Xylem Percentage Research Articles

Variations in Pedicel Structural Properties Among Four Pear Species (Pyrus): Insights Into the Relationship Between the Fruit Characteristics and the Pedicel Structure.

Fruit pedicel is the bridge linking the parent tree and the fruit, which is an important channel for water and nutrients transport to the fruit. The genetic specificity determines the characteristics of the pedicel and the fruit, but the relationship between the pedicel structure and the fruit characteristics is unexplored. Combining the investigation of fruit characteristics, the statistical analysis of the pedicel structural properties, and the 2D and 3D anatomical observation of the pedicel, this study found distinctive contributions of the pedicel elements to the fruit characteristics in four pear species. The European pear (Conference) showed distinct fruit shape index and pedicel structural properties compared with the oriental pears (Akizuki, Yali, and Nanguoli). The fruit size positively correlated with pedicel length, fiber area, pedicel diameter, the area percentage of the cortex, and the area percentage of phloem; however, fruit firmness and soluble solids concentration are showed a stronger positive correlation with xylem area, pith area, the area percentage of xylem, the area percentage of sieve tube, and the area percentage of pith. Pedicel elements, including pith, fiber, and cortex, likely play a certain role in the fruit growth due to the variations of their characteristics demonstrated in the four pear species. The porosity, the ratio of the surface area to the volume, and the spatial arrangement of the vessels showed significant variations across the pear species, indicating the distinction of the hydraulic conductance of the pedicels. Our findings provided direct evidence that pedicel structural elements contributed distinctively to the fruit characteristics among pear species.

Anatomical and Morphological Changes with Needle Removal Treatments on the Seedlings of Pinus nigra Arn. (Anatolian black pine)

The effect of needle removal treatments on the morphology, anatomy and wood density was less studied in the literature. Therefore, the aim this study was to investigate the effect of needle removal on the morphological, anatomical and wood density properties of the seedlings of Pinus nigra Arn. (Anatolian black pine). The needles of the seedlings were removed in four different amounts (0%, 25%, 50% and 75%) to determine whether there is a relationship between the properties of seedlings and the needle removal treatments. The morphological (stem diameter, node numbers, pith percentage, bark percentage, xylem percentage), anatomical properties (average annual ring width, tracheid number per mm2, tracheid height/width, tracheid lumen width, tracheid wall thickness, ray number per mm2, ray height/width) and wood densities were individually determined for each treatment. The morphological results showed that stem diameter was greatest in 0% and 25% needle removal treatments than that of two treatments. Bark% was also found to be higher in the 0% needle removal treatments than others. However, node numbers, pith% and xylem% did not differ significantly between four removal treatments. The density results showed that the seedlings of 0% and 25% needle treatments were denser than 50% and 75% needle removal treatments. The results of anatomical analysis also found surprising results between four treatments. Ray height/width, tracheid number per mm2and tracheid length were significantly greater in the 0% removal of needles than that of three treatments. 25% needle removal treatment also showed larger tracheid area and tracheid wall thickness than that of three needle removal treatments.

Relationships between population traits, nonstructural carbohydrates, and elevation in alpine stands of Vaccinium myrtillus.

PremiseDespite great attention given to the relationship between plant growth and carbon balance in alpine tree species, little is known about shrubs at the treeline. We hypothesized that the pattern of main nonstructural carbohydrates (NSCs) across elevations depends on the interplay between phenotypic trait plasticity, plant–plant interaction, and elevation.MethodsWe studied the pattern of NSCs (i.e., glucose, fructose, sucrose, and starch) in alpine stands of Vaccinium myrtillus (above treeline) across an elevational gradient. In the same plots, we measured key growth traits (i.e., anatomical stem features) and shrub cover, evaluating putative relationships with NSCs.ResultsGlucose content was positively related with altitude, but negatively related with shrub cover. Sucrose decreased at high altitude and in older populations and increased with higher percentage of vascular tissue. Starch content increased at middle and high elevations and in stands with high shrub cover. Moreover, starch content was negatively related with the number of xylem rings and the percentage of phloem tissue, but positively correlated with the percentage of xylem tissue.ConclusionsWe found that the increase in carbon reserves across elevations was uncoupled from plant growth, supporting the growth limitation hypothesis, which postulates NSCs accumulate at high elevation as a consequence of low temperature. Moreover, the response of NSC content to the environmental stress caused by elevation was buffered by phenotypic plasticity of plant traits, suggesting that, under climate warming conditions, shrub expansion due to enhanced plant growth would be pronounced in old but sparse stands.

The cell regeneration and connection of grafting between pear and quince trees are defined by the cortex and phloem

Pear cultivation in the tropics currently requires the complex use of Pyrus calleryana or Chaenomeles sinensis rootstocks with Cydonia oblonga interstocks. The objective of the present study is to quantify the different proportions of tissues in rootstock-interstock combinations established to obtain saplings. Packham's Triumph pear (scion) was double grafted by cleft grafting onto interstocks of C. oblonga and these combinations were subsequently grafted onto C. sinensis or P. calleryana rootstocks. The sprouting percentage was evaluated passed 150 days. Subsequently, the anatomy of the connections between the scion and interstock and the interstock and rootstock was examined. The following characteristics were evaluated: xylem parenchyma ray area of each grafting component (scion, interstock and rootstock); total connection area; connection areas between xylem-xylem, phloem-phloem, phloem-cortex, and cortex-cortex; percentage of xylem, phloem, and cortex for all materials; rootstock area; interstock area; scion area; rootstock/interstock connection area; interstock/scion connection area; and areas with no connection or with necrosis. The data were subjected to analysis of variance and the Scott-Knott test (P ≤ 0.05), and correlations between tissue percentages and connection areas were calculated and considered significant when R2 ≥ 0.6. Only the tissues composing the cortex and phloem were positively correlated with the connection area. The P. calleryana rootstock has greater compatibility with the interstock due to its greater proportion of cortex. The xylem parenchyma rays do not significantly influence cell regeneration or connection. Therefore, woody species that contain more cortex and phloem in the rootstock and/or scion will have greater potential for grafting success.

Histopathology of roots of three tomato cultivars infected with two separate isolates of the false root-knot nematode Nacobbus aberrans

The plant-parasitic nematode Nacobbus aberrans attacks weeds and cultivated plants, causing drastic crop yield losses. Several tomato cultivars, such as Superman and Mykonos, are produced by Seminis® as nematode resistant and are widely used in Argentina; their specific resistance response to different nematode species, however, is still unknown. In this study we explored the response of tomato cultivars to the infection of N. aberrans isolates, and determined the host status by performing histological analyses and estimating egg mass index (EMI). Two Argentina isolates (from Lules-Tucuman and Rio Cuarto-Cordoba) were tested separately in plants of Superman, Mykonos and Platense cultivars. Plants were maintained in a greenhouse for 90 days; then EMI was estimated in root systems and the material was processed to prepare histological slides and for histochemical test. Infected roots exhibited galls with females and a syncytium (feeding site) developed inside them. The vascular tissues were disorganized and displaced to the periphery; xylem percentage was lower than that in the control plants. All the cultivars were susceptible and developed a close plant-parasite relationship, with Mykonos and Platense cultivars infected with the Lules isolate being the most highly affected, as indicated by their highest EMI values. Superman was the least susceptible cultivar, as evidenced by its lowest EMI values, the amount of starch observed, the presence of thickened cell walls around the nematode and the egg mass, and the low percentage of gall occupied by syncytium.

Forest canopy reduction stimulates xylem production and lowers carbon concentration in fine roots of European beech

Forest canopy reduction is well known to affect the coarse and fine root biomass production. Seasonality, to the same extent, is acknowledged to vary the non-structural carbon content. However, the fine root response in terms of carbon concentration to both canopy cover and seasonal change remains unclear.To this aim, morphological and anatomical traits like xylem percentage, carbon concentration and starch content were measured in mid-summer and early-fall on fine roots of three beech stands differing in canopy cover and basal area.The results highlighted a significant effect of canopy cover on the xylem area percentage throughout the <2mm diameter fine root population, as the lower the canopy cover is, the larger the xylem area is. Moreover, an inverse relationship occurred between carbon concentration and xylem area percentage, highlighting the key role played by this anatomical trait. In order of magnitude, the significant carbon concentration decrease observed 5years after felling was 15kgha−1 for a mean fine root biomass of 200gm−2. For a given xylem percentage, starch concentration seasonal change partially explained the carbon concentration decrease with the incipient dormancy. Root tissue density significantly decreased with soil depth in mature and 15-yr-old conversion stands, whereas it did not in recently cut (5-yr-old) conversion stand.Outcomes are that canopy closure in the mature stand, which increases the fine root standing crop, produced a higher total carbon input into the soil. Moreover, fifteen years since felling appeared sufficient for detecting a clear trend in the recovery of fine root biomass to pre-thinning levels.

Allometric neoteny and the evolution of succulence in cacti

Abstract With the objective of analysing the role of heterochrony in the evolution of succulence in the cactus family, a comparative study of xylem development in six species with contrasting morphologies was carried out. Two woody leaf-bearing cacti and four succulent cactus species belong to different subdivisions within the family were analysed. In each species and for different ages, vessel-element length was measured, vessel-element lateral wall-pitting described and the percentage of xylem and parenchyma in the stem quantified. In the succulent species it was found that vessel element length did not change between juvenile and adult wood, that wall-pitting in adult plants was similar to that of seedlings, and that the woody tissue in adult plants was organized in vascular bundles as in the primary tissue of seedlings. Leaf-bearing cacti, in contrast, changed in both vessel element length and wall-pitting when secondary wood was produced, and the secondary woody tissue of adult plants was organized in a continuous cambial cylinder as in most dicotyledons. An allometric analysis suggests that a retardation in the developmental rate of woody tissues (allometric neoteny) is the main mechanism in the development of succulence in cacti.

Allometric neoteny and the evolution of succulence in cacti

With the objective of analysing the role of heterochrony in the evolution of succulence in the cactus family, a comparative study of xylem development in six species with contrasting morphologies was carried out. Two woody leaf-bearing cacti and four succulent cactus species belong to different subdivisions within the family were analysed. In each species and for different ages, vessel-element length was measured, vessel-element lateral wall-pitting described and the percentage of xylem and parenchyma in the stem quantified. In the succulent species it was found that vessel element length did not change between juvenile and adult wood, that wall-pitting in adult plants was similar to that of seedlings, and that the woody tissue in adult plants was organized in vascular bundles as in the primary tissue of seedlings. Leaf-bearing cacti, in contrast, changed in both vessel element length and wall-pitting when secondary wood was produced, and the secondary woody tissue of adult plants was organized in a continuous cambial cylinder as in most dicotyledons. An allometric analysis suggests that a retardation in the developmental rate of woody tissues (allometric neoteny) is the main mechanism in the development of succulence in cacti.

Association of Selected Plant Traits with Lodging of Four Determinate Soybean Cultivars

Lodging of soybean [Gfycine max (L.) Merr.] frequently reduces seed yield and quality, especially in high‐yield environments. Breeding for resistance to plant lodging is high priority in most soybean programs, but information is limited on effective techniques to evaluate this trait. This study was conducted to measure the association of selected plant traits with lodging score at maturity. Field and laboratory experiments were conducted to evaluate lodging of four determinate Maturity Group V cultivars: Essex, Narow, Forrest, and Mack. Based on four environments, Essex had the lowest lodging score (least lodging), Mack the highest score, and Narow and Forrest were intermediate. Lodging score was significantly (P ≤ 0.01) correlated with plant height at three reproductive stages, R4, R6, and R8, but not at the V8 stage. Length and diameter of basal and centrally located internodes generally were not significantly (P &gt; 0.05) associated with lodging score. Bark percentage at Stage R8 was negatively correlated with lodging score. In contrast, there was a significant (P ≤ 0.05) positive association between lodging score and xylem width and xylem percentage at Stages R6 and R8. The capacity of the plant to recover a more vertical position, measured by the angle of the stem from horizontal after bending for 4 s at R6 and R8, was negatively correlated with lodging score at maturity. Stem stiffness was measured in the laboratory by the distance a specific weight bent the stem and by the weight required to bend the stem a specific distance. Stem stiffness generally was not associated with resistance to lodging. Results indicate that plant resiliency rather than stem stiffness is associated with lodging resistance in these soybean cultivars. Plant height and bark and xylem percentage also were associated with plant lodging and may be of value in breeding for this trait.

NaCl and twig dieback along highways and cold hardiness of highway versus garden twigs

The timing and amount of stem damage and bud kill, along with the Cl content of twigs, were observed over one or two winters in Fraxinus pennsylvanica Marsh, Cornus stolonifera Michx, Malus sp. cv. Hopa, Salix pentandra L., and Syringa vulgaris L. growing along Minnesota highways. Depending on species and the year, damage occurred between January and May.Cold hardiness was compared for highway- and garden-grown Syringa vulgaris L. and Fraxinus pennsylvanica Marsh. Hardiness was assessed as percentage of xylem and cambial browning and percentage of bud kill after exposure to test temperatures between −45 and +4 °C. In November, hardiness was the same, but from mid-December into March, highway twigs showed more damage than garden twigs at the same test temperatures. The differences between highway and garden twigs coincided in time with differences in twig Cl.