Number Of Xylem Cells Research Articles

Intra-annual dynamic of opposite and compression wood formation of Pinus massoniana Lamb. in humid subtropical China

Radial growth of trees can result in opposite wood (OW) and compression wood (CW) due to the varying impact of stem mechanical stress, such as that caused by gravity or wind. Previous research has identified higher xylem production in CW compared to OW. Yet, it remains unclear whether the difference in the number of xylem cells between OW and CW results from differences in growth rate or the duration of xylem cells. In this study, we collected wood microcores on a weekly basis from March 2019 to January 2020 in Pinus massoniana Lamb. located on a steep slope. Our objective was to compare the dynamic of cambial activity and resulting cellular anatomical parameters between OW and CW in a humid subtropical environment. Our results showed that the xylem phenology of OW and CW was generally consistent with the xylem cell division process beginning in early March and ceasing in November. The last latewood cell completed its differentiation at the end of December. The response of wood formation dynamics to climate was consistent in both OW and CW. Moreover, both wood types exhibited a limited development of the enlargement phase due to the heat and drought during the summer. The rate of cell division was responsible for 90.7% of the variability in the number of xylem cells. The CW xylem obtained a larger number of cells by increasing the rate of cell division and displayed thinner earlywood cells with larger lumens than OW cells. Our findings showed that the xylem of conifer species responds to mechanical stress by accelerating the cell division rate. As a result, we suggest calculating the ratio between OW and CW widths to reconstruct wind stress changes rather than calculating the residuals used in the current study.

Genome-Wide Characterization of Laccase Gene Family from Turnip and Chinese Cabbage and the Role in Xylem Lignification in Hypocotyls

The turnip and the Chinese cabbage belong to the Brassica rapa subspecies, yet they have evolved marked differences in morphology. The turnip has a distinct swelled taproot, while the Chinese cabbage has a big leafy head. The turnip’s taproot is developed mainly by the hypocotyl. To explore the taproot formation, we firstly compared the vascular structure of the hypocotyl during the early developmental stages of the turnip and the Chinese cabbage, finding that there were observable differences in the number of xylem cells and the cell-wall lignification in the hypocotyl vascular tissues after the transition from primary to secondary growth. Laccases (LAC) play an important role in lignification by polymerizing monolignols in the cell wall, however, it is not clear whether differences in the lignification levels in the hypocotyl xylem cell walls are related to the genetic variations of the LAC gene family, between the turnip and the Chinese cabbage. Therefore, we systematically characterized the LAC genes from the turnip and the Chinese cabbage, and 27 LAC genes were identified in each. These LAC genes can be divided into six groups, and each LAC in the turnip is closely adjacent to that in the Chinese cabbage. Gene structure, conserved motif, and chromosomal localization were highly conserved between the turnip and the Chinese cabbage. We also compared the expression pattern of the laccases in the different tissues and hypocotyl’s early development stage, and the results clearly showed the different profiles between the turnip and the Chinese cabbage. Following a comprehensive analysis of these results, we predicted that LAC17.1 and LAC17.3 are two candidate genes that participate in the regulation of lignin synthesis during taproot formation. Our results provide a valuable clue for uncovering the regulation mechanism of the lower lignification level in the turnip’s hypocotyl and fundamental information for further studies of the LAC gene family in Brassica rapa.

Anatomical Adaptation of Grey Mangrove (Avicennia marina) Leaf in the Pond and Coast Located in Mangunharjo, Semarang, Central Java

Mangrove is a brackish plant that can live in habitats with extreme environmental conditions. For instance, the grey mangrove (Avicennia marina) is a mangrove species that can adapt anatomically in habitats with a wide range of salinity, such as ponds and coasts. This study examines the forms of anatomical adaptation of A. marina by comparing the anatomical structure of A. marina leaves that live in two different habitats, namely pond, and coast in the Mangunharjo area, Semarang, Central Java. The third leaf from the tip of the tree branches was used as samples and taken from three different trees in each habitat. Cross-section prepared microscope slides of the leaves were made using the embedding method and observed using a photomicrograph. The quantitative data were analyzed using the T-test at a 90% confidence level, while the qualitative data were analyzed descriptively. The results showed that different environmental conditions do not cause differences in the anatomy of A. marina leaves, but there are some histological modifications as a form of adaptation. These modifications are differences in the thickness of the cuticle, adaxial epidermis, parenchymal palisade tissue, spongy parenchyma, and the number of xylem cells in one vascular bundle. This research might initiate more advanced studies regarding the correlation between mangroves’ anatomical structure and anatomical adaptation towards diverse environmental conditions. The results of this study are expected to provide information about the anatomical structure of A. marina leaves that live in two habitats with different environmental conditions.

Auxin concentration and xylem production of Pinus massoniana in a subtropical forest in south China.

Auxin is involved in various developmental processes of plants, including cell division in cambium and xylem differentiation. However, most studies linking auxin and xylem cell production are performed in environments with a strong seasonality (i.e., temperate and boreal climates). The temporal dynamics of auxin and cambial activity of subtropical trees remain basically unknown. In this study, we sampled four microcores weekly in three individuals of Chinese red pine (Pinus massoniana Lamb.) from February to December 2015-16 to compare xylem formation with auxin concentration in subtropical China. During the entire period of sampling, the number of cambial cells varied from 2 to 7, while the number of cells in the enlarging zone ranged from 1 to 4 and from 1 to 5 in the wall-thickening zone. In 2015, the average auxin concentration was 3.46ngg-1, with 33 xylem cells being produced at the end of the year. In 2016, a lower auxin concentration (2.59ngg-1) corresponded to a reduced annual xylem production (13.7 cells). No significant relationship between auxin concentration and number of xylem cells in differentiation was found at the weekly scale. Unlike in boreal and temperate forests, the lack of wood formation seasonality in subtropical forests makes it more difficult to reveal the relationship between auxin concentration and number of xylem cells in differentiation at the intra-annual scale. The frequent and repeated samplings might have reduced auxin concentration in the developing cambium and xylem, resulting in a lower xylem cell production.

The effect of meteorological factors on the formation of the anatomical structure of Pinetum sylvestris myrtilloso-tufosum on a drained peatland

This paper investigated wood structure formation of pure pine stands (Pinus sylvestris L.) depending on meteorological indicators. Influence of average temperature and sum of precipitation on wood structure at the level of annual growth and at the level of xylem cellular structure is presented. Three series of experimental objects in the boreal zone of the European part of Russia was observed: naturally formed mature stands, plots passed by thinning, plots passed by thinning with the fertilizers application. It is shown that fluctuations of average temperature have a more significant role in the formation of the zone of early wood than late wood. Statistical analysis has determined that the effect of average temperature and precipitation factors on the formation of macrostructure elements of wood is higher in the naturally formed stands, than in the stands that have been treated. It was identified that thinning and application of fertilizers increase the role of meteorological factors influence on changes in the number of xylem cells in annual growth. At the same time, the size of xylem cells and the thickness of cell walls are in a more significant correlation with weather factors in stands unaffected by treating.

Anatomical and physiological characteristics of Raphanus sativus L. submitted to different selenium sources and forms application

Increasing food production along with the nutritional value of diets with micronutrients and vitamins (e.g., selenium) is a worldwide concern that can be overcome by many strategies, including agronomic biofortification. This study tested different application forms and sources of selenium (Se) on Raphanus sativus L, assessing for their effects on characteristics such as biomass accumulation and Se content, as well as parameters related to gas exchange and anatomical modifications. The treatments consisted of two sources of Se (sodium selenate and sodium selenite) and two forms of application (soil and foliar application). A control treatment without addition of Se was also included. The experiment was conducted in a completely randomized design with 5 replicates, arranged in a 2 × 2 + 1 factorial scheme. The sources and forms of application did not affect plant biomass accumulation. The application of Se as selenate, via soil, resulted in greater selenium content in the plant, as well as in higher values of photosynthetic rate and instantaneous carboxylation efficiency, when compared with the other treatments. All treatments with Se resulted in increasing stomatal conductance, transpiratory rate, instantaneous efficiency of water use and intrinsic efficiency of water use when compared with the control treatment. Regarding the anatomy of the plant, the values of total area of the vascular bundle, xylem area, and number of xylem cells per cross-scectional area in leaves were higher when selenate was applied in the leaves, whereas the opposite was observed following the foliar application of selenite. The number of xylem cells per cross sectional area in the root was higher in the absence of Se. Our findings showed that roots of radish can be biofortified with Se without causing harmful effects, with the application of sodium selenate, and with a greater accumulation of Se when this source is applied via soil.

Growth rate rather than growing season length determines wood biomass in dry environments

A number of studies have suggested that growing season length determines carbon sequestration of forest ecosystems. Given the possibility that drought-induced growth decline will be caused by a prolonged growing season under a warming climate, we investigated the effect of growth rate and duration of xylem production on annual wood biomass in drought-prone environments. We analyzed the intra-annual dynamics of wood formation in Qilian junipers (Juniperus przewalskii) from the semi-arid north-eastern Tibetan Plateau, China (2009–2014) and in ponderosa pine (Pinus ponderosa) from the hyperarid Mojave Desert in Nevada, USA (2015–2016). Most variability in the number of xylem cells (Ncell) was related to growth rate (rm) rather than duration of cell production (Dcell). At the Tibetan sites, 69.9% and 54.7% of variability in Ncell was attributable to rm for the lower and upper treeline, respectively. Within the Mojave Desert site, 53.9% of the variability in Ncell was related to rm. The growth rate in the Tibetan Plateau forest is affected by minimum temperature and precipitation. Thus, rm is a primary control on wood biomass in conifer species of semi-arid forests. Under warmer and drier conditions, a longer growing season will not benefit xylem formation of conifers, and in turn warming-induced drought could limit carbon sequestration by reducing the rate of cell production.

Cambial response of Norway spruce to modified carbon availability by phloem girdling.

We tested the hypothesis that increase in carbon (C) availability in Norway spruce saplings (Picea abies (L.) Karst.) intensifies cambial cell division and increases cell lumen diameter (CLD) and cell wall thickness (CWT) when water availability is adequate. To accomplish this, we experimentally subjected 6-year-old P. abies saplings (n = 80 trees) to two levels of soil humidity (watered versus drought conditions) and manipulated tree C status by physically blocking phloem transport at three girdling dates (GDs). Stem girdling occurred in mid-March (day of the year (doy) 77) and in mid-May (GD doy 138), i.e., ~4 weeks before the onset of bud break and during vigorous stem growth, respectively, and in early July (GD doy 190), i.e., 6 and 4 weeks after cessation of radial growth in drought-stressed trees and shoot growth in both soil humidity (SH) treatments, respectively. In response to phloem blockage a striking increase in the number of xylem cells at all GDs and reactivation of cambial activity in drought-stressed trees was detected above the girdling zone, while below girdling xylem formation stopped in both SH-treatments. Although girdling differently affected wood anatomical parameters (CLD, CWT and CLD:CWT ratio) during earlywood and latewood formation, GD had a minor effect on cambial cell division and xylem cell differentiation. Results also revealed that phloem girdling outweighed drought effects imposed on cambial activity. We explain our findings by accumulation of carbohydrates, osmotically active sugars and/or C based signaling compound(s) in response to girdling. Altogether, we conclude that wood formation in P. abies saplings is limited by C availability, which is most likely caused by high C demand belowground especially under drought.

Thigmomorphogenesis: changes in morphology, biochemistry, and levels of transcription in response to mechanical stress inAcacia koa

Acacia koa A. Gray, an economically important timber-wood tree growing in the Hawaiian Islands, is affected by many environmental stresses, including drought, strong wind, heavy rain, and infection by fungal pathogens. Previous studies have shown that some morphological and biochemical changes that take place as a result of environmental stresses in plants can be also induced by mechanical stresses such as touching and bending. We studied morphological and biochemical changes and levels of gene transcription in A. koa plants due to mechanical stress. For a mechanical stress treatment, A. koa seedlings were gently bent in four cardinal directions daily for 2–6 months, after which morphological and biochemical changes were quantified. The stressed A. koa had significantly increased stem diameter, number of xylem cells, and anthocyanin and lignin contents and significantly reduced stem length. The gene expression analyses showed that 53 genes, including the genes for calcium signaling, ethylene biosynthesis, abscisic acid degradation, stress-related transcriptional regulation, and disease resistance, were induced more than twofold within 10–60 min following mechanical stress. The observation that the genes for disease resistance such as NBS-LRR can be induced by mechanical stress suggests that strong wind and rain in the natural forest may also induce disease resistance in trees.

Activation tagging of the two closely linked genes LEP and VAS independently affects vascular cell number.

The complex dominant Arabidopsis thaliana mutant lettuce (let) shows the conversion of the leaf petiole into a leaf blade caused by an ectopic leaf blade formation. This is the result of the activation tagging of the LEAFY PETIOLE (LEP) gene encoding an AP2/EREBP-like transcription factor. Here, we report that in addition to this leafy petiole phenotype, the size of the vascular bundles is increased in all aerial organs in let as a result of an increase in the number of xylem, phloem (pro)cambial and pericycle cells. This vascular phenotype is caused by activation tagging of the two genes VASCULAR TISSUE SIZE (VAS) and LEP. These genes are closely linked and arranged in tandem. Activation tagging of LEP only caused a specific increase in the number of xylem cells. This increased xylem cell number, together with the ectopic leaf blade formation, indicates that LEP functions as a cell division-promoting factor. The activation tagging of VAS only resulted in a specific increase in phloem (pro)cambial and pericycle cells. We conclude that activation tagging of LEP and VAS results in additive phenotypes. Insertional mutants for LEP and VAS display wild-type vascular development, indicating the relevance of activation tagging for functional analysis of novel genes involved in plant development.

A physiological characterization of Mn-tolerant tobacco plants selected by in vitro culture

In previous research, an in vitro stepwise procedure permitted us to obtain Nicotiana tabacum regenerated plant lines able to grow in the presence of Mn at 2 and 5 mM (Mn-tolerant plants). These plants showed several morpho-physiological and cytological differences in comparison to the Mn-sensitive regenerated plants. In particular, the number of xylem cells and the degree of lignification appeared to be influenced differently by these Mn concentrations. In the present work these Mn-tolerant and Mn-sensitive N. tabacum plants, maintained in the presence of Mn 2 and 5 mM, have been characterized with regards to the uptake of Mn and Fe, the activity of extracellular peroxidases in the stems, and the activity of superoxide dismutase, ascorbate peroxidase, and glutathione reductase in the leaves. The leaf response to an increasing Mn concentration in the medium, corresponded a parallel decrease of Fe content. Plants tolerant of 5 mM Mn showed almost a doubling Mn content over that of the 5 mM Mn-sensitive plants. In the stem, 2 and 5 mM Mn inhibited the extracellular free peroxidases (guaiacol peroxidases) either in the Mn-tolerant plants or in the Mn-sensitive plants. In the Mn-sensitive plants treated with 2 mM Mn the activity of the peroxidases of the ionically and covalently bound wall peroxidases was also depressed. In 5 mM Mn-tolerant plants, an enhanced activity of the covalently bound wall peroxidases was observed. The effect of Mn on the covalently bound wall syringaldazine peroxidases was identical to that observed in the guaiacol peroxidases; the activity was significantly higher in the Mn-tolerant plants grown in the presence of 5 mM Mn. In the leaf, the increase of Mn content inhibited the activity of guaiacol peroxidase, ascorbate peroxidase and superoxide dismutase in the Mn-tolerant as well as in the Mn-sensitive plants. However, the effect was greater in the Mn-sensitive plants. Only glutathione reductase did not show significant variation except for the 2 mM Mn-sensitive plants, where an increased activity was detected.

Maturation in larch: age-related changes in xylem development in the long-shoot foliage and the main stem.

As the meristems of eastern larch (Larix laricina (Du Roi) K. Koch) mature, they produce long-shoot foliage with progressively higher chlorophyll content and net photosynthesis and progressively lower specific leaf area (Hutchison et al. 1990). Despite the apparent increase in foliar vigor, both shoot height and diameter growth rates declined during maturation. These changes were associated with changes in xylem morphology of the vascular tissue of both the long-shoot foliage and the main stem. Although the number of xylem cells remained constant in a cross section of the foliage, their diameters increased with age. With increasing maturation, the same number of xylem cells were produced per radial file in the annual rings of the main stem, but their radial diameters decreased, which accounted for the decrease in diameter growth. There was no change in tracheid length during maturation. We conclude that the decrease in growth rate with increased maturation is not due to a decrease in physiological vigor of the foliage, but is a function of reduced sink strength of the growing shoots.

Relation between Petiole Vasculature and Karyotypic Differences in Chromosomal Biotypes of Adhatoda vasica Nees

Several chromosomal biotypes of Adhatoda vasica Nees were encountered in a cytological investigation of different collections from eastern India. All of these chromosomal biotypes represent distinct patterns of branching of the petiole bundles. Various measurements and countings indicate a direct quantitative relationship between the total chromosome length of the biotypes and the number of xylem cells per unit of cross-sectional area and a very strong inverse relation between the total chromosome length and the diameters of vessels and sieve tubes.