The structure of trees.

Trees are, by definition, the tallest land plants. To grow tall over multiple years they must solve several problems: structural strength; carbohydrate and nutrient storage capacity to survive and regrow after periods of stress; and conductive capacity for water, carbohydrates and nutrients must be increased/renewed over time to keep pace with increases in canopy size. Additionally, apical meristems must be capable of surviving through periods of stress (especially over winter or during drought). Structural strength, storage capacity and water, carbohydrate and nutrient conductive capacity are provided by cells derived from a sheath of meristematic cells (vascular cambium) that surround the body of trees (shoots, stems, branches, trunk, perennial roots). This chapter describes the structure of fruit trees.

The Effect of Water Boiled in Aluminum Cookwares on Genomic Abnormalities in the Meristematic Cells of Onion Root

Introduction: One of the ways of human exposure to aluminum (Al) is Al food packaging materials and cookwares. Although many studies have examined the biotic influence of nanoparticles or ionic form of heavy metals, there are limited studies conducted on the possible health risks of metals in the form of alloy used for making utensils. In this study, the effect of water boiled in Al cookwares with defined concentrations of Al on the genomic abnormalities and cell division of meristematic cells of onion root was evaluated using Allium cepa assay. Materials and Methods: The onion roots were treated with water boiled in Al utensils (three pots) with different concentrations of Al (5 and 10 mg/l) for 42 to 43 hours and then analyzed for mitotic index (MI) and mitotic phase aberrations (MPA). Results: The percent of MI in the study groups treated with 5 mg/l of Al from pot 1 and 10 mg/l from all pots increased significantly compared to the control group (P < 0.05). Also, the frequency of total MPA in all Al treated groups significantly increased compared to the control group (P < 0.05). The most significant results were derived by sticky chromosomes, anaphase bridge, going ahead chromosome and disturbed mitosis, respectively. Conclusion: The result of this study confirmed the genotoxic effect of water boiled in Al cookwares containing the examined range of Al concentrations on the meristematic cells of onion root.

The Regulation of Plant Vegetative Phase Transition and Rejuvenation: miRNAs, a Key Regulator

In contrast to animals, adult organs in plants are not formed during embryogenesis but generated from meristematic cells as plants advance through development. Plant development involves a succession of different phenotypic stages and the transition between these stages is termed phase transition. Phase transitions need to be tightly regulated and coordinated to ensure they occur under optimal seasonal, environmental conditions. Polycarpic perennials transition through vegetative stages and the mature, reproductive stage many times during their lifecycles and, in both perennial and annual species, environmental factors and culturing methods can reverse the otherwise unidirectional vector of plant development. Epigenetic factors regulating gene expression in response to internal cues and external (environmental) stimuli influencing the plant’s phenotype and development have been shown to control phase transitions. How developmental and environmental cues interact to epigenetically alter gene expression and influence these transitions is not well understood, and understanding this interaction is important considering the current climate change scenarios, since epigenetic maladaptation could have catastrophic consequences for perennial plants in natural and agricultural ecosystems. Here, we review studies focusing on the epigenetic regulators of the vegetative phase change and highlight how these mechanisms might act in exogenously induced plant rejuvenation and regrowth following stress.

Meristematic Connectome: A Cellular Coordinator of Plant Responses to Environmental Signals?

Mechanical stress in tree roots induces the production of reaction wood (RW) and the formation of new branch roots, both functioning to avoid anchorage failure and limb damage. The vascular cambium (VC) is the factor responsible for the onset of these responses as shown by their occurrence when all primary tissues and the root tips are removed. The data presented confirm that the VC is able to evaluate both the direction and magnitude of the mechanical forces experienced before coordinating the most fitting responses along the root axis whenever and wherever these are necessary. The coordination of these responses requires intense crosstalk between meristematic cells of the VC which may be very distant from the place where the mechanical stress is first detected. Signaling could be facilitated through plasmodesmata between meristematic cells. The mechanism of RW production also seems to be well conserved in the stem and this fact suggests that the VC could behave as a single structure spread along the plant body axis as a means to control the relationship between the plant and its environment. The observation that there are numerous morphological and functional similarities between different meristems and that some important regulatory mechanisms of meristem activity, such as homeostasis, are common to several meristems, supports the hypothesis that not only the VC but all apical, primary and secondary meristems present in the plant body behave as a single interconnected structure. We propose to name this structure “meristematic connectome” given the possibility that the sequence of meristems from root apex to shoot apex could represent a pluricellular network that facilitates long-distance signaling in the plant body. The possibility that the “meristematic connectome” could act as a single structure active in adjusting the plant body to its surrounding environment throughout the life of a plant is now proposed.

Significance of selenium supplementation in root- shoot reactions under manganese stress in wheat seedlings – biochemical and cytological studies

Purpose Agronomic practices are one of the reasons for the increasing accumulation of elements in the soil, including manganese (Mn). Our previous studies have shown that selenium (Se) ions can reduce the toxic actions of metal stress. Those, we studied the effects of Mn—treated as a stressor and Se – as a potential defense in plants. Methods Mn ions (10 mM) or/and Se (15 μM) were added into hydroponic nutrients of two wheat cultivares. The evaluation of the stress-generating and protective actions were analyzed by biochemical methods and microscopic observations in leaves and roots. Moreover the level of DNA methylation for these tissues was determined. Results Mn application caused an increase of lipid peroxidation and hydrogen peroxide content in both leaves and roots and was accompanied with a greater absorption of this element by the roots. For other elements (K, Fe, S, P), with the exception of Ca, the reduced their uptake was registered, especially in roots. For roots, Mn stimulated greater, microscopically observed, desorganization in cell structure as compared to leaves, which was accompanied by a quantitative increase in 5-methylcytosine (5-metC) in root meristem. Se application diminished the effects of Mn-stress. Conclusions These studies is the first in which indicated that global 5-metC level in roots enhancing from dividing meristematic cells to elongating cells of the axial cylinder and cortex. It was suggested that the rise in Ca level can lead to modification of root cells differentiations what may be one of the steps in defense mechanisms.

Significance of Selenium Supplementation in Root- Shoot Reactions Under Manganese Stress in Wheat Seedlings – Biochemical and Cytological Studies.

Purpose Agronomic practices are one of the reasons for the increasing accumulation of elements in the soil, including manganese (Mn). Our previous studies have shown that selenium (Se) ions can reduce the toxic actions of metal stress. Those, we studied the effects of Mn - treated as a stressor and Se – as a potential defense in plants. Methods Mn ions (10 mM) or/and Se (15 µM) were added into hydroponic nutrients of two wheat cultivares. The evaluation of the stress-generating and protective actions were analyzed by biochemical methods and microscopic observations in leaves and roots. Moreover the level of DNA methylation for these tissues was determined. Results Mn application caused an increase of lipid peroxidation and hydrogen peroxide content in both leaves and roots and was accompanied with a greater absorption of this element by the roots. For other elements (K, Fe, S, P), with the exception of Ca, the reduced their uptake was registered, especially in roots. For roots, Mn stimulated greater, microscopically observed, desorganization in cell structure as compared to leaves, which was accompanied by a quantitative increase in 5-metC in root meristem. Se application diminished the effects of Mn-stress. Conclusions These studies is the first in which indicated that global 5-metC level in roots enhancing from dividing meristematic cells to elongating cells of the axial cylinder and cortex. It was suggested that the rise in Ca level can lead to modification of root cells differentiations what may be one of the steps in defense mechanisms.

Green Globular Body (GGB) Induction and Differentiation in the Medicinal fern Drynaria Roosii

Background: The green globular body (GGB) of ferns is a special propagule induced in plant in vitro culture systems. Owing to its high proliferation efficiency, GGB is widely used in the in vitro propagation of important ornamental and medicinal ferns. In addition, propagation using GGB shows great development prospects in the conservation of rare or endangered ferns and the breeding of new fern varieties. However, due to the lack of systematic studies on GGB ontogenesis, the morphogenetic aspects of GGB during induction and differentiation remain unclear.Results: We characterized the response of five types of explants of Drynaria roosii to GGB inductive medium and further investigate morphological and anatomical changes of explants that developed GGBs. We found that the rhizome explants directly produced GGBs through cell proliferation of the shoot apical meristem and lateral meristem. The leaf and petiole explants produced GGBs indirectly through the proliferation of meristematic cells of somatic embryos derived from the epidermal cells of the explants. The root and gametophyte explants failed to produce GGB under our induction conditions. We further investigated the differentiation process of GGB. During GGB differentiation, shoot primordia and leaf primordia differentiate from meristematic cells on the epidermis, and the root primordia develop from an inner meristematic tissue with developing vascular tissue connecting all these primordia, which indicates the involvement of multiple organogenesis processes.Conclusions: Our results suggested that preexisting or reestablished meristematic cells were the direct source of GGB in D. roosii. Somatic embryogenesis and organogenesis were involved in GGB induction and differentiation, respectively. The comparison with other common propagules revealed that GGB in D. roosii was largely different from somatic embryos, callus, and protocorm or protocorm-like bodies.