Number Of Xylem Vessels Research Articles

Anatomical root variations in response to water deficit: wild and domesticated common bean (Phaseolus vulgaris L)

Root anatomical responses to water deficit are diverse and regulation of water uptake strongly depends on plant anatomy. The ancestors of common bean (Phaseolus vulgaris L.) cultivars are the wild common beans. Because wild beans adapt and survive well in the natural environment, it is hypothesized that wild common bean roots are less affected than those of domesticated beans at low substrate water potential (ψW). A wild common bean accession from Chihuahua Mexico and cv. Bayomex were studied. Seedlings with a mean root length between 3 and 4 cm were maintained for 24 h in vermiculite at ψW of -0.03 (well hydrated), -0.65, -1.48 and -2.35 MPa (partially dry). Ten anatomical characteristics of differentiation and cell division in root regions were evaluated. Thickness of epidermis and protoderm diminished similarly in wild and domesticated beans growing at low substrate ψW (between -0.65 and -2.35 MPa). At the same time, parenchymatic cell area diminished by 71 % in the domesticated variety, but by only 32 % in the wild bean at -2.35 MPa. The number of cells in the cortex and the thickness of the xylem wall increased in both wild and domesticated beans at low substrate ψW; nevertheless, the effect was significantly lower in the wild bean. The number of xylem vessels increased in the cultivar (up to 40 %) while in the wild bean it decreased (up to 33 %). The diameter of xylem vessels and transverse root area diminished (15 and 57 %, respectively) in the cultivar, but in the wild common bean were not affected. Anatomical root characteristics and their modifications in both differentiation and cell division in root regions demonstrated that the wild bean reacted quite differently to substrate ψW than the domesticated common bean.

The impact of the overexpression of human UDP-galactose transporter gene hUGT1 in tobacco plants

When the human UDP-galactose transporter 1 gene (hUGT1) was introduced into tobacco plants, the plants displayed enhanced growth during cultivation, and axillary shoots had an altered determinate growth habit, elongating beyond the primary shoots and having a sympodial growth pattern similar to that observed in tomatoes at a late cultivation stage. The architecture and properties of tissues in hUGT1-transgenic plants were also altered. The leaves had an increase in thickness, due to an increased amount of spongy tissue, and a higher content of chlorophyll a and b; the stems had an increased number of xylem vessels and accumulated lignin and arabinogalactan proteins (AGPs). Some of these characteristics resembled a gibberellin (GA)-responsive phenotype, suggesting involvement of GA. RT-PCR-based analysis of genes involved in GA biosynthesis suggested that the GA biosynthetic pathway was not activated. However, an increase in the proportion of galactose in polysaccharide side chains of AGPs was detected. These results suggested that because of higher UDP-galactose transport from the cytosol to the Golgi apparatus, galactose incorporation into polysaccharide side chains of AGP is involved in the gibberellin response, resulting in morphological and architectural changes.

Anatomical changes induced by increasing NaCl salinity in three fodder shrubs, Nitraria retusa, Atriplex halimus and Medicago arborea

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Plants were harvested after 120 days of salt-treatment. The present study was designed to study the effect of salinity on root, stem and leaf anatomy, water relationship, and plant growth in greenhouse conditions. Salinity induced anatomical changes in the roots, stems and leaves. The cuticle and epidermis of N. retusa and A. halimus stems were unaffected by salinity. However, root anatomical parameters (root cross section area, cortex thickness and stele to root area ratio), and stem anatomical parameters (stem cross section area and cortex area) were promoted at 100–200 mM NaCl. Indicating that low to moderate salinity had a stimulating effect on root and stem growth of these xero-halophytic species. At higher salinities, root and stem structures were altered significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea, they were strongly altered as salinity rose. NaCl (100–300 mM) reduced leaf water content by 21.2–56.2% and specific leaf area by 51–88.1%, while increased leaf anatomical parameters in M. arborea (e.g. increased thickness of upper and lower epidermis, palisade and spongy mesophyll, entire lamina, and increased palisade to spongy mesophyll ratio). Similar results were evidenced in A. halimus leaves with salinity exceeding 100 mM NaCl. Leaves of N. retusa were thinner in salt-stressed plants while epidermis thickness and water content was unaffected by salinity. The size of xylem vessel was unchanged under salinity in the leaf’s main vein of the three species while we have increased number in M. arborea leaf main vein in the range of 200–300 mM NaCl. A longer distance between leaf vascular bundle, a reduced size and increased number of xylem vessel especially in stem than in root vascular system was evidenced in M. arborea treated plants and only at (400–800 mM) in the xero-halophytic species. The effects of NaCl toxicity on leaf, stem and root ultrastructure are discussed in relation to the degree of salt resistance of these three species. Our results suggest that both N. retusa and A. halimus show high tolerance to salinity while M. arborea was considered as a salt tolerant species.

Scanning Electron Microscopy Reveals Different Response Pattern of Four Vitis Genotypes to Xylella fastidiosa Infection.

The xylem-limited bacterium Xylella fastidiosa causes Pierce's disease (PD), whose disease symptoms are primarily the result of xylem vessel blockage in susceptible grapevines. Stem internode and petiole tissues from infected and uninfected control plants of four grape genotypes (Vitis vinifera, V. rufotomentosa, V. smalliana, and V. arizonica/candicans) differing in PD susceptibility were examined using scanning electron microscopy (SEM). Tyloses, fibrillar networks, and gum plugs were observed in lumens of tracheary elements in petioles and internodes of both water-inoculated control plants and X. fastidiosa-inoculated plants of all genotypes. Bacteria were not observed in control plants. In both petiole and internode tissues, the greatest number of occluded xylem vessels were observed in V. vinifera and the smallest number in V. arizonica/candicans. The number of xylem vessels infested with X. fastidiosa was greatest in V. vinifera and did not differ among the other three genotypes. Systemic infection was found in all genotypes. The frequency with which X. fastidiosa infested vessels were observed using SEM corresponded well with bacterial levels estimated by enzyme-linked immunosorbent assay. Among infected plants, tylose formation in internodes was lowest in V. arizonica/candicans and did not differ among the other three genotypes. Infection with X. fastidiosa strongly induced tylose formation in V. vinifera and V. smalliana but not in V. arizonica/candicans. Analysis across tissues and genotypes indicated an induction of fibrillar networks and gum occlusions in response to X. fastidiosa infection, whereas treatment comparisons within genotypes were not significant except for V. vinifera petioles. Limiting the spread of X. fastidiosa infection by xylem conduit occlusions does not appear to be the mechanism conferring PD resistance or tolerance to V. arizonica/candicans, V. smalliana, or V. rufotomentosa. In contrast, the strong induction of tyloses may be detrimental rather than beneficial for V. vinifera survival after X. fastidiosa infection.

Effects of water stress and night temperature preconditioning on water relations and morphological and anatomical changes of Lotus creticus plants

The water relations and anatomical and morphological changes of Lotus creticus sub. creticus seedlings to two irrigation treatments (water stress and control) and temperature (unheated and night-heated greenhouse) was investigated in nursery conditions. Shoot and root growth, leaf stomatal density, leaf trichome density, xylem vessels in roots and stems and water relations were studied because of their relation with drought resistance. Water stress led to substantial losses in dry weight, leaf area, root dry weight and length. The limited osmotic adjustment reached by the plants may not maintain leaf turgor and growth. In general deficit irrigation produced Lotus plants with greater leaf trichome densities and number of xylem vessels of stems and roots. Night-time heating had little influence on these aspects, temperature reduced leaf water potential of water stressed plants but had no effect on well-watered plants. Deficit irrigation under nursery conditions induced a suite of morphological and physiological adaptations (reduction in leaf area, development of osmotic adjustment, increments of leaf hairs and number of xylem vessels of stem and roots) that might allow a considerable capacity to adapt to adverse conditions after transplanting.

The response to exogenous abscisic acid of the roots of notabilis and its wild-type tomato under drought stress

To determine whether exogenous abscisic acid (ABA) changes the anatomy of root tissue under stress, an ABA-deficient mutant tomato, notabilis, and its wild type, the cultivar Ailsa Craig, were exposed to drought stress. Plants were grown for four weeks under controlled conditions. Then they were exposed to ABA (10-5 M) for 6 days under drought or well-watered conditions. Exogenous ABA and/or drought increased the number of xylem vessels in notabilis. Endodermis layer appeared clearly in drought-stressed and/or ABA-treated notabilis. Exogenous ABA increased cambium layers in wild type but drought decreased them. On the other hand, these layers were not visible clearly in ABA-applied notabilis under drought. ABA significantly induced differentiation of pith section of notabilis. The wild type already possesses sclerenchymatic pith section under normal conditions. However, sclerenchymatic pith section only formed in notabilis when ABA was applied under drought stress. It was concluded that exogenous ABA in r...

Influence of xylem development on axial hydraulic conductance within Prunus root systems

The effect of secondary growth on the distribution of the axial hydraulic conductance within the Prunus root system was investigated. Secondary growth resulted in a large increase in both the number (from about 10 to several thousand) and diameter of xylem vessels (from a few micrometres to nearly 150 µm). For fine roots (<3 mm), an increase in root diameter was correlated with a slight increase in the number of xylem vessels and a large increase in their diameter. Conversely, for woody roots, an increase in root diameter was associated with a dramatic increase in the number of xylem vessels, but little or no change in vessel diameter. The theoretical axial conductivity (Kh, m4.s–1.MPa–1) of root segments was calculated with the Poiseuille-Hagen equation from measurements of vessel diameter. Kh measured using the tension-induced technique varies over several orders of magnitude (7.4×10–11 to 5.7×10–7 m4.s–1.MPa–1) and shows large discrepancies with theoretical calculated Kh. We concluded that root diameter is a pertinent and useful parameter to predict the axial conductance of a given root, provided the root type is known. Indeed, the relationship between measured Kh and root diameter varies according to the root type (fine or woody), due to differences in the xylem produced by secondary growth. Finally, we show how the combination of branching pattern and axial conductance may limit water flow through root systems. For Prunus, the main roots do not appear to limit water transfer; the axial conductance of the main axes is at least 10% higher than the sum of the axial conductance of the branches.

Induced Resistance by Penicillium oxalicum Against Fusarium oxysporum f. sp. lycopersici: Histological Studies of Infected and Induced Tomato Stems

ABSTRACT Tomato (Lycopersicon esculentum) plants of 'Lorena' were induced with a conidial suspension (10(7) conidia per ml) of Penicillium oxalicum before inoculation with Fusarium oxysporum f. sp. lycopersici, the wilt pathogen. Histological changes occurred in plants under both growth chamber and glasshouse culture conditions and there was a reduction of disease severity. In noninduced plants, the pathogen produced almost a complete loss of cambium (75 to 100% reduction), an increase in the number of bundles, and a decrease in the number of xylem vessels (20% reduction), in which the diameter also was reduced by 20 to 30% in hypocotyls and epicotyls. The percentage of vessels colonized by F. oxysporum f. sp. lycopersici was positively correlated to the area under the disease progress curve (AUDPC). However, plants induced with P. oxalicum showed less disease, did not lose the cambium, had a lower number of bundles, and had less vascular colonization by F. oxysporum f. sp. lycopersici (35 to 99%). These effects also were observed in 'Precodor', which is susceptible to races 1 and 2 of F. oxysporum f. sp. lycopersici, and partially in 'Ramón', which is resistant to both races. Renewed or prolonged cambial activity that led to the formation of additional secondary xylem could be one of the reasons for disease reduction in P. oxalicum-induced tomato plants.

Stem anatomical characters in relation to tree vigour in mango ( Mangifera indica L.)

Studies conducted with 24 mango cultivars of widely varying vigour indicated that low vigour of trees was associated with a higher primary phloem to primary xylem ratio in young shoots. Width of cortex or pith did not show any relationship with tree vigour. There was no significant difference among the cultivars with respect to the number of xylem vessels or size of metaxylem vessels. Higher phloem to xylem ratio was also observed in the case of trees of cultivar ‘Alphonso’ dwarfed by the external application of paclobutrazol mainly due to fewer xylem vessels and smaller diameter for the metaxylem vessels. The radial width of half pith was also drastically reduced by the chemical but those of cortex and phloem were unaffected. Since there was significant negative association of phloem to xylem ratio with tree vigour and size, this character could possibly be employed in the early screening of genotypes for tree vigour.

Path-coefficient analysis of anatomical characters affecting peg strength in groundnut

Correlation and path-coefficient analysis for anatomical characters affecting peg strength was carried out in eleven strains of groundnut. Bundle cap length and number of xylem vessels per vascular bundle showed a significant positive correlation with peg strength. Path-coefficient analysis revealed that bundle cap length had the highest direct positive effect on peg strength whereas number of xylem vessels per vascular bundle played only a minor role directly. All the characters positively affected peg strengh in an indirect manner mostly via bundle cap lengh. All other direct effects and such indirect effects where bundle cap length was not involved were found to be unimportant. Thus bundle cap length emerged as a reliable anatomical character which can serve as a selection criterion in breeding cultivars with strong pegs to reduce harvesting losses in groundnut.

Water Flow Through Cotton Roots in Relation to Xylem Anatomy

Oosterhuis, D. M. and Wullschleger, S. D. 1987. Water flow through cotton roots in relation to xylem anatomy.—J. exp. Bot. 38: 1866-1874. The effect of root anatomy on water flow was studied in 7-d-old cotton (Gossypium hirsutum L.) seedlings grown in solution culture. The total water flux of the intact root system was measured using a pressure chamber. Then successive terminal root sections were removed at 2,6,10 and 12 cm behind the root tip and the flux was remeasured after each successive cut was made. Xylem development at different distances behind the root apex was studied with a microscope using sections cut free-hand and stained with toluidine blue. Water flux increased with the removal of successive terminal root sections and this coincided with the degree of basipetal primary xylem development. The large increase in water flux at 10 to 12 cm was associated with secondary xylem development and increased xylem vessel number. A comparison of water flow and xylem anatomy between roots with tetrarch (Stoneville 506 and Deltapine 41) and pentarch (T25 strain) vascular bundle arrangements showed no significant differences in the measured values of water flux for the primary root. Water flux, estimated using Poiseuille's equation and measured xylem dimensions, was greater for the tetrarch roots, primarily because of the larger diameter of individual vessel elements. The increased number of vessel elements in the pentarch primary root of T25 did not result in any apparent decrease in axial resistance to water flow.

THE EFFECT OF WATERLOGGING ON SEEDLINGS OF EUCALYPTUS MARGINATA

SummaryThree‐ to four‐month‐old Eucalyptus marginata Donn ex Sm. (jarrah) were grown in the glasshouse in peat/sand at 20 °C root temperature, and either waterlogged continuously for up to 14 d, or waterlogged for a shorter time and then drained. During waterlogging, the O2 concentration of the soil solution declined to less than 1 mg l−1within 1 d. There was an increase in the resistance to water movement into or through the plant within 4 d of flooding the pots. The number of xylem vessels blocked by tyloses increased with the duration of flooding, and did not increase further when waterlogging ceased. The transpiration rate of plants continuously waterlogged and maintained in a dry atmosphere for 13d was closely correlated (r =− 0.98) with the proportion of occluded vessels in the tap‐root. The rate at which wilting developed depended on both the duration of waterlogging and the transpiration rate.

VASCULAR BUNDLES IN PETIOLES OF SOME HERBACEOUS AND WOODY DICOTYLEDONS

Structure and distribution of vascular bundles (VB) have been investigated in petioles of 26 herbaceous and woody dicotyledons. No single pattern of vascular bundle distribution could be found for both groups of plants. Both groups of plants had VB patterns ranging from a cylinder to separate bundles arranged in a variety of patterns, e.g., distorted cylinder, various configurations of a crescent, and other types. The total number of xylem vessels in herbaceous and woody plant petioles varied between 110 and 1756.

Resistance to water flow in the intracoleoptile internode of wheat

Measurements of xylem vessel number and radii in the seminal roots and intra-coleoptile internode (I.C.I.) of five wheat genotypes showed that the conducting capacity of the I.C.I. was close to the main seminal axis, and would restrict flow when the usual 3–5 seminal axes contributed to uptake. The length and hence resistance of the I.C.I. increased with sowing depth, whilst xylem diameter also fell in two genotypes, which would further restrict flow. The resistance per unit length of I.C.I., assuming Poiseuille flow, was 4×10−4 cm−4 day MPa. A pressure drop of 0.15 MPa along an I.C.I. 5 cm long would be required to maintain transpiration under typical field conditions in southern Australia in spring.

Image-analyzing computer in plant science: more and larger vascular rays in sugar maples of high sap and sugar yield

The total area and number of xylem rays and vessels from tangential and cross sections of twigs of 12 sugar maples (Acer saccharum Marsh.) were determined by the use of an image-analyzing computer. A nested analysis of variance indicated that xylem rays of trees of high sap and sugar yield are more numerous and larger than the rays of other sugar maples. The total area and number of xylem vessels were about the same in all 12 trees.

The response of ethylene-treated tomato plants to infection by Verticillium albo-atrum

Tomato plants cv. Craigella susceptible (S) and resistant (R) to Verticillium albo-atrum were gassed with ethylene at different concentrations immediately following inoculation with the pathogen. Partial resistance was conferred on the S isoline and almost complete resistance on R plants. Stem height, leaf area, leaf number and water content of inoculated plants were all significantly increased in S plants compared with ungassed controls. Microscopic examination of inoculated gassed plants showed an increase in the number of xylem vessels, particularly at the base of plants, accompanied by a reduction in the number of vessels containing hyphae. Tyloses were few in S plants and numbers were unaffected by ethylene. Tylosis was greater in R plants and numbers were increased following exposure to ethylene. Exogenous ethylene had no effect on endogenous ethylene production. Host 1,3-β-glucanase activity was increased in leaves following gassing of whole plants, and in gassed excised stem segments. Chitinase, peroxidase and phenylalanine ammonia lyase were unaffected or depressed after ethylene gassing. Polyphenoloxidase activity increased significantly in diseased tissue and in gassed excised stem segments, but not following gassing of intact plants. No interaction of ethylene and tissue wounding could be demonstrated. No evidence was found of enhanced antifungal substances, or rishitin specifically, following gassing with ethylene. It was concluded that ethylene-induced resistance resulted from a net increase in fungus-free vascular tissue. The hypothesis was advanced for a multiple rôle for ethylene in vascular with pathogenesis; as an inducer of resistance and also as a toxin synergist when interacting with pathogenic metabolites after the establishment of the pathogen.

Effects of phosphorus deficiency on anatomical structures in maize (&lt;i&gt;Zea mays&lt;/i&gt; L.)

Anatomical response of maize (Zea mays L.) to phosphorus deficiency grown in sand culture and half strength Hoagland solution revealed that phosphorus deficiency caused a decrease in diameter of the root and stem as well as thickness of the leaf. Epidermal cells of the root, stem and leaf became thickened, cortical zone of root and stem was reduced, endodermal and pericycle cells became smaller and thick walled in phosphorus deficient plants. The prominent structural changes due to phosphorus deficiency occurred in the vascular system where the vascular area is decreased with less number of xylem vessels and smaller size of the cavity. Phosphorus deficiency also resulted in decreased number and smaller sized stomata in leaves. Key words: Phosphorus deficiency; Anatomy; Maize; Zea mays L. DOI: 10.3329/bjb.v39i1.5527Bangladesh J. Bot. 39(1): 57-60, 2010 (June)