Showing papers on "Vascular bundle published in 1996"
TL;DR: In this paper, the authors measured the concentrations of each of the components of the raffinose oligosaccharide synthetic pathway in mesophyll and sieve element-intermediary cell complexes (SE-ICCs) in the leaves of melon (Cucumis melo L. cv).
Abstract: Raffinose, stachyose, and galactinol are synthesized in intermediary cells (specialized companion cells) of the minor-vein phloem of cucurbits. To better understand the role of these carbohydrates and the regulation of their synthesis and transport, we measured the concentrations of each of the components of the raffinose oligosaccharide synthetic pathway in mesophyll and sieve element-intermediary cell complexes (SE-ICCs) in the leaves of melon (Cucumis melo L. cv. Hale's Best Jumbo). These concentrations are consistent with a polymer-trapping mechanism for phloem loading, with sucrose diffusing from mesophyll into intermediary cells and being made into raffinose and stachyose, which are too large to diffuse back to the mesophyll. To determine carbohydrate concentrations, we developed a method involving microdissected tissues. Blind endings of areoles, and mesophyll surrounding these veins, were separately removed from lyophilized leaf tissue. Carbohydrates were quantitated by high-performance liquid chromatography with pulsed amperometric detection. A small amount of mesophyll remained attached to the blind endings; the carbohydrate contribution of these cells to the vein sample was eliminated by subtraction, based on the amount of chlorophyll. Volumes of cells and subcellular compartments were calculated by morphometric analysis and were used to calculate carbohydrate concentrations. Assuming no subcellular compartmentation, the additive concentration of sugars in the SE-ICCs of minor veins is about 600 mM. Stachyose and raffinose concentrations are about 330 mM and 70 mM, respectively, in SE-ICCs; concentrations of these sugars are much lower in mesophyll (0.2 and 0.1 mM). This is consistent with the view that stachyose and raffinose are unable to pass through the plasmodesmata between intermediary cells and bundle-sheath cells. Sucrose levels appear to be higher in the SE-ICC (about 130mM) than in the mesophyll (about 10 mM), but if compartmentation is taken into account the gradient for sucrose is probably downhill from mesophyll to intermediary cells. Flux through plasmodesmata between the bundle sheath and intermediary cells was calculated and was found to be within the range of values of flux through plasmodesmata reported in the literature.
131 citations
TL;DR: It is suggested that a primary role of the suberin lamellae may be to prevent leakage of sucrose from the bundles, and maturation of bundles involved with phloem loading is not closely correlated with initiation of export from the blade.
Abstract: We studied the anatomical and ultrastructural changes accompanying sink-to-source transition in developing maize (Zea mays L. cv. W273) leaves, in which sink, transition, and source regions had been identified by whole-leaf autoradiography. In the leaves examined, a complete structural gradient existed from nonimporting to importing regions of the blade. Although all components, except metaxylem elements. of the large (transport) bundles reach maturity before their counterparts in intermediate and small (loading) bundles, the final events in structural maturation are uniform for all bundle types across the blade. Among the very last structures to mature are the plasmodesmata at the interfaces between mesophyll cells and between mesophyll cells and bundle sheath cells. Maturation of the plasmodesmata coincides with maturation of the thick-walled sieve tubes, the last components of the vascular bundles to mature. Significantly, the vasculature reaches structural maturity in advance of cessation of import, a...
115 citations
TL;DR: The observation that Tp2 leaves are quantitatively intermediate between juvenile and adult leaves supports the hypothesis that some phase-specific aspects of leaf identity are regulated in a combinatorial fashion rather than by mutually exclusive patterns of gene expression.
Abstract: Heteroblastic features of leaf anatomy in maize were identified by conducting a quantitative analysis of leaf anatomy. Heteroblastic variation in cuticle thickness and epidermal cell shape paralleled changes in previously defined juvenile- and adult-specific traits. The other traits examined in this study (thickness of the leaf blade, epidermal and bundle sheath cell size, vascular area, interveinal distance, mesophyll area : bundle sheath area ratio) varied in a more complex fashion. To determine which of these traits are regulated by genes involved in shoot maturation, we examined the effect of the Teopod2 (Tp2) mutation on their expression. Tp2 increases the number of leaves that express the juvenile form of cuticle thickness, epidermal cell shape, and vascular area and causes all other leaves to produce intermediate (juvenile/adult) forms of these traits. It has little or no effect on any of the other traits we examined. Thus, much of the heteroblastic variation in the internal anatomy of the maize le...
86 citations
TL;DR: Various in-vitro grafts of explanted internodes - the heterografts Nicandra physaloides on Lycopersicon esculentum and Vicia faba on Helianthus tuberosus as well as autografta - were established in sterile culture, characterised by a complete loss of vascular regeneration between the scion and stock and by an extremely low rate of 14C-translocation into the stock.
83 citations
TL;DR: It is proposed that the Bsd2 gene plays a direct role in the post-transcriptional control of rbcL transcript accumulation and/or translation, both in bundle sheath and mesophyll cells, and an indirectrole in the maintenance of bundle she Heath cell chloroplast structure.
Abstract: Within the maize leaf primordium, coordinated cell division and differentiation patterns result in the development of two morphologically and biochemically distinct photosynthetic cell types, the bundle sheath and the mesophyll. The bundle sheath defective2-mutablel (bsd2-ml) mutation specifically disrupts C4 differentiation in bundle sheath cells in that the levels of bundle sheath cell-specific photosynthetic enzymes are reduced and the bundle sheath chloroplast structure is aberrant. In contrast, mesophyll cell-specific enzymes accumulate to normal levels, and the mesophyll cell chloroplast structure is not perturbed. Throughout mutant leaf development, the large and small subunits of ribulose bisphosphate carboxylase are absent; however, both rbcL and RbcS transcripts accumulate. Moreover, chloroplast-encoded rbcL transcripts accumulate ectopically in mesophyll cells. Although the bundle sheath cell chloroplast structure deteriorates rapidly when plants are exposed to light, this deterioration is most likely a secondary effect resulting from cell-specific photooxidative damage. Therefore, we propose that the Bsd2 gene plays a direct role in the post-transcriptional control of rbcL transcript accumulation and/or translation, both in bundle sheath and mesophyll cells, and an indirect role in the maintenance of bundle sheath cell chloroplast structure.
83 citations
TL;DR: Results show that, within the shoot apex, MSV is present only in the vascular tissues and does not invade the apical meristem, and implied that host DNA replication was not essential for viral replication.
Abstract: Maize streak virus (MSV) is a single-stranded DNA virus and type member of subgroup I of the Geminiviridae, members of which have been considered generally as viruses limited to phloem tissues. We have studied this characteristic and the extent of MSV penetration into the shoot apical meristem of maize using immunohistochemical and in situ hybridization techniques. This approach has been used to investigate the suggestion that host cell division might be required for the replication of MSV. The results show that, within the shoot apex, MSV is present only in the vascular tissues and does not invade the apical meristem. In mature leaves, virus is located only in areas of the leaf displaying the characteristic chlorotic streak symptoms of infection and, in contrast to the situation in apical and stem tissues, it is no longer restricted to the vasculature. Viral coat protein and both positive and negative strands of the DNA genome were found in mesophyll, vascular-associated parenchyma, and bundle sheath cells of the leaf. MSV was not usually found in nonphotosynthetic tissues outside of the vasculature. Localization of both double-stranded viral DNA and transcripts encoding proteins involved in virus replication identified cells in which virus replication was active. Further spatial comparison with the distribution of transcripts of histone H2b, an S-phase specific gene, implied that host DNA replication was not essential for viral replication.
80 citations
TL;DR: The leaf permease 1-mutable 1 (lpe1-m1) mutant of maize exhibits disrupted chloroplast ultrastructure, preferentially affecting bundle sheath choroplasts under lower light.
Abstract: Adjacent bundle sheath and mesophyll cells cooperate for carbon fixation in the leaves of C4 plants. Mutants with compromised plastid development should reveal the degree to which this cooperation is obligatory, because one can assay whether mesophyll cells with defective bundle sheath neighbors retain C4 characteristics or revert to C3 photosynthesis. The leaf permease1-mutable1 (lpe1-m1) mutant of maize exhibits disrupted chloroplast ultrastructure, preferentially affecting bundle sheath choroplasts under lower light. Despite the disrupted ultrastructure, the metabolic cooperation of bundle sheath and mesophyll cells for C4 photosynthesis remains intact. To investigate this novel mutation, the Activator transposon-tagged allele and cDNAs corresponding to the Lpe1 mRNA from wild-type plants were cloned. The Lpe1 gene encodes a polypeptide with significant similarity to microbial pyrimidine and purine transport proteins. An analysis of revertant sectors generated by Activator excision suggests that the Lpe1 gene product is cell autonomous and can be absent up to the last cell divisions in the leaf primordium without blocking bundle sheath chloroplast development.
65 citations
TL;DR: There is strong evidence that nymphs of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, are obligate feeders on vascular bundles and that there are large differences between different host plants as to the availability of vascular bundles to silverleafwhitefly nymphS.
Abstract: This study revealed strong evidence that nymphs of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, are obligate feeders on vascular bundles and that there are large differences between different host plants as to the availability of vascular bundles to silverleaf whitefly nymphs. The relationship between nymphs and leaf vascular bundles was studied using 1) leaf sectioning and 2) techniques of leaf clearing of intact leaves. A geometric model is presented of the feeding relationship of vascular bundle-using homopterans. The relative abundance of vascular bundles was examined in six species of host plants that varied from highly preferred to tolerably acceptable. Included in order of acceptance were cantaloupe, cotton, hibiscus, broccoli, lantana and lettuce. The length of vascular bundle per 1.0 mm 2 of leaf surface ranged from about 10 mm in cantaloupe to 2.8 mm in lettuce. Salivary sheaths were found to connect with vascular bundles in 100% of the intact nymphs examined by the staining and clearing technique. However only 64% of those examined by the sectioning technique appeared to be connected to vascular bundles. This indicates that the sectioning technique leads to a high rate of error, causing an underestimation of the importance of direct contact with vascular bundles. About 50% of epidermal stylet penetrations were through epidermal cells ; the remaining 50% went through intercellular junctions. On cotton leaves, the distance between the point of labial contact with the leaf surface and the nearest point of the vascular bundle rarely exceeded 60 μm. Our studies show that while 50% of lettuce leaf-surface was beyond 60 μm of a vascular bundle, only 10% of cantaloupe leaf surface area was outside of the 60 μm range. In cotton, mean distance from labium to the nearest point of the vascular bundle was 40.9 μm (SEM = 2.66, N = 50, range 0-80 μm). Over 98% of all salivary sheaths went to minor veins (78% to single-filament vascular bundles, nearly 20% to double filament bundles). Fewer than 2% went to bundles with 3 or more filaments.
56 citations
TL;DR: Data on plamodesmatal frequency between protophloem sieve tubes and other cell types in intermediate and large bundles indicate that both phloem loading and unloading in the barley leaf involve apoplastic mechanisms.
Abstract: Large, intermediate, and small bundles and contiguous tissues of the leaf blade of Hordeum tvulgare L. ‘Morex’ were examined with the transmission electron microscope to determine their cellular composition and the distribution and frequency of the plasmodesmata between the various cell combinations. Plasmodesmata are abundant at the mesophyll/parenchymatous bundle sheath, parenchymatous bundle sheath/mestome sheath, and mestome sheath/vascular parenchyma cell interfaces. Within the bundles, plasmodesmata are also abundant between vascular parenchyma cells, which occupy most of the interface between the sieve tube-companion cell complexes and the mestome sheath. Other vascular parenchyma cells commonly separate the thick-walled sieve tubes from the sieve tube-companion cell complexes. Plasmodesmatal frequencies between all remaining cell combinations of the vascular tissues are very low, even between the thin-walled sieve tubes and their associated companion cells. Both the sieve tube-companion cell complexes and the thick-walled sieve tubes, which lack companion cells, are virtually isolated symplastically from the rest of the leaf. Data on plamodesmatal frequency between protophloem sieve tubes and other cell types in intermediate and large bundles indicate that they (and their associated companion cells, when present) are also isolated symplastically from the rest of the leaf. Collectively, these data indicate that both phloem loading and unloading in the barley leaf involve apoplastic mechanisms.
55 citations
TL;DR: The terrestrial form has Kranz anatomy and the biochemical traits of C4 plants while the submerged form develops structural and biochemical traits similar to those of C3 plants, which are related to the functional differences in their mechanisms of photosynthesis.
Abstract: Eleocharis vivipara Link is a unique amphibious leafless sedge. The terrestrial form has Kranz anatomy and the biochemical traits of C4 plants while the submerged form develops structural and biochemical traits similar to those of C3 plants. The structural features of the culms, which are the photosynthetic organs, of the two forms were examined and compared. The culms of the terrestrial form have mesophyll cells and three bundle sheaths which consist of three kinds of cell, namely, the innermost Kranz cells that contain large numbers of organelles, the middle mestome sheath cells that lack chloroplasts, and the outermost parenchyma sheath cells that contain chloroplasts. The culms of the submerged form had a tendency towards reduction in numbers and size of Kranz cells and vascular bundles, as compared to the terrestrial form, and they had spherical mesophyll cells that were tightly packed without intercellular spaces inside the epidermis. The submerged form had a higher ratio of cross-sectional area of mesophyll cells plus parenchyma sheath cells to that of Kranz cells than the terrestrial form. The difference was mainly due to a decrease in the number and the size of the Kranz cells and to a marked increase in the size of the mesophyll cells and the parenchyma sheath cells in the submerged form, as compared to the terrestrial form. The Kranz cells of the terrestrial form had basically the structural characteristics of plants of the NAD-malic enzyme type, with the exception of the intracellular location of organelles. The Kranz cells of the submerged form included only a few organelles, and the percentage of organelles partitioned to the Kranz cells was significantly smaller in the submerged form than in the terrestrial form. In addition, the size of chloroplasts of the Kranz cells was 60–70% of that of the terrestrial form. These structural differences between the two forms may be related to the functional differences in their mechanisms of photosynthesis.
52 citations
TL;DR: In mature leaves of C4 plants the values of rc are substantially lower than previous suggested and there is considerable leakage of CO2 from bundle sheath cells, Nevertheless, rc and Cbs values are sufficiently high in mature leaves to minimize photorespiration in C 4 plants under normal levels of CO 2.
Abstract: Bundle sheath resistance to diffusion of CO2 (rc) is a critical component of C4 photosynthesis which allows accumulation of inorganic carbon in bundle sheath cells of C4 plants. Several analyses were made to evaluate the magnitude of rc in C4 plants. Experimental data on the O2 inhibition of photosynthesis (Dai et al. (1993) Plant Physiol 103: 83–90; (1995) Plant Physiol 107: 815–825) and rates of photorespiration (de Veau and Burris (1989) Plant Physiol 90: 500–511) in Z. mays at different stages of development were analyzed using mathematical models of C4 photosynthesis. In young and senescing leaves modeled values of rc and the CO2 partial pressure in bundle sheath cells (Cbs) were lower and fractional leakage of CO2 from bundle sheath cells (fL) was higher than in mature leaves. Diffusive resistance of bundle sheath cells of C4 plants was also evaluated by analyzing the response of photosynthetic rates to varying CO2 in Amaranthus edulis in which the C4 cycle was dysfunctional by chemical mutagenesis (Dever et al. (1995) J Exp Bot 46: 1363–1376) and in Sorghum bicolor, Panicum maximum and Panicum miliaceum in which the C4 cycle was chemically inhibited (Brown and Byrd (1993) Plant Physiol 103: 1183–1188). These analyses indicate that in mature leaves of C4 plants the values of rc are substantially lower (ca. 50–200 m2 s mol−1) than previous suggested (ca. 500–1500 m2 s mol−1) for C4 photosynthesis and that there is considerable leakage of CO2 from bundle sheath cells. Nevertheless, rc and Cbs values are sufficiently high in mature leaves to minimize photorespiration in C4 plants under normal levels of CO2.
TL;DR: The terrestrial form has a unique pattern of cellular localization of C3 and C4 enzymes, and it is suggested that this pattern and the changes in the extent of accumulation of the various enzymes are the main factors responsible for the difference in photosynthetic traits between the two forms.
Abstract: Eleocharis vivipara link, an amphibious leafless sedge, develops traits of C4 photosynthesis and Kranz anatomy in the terrestrial form but develops C3-like traits with non-Kranz anatomy when submerged. The cellular localization of C3 and C4 enzymes in the photosynthetic cells of the two forms was investigated by immunogold labeling and electron microscopy. The terrestrial form has mesophyll cells and three kinds of bundle sheath cell, namely, parenchyma sheath cells, non-chlorophyllous mestome sheath cells, and Kranz cells. Phosphoenol-pyruvate carboxylase (PEPCase) was present in the cytosol of both the mesophyll cells and the parenchyma sheath cells, with higher-density labeling in the latter, but not in the Kranz cells. Pyruvate, Pi dikinase (PPDK) was found at high levels in the chloroplasts of both the mesophyll cells and the parenchyma sheath cells with some-what stronger labeling in the latter. This enzyme was also absent from the Kranz cells. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was found in the chloroplasts of all types of photosynthetic cell, but labeling was significantly less intense in the parenchyma sheath cells than in other types of cell. The submerged form also has three types of photosynthetic cell, as well as non-chlorophyllous mestome sheath cells, but it lacks the traits of Kranz anatomy as a consequence of modification of the cells. Rubisco was densely distributed in the chloroplasts of all the photosynthetic cells. However, PEPCase and PPDK were found in both the mesophyll cells and the parenchyma sheath cells but at lower levels than in the terrestrial form. These data reveal that the terrestrial form has a unique pattern of cellular localization of C3 and C4 enzymes, and they suggest that this pattern and the changes in the extent of accumulation of the various enzymes are the main factors responsible for the difference in photosynthetic traits between the two forms.
TL;DR: The C4 grass Arundinella hirta is characterized by unusual leaf blade anatomy: veins are widely spaced and files of bundle-sheath-like cells, the distinctive cells, form longitudinal strands that are not associated with vascular tissue.
Abstract: The C4 grass Arundinella hirta is characterized by unusual leaf blade anatomy: veins are widely spaced and files of bundle-sheath-like cells, the distinctive cells, form longitudinal strands that are not associated with vascular tissue. While distinctive cells (DCs) appear to function like bundle sheath cells (BSCs), they differ developmentally in two ways: they are derived from ground meristem rather than procambium and they are formed 1-2 plastochrons later. This study describes ultrastructural features of differentiating of BSCs, DCs, and associated mesophyll cells (MCs) during leaf development. BSCs and DCs differ from adjacent MCs by undergoing earlier cell enlargement, greater rates of chloroplast enlargement, reduction of chloroplast thylakoids at late stages of differentiation, more extensive starch formation, greater wall thickening, and deposition of a suberin lamella. The precocious delimitation of the bundle sheath layer is reflected in earlier BSC enlargement and vacuole growth. Derivation of DCs from ground meristem is correlated with late developmental changes in chloroplast size, wall thickness, and plasmodesmatal density. Despite these differences in timing of events, particularly at early stages, the development of the specialized structural features of BSCs and DCs is essentially similar. Thus, proximity to vascular tissue appears to be nonessential for the coordination and regulation of BSC- and MC-specific developmental events.
TL;DR: It is proposed that the dense network of phloem anastomoses developed during evolution as a mechanism of adaptation to possible damage in mature internodes by providing flexible alternative pathways for efficient xylem regeneration in plants with limited or no interfascicular cambium.
Abstract: The differentiation of phloem anastomoses linking the longitudinal vascular bundles has been studied in stem internodes of Cucurbita maxima Duchesne, C. pepo L. and Dahlia pinnata Cav. These anastomoses comprise naturally occurring regenerative sieve tubes which redifferentiate from interfascicular parenchyma cells in the young internodes. In all three species, severing a vascular bundle in a young internode resulted in regeneration of xylem to form a curved by-pass immediately around the wound. The numerous phloem anastomoses in these young internodes were not involved in this process, the regenerated vessels originating from interfascicular parenchyma alone. Conversely, in mature internodes of Dahlia, the regenerated vessels originated from initials of the interfascicular cambia, and their phloem anastomoses did not influence the pattern of xylogenesis. On the other hand, in old internodes of Cucurbita, in which an interfascicular cambium was not yet developed, the parenchyma cells between the bundles had lost the ability to redifferentiate into vessel elements, and instead, regenerated vessels were produced in the phloem anastomoses. Thus, the wounded region of the vascular bundle was not bypassed via the shortest, curved pathway, but by more circuitous routes further away from the wound. Some of the regenerated vessels produced in the phloem anastomoses were extremely wide, and presumably efficient conductors of water. It is proposed that the dense network of phloem anastomoses developed during evolution as a mechanism of adaptation to possible damage in mature internodes by providing flexible alternative pathways for efficient xylem regeneration in plants with limited or no interfascicular cambium.
TL;DR: Primary vascularization following a vascular bundle implantation may enhance the biological properties of an allograft and therefore has significant potential clinical applications.
Abstract: Revascularisation and cellular repopulation of fresh and cryopreserved allografts was observed following implantation of a vascular bundle in an experimental study in rats. Fresh and cryopreserved rat allografts were harvested from Lewis rats and implanted into Spraque-Dawley rats. The femoral vascular bundle was implanted into 2-cm segments of allograft placed in the medial aspect of the thigh of the recipient rats. Non-vascularised controls were used for comparison. Histological studies indicated the revascularisation pattern. Cryopreserved allografts with vascular bundle implantation showed early neovascularisation from the endosteal surface, 20% of the necrotic lacunae was repopulated with living cells at the end of 24 weeks. Fresh allografts with vascular implantation were rejected by the host immune mechanisms and showed early breakdown and fragmentation. Cellular repopulation was not observed in the non-vascularized allografts. Secondary vascularization following a vascular bundle implantation may enhance the biological properties of an allograft and therefore has significant potential clinical applications.
TL;DR: The number and size of xylem vessels in the vascular bundles at the proximal and distal positions of both pericarp and placental tissues of tomato fruit were measured in three cultivars with different susceptibilities to blossom-end rot grown at two salinity levels.
Abstract: SummaryThe number and size of xylem vessels in the vascular bundles at the proximal and distal positions of both pericarp and placental tissues of tomato fruit were measured in three cultivars with different susceptibilities to blossom-end rot grown at two salinity levels. While the total number of vascular bundles in the pericarp is greater than in the placenta, the average bundle size in the distal pericarp is larger than that in the distal placenta. Salinity reduced the total bundle area in the distal tissue more in the susceptible cultivars, i.e. Calypso and Spectra than in the less susceptible cultivar, Counter. Both the number and size of xylem vessels in the bundles of proximal placenta tissue were greater than in the proximal pericarp; while the reverse was true in the distal tissue. Salinity reduced the total xylem area in the bundle of the distal tissue significantly, particularly in ‘Spectra’. Thus, the total xylem area in the distal layer was reduced more by salinity in the placenta of the sus...
TL;DR: Foliar anatomy provides important characters for the recognition of subgroups within Bonnetsiaceae and is consistent with the segregation of Bonnetiaceae from Theaceae.
Abstract: A comprehensive study of the nodal and leaf anatomy of Bonnetiaceae was completed in order to provide evidence for evaluation in relation to systematics. Nodal anatomy is trilacunar, three-trace or unilacunar, one-trace. Basic leaf anatomical features of the family include: complete or incomplete medullated vascular cylinder in petiole; paracytic mature stomata with encircling ridges; large mucilaginous cells in the adaxial surface of mesophyll; periclinal divisions in upper surface layers; and discrete patches of phloem within the vascular bundles. Especially noteworthy is the presence in some genera of foliar vascular bundles enveloped by a sheath composed of two concentric regions, i.e., an inner region consisting of multiple layers of fibers and an outer specialized endodermis composed of thin-walled cells with Casparian strips. Leaves are variable with respect to lamina and cuticle thickness, relative amount and number of palisade and spongy layers, venation of lamina, and the presence or absence of sclereids and crystals in the mesophyll. A major feature in the evolution of Bonnetiaceae is development of a highly divergent, essentially parallel, leaf venation that is superficially similar to that of some monocotyledons and apparently unique among dicotyledons. Foliar anatomy provides important characters for the recognition of subgroups within Bonnetiaceae and is consistent with the segregation of Bonnetiaceae from Theaceae.
TL;DR: Under conditions of undisturbed growth in a controlled environment xylem architecture was found to have an important influence on the intraplant distribution of 32 P from nodal roots and allocation to a particular node along the branch was influenced by its nodal position relative to the fed root and the sink strength of its tissues for the transpiration stream.
Abstract: Our objective was to establish whether the xylem vascular connections (architecture) of a genotype of Trifolium repens L. had implications for the intraplant allocation of recently assimilated phosphorus (P). One nodal root of each plan! was isolated and fed 32 P-labelled nutrient solution for 24 h. The fed root was either on the parent axis (11-12 nodes proximal CO the apex) or on a branch at the third or fourth node along the branch when counting from the junction with the parent stolon. Allocation patterns were obtained by dissecting plants and assaying each dissected component for 32 P. Under conditions of undisturbed growth in a controlled environment xylem architecture was found to have an important influence on the intraplant distribution of 32 P from nodal roots. Allocation patterns of 32 P were consistent with those predicted from knowledge of the xylem vascular architecture of the genotype and a predominantly acropetal direction of the transpiration stream. For instance, very little 32 P (< 1 % of exported 32 P from the fed root) was found in branches on the opposite side of the stolon to the fed root, and the strong acropetal direction of the transpiration stream resulted in little allocation of 32 P to leaves that had traces that arose from axial bundles at positions proximal to that of the fed root (the leaf subtending the fed root and the next distal leaf had low 32 P content), to all plant organs proximal to the fed root (< 6%) and to all other roots (<4%). The high allocation of 32 P to the branch arising at the same node as the fed root (64%) reflects the numerous links that the- fed root has to vascular bundles in the branch (3-6, of which two are axial bundles) against the single connection it has to the adjacent lower axial bundle in the parent stolon. Allocation of 32 P to the leaf and axillary bud at each node along the branch strongly favoured nodes on the adaxial side, a result consistent with the fact that the root connections are to the upper and lower axial bundles on the adaxial side of the branch. Allocation to a particular node along the branch was also influenced by its nodal position relative to the fed root and the sink strength of its tissues for the transpiration stream.
1 Oct 1996
TL;DR: Results indicate primary independence of phloem unloading of CWI in tumors, and the activity of acid cell wall invertase (CWI) was about tenfold higher in tumor than in the adjacent host stem tissue.
Abstract: :
In stems of Ricinus communis and leaves of Kalanchoe daigremontiana, rapidly growing tumors were induced by the wild type strains of Agrobacterium tumefaciens C58 and A281 (p35 Sgusint). Transformed cells, monitored by histochemical β-glucuronidase (GUS) staining, showed GUS activity in K. daigremontiana tumors in up to 100% of the tissue. In R. communis tumors, however, GUS activity was patchy, probably due to interference in gus expression from highly active phenolic compounds. Functionality of the sieve elements within the vascular bundles of the tumor and their connection with host stem bundles were shown by applying fluorescein to source leaves as a tracer of phloem-mobile solutes. The transport pathway within the tumor and the mechanism of phloem unloading were investigated by iontophoretic injection of Lucifer yellow CH into sieve tubes. Apparent symplastic solute unloading into parenchyma cells was confirmed by localizing common primary pit fields by staining them with aniline blue. In spite of the evidence for symplastic unloading, the activity of acid cell wall invertase (CWI) was about tenfold higher in tumor than in the adjacent host stem tissue. These results indicate primary independence of phloem unloading of CWI in tumors.
TL;DR: It is demonstrated for the first time that the entire rolA promoter, composed of domains, A, B and C, is silent in seeds, activated at the onset of germination in the cotyledons and in the elengation zone of the radicle and is finally expressed throughout the vegetative and floral phases.
Abstract: The spatial and temporal activity of the entire and individual promoter domains of the rolA gene of Agrobacterium rhizogenes was investigated and correlated with the distinctive features of the phenotypes of transgenic tobacco plants. The GUS assay was performed in the presence of an oxidative catalyst during the development of transgenic plants expressing chimeric genes containing the β-glucuronidase coding sequence under the control of the different promoter domains. In situ hybridization was also used on transgenic plants harbouring rolA under the control of the entire or deleted promoter. This paper demonstrates for the first time that the entire rolA promoter, composed of domains, A, B and C, is silent in seeds, then activated at the onset of germination in the cotyledons and in the elengation zone of the radicle and is finally expressed throughout the vegetative and floral phases. Domains B+C, which were sufficient to induce wrinkled leaves and short internodes, were active in all the stem tissues, but only in the companion cells of the phloem strands of the leaves. Domain C, which specified a dwarf phenotype with normal leaves, was weakly expressed in the stem vascular bundles and in the leaf internal phloem. These results indicate that the vascular bundles are the primary targets for the generation of the short internode phenotype. Furthermore, the local expression of rolA in the stem vascular bundles induced a size reduction of the surrounding parenchyma cells, suggesting the existence of some diffusible factor(s) associated with the expression of the rolA gene.
TL;DR: This study emphasizes the importance of the dimension of the vascular system for fruit set and provides a possible explanation for the better fruit set on both leafy and leafless inflorescence with several flowers compared with single-flowered inflorescences.
TL;DR: The data suggest that the sugars in germinating barley seeds are primarily transported through the vascular bundles and, at the same time, rapidly incorporated into mesophyll cells in the leaves.
Abstract: The distribution and fluctuation of sugars in germinating barley seeds were examined by 13 C nuclear magnetic resonance (NMR) spectroscopy, 1 H-NMR imaging and 1 H-NMR localized spectroscopy in relation to morphology. Maltose, sucrose, fructose and oils were detected in intact imbibed seeds by 13 C-NMR spectra. During the first 6d of germination, the maltose content increased and the oil content gradually decreased, whilst the levels of sucrose and fructose remained constant. Sugars were located by 1 H-NMR images and 1 H-NMR localized spectra in the vascular bundle of the seeds as well as in the solubilized endosperm. They were also detected in the shoots. The sugars detected in an 80% ethanol shoot extract were sucrose and glucose, which were located in the vascular bundles but not in the mesophyll cells of the coleoptile. They were also located in the basal part of the shoot, but not above 7 mm from the scutellum. The data suggest that the sugars are primarily transported through the vascular bundles and, at the same time, rapidly incorporated into mesophyll cells in the leaves.
TL;DR: It was shown that this plant model is characterized by two major developmental processes: a) confined elongation of the cotyledon petiole caused by a limited number of cell divisions and b) formation of a morphogenetic zone around each initially wounded vascular bundle within 36 h after detachment of the embryonic axis.
Abstract: Rapid formation of adventitious roots by walnut cotyledon fragments in vitro was traced by light microscopy It was shown that this plant model is characterized by two major developmental processes: a) confined elongation of the cotyledon petiole caused by a limited number of cell divisions and b) formation of a morphogenetic zone around each initially wounded vascular bundle within 36 h after detachment of the embryonic axis During the first phase of development, granular storage protein bodies dissolved, and starch grains were deposited mainly in the distal portion of the cotyledon fragments Rapidly, new globular protein bodies were formed, and phenolic inclusions accumulated in the vacuoles of epidermal and subepidermal cells and of individual cells close to the vascular bundles Each adventitious root was found to be in continuity with a single vascular bundle of the cotyledon petiole A short auxin treatment suppressed the formation of large roots and induced numerous tiny rootlets dispersed all over the surface of the cotyledons
TL;DR: The previously reported presence of LHC II in bundle sheath chloroplasts of maize can be attributed to mesophyll contamination, and the major light-harvesting complex of PS II (LHC II) was unable to detect in the pure bundle she Heath thylakoids using fluorescence excitation spectroscopy.
Abstract: Chlorophyll fluorescence at short and long wavelengths was used to sort thylakoid membranes of maize, a plant with the C4 dicarboxylic acid pathway of photosynthesis, in a flow cytometer. The method yielded two distinct particle populations that were identified as mesophyll and bundle sheath thylakoids by low-temperature fluorescence spectroscopy and by the pigment ratio of chlorophyll a/b. Mesophyll and bundle sheath thylakoids were essentially pure after sorting by flow cytometry. Fluorescence data and chlorophyll a/b pigment ratios of thylakoids separated by flow cytometry were compared with earlier data of preparations obtained by conventional isolation procedures. Our results indicate that impure mesophyll and bundle sheath membranes were used in most previous investigations. We were unable to detect the major light-harvesting complex of PS II (LHC II) in our pure bundle sheath thylakoids using fluorescence excitation spectroscopy. Therefore, we believe that the previously reported presence of LHC II in bundle sheath chloroplasts of maize can be attributed to mesophyll contamination.
TL;DR: It was concluded that genotypic variation exists within T repens for potential to alter intra-plant allocation of mineral nutrients in response to treatments that modify source-sink relationships within plants; and that this variation is correlated with differences among genotypes in the organisation of the vasculature of their stolons.
Abstract: To assess genotypic variability in nutrient supply of shoot branches, the distribution of 32 P and 45 Ca exported from a source nodal root (24-h uptake period) was measured within a genotype of a large-leaved (Kopu) and a small-leaved (Tahora) cultivar of Trifolium repens. Source-sink relationships of plants were modified by root severance, defoliation, and shade treatments. In control plants of both genotypes distribution of 32 P and 45 Ca closely followed the pathways that could be predicted from the known phyllotactic constraints on the vascular system. As such there was little allocation of radioisotopes (3.1% and 2.5% of exported 32 P and 45 Ca, respectively) from the source root to branches on the opposite side of the parent axis (far-side branches). However, genotypic differences in nutrient allocation were apparent, when treatments were imposed to alter intra-plant source-sink relationships. In the large-leaved genotype, the imposed treatments had minor effects on the allocation to far-side branches; whereas, in the small-leaved genotype, root severance and defoliation treatments increased lateral transport to far-side branches to 30% ( 32 P) and 10% ( 45 Ca) of exported radioisotopes. Genotypes with low (8-9) and high (12-13) numbers of vascular bundles were selected from within the large-leaved cultivar. Distribution of 32 P was then measured after plants had been pre-treated by removal of all far-side roots two days prior to labelling. Genotypes with low vascular bundle number allocated 20% and those with high vascular bundle number 3.2% of exported 32 P to far-side branches. It was concluded (1) that genotypic variation exists within T repens for potential to alter intra-plant allocation of mineral nutrients in response to treatments that modify source-sink relationships within plants; and (2) that this variation is correlated with differences among genotypes in the organisation of the vasculature of their stolons.
TL;DR: The spatial and temporal analysis of the expression of an alfalfa flavanone 3-hydroxylase (f3h) promoter-gus fusion introduced into Nicotiana benthamiana indicates that this construct can be very useful to study factors controlling the production of flavonoids.
Abstract: Flavanone 3-hydroxylase is an enzyme acting in the central part of the flavonoid biosynthesis pathway. It is generally encoded by a single gene and seems to have a key position for the regulation in this pathway. These two features make a single f3h promoter-gus fusion a suitable tool to study both the f3h expression and the regulation of this pathway. We present here the spatial and temporal analysis of the expression of an alfalfa flavanone 3-hydroxylase (f3h) promoter-gus fusion introduced into Nicotiana benthamiana. The Medicago sativa (alfalfa) f3h promoter directed gus expression in flowers, stems, leaves and roots. In flowers, GUS activity was observed in pollen grains, in ovules, in ovary placenta and in the epidermis, medullary parenchyma, trichomes and second cortical cellular layer surrounding the vascular bundles of the peduncle. In stems, GUS activity was detected at the same places as in the peduncle except for the medullary parenchyma. In roots, we found GUS staining in root hairs, epidermis and in the vascular bundles of the elongated zone. Finally, in leaves, the f3h promoter expressed essentially in the stalk cells of the multicellular trichomes. The expression pattern of the f3h-gus fusion was correlated to the presence of flavonoids in situ. These data indicate that this construct can be very useful to study factors controlling the production of flavonoids.
TL;DR: Tissue-print immunoblots of rape petioles and stems showed that the rape ptGRP1 homologue is primarily located in the vascular tissue, and that its expression decreases with developmental age of the tissue.
Abstract: The presence of specific glycine-rich proteins (GRP) related to petunia GRP1 (ptGRP1) was examined in three species of monocots (wheat, barley and maize) and five species of dicots (rape, turnip, soybean, crabapple and tomato). Protein blot analysis showed that anti-ptGRP1 antibody cross-reacted with a single different polypeptide in all species except maize. The molecular mass of these polypeptides ranged from 14 to 55 kDa. Tissue-print immunoblots of rape petioles and stems showed that the rape ptGRP1 homologue, like ptGRP1, is primarily located in the vascular tissue, and that its expression decreases with developmental age of the tissue. In barley, the ptGRP1 homologue is found in leaf vascular bundles, and may also be present in the surrounding bundle sheaths. Unlike the dicots examined, expression of the protein did not appear to decrease significantly with developmental age.
1 Jan 1996
TL;DR: In this paper, the authors define phloem loading as the transfer of photosynthates from the site of production via the mesophyll symplast to the sieve tubes.
Abstract: According to a recent proposal (Oparka and Van Bel 1992), phloem loading is the transfer of photosynthates from the site of production via the mesophyll symplast to the sieve tubes. The definition implies that phloem loading comprises a range of sequential processes of which carbohydrate metabolism in the mesophyll and sieve element loading have received ample attention.
TL;DR: Investigation of chlorenchyma of Portulaca grandiflora revealed that ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) accumulated in bundle sheath chloroplast and in the chloroplasts of the water storage cells adjacent to the central vascular bundle.
TL;DR: The tissue- and cell-specific localization of sucrose synthase changes along the growing leaf as a function of the developmental state and the associated need for sucrose import or export.
Abstract: A developing maize leaf grows by the activity of a basal meristematic region and an adjacent elongating zone, resulting in a morphological and functional gradient along the leaf. We have used this system to detect the spatial and temporal expression of an enzyme, sucrose synthase, which plays a pivotal role in the sucrose import-export transition which occurs along a monocotyledon leaf. Immunogold labeling was used to detect the cellular and sub-cellular distribution of sucrose synthase (SS) at the electron microscopical level; the protein was visualized using a polyclonal antiserum on embedded tissue sections. Immunolabel was observed in the cytosol of dividing meristematic cells, expanding cells of the elongation zone, and in differentiating cells of young photosynthetic tissue. In fully differentiated leaf tissue, however, the protein was no longer immuno-detectable in photosynthetic cells, but was present in the guard and subsidiary cells of stomata and in companion cells within the phloem tissue of vascular bundles. The tissue- and cell-specific localization of sucrose synthase changes along the growing leaf as a function of the developmental state and the associated need for sucrose import or export.