Izabela Potocka

Distribution of lipid transfer protein 1 (LTP1) epitopes associated with morphogenic events during somatic embryogenesis of Arabidopsis thaliana

AbstractUsing immunocytochemical methods, at both the light and electron microscopic level, we have investigated the spatial and temporal distribution of lipid transfer protein 1 (LTP1) epitopes during the induction of somatic embryogenesis in explants of Arabidopsis thaliana. Immunofluorescence labelling demonstrated the presence of high levels of LTP1 epitopes within the proximal regions of the cotyledons (embryogenic regions) associated with particular morphogenetic events, including intense cell division activity, cotyledon swelling, cell loosening and callus formation. Precise analysis of the signal localization in protodermal and subprotodermal cells indicated that cells exhibiting features typical of embryogenic cells were strongly labelled, both in walls and the cytoplasm, while in the majority of meristematic-like cells no signal was observed. Staining with lipophilic dyes revealed a correlation between the distribution of LTP1 epitopes and lipid substances within the cell wall. Differences in label abundance and distribution between embryogenic and non-embryogenic regions of explants were studied in detail with the use of immunogold electron microscopy. The labelling was strongest in both the outer periclinal and anticlinal walls of the adaxial, protodermal cells of the proximal region of the cotyledon. The putative role(s) of lipid transfer proteins in the formation of lipid lamellae and in cell differentiation are discussed. Key message Occurrence of lipid transfer protein 1 epitopes in Arabidopsis explant cells accompanies changes in cell fate and may be correlated with the deposition of lipid substances in the cell walls.

Effect of mechanical stress on Zea root apex. I. Mechanical stress leads to the switch from closed to open meristem organization

The effect of mechanical stress on the root apical meristem (RAM) organization of Zea mays was investigated. In the experiment performed, root apices were grown through a narrowing of either circular (variant I) or elliptical (variant II) shape. This caused a mechanical impedance distributed circumferentially or from the opposite sides in variant I and II, respectively. The maximal force exerted by the growing root in response to the impedance reached the value of 0.15 N for variant I and 0.08 N for variant II. Significant morphological and anatomical changes were observed. The changes in morphology depended on the variant and concerned diminishing and/or deformation of the cross-section of the root apex, and buckling and swelling of the root. Anatomical changes, similar in both variants, concerned transformation of the meristem from closed to open, an increase in the number of the cell layers at the pole of the root proper, and atypical oblique divisions of the root cap cells. After leaving the narrowing, a return to both typical cellular organization and morphology of the apex was observed. The results are discussed in terms of three aspects: the morphological response, the RAM reorganization, and mechanical factors. Assuming that the orientation of division walls is affected by directional cues of a tensor nature, the changes mentioned may indicate that a pattern of such cues is modified when the root apex passes through the narrowing, but its primary mode is finally restored.

Cellular Markers for Somatic Embryogenesis

Somatic embryogenesis (SE) is a process in which somatic cells under special conditions develop into embryos and in the end into a plant. That is why SE is a good model system for studying the genetic, molecular, physiological, biochemical, histological and cellular mechanisms underlying not only somatic but also zygotic embryogenesis and the totipotency of plant cells. SE begins with a transition of somatic cells to an embryogenic state and it can be induced under certain in vitro conditions. The mechanisms which determine SE induction the transition of cells from the vegetative to the embryogenic state and the conditions underlying such changes are the main questions of developmental biology (for a review see: de Jong et al., 1993; von Arnold et al., 2002; Feher et al., 2003; Namasivayam, 2007; Yang & Zhang, 2010).

Spatio-temporal distribution and methyl-esterification of pectic epitopes provide evidence of developmental regulation of pectins during somatic embryogenesis in Arabidopsis thaliana

The aim of the present study was to describe the occurrence of three pectic epitopes, recognized by JIM7, LM19, and LM5 antibodies, during somatic (SE) and zygotic (ZE) embryogenesis in Arabidopsis thaliana. The epitopes recognized by JIM7 and LM19 antibodies showed different distributions during SE stages. Moreover, in the early stages of somatic embryo development, a cytoplasmic occurrence of LM19 epitope was detected. Distribution of a pectic epitope recognized by LM5 antibody corresponded to a vascular system differentiation pattern. Occurrence of LM5 epitope was the same in both zygotic and somatic embryos and often restricted to newly synthesized walls of two adjacent cells. These data suggest that both low and high methyl-esterified pectins (recognized by LM19 and JIM7 antibodies, respectively) are developmentally regulated during SE stages and (1→4)-β-D-galactan epitope (recognized by LM5 antibody) may play a role in cell cytokinesis.

Principal growth directions in development of the lateral root in Arabidopsis thaliana

BACKGROUND AND AIMS During lateral root development a new meristem is formed within the mother root body. The main objective of this work was to simulate lateral root formation in Arabidopsis thaliana and to study a potential role of the principal directions in this process. Lateral root growth is anisotropic, so that three principal directions of growth can be distinguished within the organ. This suggests a tensorial character of growth and allows for its description by means of the growth tensor method. METHODS First features of the cell pattern of developing lateral roots were analysed in A. thaliana and then a tensorial model for growth and division of cells for this case was specified, assuming an unsteady character of the growth field of the organ. KEY RESULTS Microscopic observations provide evidence that the principal directions of growth are manifested at various developmental stages by oblique cell walls observed in different regions of the primordium. Other significant features observed are atypically shaped large cells at the flanks of young apices, as well as distinct boundaries between the mother root and the primordium. Simulations were performed using a model for growth. In computer-generated sequences the above-mentioned features could be identified. An attempt was made to reconstruct the virtual lateral root that included a consideration of the formation of particular tissue types based on literature data. CONCLUSIONS In the cell pattern of the developing lateral root the principal directions of growth can be recognized through occurrence of oblique cell divisions. In simulation the role of these directions in cell pattern formation was confirmed, only when cells divide with respect to the principal directions can realistic results be obtained.

Histology and Histochemistry of Somatic Embryogenesis

The seminal reports of somatic embryogenesis in the umbellifers Oenanthe aquatica by Harry Waris in 1957 (Krikorian and Simola, Physiol Plant 105:348–355 (1999)) and carrot (Steward et al., Am J Bot 45:693–703 (1958)) paved the way for current studies on the mechanisms involved in the transition of somatic cells to the embryogenic state for many species (Feher et al., Plant Cell Tiss Org 74:201–228, 2003; Elhiti and Stasolla, Plant embryo culture: methods and protocols, Humana Press, New York, 2011; Feher, Biochim Biophys Acta 1849:385–402, 2015). Somatic embryogenesis has been a focal point of research in plant development. This process relies on somatic cell totipotency (i.e., the capacity to regenerate the entire plant from single somatic cells), and it has been long used in biotechnological breeding techniques as an efficient system for regenerating plants in a large-scale basis. Also, because it is a unique system which includes a large number of events—such as physiological reprogramming of explants as well as changes in the gene expression and cell division patterns, and in cell fate (Feher, Acta Biol Szeged 52:53–56, 2008; Rose et al., Plant developmental biology-biotechnological perspectives. Springer, Heidelberg, 2010)—somatic embryogenesis has also become an appropriate method for studying the morphophysiological and molecular aspects of cell differentiation. The comprehension of the developmental events during the induction phase as well as the development of somatic embryos is essential to regulate each stage of the somatic embryogenesis developmental program efficiently. Additionally, it may be useful for the development of efficient protocols for somatic embryogenesis induction and validation in genetic transformation systems (Feher et al., Plant Cell Tiss Org 74:201–228, 2003; Yang and Zhang, Crit Rev Plant Sci 29:36–57, 2010; Rocha and Dornelas, CAB Rev 8:1–17, 2013; Mahdavi-Darvari et al., Plant Cell Tiss Org 120:407–422, 2015). Anatomical and ultrastructural studies have contributed to the better understanding of the basic cellular mechanisms involved in the acquisition of competence and histodifferentiation of somatic embryos (Canhoto et al., Ann Bot 78:513–521, 1996; Verdeil et al., Trends Plant Sci 12:245–252, 2001; Moura et al., Plant Cell Tiss Org 95:175–184, 2008; Moura et al., Sci Agric 67:399–407, 2010 ; Almeida et al., Plant Cell Rep 31:1495–1515, 2012; Rocha et al., Protoplasma 249:747–758, 2012; Rocha et al., Plant Cell Tiss Org 120:1087–1098, 2015; Rocha et al., Protoplasma 111:69–78, 2016). In addition, histochemical methods have enabled the monitoring of the mobilization and synthesis of reserve compounds during embryogenic development. This way, the dynamic and fate of cells committed to the somatic embryogenesis can be supported by microscopy techniques. The formation of an embryogenic callus and the subsequent differentiation of somatic embryos can be analyzed over time, and the cytological changes that have occurred during these processes can also be of great value, by associating the observed cytological changes with the expression patterns of several genes from the initial explant through competence acquisition to the formation of somatic embryos. Somatic embryogenesis has been intensively studied over the past decades. A range of descriptive studies using light and electron microscopy has provided a detailed characterization of histocytological events underlying the progression from somatic cells to the formation of embryos. Here, we review recent studies that have advanced our understanding of the anatomical and ultrastructural changes that characterize the somatic embryogenesis developmental pathway.

Spatio-temporal localization of selected pectic and arabinogalactan protein epitopes and the ultrastructural characteristics of explant cells that accompany the changes in the cell fate during somatic embryogenesis in Arabidopsis thaliana

During somatic embryogenesis (SE), explant cells undergo changes in the direction of their differentiation, which lead to diverse cell phenotypes. Although the genetic bases of the SE have been extensively studied in Arabidopsis thaliana, little is known about the chemical characteristics of the wall of the explant cells, which undergo changes in the direction of differentiation. Thus, we examined the occurrence of selected pectic and AGP epitopes in explant cells that display different phenotypes during SE. Explants examinations have been supplemented with an analysis of the ultrastructure. The deposition of selected pectic and AGP epitopes in somatic embryos was determined. Compared to an explant at the initial stage, a/embryogenic/totipotent and meristematic/pluripotent cells were characterized by a decrease in the presence of AGP epitopes, b/the presence of AGP epitopes in differentiated cells was similar, and c/an increase of analyzed epitopes was detected in the callus cells. Totipotent cells could be distinguished from pluripotent cells by: 1/the presence of the LM2 epitope in the latest one, 2/the appearance of the JIM16 epitope in totipotent cells, and 3/the more abundant presence of the JIM7 epitope in the totipotent cells. The LM5 epitope characterized the wall of the cells that were localized within the mass of embryogenic domain. The JIM8, JIM13 and JIM16 AGP epitopes appeared to be the most specific for the callus cells. The results indicate a relationship between the developmental state of the explant cells and the chemical composition of the cell walls.

Morphological responses of plant roots to mechanical stress

Background Roots are continuously exposed to mechanical pressure and this often results in their morphological modification. Most obvious are changes in the overall form of the root system as well as in the shapes of particular roots. These changes are often accompanied by modifications of the cell pattern and cell morphology. Scope This review focuses on the morphological responses of roots to mechanical stress. Results of early and recent experiments in which roots have been exposed to mechanical pressure are assembled, analysed and discussed. Research applying different experimental sets, obstacles, media of various compactness and structure are reviewed. An effect of the combination of mechanical stresses with other abiotic stresses on roots, and results of estimating the force exerted by the roots are briefly discussed. Possible consequences of the cell pattern rearrangements are considered. Conclusions Several modifications in root morphology are commonly reported: (1) decreased root size, (2) radial swelling accompanied by increased radial dimension of the cortex cell layers and (3) enhanced cap cell sloughing. Nevertheless, because of differences between species and individual plants, a universal scenario for root morphological changes resulting from externally applied pressures is not possible. Thus, knowledge of the root response to mechanical impedance remains incomplete. Studies on the mechanical properties of the root as well as on possible modifications in cell wall structure and composition as the elements responsible for the mechanical properties of the plant tissue are required to understand the response of root tissue as a biomaterial.