Morphogenesis in Plant Tissue Cultures

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As totipotent cells are the basis of whole plant tissue culture techniques, so, by the exploitation of this potential of plant cells, biotechnologists are trying to improve the crop plants and other commercially important plants. The somatic cells in plant body are totipotent. Different plant parts have different totipotent abilities. For example, in tobacco plant, the type of bud formed by in-vitro culture of the epidermis of different regions of the plant are different in their form.

Another example to add here may be given about the totipotency of crown-gall cells which have the capacity to grow as an un-organised mass of cells under normal conditions, however whole plants can be recovered from them in culture.

Growth and Morphogenesis of Asparagus Cells cultured in vitro | Nature

Thus, it is clear that totipotency is not similar in all plant parts. Cellular totipotency of plants cells has proved to be a boon to mankind as it is the basis of plant tissue culture. The plant tissue culture exploits this unique property of plant-cells to attain commercial benefits. Helps in cultivation of those plants whose seeds are very minute and difficult to germinate. While studying totipotency, it is stated that the dedifferentiation and redifferentiation processes result in the differentiated plant organs, finally producing a whole plant.

In case of plants, the differentiation is reversible but in animals, it is irreversible. The term differentiation describes the development of different cell types as well as the development of organised structures like roots, shoots, buds, etc.

Essay on Plant Tissue Culture: History, Methods and Application

However, normally morphological characteristics. For example, differentiation accounts for the origin of different types of cells, tissues and organs during the formation of a complete multicellular organism or an organ from a single-celled zygote. Actually, the development of an adult organism starting from a single cell occurs as a result of the combined functioning of cell division and cell differentiation.

Various techniques of tissue culture provide not only a scope of studying the factors governing totipotency of cells but also serves for the investigation of patterns and factors controlling the differentiation. As stated earlier also, the plant cells have a tendency to remain in a quiescent stage which may be reverted to the meristematic stage. This process is termed as dedifferentiation and as a result of this, a homogeneous undifferentiated mass of tissue i. There callus cells then differentiate into different types of cells or an organ or an embryo. The differentiation of the cells is an important event of the development of plants.

The differentiation of different types of cells from the cultured cells is known as cytodifferentiation. When an undifferentiated callus re-differentiates into whole plant, it first undergoes cytodifferentiation. Amongst different cytodifferentiations, the differentiation into vascular tissues has received maximum attention.

However, it is important here to mention that the cells of mature xylem elements and phloem cells cannot be re-differentiated or cannot be reverted back to the meristematic state due to lack of cytoplasm in them. Although, in initial stages of their development, they can be reverted to meristematic cells.

Xylogenesis is the differentiation of parenchymatous cells of callus into xylem-like cells of vascular plants. Phloem differentiation is the formation of phloem-cells from parenchyma in culture. It is synonymous to organogenesis or organogenic differentiation. Organogenesis literally means the birth of organ or the formation of organ. It may occur either by shoot bud differentiation or by the formation of root. Organogenesis commences with the stimulus produced by the components of culture medium, the substances initially present in the original explants and also by the compounds produced during culturing.

Among different organs, which can be induced in plant tissue culture are included the roots, shoots, flower buds and leaves. Regenerations into flower buds and leaves occur in a very low frequency. However, the roots and shoot bud regenerations are quite frequent. Out of all these types of organogenic differentiation, only the shoot bud differentiation can give rise to the complete plantlets therefore, it is of great importance in tissue culture practices. The initiation of roots is termed as rhizogenesis while the initiation of shoots is called as caulogenesis and these two phenomena are affected by alterations in the auxin : cytokinin ratio in the nutrient medium.

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A group of meristematic cells called as meristemoids is the site of organogenesis in callus. Such meristemoids are capable of producing either a root or a shoot. Organogenesis may occur either through callus formation or through the direct formation of adventitious organs like adventitious shoot. Latter mode of organogenesis does not involve the intervening callus phase. Further, in , Skoog indicated that organogenesis could be chemically controlled.

Shoot bud differentiation refers to the formation of shoot buds from the cultured cells by providing appropriate culture conditions and nutrient medium. The chemical and physical factors required for shoot bud differentiation vary for explants from different plant species. The embryos formed from the somatic cells of plant in culture under in-vitro conditions are called as somatic embryos. When the somatic cells of plant organs result into the regeneration into embryos, then the process is called as somatic embryogenesis or embryo genic differentiation or embryogenesis Fig.

Somatic embryos are also referred to as embryoids, and they can be obtained either indirectly with formation of callus or directly from the explant without intervening callus formation. However, direct embryogenesis is not a normal process because the medium requirement for this is complex. Somatic embryogenesis under in-vitro conditions was first of all observed by Steward et. Thereafter, somatic embryoids have been induced in many plants namely Citrus, Coffea, Zea mays, etc.

To obtain embryoids, there is a requirement of two nutrient media, first for initiation and the other medium for proper development of the embryoid. The development of somatic embryo passes through the stages like globular, heart-shaped, torpedo-shaped and finally giving rise to the cotyledonary stage of somatic embryo. A somatic embryo does not have any vascular connection with the explant or callus therefore it can be separated easily. Somatic embryogenesis is not used very frequently for propagation of plants because, the technique is usually difficult and also, there is a high risk of occurrence of mutations.

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Another major drawback of somatic embryogenesis is that there are greater chances of loss of regenerative capacity on repeated sub-culturing. There are different methods of culturing plant material. These methods differ on the basis of explants used and their resultant products.

Some of the most popular and advantageous methods in plant tissue culture are discussed below:. Cell culture is actually, the process of producing clones of a single cell. The clones of cell are the cells which have been derived from the single cell through mitosis and are identical to each other as well as to parental cell.

First attempts for cell culture were made by Haberlandt in However, he failed to culture single cell but his attempts stimulated other workers to achieve success in this direction. The method of cell culture is meritorious over other methods of culturing because it serves as the best way to analyse and understand the cell metabolism and effects of different chemical substances on the cellular responses. Single cell culturing is of immense help in crop improvement programmes through the extension of genetic engineering techniques in higher plants.

It is important to note here that the cell cultures require a suitably enriched nutrient medium and it should be done in dark because light may deteriorate the cell culture. Large scale culturing of plant cells under in-vitro conditions provides a suitable method for production of large varieties of commercially important phytochemicals.

IN VITRO PROPAGATION

A culture which consists of cells or cell aggregates initiated by placing callus tissues in an agitated liquid medium is called as a suspension culture. Agitation with shaker is important because it breaks the cell aggregates into single cell or smaller groups of cells and it helps in maintaining the uniform distribution of single cell and groups of cells in the liquid medium.

A good suspension is the one which has high proportion of single cells than the groups of cells. Changes in the nutritional composition of medium may also serve as a useful technique for breakage of larger cell clumps Fig. The general technique of suspension culture involves basically two types of cultures: batch culture and continuous cultures. A batch culture is a suspension culture in which cells grow in a finite volume of the culture medium and as a result, medium gradually depletes.

On the other hand, a continuous suspension culture is the one which is continuously supplied with nutrients by the inflow of fresh medium but the culture volume is normally constant. Pioneering attempts for root culture were made by Robbins and Kotte during s. Later on, many workers tried for achieving successful root cultures. In , it was White who successfully cultured the continuously growing tomato root tips. Subsequently, root culturing of a number of plant species of angiosperms as well as gymnosperms has been done successfully.

They provide beneficial information regarding the nutritional needs, physiological activities, nodulations, infections by different pathogenic bacteria or other microbes, etc. Shoot cultures have great applicability in the fields of horticulture, agriculture and forestry. The practical application of this method was proposed by Morel and Martin after they successfully recovered the complete Dahalia plant from shoot-tips cultures.

Proteomics as a Tool to Study Molecular Changes During Plant Morphogenesis In Vitro

Later on, Morel realized that the technique of shoot culturing can prove to be a potent method for rapid propagation of plants i. Micro propagation. In this technique, the shoot apical meristem is cultured on a suitable nutrient medium.

This is also referred to as Meristem Culture Fig. The apical meristem of a shoot is the portion which is lying beyond the youngest leaf primordium. Meristem tip culture is also beneficial for recovery of pathogen-free specially virus-free plants through the tissue culture techniques. Various stages in this culture process are the initiation of culture, shoot multiplication, rooting of shoots and finally the transfer of plantlets to the pots or fields.

A protoplast is described as a plasma membrane bound vesicle which consists of a naked cell formed as a result of removal of cell wall. The cell wall can be removed by mechanical or enzymatic methods. In-vitro culturing of protoplasts has immense applications in the field of plant biotechnology. It not only serves for genetic manipulations in plants but also for biochemical and metabolic studies in plants. For protoplast culture, firstly the protoplasts are isolated from the plants utilizing some chemical or enzymatic procedure.

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