Xylem Vessel Size Research Articles

Anatomy of the olive inflorescence axis at flowering and fruiting

In spite of the importance of the peduncle and pedicel in supporting and connecting flowers and fruits to the mother plant, these structures are little known in the olive, and more detailed information can be instrumental in studies of fruit development, ripening and abscission. The structure of pedicel and peduncle was studied at flowering and at fruit maturation for the Spanish olive cultivar “Picual”. Both organs have a stem-like structure. At flowering the pedicel is less developed as the transport requirements to individual flowers are minimal compared to that of the complete inflorescence, and the structure has high chances of being shed in the heavy flower abscission in this species. The peduncle is thicker, due to a ridged cortex, and has larger xylem vessel size. By fruit maturation in November, the overall diameter of both pedicel and peduncle increases, due to both conducting tissues and support tissues: in the pedicel the xylem increases 6-fold, in the peduncle 3-fold, while the phloem undergoes smaller increases. An important developmental feature of pedicel and peduncle is the increase in their capacity to mechanically support the growing fruit. To this end both organs, in addition to the increased thickness of the conducting tissues, produce a lignified sclerenchyma ring. Unlike the stem, however, which produces numerous sclereids, the sclerenchymatous ring only consists of fibres, which offer greater flexibility and make the structure less prone to breaking.

Dosage effect of the short arm of chromosome 1 of rye on root morphology and anatomy in bread wheat.

The spontaneous translocation of the short arm of chromosome 1 of rye (1RS) in bread wheat is associated with higher root biomass and grain yield. Recent studies have confirmed the presence of QTL for different root morphological traits on the 1RS arm in bread wheat. This study was conducted to address two questions in wheat root genetics. First, does the presence of the 1RS arm in bread wheat affect its root anatomy? Second, how does root morphology and anatomy of bread wheat respond to different dosages of 1RS? Near-isogenic plants with a different number (0 to 4 dosages) of 1RS translocations were studied for root morphology and anatomy. The F1 hybrid, with single doses of the 1RS and 1AS arms, showed heterosis for root and shoot biomass. In other genotypes, with 0, 2, or 4 doses of 1RS, root biomass was incremental with the increase in the dosage of 1RS in bread wheat. This study also provided evidence of the presence of gene(s) influencing root xylem vessel number, size, and distribution in bread wheat. It was found that root vasculature follows a specific developmental pattern along the length of the tap root and 1RS dosage tends to affect the transitions differentially in different positions. This study indicated that the inherent differences in root morphology and anatomy of different 1RS lines may be advantageous compared to normal bread wheat to survive under stress conditions.

Infection Biology of Moniliophthora perniciosa on Theobroma cacao and Alternate Solanaceous Hosts

The C-biotype of Moniliophthora perniciosa is the causal agent of witches’ broom disease of Theobroma cacao L. While this disease is of major economic importance, the pathogenicity mechanisms and plant responses underlying the disease are difficult to study given the cacao tree’s long life cycle and the limited availability of genetic and genomic resources for this system. The S-biotype of M. perniciosa infects solanaceous hosts, particularly pepper (Capsicum annuum) and tomato (Solanum lycopersicum). These species are much more amenable for performing studies of mechanisms underpinning host-pathogen interactions as compared to cacao. A phylogenetic analysis performed in this study demonstrated that S-biotype strains clustered with C-biotype strains, indicating that these biotypes are not genetically distinct. A comparative analysis demonstrated that disease progression in tomato infected with the S- biotype is similar to that described for cacao infected with the C- biotype. The major symptoms observed in both systems are swelling of the infected shoots and activation and proliferation of axillary meristems. Cellular changes observed in infected tissues correspond to an increase in cell size and numbers of xylem vessels and phloem parenchyma along the infected stem. Observations revealed that fungal colonization is biotrophic during the first phase of infection, with appearance of calcium oxalate crystals in close association with hyphal growth. In summary, despite different host specificity, both biotypes of M. perniciosa exhibit similar disease-related characteristics, indicating a degree of conservation of pathogenicity mechanisms between the two biotypes.

Effects of iron chlorosis and iron resupply on leaf xylem architecture, water relations, gas exchange and stomatal performance of field-grown peach (Prunus persica)

There is increasing evidence suggesting that iron (Fe) deficiency induces not only leaf chlorosis and a decline of photosynthesis, but also structural changes in leaf morphology, which might affect the functionality of leaves. In this study, we investigated the effects of Fe deficiency on the water relations of peach (Prunus persica (L.) Batsch.) leaves and the responses of previously chlorotic leaves to Fe resupply via the root or the leaf. Iron deficiency induced a decline of maximum potential photosystem II (PSII) efficiency (F(V)/F(M)), of rates of net photosynthesis and transpiration and of water use efficiency. Iron chlorosis was associated with a reduction of leaf xylem vessel size and of leaf hydraulic conductance. In the course of the day, water potentials in chlorotic leaves remained higher (less negative) than in green leaves. In chlorotic leaves, normal stomatal functioning was disturbed, as evidenced by the lack of opening upon withdrawal of external CO(2) and stomatal closure after sudden illumination of previously darkened leaves. We conclude that the Fe deficiency induced limitations of xylem conductivity elicited a water saving strategy, which poses an additional challenge to plant growth on high pH, calcareous soils. Fertilisation with Fe improved photosynthetic performance but the proper xylem structure and water relations of leaves were not fully restored, indicating that Fe must be available at the first stages of leaf growth and development.

Hydraulic properties of naturally regenerated beech saplings respond to canopy opening

Enhanced sapling growth in advance regeneration requires gaps in the canopy, but is often delayed after canopy opening, because acclimation of saplings to the new environment is gradual and may last for several years. Canopy opening is expected to result in an increased transpiration because of a larger climatic demand and a higher stomatal conductance linked to the higher rates of photosynthesis. Therefore, we focused on the changes in water relations and the hydraulic properties of beech (Fagus sylvatica L.) saplings during 2 years after canopy opening. We tested the hypothesis that an increase in leaf-specific hydraulic conductance and a decrease in vulnerability to cavitation occur to sustain an enhanced transpiration. Hydraulic conductance of defoliated shoots, vulnerability to cavitation, size and density of xylem vessels as well as stomatal conductance were recorded on saplings growing in shade (S saplings) or in gaps created by opening the canopy (shade-to-light, SL saplings). Hydraulic conductance per unit cross-sectional area (K(AS)) did not differ in the shoots of S and SL saplings. But a higher ratio stem cross-sectional area/leaf area resulted in a higher leaf-specific hydraulic conductance of the shoots (K(AL)) of SL saplings. Contrary to expectations, vulnerability to cavitation increased transitorily in stems during the first year after canopy opening and no difference was observed between the two treatments in light-saturated stomatal conductance. During the second year, vulnerability to cavitation was similar in the S and SL saplings and light-saturated stomatal conductance increased in SL saplings. These results demonstrate a release of the hydraulic constraints after canopy opening with an adjustment of the ratio stem cross-sectional area/leaf area. But the larger vulnerability to cavitation during the first year could limit stomatal opening and therefore the ability of beech saplings to use the available light for photosynthesis and could therefore partly explain why the growth increase was delayed to the second growing season after canopy opening.

Effects of stem anatomical and structural traits on responses to stem damage: an experimental study in the Bolivian Amazon

Persistence of tree species in a habitat depends on their ability to avoid and respond to disturbance-related damage. Responses to stem damage vary among species but typically include bark wound closure and prevention of xylem decay spread. These responses are associated with anatomical, structural, and physiological traits. This study explores how xylem (vessel size and (or) abundance, parenchyma abundance, ray width, and wood density) and phloem (bark thickness, proportion of live inner bark, ray width and (or) dilation, inter-ray distance, and tissue density) traits relate to responses to stem damage in seven species from the Bolivian Amazon. Rates of bark wound closure and radial xylem decay penetration were compared 2 years after experimental damage. A species that closed bark wounds rapidly (100% in Chorisia speciosa A. St.-Hil.) was not efficient at constraining xylem radial decay spread (1.7 mm). The opposite was true for Pseudolmedia laevis (Ruiz & Pav.) J.F. Macbr., a species that closed wounds slowly (30%) but efficiently controlled decay spread (0.5 mm). The relationship between anatomical and (or) structural traits and damage response variables revealed that species with favorable traits for rapid wound closure (e.g., widely dilating rays) had traits that favored xylem decay spread (e.g., low wood density). It is plausible that this apparent trade-off is based on physiological and phylogenetic constraints.

Linking physiological processes with mangrove forest structure: phosphorus deficiency limits canopy development, hydraulic conductivity and photosynthetic carbon gain in dwarf Rhizophora mangle

Spatial gradients in mangrove tree height in barrier islands of Belize are associated with nutrient deficiency and sustained flooding in the absence of a salinity gradient. While nutrient deficiency is likely to affect many parameters, here we show that addition of phosphorus (P) to dwarf mangroves stimulated increases in diameters of xylem vessels, area of conductive xylem tissue and leaf area index (LAI) of the canopy. These changes in structure were consistent with related changes in function, as addition of P also increased hydraulic conductivity (Ks), stomatal conductance and photosynthetic assimilation rates to the same levels measured in taller trees fringing the seaward margin of the mangrove. Increased xylem vessel size and corresponding enhancements in stem hydraulic conductivity in P fertilized dwarf trees came at the cost of enhanced mid-day loss of hydraulic conductivity and was associated with decreased assimilation rates in the afternoon. Analysis of trait plasticity identifies hydraulic properties of trees as more plastic than those of leaf structural and physiological characteristics, implying that hydraulic properties are key in controlling growth in mangroves. Alleviation of P deficiency, which released trees from hydraulic limitations, reduced the structural and functional distinctions between dwarf and taller fringing tree forms of Rhizophora mangle.

Foliar and Axial Aspects of Vascular Differentiation: Hypotheses and Evidence

A comparison is made between foliar and axial vascular differentiation. Current thoughts and new evidence are presented on the role of hormones in controlling the differentiation of vascular tissues in organized and tumorous tissues, focusing on the role of auxin and cytokinin in controlling phloem and xylem relationships, vessel size and density, cambium sensitivity, vascular adaptation and xylem evolution in deciduous hardwood trees. The possible role of wounding is also considered. A new hypothesis, namely, the leaf-venation hypothesis, is proposed to explain the hormonal control of vascular differentiation in leaves of dicotyledonous plants. Experimental evidence in support of the hypothesis is presented showing that hydathodes, the watersecreting glands, are the primary sites of auxin synthesis during leaf morphogenesis. Vessel element patterns similar to those found in hydathodes were experimentally induced by exogenous auxin application.

Growth and Potential Conductivity of White Clover Roots in Dry Soil with Increasing Phosphorus Supply and Defoliation Frequency

Shallow‐rooted white clover can be exposed to severe water stress during dry periods, leading to poor growth and persistence in pastures. Root growth is a primary determinant of drought tolerance and water uptake in dry soils, which may interact with P supply and defoliation frequency for grazed white clover in legume‐based pastures. Effects of four levels of P supply (0, 17, 50, and 150 mg P kg−1 soil), two defoliation frequencies (frequent and infrequent), and two soil water regimes (wet and dry) were determined on various parameters associated with root growth and plant water uptake. A microscopy study was also undertaken to measure the relative size and abundance of xylem vessels in the primary roots of frequently defoliated low (P0) and high P (P150) plants. Increased P supply increased the rate of water loss per pot, which was better related to the coarse root length density compared with the fine root length density in dry soil. Coarse root length density, leaf area, mean number and diameter of xylem vessels, and potential root hydraulic conductance increased 6.2‐, 12.4‐, 2.4‐, 1.5‐, and 12.7‐fold, respectively, for the frequently defoliated plants in dry soil between P0 and P150 treatments. It also appeared that leaf area and rate of water loss were dependent on the mean xylem diameter and associated hydraulic conductance. Increased P supply improved the ability of frequently defoliated white clover plants to tolerate dry soil conditions by lowering the resistance to water flow in roots and increasing the water uptake.

Salinity effects on the xylem vessels in tomato fruit among cultivars with different susceptibilities to blossom-end rot

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...

Interactions between Globodera pallida juveniles, Verticillium dahliae and three potato cultivars, with descriptions of associated histopathologies

Experiments carried out in agar culture showed that the potato cultivar Pentland Javelin is relatively resistant to infection by Verticillium dahliae because it has a multilayered cortex of thick‐walled cells, each producing lignituber appositions to invading hyphae. Its thick‐walled xylem vessels are difficult to penetrate, its large vessel lumens difficult to obstruct, and its ability to produce tyloses limits the spread of the fungus, By comparison. Maris Anchor roots have fewer cortical layers and very small xylem vessels which are more easily blocked by hyphae. Maris Peer is intermediate in both the number of cortical cell layers and the size of xylem vessels. Globodera pallida juveniles assist V. dahliae to evade the natural defences of the root by opening an invasion channel for the fungus. In Maris Anchor and Maris Peer, but not in Pentland Javelin, the nematode provokes a widespread hypersensitive response; the resulting cell wall lignification impedes the growth of those hyphae which invade several days after the nematode. Hyphae grow well in syncytia and this enhances the probability of their penetrating xylem vessels. Although V. dahliae is generally held to induce symptoms through xylem blockage, the phloem colonization which was noted may affect the growth of both plant and nematode through its effect on assimilate movement towards root lips and into syncytia.

Differences in the photosynthetic response to air humidity among rice varieties with special reference to the xylem-vessel size.

Photosynthetic response to air humidity and leaf characters were observed in fourteen rice varieties. In the indica type varieties the water-conduction system relative to their specific leaf weight and leaf nitrogen content was found to be more developed than in the japonica type varieties. The water-conduction system in the leaf was evaluated based on the ratio of the total cross-sectional area of xylem-vessels at the leaf blade, base to the leaf area (RVA). Higher positive correlations between the photosynthetic rates and the RVA, and specific leaf weight were detected under dry than humid air conditions. The present study suggests that RVA may be related to varietal differences in the photosynthetic rate, at least under low air humidity conditions, and that RVA can be used as an index for evaluating the development of the water supply system. The well-developed water conduction svstem of indica type varieties may have evolved as an adaptation to high temperature conditions.

Water Status of Cotton as Related to Taproot Length1

AbstractIn dryland crop areas it is common for plants to depend on subsoil water for some part of the growing season. In this situation, water moves through a considerable length of root axis to reach the plant top. Resistance to this movement of water (axial resistance) can become significant. This experiment was designed to assess the interaction of root geometry and plant water status and to compare values of root resistance calculated for two contrasting cotton (Gossypium hirsutum L.) root systems. Cotton plants were grown in a greenhouse either in pots (26‐cm‐deep) or in soil‐filled tubes (120 cm‐long) supported in base pots. After initial watering of the soil in tubes, only the base pots were watered, so that plants developed long taproots and depended on water in the base pots.Except for the strong development of the taproot with in the tube, little other root growth occurred there because of soil drying. The taproots of pot‐grown plants were not well defined 20 cm from the plant base because of extensive branching. Rooting density in the base pot of plants with long taproots was 5.2 ± 0.7 cm cm−3 and compared with 13.7 — 5.6 cm −3 for plants grown in pots. Plants of the two treatments had similar leaf area, rate of water uptake, and value of both covered and exposed leaf water potential. Within the long taproots many secondary xylem vessels had been laid down. Individual xylem vessel size tended to increase with distance from the plant base. Calculated values of axial resistance (0.0097 cm−3 day bar) for long taproot were less than for the taproot of pot‐grown plants (0.0153 cm−3 day bar) because the increase in equivalent xylem vessel size more than offset the effect of the increased length. Values of total root resistance were calculated from the potential difference between covered leaf water potential and soil water potential divided by the water uptake rate. Total root resistance values were similar, and so, by difference, radial root resistance was larger for the long‐rooted plants. This difference is explained by the difference in rooting density. We concluded that a balance was apparently maintained between the absorbing length of the root system and the longitudinal transport system.

Phenomena associated with the disintegration of fuse wires

Puerariae Lobatae Radix (PLR) and Puerariae Thomsonii Radix (PTR) are traditional Chinese medicines used for the treatment of diabetes and cardiovascular diseases. These two herbs are used interchangeably in clinical practice, even though they possess significantly different chemical profiles. In the case of Pueraria species, the misidentification is related to the multiple Chinese common names in clinical practice and variable pharmaceutical Latin names in different versions of the Pharmacopoeia of the People׳s Republic of China. In addition, there is lack of evidence demonstrating how the differences in the chemical profile would impact on the pharmacological activity of the two herbs. Therefore, the aim of this study was to compare the microscopic, phytochemical profiles and anti-diabetic activity of PLR and PTR so that the two species can be differentiated.The microscopic characteristics of the PLR and PTR were observed and measured by an optical microscope. The major compounds were quantified by ultra-performance liquid chromatography (UPLC) and total flavonoid content (TFC) colorimetric assay. The free radical scavenging capacity was assessed by 2,2-diphenyl-2-picrylhydrazyl (DPPH) antioxidant assays. Anti-diabetic activity was determined by the inhibition of porcine pancreatic α-amylase and rat intestinal α-glucosidase activities.Microscopic results illustrated that the size of xylem vessels (PLR: 0.1390±0.0184 mm; PTR: 0.0471±0.0109 mm), number of fibre per bundle (PLR: 32.6800±2.8780; PTR: 16.5900±0.9982) and the size of fibre (PLR: 0.0075±0.0003 mm2; PTR: 0.0025±0.0002 mm2) in PLR were significantly greater than that in PTR (p<0.01). PLR possessed a significantly lower total starch content (PLR: 0.5288±1.2559 mg starch/g DM; PTR: 76.7954±2.9905 mg starch/g DM) and total dietary fibre content (PLR: 4.2886±0.3466 g/100 g DM; PTR: 12.4148±0.4541 g/100 g DM) as compared to PTR. Isoflavonoids including puerarin, daidzin, genistin and daidzein were the major chemical constituents in both species. However, the average content of puerarin in PLR was found to be eleven times greater than that in PTR. Furthermore, the TFC, DPPH free radical scavenging capacity, anti-α-amylase and anti-α-glucosidase in the PLR extracts were 4.42, 4.91, 3.10 and 4.22 times greater than in the PTR extracts.This study provides a comprehensive investigation on the two medicinal valuable Pueraria species and allows differences to be ascertained. This information can be used to update monographs which will help practitioners and dispensers differentiate the herbs. Further study on the interchangeable use of PLR and PTR in clinical practice is urgently warranted.