bjelica M. Alejandra Rey Rincon Karina M. Kaberi Mark A. Bernards 《The Plant journal : for cell and molecular biology》2018,93(5):931-942
Wound‐induced suberin deposition involves the temporal and spatial coordination of phenolic and fatty acid metabolism. Phenolic metabolism leads to both soluble metabolites that accumulate as defense compounds as well as hydroxycinnamoyl derivatives that form the basis of the poly(phenolic) domain found in suberized tissue. Fatty acid metabolism involves the biosynthesis of very‐long‐chain fatty acids, 1‐alkanols, ω‐hydroxy fatty acids and α,ω‐dioic acids that form a poly(aliphatic) domain, commonly referred to as suberin. Using the abscisic acid (ABA) biosynthesis inhibitor fluridone (FD), we reduced wound‐induced de novo biosynthesis of ABA in potato tubers, and measured the impact on the expression of genes involved in phenolic metabolism (StPAL1, StC4H, StCCR, StTHT), aliphatic metabolism (StCYP86A33, StCYP86B12, StFAR3, StKCS6), metabolism linking phenolics and aliphatics (StFHT) or acyl chains and glycerol (StGPAT5, StGPAT6), and in the delivery of aliphatic monomers to the site of suberization (StABCG1). In FD‐treated tissue, both aliphatic gene expression and accumulation of aliphatic suberin monomers were delayed. Exogenous ABA restored normal aliphatic suberin deposition in FD‐treated tissue, and enhanced aliphatic gene expression and poly(aliphatic) domain deposition when applied alone. By contrast, phenolic metabolism genes were not affected by FD treatment, while FD + ABA and ABA treatments slightly enhanced the accumulation of polar metabolites. These data support a role for ABA in the differential induction of phenolic and aliphatic metabolism during wound‐induced suberization in potato. 相似文献
9.
10.
Suberin--a biopolyester forming apoplastic plant interfaces 总被引:1,自引:0,他引:1
Suberized cell walls form physiologically important plant-environment interfaces because they act as barriers that limit water and nutrient transport and protect plants from invasion by pathogens. Plants respond to environmental stimuli by modifying the degree of suberization in root cell walls. Salt stress or drought-induced suberization leads to a decrease in radial water transport in roots. Although reinforced, suberized cell walls never act as absolutely impermeable barriers. Deeper insights into the structure and biosynthesis of suberin are required to elucidate what determines the barrier properties. Progress has been obtained from analytical methods that enabled the structural characterization of oligomeric building blocks in suberin, and from the opening of suberin research to molecular genetic approaches by the elucidation of the chemical composition and tissue distribution of suberin in the model species Arabidopsis. 相似文献
11.
Hydroxycinnamates in suberin formation 总被引:1,自引:0,他引:1
José Graça 《Phytochemistry Reviews》2010,9(1):85-91
Hydroxycinnamates are found associated with suberin in several forms: covalently linked to the aliphatic suberin; in the residue
after suberin-removal; and in the non-polar extractives of suberized tissues in the form of alkyl ferulates. Suberin-associated
hydroxycinnamates have been found mainly as ferulic acid-derivatives, sometimes as feruloylamides and in a lesser extent as
caffeates. Ferulic acid esters of long-chain ω-hydroxyacids are prevalent in the partial depolymerisation products of suberin.
Also, enzymes able to catalyze the feruloylation of ω-hydroxyacids were found timely-associated with the suberization process.
It is proposed that ferulic acid, and its dimers, through esterification to ω-hydroxyacids, covalently link the suberin aliphatic
polyester to suberin-associated polyaromatics. In this case, the known role of ferulates, and related hydroxycinnamates, as
cross-linkers of structurally different polymers would be enlarged to suberized cell-walls. 相似文献
12.
Structural aspects of the leaves of two common festucoids,Festuca ovina andPoa sphondylodes, have been examined employing the electron microscopy. The nature of vascular bundles and of sheaths that surround vascular
tissues was discussed in the study. The festucoids exhibited a non-Kranz C-3 anatomy with more than four mesophyll cells separating
the bundle sheaths of a leaf blade. Vascular tissues in theseFestuca andPoa leaves were surrounded by a double sheath: an inner distinct mestome sheath (MST) and an outer indistinctive layer of parenchymatous
bundle sheath (PBS) cells. The PBS cells were much larger than the MST and had thin walls. The MST cells were relatively small
and rectangular inP. sphondylodes and more or less hexangular in transverse sections ofF. ovina. InP. sphondylodes, MST had conspicuously thickened inner tangential walls with asymmetrically uninterrupted suberized lamellae in radial and
tangential walls. In most differentiated MST cells, all walls were highly suberized. During suberin deposition, MST cells
were quite vacuolated and most of the cytoplasm was present as a thin peripheral layer. However, MST walls inF. ovina revealed very thin suberized lamellae with translucent striations. No chloroplasts were detected inP. sphondylodes, whereas the MST inF. ovina contained small chloroplasts. Plasmodesmata were well developed in the primary pit fields of walls between MST and vascular
cells, and between adjacent MST cells. Plasmodesmata were less frequent in the walls between the inner and outer sheath cells.
Suberized lamellae were totally absent from the PBS cell walls in all veins. External to the PBS, the mesophyll comprised
thin walled cells with abundant intercellular spaces. Peripherally arranged chloroplasts in the mesophyll were numerous and
often larger than those of PBS and MST cells. Characteristics associated with C-3 and other ultrastructural features were
also discussed in the study. 相似文献
13.
Apoplasmic barriers and oxygen transport properties of hypodermal cell walls in roots from four amazonian tree species 总被引:1,自引:0,他引:1
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De Simone O Haase K Müller E Junk WJ Hartmann K Schreiber L Schmidt W 《Plant physiology》2003,132(1):206-217
The formation of suberized and lignified barriers in the exodermis is suggested to be part of a suite of adaptations to flooded or waterlogged conditions, adjusting transport of solutes and gases in and out of roots. In this study, the composition of apoplasmic barriers in hypodermal cell walls and oxygen profiles in roots and the surrounding medium of four Amazon tree species that are subjected to long-term flooding at their habitat was analyzed. In hypodermal cell walls of the deciduous tree Crateva benthami, suberization is very weak and dominated by monoacids, 2-hydroxy acids, and omega-hydroxycarboxylic acids. This species does not show any morphological adaptations to flooding and overcomes the aquatic period in a dormant state. Hypodermal cells of Tabernaemontana juruana, a tree which is able to maintain its leaf system during the aquatic phase, are characterized by extensively suberized walls, incrusted mainly by the unsaturated C(18) omega-hydroxycarboxylic acid and the alpha,omega-dicarboxylic acid analogon, known as typical suberin markers. Two other evergreen species, Laetia corymbulosa and Salix martiana, contained 3- to 4-fold less aliphatic suberin in the exodermis, but more than 85% of the aromatic moiety of suberin are composed of para-hydroxybenzoic acid, suggesting a function of suberin in pathogen defense. No major differences in the lignin content among the species were observed. Determination of oxygen distribution in the roots and rhizosphere of the four species revealed that radial loss of oxygen can be effectively restricted by the formation of suberized barriers but not by lignification of exodermal cell walls. 相似文献
14.
Tino Kreszies Stella Eggels Victoria Kreszies Alina Osthoff Nandhini Shellakkutti Jutta A. Baldauf Viktoria V. Zeisler-Diehl Frank Hochholdinger Kosala Ranathunge Lukas Schreiber 《Plant, cell & environment》2020,43(2):344-357
Wild barley, Hordeum vulgare spp. spontaneum, has a wider genetic diversity than its cultivated progeny, Hordeum vulgare spp. vulgare. Osmotic stress leads to a series of different responses in wild barley seminal roots, ranging from no changes in suberization to enhanced endodermal suberization of certain zones and the formation of a suberized exodermis, which was not observed in the modern cultivars studied so far. Further, as a response to osmotic stress, the hydraulic conductivity of roots was not affected in wild barley, but it was 2.5-fold reduced in cultivated barley. In both subspecies, osmotic adjustment by increasing proline concentration and decreasing osmotic potential in roots was observed. RNA-sequencing indicated that the regulation of suberin biosynthesis and water transport via aquaporins were different between wild and cultivated barley. These results indicate that wild barley uses different strategies to cope with osmotic stress compared with cultivated barley. Thus, it seems that wild barley is better adapted to cope with osmotic stress by maintaining a significantly higher hydraulic conductivity of roots during water deficit. 相似文献
15.
Karin Ruth Jacobsen D. G. Fisher A. Maretzki P. H. Moore 《Plant biology (Stuttgart, Germany)》1992,105(1):70-80
Transverse sections of immature and mature sugarcane internodes were investigated anatomically with white and fluorescence light microscopy. The pattern of lignification and suberization was tested histo-chemically. Lignification began in the xylem of vascular bundles and progressed through the sclerenchymatic bundle sheath into the storage parenchyma. Suberization began in parenchyma cells adjacent to vascular bundle sheaths and spread to the storage parenchyma and outer sheath cells. In mature internodes most of the storage parenchyma was lignified and suberized to a significant degree, except in portions of walls of isolated cells. The pattern of increasing lignification and suberization in maturing internodes more or less paralleled an increase of sucrose in stem tissue. In mature internodes having a high sucrose concentration, the vascular tissue was surrounded by thick-walled, lignified and suberized sclerenchyma cells. The apoplastic tracer dyes triso-dium 3-hydroxy-5,8,10-pyrenetrisulfonate (PTS) and amido black 10 B, fed into cut ends of the stalk, wereconfined to the vascular bundles in all internodes above the one that was cut — with no dye apparently in storage parenchyma tissue. Thus both structural and experimental evidence is consistent with vascular tissue being increasingly isolated from the storage parenchyma as maturation of the tissue proceeds. We conclude that in mature internodes the pathway for sugars from the phloem to the storage parenchyma is symplastic. The data suggest that an increasingly greater role for a symplastic pathway of sugar transfer occurs as the tissue undergoes lignification/suberization. 相似文献
16.
Chlo Champeyroux Jorge Bellati Marie Barberon Valrie Rofidal Christophe Maurel Vronique Santoni 《Plant, cell & environment》2019,42(6):1788-1801
The absorption of soil water by roots allows plants to maintain their water status. At the endodermis, water transport can be affected by initial formation of a Casparian strip and further deposition of suberin lamellas and regulated by the function of aquaporins. Four Casparian strip membrane domain protein‐like (CASPL; CASPL1B1, CASPL1B2, CASPL1D1, and CASPL1D2) were previously shown to interact with PIP2;1. The present work shows that CASPL1B1, CASPL1B2, and CASPL1D2 are exclusively expressed in suberized endodermal cells, suggesting a cell‐specific role in suberization and/or water transport regulation. When compared with wild‐type plants, and by contrast to caspl1b1*caspl1b2 double loss of function, caspl1d1*caspl1d2 double mutants showed, in some control or NaCl stress experiments and not upon abscisic acid (ABA) treatment, a weak enlargement of the continuous suberization zone. None of the mutants showed root hydraulic conductivity (Lpr) phenotype, whether in control, NaCl, or ABA treatment conditions. The data suggest a slight negative role for CASPL1D1 and CASPL1D2 in suberization under control or salt stress conditions, with no major impact on whole root transport functions. At the molecular level, CASPL1B1 was able to physically interact with PIP2;1 and potentially could influence the regulation of aquaporins by acting on their phosphorylated form. 相似文献
17.
The aerobiological behaviour of Fagaceae in Trieste and the correlations with the meteorological parameters were examined.
Airborne pollen grains of Castanea, Fagus and Quercus were collected from 1990 to 2003 using a Hirst type spore trap. The main pollen season (MPS) takes place in April and May
for Quercus and Fagus, in June and July for Castanea. The highest values occur in year 1993 for Quercus, in 1998 for Castanea and in 1992 for Fagus. The Fagaceae content of the air is mainly due to Quercus and Castanea pollen, Fagus usually having a scarce pollen shedding in Trieste. The highest counts of Fagaceae pollen grains are found from late April
to mid May and are mainly due to the pollen shedding of oaks. The cumulative counts vary over the years, with a mean value
of 2.719 pollen grains, a lowest total of 1.341 in 2002 and a highest total of 4.704 in 1993. No positive nor negative long-term
trends in pollen shedding are found. No cyclic variations were observed. Spearman’s correlation was used to establish the
relationship between the daily pollen counts and the daily meteorological data. Daily pollen concentrations present sometimes
positive correlation with temperature, negative with rainfall and wind speed, and no correlation with humidity. Fagus and Quercus start dates result positively correlated between themselves. Significant correlations are found between the start of MPS
and the mean and maximum temperature in March for Fagus and Quercus, and May for Castanea. 相似文献
18.
Summary The development of mestome sheath cells ofAegilops comosa var.thessalica was studied by electron microscopy. Anatomical and cytological observations show that this grass belongs to the C3 or non-Kranz plants. In the asymmetrically thickened walls of mestome sheath cells a suberized lamella is present. This lamella is deposited asynchronously. In the midrib and the large lateral bundles it appears first in the outer and inner walls and usually later in the radial walls. In the small lateral bundles its appearance is delayed in the inner walls of those cells situated on the xylem side. At maturity the suberized lamella is observed in all cell walls; however, in the small lateral bundles it is partly or totally absent from the walls of some cells situated on the xylem side. Tertiary wall formation is asynchronous as well, for it generally follows the deposition pattern of the suberized lamella.During the development of the mestome sheath cells microtubules show marked changes in their number and orientation, being fewer and longitudinal during suberin deposition. Dictyosomes are very active and may be involved in primary and tertiary wall formation. Endoplasmic reticulum cisternae are abundant and partly smooth, while plasmalemmasomes may function to reduce the plasmalemma extension. However, cytoplasmic structures that are clearly involved in suberin synthesis could not be identified.Suberized lamellae react strongly with silver hexamine. This is probably due to post-fixation with osmium tetroxide.On the basis of structural characteristics the mestome sheath may be regarded as an endodermis (cf., alsoFahn 1974). The significance of this view for water and assimilate exchange between the mesophyll and the bundle is discussed.This report represents a portion of a doctoral dissertation. 相似文献
19.
The fine structure of primary, secondary, and tertiary stages of Zea endodermal cell development was investigated. The casparian strip formed in situ in the anticlinal walls and remained at a fixed point relative to the endodermis-pericycle boundary. The only protoplasmic structure that had a constant spatial association with the developing strip was the plasmalemma. Plasmodesmata appeared to be more numerous on the tangential walls than on radial walls; only rarely were they located in the casparian strip. The suberized lamella developed on inner and outer tangential walls before it appeared on the radial walls. No cytoplasmic organelles were found to have any particular spatial association with this layer. The suberized lamella was about 0.04 μm thick except near plasmodesmata and along the adaxial margin of the casparian strip, where it was thicker. Occasionally it failed to form along the abaxial margin of the strip. The adherent affinity between plasmalemma and casparian strip was lost after the strip was covered by suberized lamella. The secondary wall became asymmetrically thickened by differential deposition of successive lamellae. A thin layer of secondary wall material extended across the floor of each pit. Pit cavities often contained mitochondria, and plasmodesmata were restricted to the pits. The plasmodesmata were constricted where they entered the thin layer of secondary wall material and where they penetrated the suberized lamella. The various stages of cell development tended to be asynchronous. No passage cells were observed. Endodermal cell development in Zea closely resembles that described for barley. 相似文献
20.
The nature of the wall layers observed in suberized tyloses was studied in Populus basalmifera L., Ulmus americana L. and Quercus rubra L. As the suberin layers were present only in tyloses that had completed their expansion, most of the results concern mature tyloses. The cyto- and immunocytochemical tests were conducted, respectively, with an exoglucanase having a binding affinity for β(1→4)-D-glucans, the subunits of cellulose, and with two monoclonal antibodies specific for un-esterified and esterified pectic molecules. In the three species, labelling for pectic compounds was intense over the external layer of tyloses but usually more dispersed or nearly absent over the layer corresponding to a primary wall that was, however, intensely labelled for β(1→4)-D-glucans. The outer wall layer, comparable to a middle lamella in mature tyloses, was continuous with similar material that appeared to be secreted by the tylosis. This material was particularly abundant in pit chambers, in void spaces between the tylosis and the vessel wall, particularly at the junction of the vessel and two adjacent cells, and close to the rim of vessel perforation plates. In P. balsamifera, a single suberized layer or occasionally a succession of suberized and cellulose-containing layers was observed internal to the tylosis primary wall. In U. americana, the wall of tylosis was similar to that of P. balsamifera except that, at times, a secondary-wall-like layer was formed and only a single suberized layer was observed. In Q. rubra, the suberized layer was always observed internal to the tylosis secondary wall. Simple pits were also constantly noted in Q. rubra tyloses. The occasional occurrence of a cellulosic layer internally to the suberized layer was observed in the three species. Histochemical tests revealed that lignin was also an important component of the tylosis wall. The tyloses frequently contained phenolic compounds in close association with the suberized layers. The significance of the formation of suberized tyloses in trees is discussed. 相似文献