Endodermal Cell Walls Research Articles

Comparative anatomy and systematics of the orchid tribe Vanilleae excluding Vanilla

Vanilleae have been divided into three subtribes consisting of ten genera. We had material for study of all except Dictyophyllaria in subtribe Vanillinae. All genera except Vanilla have few species Clematepistephium and Dictyophyllaria are monospecific. Leafy types have adaxial and abaxial stomata except Clematepistephium , Epistephium, and Eriaxis which have only abaxial tetracytic and anomocytic stomatal apparatuses. Cyrtosia, Erythrorchis, Galeola, and Lecanorchis are leafless. Hypodermis occurs in leaves of Pseudovanilla, Clematepistephium, and Eriaxis; leaves of Epistephium lack a hypodermis. Mesophyll is homogeneous. Stems of Cyrtosia, Galeola, and Eriaxis and rhizomes of Cyrtosia have a hypodermis. A uniseriate velamen occurs in roots of Erythrorchis, Pseudovanilla, Clematepistephium , and Lecanorchis; roots of other genera are bounded by a simple epidermis. Exodermal cell walls are -thickened; endodermal cell walls are ○-thickened. Vascular tissue of roots is variously embedded in sclerenchyma or parenchyma; similarly, pith may be sclerenchymatous or parenchymatous. Cladistic analyses result in two equally parsimonious trees with Epistephium and Eriaxis reversed in placement in each tree. Both trees constitute a paraphyletic complex giving rise to a clade containing the monophyletic Lecanorchidinae and Galeolinae. Vegetative anatomical characters have some phylogenetic value in Vanilleae, but they are not useful in resolving placement of the large and polymorphic genus Vanilla .

Cortical development in roots of the aquatic plant Pontederia cordata (Pontederiaceae)

Adventitious roots of marsh-grown Pontederia cordata were examined to determine cortical development and structure. The innermost layer of the ground meristem forms the endodermis and aerenchymatous cortex. The outermost layer of the early ground meristem undergoes a precise pattern of oblique and periclinal cell divisions to produce a single or double layer of prohypodermis with an anchor cell for each radial file of aerenchyma cells. At maturity, endodermal cell walls are modified only by narrow Casparian bands. The central regions of the ground meristem become proaerenchyma and exhibit asymmetric cell division and expansion. They produce an aerenchymatous zone with barrel-shaped large cells and irregularly shaped small cells traversing the aerenchyma horizontally along radii; some crystalliferous cells with raphides are present in the aerenchyma. The walls of the hypodermis are modified early by polyphenols. The outermost layer of the hypodermis later matures into an exodermis with Casparian bands that are impermeable to berberine, an apoplastic tracer dye. The nonexodermal layer(s) of the hypodermis has suberin-modified walls. Radial files of aerenchyma are usually connected by narrow protuberances near their midpoints, the aerenchyma lacunae having been produced by expansion of cells along walls lining intercellular spaces. We are terming this type of aerenchyma development, which is neither schizogenous nor lysigenous, "differential expansion."

Fourier transform infrared-spectroscopic characterisation of isolated endodermal cell walls from plant roots: chemical nature in relation to anatomical development

The chemical nature of enzymatically isolated endodermal cell walls from Cicer arietinum L., Clivia miniata Reg. and Iris germanica L. was studied by FTIR (Fourier transform infrared) spectroscopy. Observed frequencies were assigned to functional groups present in the cell wall and relative amounts of the biopolymers suberin and lignin, cell wall carbohydrates and proteins were determined. Infrared absorption spectra indicated structural characteristics for the three different developmental states of the isolated endodermal cell wall: primary endodermis with Casparian strips (state I), secondary endodermis with suberin lamellae (state II), and tertiary endodermis with U-shaped cell wall depositions (state III). The data obtained from this study are compared with previous results obtained by chemical degradation of isolated endodermal cell walls and subsequent determination of monomeric degradation products by gas chromatography and mass spectrometry. It is concluded that FTIR spectroscopy represents a direct and nondestructive method suitable for the rapid investigation of isolated plant cell walls. Furthermore, the observation that the suberin-assigned absorption bands disappeared after transesterification of the samples with BF(3)-methanol confirmed that suberin is completely degraded by this treatment.

Apoplastic barriers in roots: chemical composition of endodermal and hypodermal cell walls

Based on the characterization of the chemical composition of endodermal and hypodermal cell walls isolated from seven monocotyledonous and three dicotyledonous plant species, a model of the composition of apoplastic barriers in roots is proposed. Depending on the species, endodermal and hypodermal cell walls of roots contained varying amounts of the biopolymers suberin, lignin, cell wall proteins, and carbohydrates. Although analysis of the chemical composition of these apoplastic barriers of roots is now possible, it is pointed out that conclusions from these data concerning the functional properties of these cell walls can not easily be drawn. However, in analogy to suberized periderms it is argued that the suberin should play a role in establishing an apoplastic transport barrier in roots, albeit not a perfect barrier. Furthermore, due to the combined occurrence of suberin, lignin and cell wall proteins it is argued that endodermal and hypodermal cell walls also have an important function as barriers towards pathogens. Finally, it is pointed out that additional experimental approaches combining the investigation of transport properties and of the chemical composition of apoplastic transport barriers in roots are necessary before the function of endodermal and hypodermal cell walls in roots can be fully understood.

Review article. Apoplastic barriers in roots: chemical composition of endodermal and hypodermal cell walls

Review article. Apoplastic barriers in roots: chemical composition of endodermal and hypodermal cell walls

Chemical analysis and immunolocalisation of lignin and suberin in endodermal and hypodermal/rhizodermal cell walls of developing maize (Zea mays L.) primary roots.

The composition of suberin and lignin in endodermal cell walls (ECWs) and in rhizodermal/hypodermal cell walls (RHCWs) of developing primary maize (Zea mays L.) roots was analysed after depolymerisation of enzymatically isolated cell wall material. Absolute suberin amounts related to root length significantly increased from primary ECWs (Casparian strips) to secondary ECWs (suberin lamella). During further maturation of the endodermis, reaching the final tertiary developmental state characterised by the deposition of lignified secondary cell walls (u-shaped cell wall deposits), suberin amounts remained constant. Absolute amounts of lignin related to root length constantly increased throughout the change from primary to tertiary ECWs. The suberin of Casparian strips contained high amounts of carboxylic and 2-hydroxy acids, and differed substantially from the suberin of secondary and tertiary ECWs, which was dominated by high contents of omega-hydroxycarboxylic and 1,omega-dicarboxylic acids. Furthermore, the chain-length distribution of suberin monomers in primary ECWs ranged from C(16) to C(24), whereas in secondary and tertiary ECWs a shift towards higher chain lengths (C(16) to C(28)) was observed. The lignin composition of Casparian strips (primary ECWs) showed a high syringyl content and was similar to lignin in secondary cell walls of the tertiary ECWs, whereas lignin in secondary ECWs contained higher amounts of p-hydroxyphenyl units. The suberin and lignin compositions of RHCWs rarely changed with increasing root age. However, compared to the suberin in ECWs, where C(16) and C(18) were the most prominent chain lengths, the suberin of RHCWs was dominated by the higher chain lengths (C(24) and C(26)). The composition of RHCW lignin was similar to that of secondary-ECW lignin. Using lignin-specific antibodies, lignin epitopes were indeed found to be located in the Casparian strip. Surprisingly, the mature suberin layers of tertiary ECWs contained comparable amounts of lignin-like epitopes.

Structure and chemical composition of endodermal and rhizodermal/hypodermal walls of several species

CWM, isolated cell wall material ECW, isolated endodermal cell walls G, guaiacyl monomer H, p‐hydroxyphenyl monomer HCW, isolated hypodermal cell walls RHCW, isolated rhizodermal and hypodermal cell walls S, syringyl monomer XV, isolated xylem vessels Endodermal cell walls of the three dicotyledoneous species Pisum sativum L., Cicer arietinum L. and Ricinus communis L. were isolated enzymatically and analysed for the occurrence of the biopolymers lignin and suberin. From P. sativum, endodermal cell walls in their primary state of development (Casparian strips) were isolated. Related to the dry weight, these isolates contained equal amounts of suberin (2·5%) and lignin (2·7%). In contrast, the endodermal cell walls of C. arietinum and R. communis, which were nearly exclusively in their secondary state of development, contained significantly higher proportions of suberin (10–20%) and only traces of lignin (1–2%). The results of the chemical analyses were supported by a microscopic investigation of Sudan III‐stained root cross‐sections, showing a Casparian strip restricted to the radial walls of the endodermis of P. sativum and well‐pronounced red suberin lamellae in C. arietinum and R. communis roots. Compared with recently investigated monocotyledoneous species, higher amounts of suberin by one order of magnitude were detected with the secondary state of development of dicotyledoneous species. Furthermore, the carbohydrate and protein contents of primary (Clivia miniata Reg. and Monstera deliciosa Liebm.), secondary (C. arietinum and R. communis) and tertiary endodermal cell walls (Allium cepa L. and Iris germanica L.) were determined. The relative carbohydrate content of secondary endodermal cell walls was low (14–20%) compared with the content of primary (42–50%) and tertiary endodermal cell walls (60%), whereas the protein content of isolated endodermal cell walls was high in primary (13%) and secondary (8%) and low in tertiary endodermal cell walls (0·9–2%). The results presented here indicate that the quantitative chemical composition of primary, secondary, and tertiary endodermal cell walls varies significantly. Finally, cell wall proteins are described as an additional important constituent of endodermal cell walls, with the highest concentrations occurring in primary (Casparian strips) and secondary endodermal cell walls.

Structural modifications of the apoplast and their potential impact on ion uptake

AbstractNutrient ions entering the plant root from the soil solution, whether directly or through mycorrhizal fungi, first encounter the apoplast, a chemically complex compartment. The movement of ions in unmodified walls occurs in water‐filled channels (diameter about 10 nm) and is influenced by electrical charges. Some positive charges occur in the wall, but the majority are negative. The permeability of the wall is variable, depending on its age and whether or not it has been further modified. Very young walls are less permeable than older walls, and the permeability of mature walls may be reduced by suberin and/or lignin deposits. It is not clear whether or not the other two main wall‐modifying substances, mucilages and condensed tannins, also significantly reduce wall permeability. Casparian bands, which consist of suberin and lignin within radial and transverse walls, occur in the endodermis and exodermis. These layers form continuous cylinders within the root so that ion movement into the entire areas they surround is prevented. An important corollary is that Casparian bands dictate which cells are accessed by the soil solution and thus are in a position to absorb ions. It is postulated that a Casparian band‐like modification also occurs in the walls of cork cells, based on observations of their impermeability to dyes. Suberin can occur in the form of lamellae which are deposited on all walls of endodermal, exodermal and cork cells. Unlike the Casparian bands, these lamellae limit movement between the apoplast and plasmalemma surface of the individual cells in which they occur. Condensed tannins, an addition to the walls of tree roots which results in them becoming brown, appear to function as antimicrobial agents rather than as permeability barriers. Further research is needed to investigate the structure of both unmodified and modified walls in a variety of species and under a variety of growing conditions.

Comparative investigation of primary and tertiary endodermal cell walls isolated from the roots of five monocotyledoneous species: chemical composition in relation to fine structure

The chemical composition of isolated endodermal cell walls from the roots of the five monocotyledoneous species Monstera deliciosa Liebm., Iris germanica L., Allium cepa L., Aspidistra elatior Bl. and Agapanthus africanus (L.) Hoffmgg. was determined. Endodermal cell walls isolated from aerial roots of M. deliciosa were in their primary developmental state (Casparian bands). They contained large amounts of lignin (6.5% w/w) and only traces of suberin (0.5% w/w). Endodermal cell walls isolated from the other four species were in their tertiary developmental state. Lignin was still the more abundant cell wall polymer with amounts ranging from 3.8% (w/w, A. cepa) to 4.5% (w/w, I. germanica). However, compared to endodermal cell walls in their primary state of development (Casparian bands), tertiary endodermal cell walls contained significantly higher amounts of suberin, ranging from 1.8% (w/w, I. germanica) to 3.0% (w/w, A. africanus). Thus, chemical characterization of endodermal cell walls from five different species revealed that lignin was the dominant cell wall polymer in the Casparian band of M. deliciosa, whereas tertiary endodermal cell walls contained, in addition to lignin, increasing amounts of suberin (I. germanica, A. cepa, A. elatior and A. africanus). Besides the two biopolymers lignin and suberin, cell wall carbohydrates in the range of between 40 and 60% were also quantified. The sum of all cell wall compounds investigated by gas chromatography resulted in a recovery of 50–80% of the dry weight of the isolated cell wall material. Quantitative chromatographic results in combination with microscopic studies are consistent with the existence of a distinct suberin lamella and lignified tertiary wall deposits. From these data it can be concluded that the barrier properties of the endodermis towards the apoplastic transport of ions and water will increase from primary to tertiary endodermal cell walls due to their increasing amounts of suberin.

Comparative anatomy and systematics of Senghas's cushion species of Maxillaria (Orchidaceae)

Abstract Using data obtained through anatomy and morphology, we used cladistics to examine the monophyly of Senghas's proposed classification of Maxillaria cushion plants and his placement of Mormolyca ringens. Trigonidium obtusum was chosen as the outgroup. Leaves have multicellular hairs sunken in crypts, primarily anomocytic or primarily tetracytic stomatal apparatuses, homogeneous mesophyll, and scattered fibre bundles. Three types of adaxial hypodermis were observed: (1) water-storage cells, (2) fibre bundles scattered among water-storage cells, and (3) fibre bundles scattered among chlorenchymatous cells. Abaxial hypodermis of fibre bundles occurs in several Maxillaria species and in Trigonidium obtusum. At the midvein of the leaf, adaxial mesophyll cells of most species are anticlinally extended and empty, and the abaxial mesophyll is usually collenchymatous. Vascular bundles are collateral and usually in a single series. Pseudobulb epidermal cell walls are thin, or outer walls are thickened. Ground tissue consists of water-storage and assimilatory cells with vascular bundles and associated lacunae scattered throughout. Roots are velamentous and exodermal cell walls are usually ∏-thickened with tenuous bands of scalariform thickenings on longitudinal walls. Tilosomes may be plaited, baculate, or spongy. Endodermal cell walls are usually ∑-thickened and pericycle cell walls are usually O-thickened opposite phloem sectors. Stegmata line the periphery of the thickened pericycle cells opposite phloem sectors in M. picta. Pith may be parenchymatous or sclerenchymatous. According to our phylogenetic analysis, Mormolyca ringens is consistently nested within the cladistic structure of Maxillaria. Therefore, Maxillaria likely is paraphyletic if Mormolyca ringens is recognized as generically distinct. It appears that Senghas's subgroup divisions of the unifoliate pseudobulbous maxillarias may also be artificial.

Comparative anatomy and systematics of Senghas's cushion species ofMaxillaria(Orchidaceae)

Using data obtained through anatomy and morphology, we used cladistics to examine the monophyly of Senghas's proposed classification ofMaxillariacushion plants and his placement ofMormolyca ringens. Trigonidium obtusumwas chosen as the outgroup. Leaves have multicellular hairs sunken in crypts, primarily anomocytic or primarily tetracytic stomatal apparatuses, homogeneous mesophyll, and scattered fibre bundles. Three types of adaxial hypodermis were observed: (1) water-storage cells, (2) fibre bundles scattered among water-storage cells, and (3) fibre bundles scattered among chlorenchymatous cells. Abaxial hypodermis of fibre bundles occurs in severalMaxillariaspecies and inTrigonidium obtusum.At the midvein of the leaf, adaxial mesophyll cells of most species are anticlinally extended and empty, and the abaxial mesophyll is usually collenchymatous. Vascular bundles are collateral and usually in a single series. Pseudobulb epidermal cell walls are thin, or outer walls are thickened. Ground tissue consists of water-storage and assimilatory cells with vascular bundles and associated lacunae scattered throughout. Roots are velamentous and exodermal cell walls are usually ∏-thickened with tenuous bands of scalariform thickenings on longitudinal walls. Tilosomes may be plaited, baculate, or spongy. Endodermal cell walls are usually ∑-thickened and pericycle cell walls are usually O-thickened opposite phloem sectors. Stegmata line the periphery of the thickened pericycle cells opposite phloem sectors inM. picta.Pith may be parenchymatous or sclerenchymatous. According to our phylogenetic analysis,Mormolyca ringensis consistently nested within the cladistic structure ofMaxillaria.Therefore,Maxillarialikely is paraphyletic ifMormolyca ringensis recognized as generically distinct. It appears that Senghas's subgroup divisions of the unifoliate pseudobulbous maxillarias may also be artificial.

Chemical Composition of Hypodermal and Endodermal Cell Walls and Xylem Vessels Isolated from Clivia miniata (Identification of the Biopolymers Lignin and Suberin).

The occurrence of the biopolymers lignin and suberin was investigated with hypodermal (HCW) and endodermal cell walls (ECW) and xylem vessels (XV) isolated from Clivia miniata Reg. roots. Both biopolymers were detected in HCW and ECW, whereas in XV, typical aliphatic suberin monomers were missing and only representative lignin monomers such as guaiacyl (G) and syringyl (S) units could be detected. The absolute amounts of lignin were about one order of magnitude higher compared with suberin in both HCW and ECW. The ratios of the two aromatic lignin units (G/S) decreased from 39 in XV and 10 in HCW to about 1 in ECW, indicating significant differences in lignin structure and function between the three investigated samples. Additionally, compared with the detectable lignin-derived aromatic units G and S, significantly higher amounts of esterified p-coumaric acid-derived aromatic monomers were obtained with HCW, but not with ECW. This is interpreted as a functional adaption of HCW toward pathogen defense at the root/soil interface. The final aim of this study was to provide a thorough chemical characterization of the composition of HCW, ECW, and XV, which in turn will form the basis for a better understanding of the relevant barriers toward the passive, radial, and apoplastic diffusion of solutes from the soil across the root cortex into the root cylinder.

Early stages of infection of maize (Zea mays) and Pennisetum setosum roots by the parasitic plant Striga hermonthica

Infection of young roots of maize (Zea mays L.) by the parasitic plant Striga hermonthica (Del.) Benth. was examined. Attachment to and penetration of roots occurred within 1–2 days after inoculation. Subsequent growth through the cortex to the host stele and proliferation of parasite xylem tissue was commonly completed by 3–4 days after inoculation. Histochemical staining showed that young maize roots do not contain major wall-thickening components. However, an increase in cell wall fluorescence and endodermal cell wall thickness was often seen at the site of infection and in the surrounding maize root tissue at 3 days after inoculation. This host response was variable and did not prevent rapid and successful penetration by the parasite. In contrast, uninfected roots of Pennisetum setosum (Sw.) L. Rich., a species resistant to S. hermonthica, had substantial thickening of the inner endodermal cell walls and exhibited further cell wall thickening at the stele upon infection. Examination of infections on both hosts demonstrated the presence of autofluorescent material at the host-parasite interface. This material was thicker and more extensive at the P. setosum-S. hermonthica interface than at the maize-S. hermonthica interface, and contained polyphenols and lignin. Examination of the host-parasite xylem connections in maize revealed substantial invasion of the host stele by both parenchyma and tracheary elements. In a few cases of P. setosum infection, parasite cells entered the stele; however, this did not lead to successful establishment of the parasite.

Chemical composition of Casparian strips isolated from Clivia miniata Reg. roots: evidence for lignin

Endodermal cell walls and xylem vessels were isolated enzymatically from Clivia miniata Reg. roots. Transmission-electron-microscopic investigation of cross-sections of intact C. miniata roots and scanning-electron-microscopic investigation of isolated endodermal cell walls indicated that the root endodermis of C. miniata is essentially in its primary state of development. Isolated Casparian strips and xylem vessels were subjected to two different degradation methods usually applied to prove the existence of lignin, namely, cupric oxide oxidation and thioacidolysis. The reaction products obtained were typical aromatic derivatives of the natural lignin precursors coniferyl and sinapyl alcohols, and, in traces, of p-coumaryl alcohol, indicating the occurrence of lignin in the polymers from both Casparian strips and xylem vessels. The qualitative chemical compositions of the polymers from the two sources were similar, whereas the quantitative compositions were different, indicating that the molecular structure of the lignin polymer in the Casparian strips was different from that in the xylem vessels. Thus, for the first time, direct chemical evidence has been obtained that Casparian strips of C. miniata roots contain lignin as a major cell wall polymer.

The Casparian Strip of Clivia miniata Reg. Roots: Isolation, Fine Structure and Chemical Nature*

AbstractThe root endodermis of Clivia miniata Reg. was successfully isolated using the cell wall degrading enzymes cellulase and pectinase. The enzymes did not depolymerize those regions of the primary cell walls of anticlinal endodermal root cells where the Casparian strips were located. Since the endodermis of C. miniata roots remained in its primary developmental state over the whole root length, endodermal isolates essentially represented Casparian strips. Thus, sufficient amounts of isolated Casparian strips could be obtained to allow further detailed investigations of the isolates by microscopic, histochemical and analytical methods. Scanning electron microscopy revealed the reticular structure of the Casparian strips completely surrounding the central cylinder of the roots. Whereas in younger parts of the root only the anticlinal cell walls of the endodermis remained intact in the isolates, in older parts of the root the periclinal walls also restricted enzymatic degradation due to the deposition of lignin. Extracts of the isolates with organic solvents did not reveal any wax‐like substances which might have been deposited within the cell wall forming a transport barrier, as is the case with cutin and suberin. However, several histochemical and analytical methods (elemental analysis and FTIR spectroscopy) showed that the chemical nature of the Casparian strips of C. miniata roots can definitely be a lignified cell wall. These findings are in complete agreement with studies carried out at the beginning of this century on the chemical nature of the Casparian strips of several other plant species. The implications of these results concerning apoplasmatic transport of solutes and water across Casparian strips are discussed.

Comparative vegetative anatomy and systematics of Spiranthoideae (Orchidaceae)

Abstract The anatomy of leaf, stem and root of plants in the orchid subfamily Spiranthoideae was studied and described from the viewpoint of systematics. Plants were available from most of the geographic range. Tribes Diceratosteleae and Tropidieae show sinuous anticlinal epidermal cell walls in leaves, glandular foliar hairs, tetracytic para-mesoperigenous stomata, unitary tracheary components in the foliar midrib, foliar and cauline stegmata and sclerenchyma, typical cruciate starch grains, thick-walled exodermal, endodermal, and pericyclic cells, and conductive strands of the root embedded in sclerenchyma. The tribe Cranichideae shows straight to curvilinear anticlinal epidermal cell walls in leaves, lack glandular foliar hairs, have variably patterned mesoperigenous stomata, lack sclerenchyma throughout the parts studied, have a binary tracheary component in the foliar midrib, store starch in specialized amyloplasts (spiranthosomes), lack stegmata, have thin-walled exodermal, endodermal, and pericyclic cells, show scalariform thickenings in exodermal cells, and have conductive strands of the root embedded in parenchyma. In Cryptostylis the tracheary component of the foliar midrib is unitary, stomata lack subsidiary cells, starch grains are of the typical cruciate configuration, and passage cells of the endodermis are apparently associated with tilosomes. Anatomical data, when analysed cladistically, support the hypothesis that Spiranthoideae, as currently delimited, are polyphyletic. Corymborkis, Tropidia, and Diceratostele are more closely related to Palmorchis, a likely representative of a basal clade within subfamily Epidendroideae, than to genera of Cranichideae. Likewise, members of Cranichideae are more closely related to Diuris , a representative of subfamily Orchidoideae-tribe Diurideae, than to Corymborkis, Tropidia and Diceratostele. The Corymborkis-Tropidia-Diceratostele -basal epidendroid (Palmorchis) clade may be diagnosed by the foliar synapomorphies of sinuous anticlinal walls of epidermal cells and presence of glandular hairs. The Cranichideae-orchidoid (Diuris) clade may be diagnosed by its variably patterned, mesoperigenous stomata, lack of vascular bundle sclerenchyma, absence of stegmata, unthickened endodermal cell walls in roots, and conductive cells of roots embedded in parenchyma. Relationships within this clade are quite unresolved, when only anatomical data are employed; however all studied genera of Cranichideae, except Cryptostylis, posess a binary tracheary component in the foliar midrib. Cranichideae, excluding Cryptostylis, may be considered monophyletic. All Cranichideae, except Hetaeria and Cryptostylis , possess spirathosomes. Hetaeria may be a basal member within Cranichideae. We consider the phylogenetic position of Crptostylis , in relation to Cranichideae vs. Diurideae, to be equivocal.

Comparative vegetative anatomy and systematics of Spiranthoideae (Orchidaceae)

The anatomy of leaf, stem and root of plants in the orchid subfamily Spiranthoideae was studied and described from the viewpoint of systematics. Plants were available from most of the geographic range. Tribes Diceratosteleae and Tropidieae show sinuous anticlinal epidermal cell walls in leaves, glandular foliar hairs, tetracytic para-mesoperigenous stomata, unitary tracheary components in the foliar midrib, foliar and cauline stegmata and sclerenchyma, typical cruciate starch grains, thick-walled exodermal, endodermal, and pericyclic cells, and conductive strands of the root embedded in sclerenchyma. The tribe Cranichideae shows straight to curvilinear anticlinal epidermal cell walls in leaves, lack glandular foliar hairs, have variably patterned mesoperigenous stomata, lack sclerenchyma throughout the parts studied, have a binary tracheary component in the foliar midrib, store starch in specialized amyloplasts (spiranthosomes), lack stegmata, have thin-walled exodermal, endodermal, and pericyclic cells, show scalariform thickenings in exodermal cells, and have conductive strands of the root embedded in parenchyma. In Cryptostylis the tracheary component of the foliar midrib is unitary, stomata lack subsidiary cells, starch grains are of the typical cruciate configuration, and passage cells of the endodermis are apparently associated with tilosomes. Anatomical data, when analysed cladistically, support the hypothesis that Spiranthoideae, as currently delimited, are polyphyletic. Corymborkis, Tropidia, and Diceratostele are more closely related to Palmorchis, a likely representative of a basal clade within subfamily Epidendroideae, than to genera of Cranichideae. Likewise, members of Cranichideae are more closely related to Diuris , a representative of subfamily Orchidoideae-tribe Diurideae, than to Corymborkis, Tropidia and Diceratostele. The Corymborkis-Tropidia-Diceratostele -basal epidendroid ( Palmorchis) clade may be diagnosed by the foliar synapomorphies of sinuous anticlinal walls of epidermal cells and presence of glandular hairs. The Cranichideae-orchidoid ( Diuris) clade may be diagnosed by its variably patterned, mesoperigenous stomata, lack of vascular bundle sclerenchyma, absence of stegmata, unthickened endodermal cell walls in roots, and conductive cells of roots embedded in parenchyma. Relationships within this clade are quite unresolved, when only anatomical data are employed; however all studied genera of Cranichideae, except Cryptostylis, posess a binary tracheary component in the foliar midrib. Cranichideae, excluding Cryptostylis, may be considered monophyletic. All Cranichideae, except Hetaeria and Cryptostylis , possess spirathosomes. Hetaeria may be a basal member within Cranichideae. We consider the phylogenetic position of Crptostylis , in relation to Cranichideae vs. Diurideae, to be equivocal.

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye (Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16‐ or 24‐h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24‐h photoperiod in 20°C plants and at a 16‐h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.

A Contribution to the Root Study of the Evergreen Sclerophylls Anatomy of the Primary Root of Quercus coccifera L.

The structure of the primary root of Quercus coccifera , an evergreen sclerophyllous species common in maquis formations in Greece, has been studied by light and electron microscopy with special reference to the differentiation of endodermis. Histochemical identification of phenolic compounds in root tissues has also been carried out. Polyphenolic compound accumulation and extremely thin radial walls of endodermal cells observed in these roots are proposed to be adaptations contributing to a more effective water uptake and transport by the plant.

Magnesium Deficiency Results in Increased Suberization in Endodermis and Hypodermis of Corn Roots

The composition of the aliphatic components of suberin in the stele and cortex of young corn (Zea mays L.) roots was determined by combined gas-liquid chromatography/mass spectrometry of the LiAlD(4) depolymerization products. omega-Hydroxy acids were shown to be the major class of the aliphatic components of both the hypodermal (35%) and endodermal (28%) polymeric materials with the dominant chain length being C(24) in the former and C(16) in the latter. Nitrobenzene oxidation of the roots generated p-hydroxybenzaldehyde and vanillin with much less syringaldehyde. Electron microscopic examination of the hypodermal and endodermal cell walls from roots of corn plants grown in a Mg(2+) -deficient (0.03 millimolar) nutrient solution showed that these walls were more heavily suberized than the analogous walls of roots from plants grown in normal (2 millimolar) Mg(2+) levels. Analysis of the LiAlD(4) depolymerization products of the suberin polymers from these roots showed that the roots grown in low Mg(2+) had 3.5 times as much aliphatic suberin monomers on a weight basis as the roots from plants grown in nutrient with normal Mg(2+) levels. Roots from plants grown in Mg(2+) -deficient nutrient solution released 3.8 times the amount of aromatic aldehydes upon nitrobenzene oxidation as that released from normal roots. As the degree of Mg(2+) deficiency of the nutrient solution was increased, there was an increase in the aliphatic and aromatic components characteristic of suberin. Thus, both ultrastructural and chemical evidence strongly suggested that Mg(2+) deficiency resulted in increased suberization of the cell walls of both hypodermis and endodermis of Zea mays roots. The roots from Mg(2+) -deficient plants also had a higher amount of peroxidase activity when compared to control roots.