Therefore, the view formulated by Steward and colleagues in 1970 that “in principle, all normally diploid somatic cells are essentially totipotent and that present failures to rear them into plants merely present the challenge to find the right conditions for their development” ( Steward et al., 1970) became widely accepted. Based on the above studies, plant cell/tissue culture and regeneration systems were successfully applied for plant propagation in the case of hundreds of plant species and their various explants. This view was further supported by the isolation and culture of leaf protoplasts (single cells devoid of cell wall) and their development into whole plants ( Takebe et al., 1971). This process was considered to be the experimental proof of the “totipotency” of plant cells, namely that each somatic plant cell has the capability to regenerate into an entire plant. This pathway was later termed as “somatic embryogenesis” and its initiation was confined to single cells ( Backs-Hüsemann and Reinert, 1970). In the late 1950th, it was proved that besides sequential shoot and root organogenesis whole plants can be regenerated from cultured plant cells in only one step via embryo formation ( Steward et al., 1958 Reinert, 1959). This proliferating cell mass was termed as “callus” due to its resemblance to the wound-healing plant tissue. Moreover, it was revealed that the ratio of these hormones determines the morphogenetic pathway that the in vitro cultured tissue will follow: high and low ratios of cytokinin to auxin favored shoot and root regeneration, respectively, whereas more balanced concentrations resulted in unorganized growth of a cell mass ( Skoog and Miller, 1957). It was followed by the observation that the phytohormones auxin and cytokinin are both required for in vitro cell proliferation. Long-term proliferation and maintenance of cultured plant tissues were worked out during the 1930th and provided experimental proofs for this hypothesis. The start of in vitro plant cell and tissue culture research is dated to 1902, when Gottlieb Haberlandt presented his hypothesis on the intrinsic capability of isolated plant cells for autonomous life ( Haberlandt, 1902). Histological wound responses and callus formation had been observed and the term “dedifferentiation” was already used at this early period. Besides, the regeneration ability of plants attracted scientific interest as early as the end of the 19th century (for a recent review of plant cell culture history see Sugiyama, 2015). These pathways have been exploited for vegetative plant propagation long since. To ensure survival, they have dedicated developmental pathways to close injuries and/or replace lost parts/organs.
![polarity in embryogenesis and yin and yang theory polarity in embryogenesis and yin and yang theory](https://www.internalartsinternational.com/wp-content/uploads/2012/11/tai-ji-2.gif)
Plants, from time to time, need to cope with physical damages caused by their biotic or abiotic environment. This is manifested, among others, in their high regeneration capacity. Plants exhibit a remarkable developmental plasticity. Introduction – a Short Historical Preview Clarification of it might help to avoid further misunderstanding and to overcome potential “terminology-raised” barriers in plant research. The main aim of this review is to provide a theoretical framework supported by recent experimental findings to reconsider certain historical, even dogmatic, statements widely used by plant scientists and teachers such as “plant cells are totipotent” or “callus is a mass of dedifferentiated cells,” or “somatic embryos have a single cell origin.” These statements are based on a confused terminology. Recent progress in molecular and cell biology techniques allowed unprecedented insights into the underlying processes of plant cell/tissue culture and regeneration. Its basic methodology and terminology were formulated preceding modern plant biology. The history of plant cell and tissue culture dates back to more than a century. Besides, they are useful research tools and objects of plant developmental biology. Plant cell and tissue culture methods are efficient means to preserve and propagate genotypes with superior germplasm as well as to increase genetic variability for breading. Recent findings call for the critical overview of some incorrectly used plant cell and tissue culture terminology such as dedifferentiation, callus, totipotency, and somatic embryogenesis. 2Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary.
![polarity in embryogenesis and yin and yang theory polarity in embryogenesis and yin and yang theory](https://image.slideserve.com/244061/slide10-l.jpg)