Application of Plant Hormones

 

 

Agriculturists all over the world have developed certain unusual methods by which they successfully cultivate the crop plants.  It is only in recent year’s plant physiologists discovered how plant hormones can be effectives used in agriculture, horticultures, pomiculture and other related fields.  As described earlier, plant hormones have a wide variety of effects and most of these responses are concentration dependent.  Fortunately phyto chemists have also identified many synthetic hormones, some of which are more potent than natural hormones.  Experimentation and experience have shown that the judicial use of hormones or combination of hormones can be employed in agriculture and related industries to get the maximum benefit.  Quantity and quality of agricultural products are very important factors in the agricultural economics.  How best the phytohormones can be utilized in this direction requires imagination and training.

 

There are many areas in agriculture, horticulture, pomiculture, moriculture, etc., where phytohormones can be used in successful cultivation to obtain greater yield.  The high percentage of germination of sown seeds in the field has a bearing on the output.  Pretreatment of seeds with IAA, NAA, GA, etc. has been found to be very effective not only in increased the percentage of germination but also in the total yield of the crop plants.  Suitable concentration and combination have to be determined for each and every crop plants.

 

The overall growth of plants, number of tillers and branches that produce from every plant in the field contribute to the total yield.  Use of GA or IAA greatly enhances the growth of plants and total area of leaf surfaces.  Some morphactins can also be used to produce more tillers.  In the case of sugar cane, use of GA has been found to increase the length of the internodes and also the sugar content.

 

Plants can be multiplied by vegetative propagation.  Many horticultural plants are propagated by this way.  The success of this method depends upon rooting.  Hormones like NAA and IBA are very effective in inducing roots in stem cuttings.  These hormones can also be used fro in grafting propagation.  This way most of the plants can be propagated in large numbers and is quick time.

 

Use of hormones like IAA, NAA, IBA and Gibberellins ensures fruit setting and many of the fruits which develop from such hormone treatments are seedless, larger in size and sweeter in content.  In many cases the total yield will be very high.  Quantitatively and qualitatively such products yield more income to the farmer.  Grapes, apples, oranges, mangoes and other fruit yielding crop plants can be treated with some of these phytohormones for the better yield.  Furthermore, these hormones prevent premature falling of fruits, otherwise nearly 50-70% of the set fruits fail to mature and most of them fall off because of the formation of abscission layer in their stalks.

 

Preservation of agricultural products before marketing is another area in which hormones can be used effectively.  Tubers, rhizomes, bulbs and such products sprout while they are stored.  This will affect the farmer in terms of financial gain.  Some of the synthetic hormones like NAA, maleic hydrazide can be used to preserve the said products for quite a period of time, thus one can improve the keeping quality of agricultural products.

 

Another judicial use which can be commercially exploited is the use of GA and other hormones in inducing flowering in unseasonal periods.  But one should known which hormone is effective on which plant; otherwise phytohormones fail to produce the desired results.

 

Today farming is labor oriented and economically it is becoming impossible.  Particularly removing weeds in the field is a nuisance, costly and time consuming.  However specific synthetic hormones are available in the market to destroy the weeds selectively.  2, 4-D, 2, 4, 5-T can be sued in paddy fields to destroy weeds.  Similarly, monocot grasses can be destroyed by using specific weedicide hormones.  Sometimes, water hyacinth and such water plants grow and multiply so fast they spread and establish their population in large tracts of tanks and streams.  This causes considerable damage to water storing capacity of tanks.  For example, 2 methyl 4 chloro 5 isopropyl phenoxyacetic acids can be effectively used to destroy water hyacinth and save the tanks.  Thus one can use different hormones for different purposes; it can be far good or far bad.  It is left to the man who uses it.

 

Application of plant hormones:

Experimental morphogenesis

 

Tissue Culture:

 

Since the days of Haberlandt attempts to grow plant cells, tissues and organs in an artificial but defined nutrient medium have met with great success.  Various methods have been established to raise plantlets starting from single cells, pith, leaf, roots, etc.  By modulating the nutrients and hormonal concentration, it is possible to regenerate the entire plant body from any living cell from any part of the plant body, which suggests that all cells are totipotent.  Hormonal concentrations play a significant role in culturing explants into undifferentiated callus and callus to differentiate into roots, shoots or the entire plant from eh callus.

 

Plantlets from Callus:

 

Tissue culture techniques have been very well exploited in understanding the role of different hormones and their interaction in organogenesis.  Such systems offer excellent experimental materials for biochemical or molecular studies.  Tissue explants in the presence of a particular concentration of auxin, proliferate and produce an undifferentiated mass of cells called callus.  However, further growth of the callus depends upon the availability of cytokinin, for the callus by itself cannot synthesize cytokinins.

 

The callus cells can be further induced to develop into shoots, roots or both by providing auxins and cytokinins in a defined ratio.  As shown in the figure, at high ratio of auxin to cytokinin callus produces only shoots, at lower ratio the callus induces only roots, but at an intermediate ratio both shoots and roots develop.  In certain tissues, by manipulating the concentration of auxin, cytokinins and gibberellins one can induce flowering directly from the callus.

 

Tissue culture methods can be employed in propagating somoclonal variations from the same callus.  By inducing numerous plantlets from the single callus, the plantlets can be transplanted to field conditions and then desirable varieties can be elected in a shortest possible time.  This is because cells in the callus show cot of variation in the chromosomal number.  Tissue culture systems also provide an opportunity to understand the effects of each hormone, nutrients, interactions between the hormones and their effects on plant systems.  Using the same methods, it is also possible to study molecular events that lead to organogenesis.  The potentiality of this technique in the applied fields like horticulture, agriculture and other related fields is great; actually thee is not limit. These methods can be employed to create haploid plants from pollen grains, which is very useful in hybridization techniques.

 

Somatic Cell Hybridization

 

Protoplasts:  Plant cells from leaves, stem and roots, for that matter from any source, can be separated from one another by subjecting the tissues to certain cell wall digesting enzymes like pectinases.  The enzyme pectinase digests the middle wall, thereby the cells get separated.  Once the cells are freed from one another, cellulase can be used to remove the surrounding cell walls.  The resultant cells lacking is cell walls are called protoplasts which contain only plasma lemma as the outer membrane and such cells assume spherical shape.

 

Cell Hybridization:

 

Insolated protoplasts can be used for single cell cultures in a defined medium and the calluses can be obtained from such cells.  Further, embryoids or organs can be raised from such callus tissue.  For every plant species the defined nutrient medium has to be determined for obtaining callus and plantlets.

 

Protoplasts obtained from two different species can be forced or induced to fuse with one another by various methods.  It can be done by treating the protoplasts with polyethylene glycol (PEG) or (X) viruses.  These agents make the cell membrane labile and favor the binding of the membranes between two protoplasts.  Once the cells bind to each other, the membranes fuse with one another leading to the fusion of cytoplasm between the cells.  If the protoplasts thus fused belong to two different species variety or genera, the product is called as somatic cell hybrid. 

 

It is also very important to note that just fusion of two cells by their cytoplasm is not an end.  The fusion of nuclei is also very important.  Once the nuclei fuse, the hybrid cell is ready for propagation.  Such cells can be plated onto a defined medium which is suitable for the development of both the species.  In such a medium the hybrid cell divides and redivides to produce the callus; again by manipulating hormonal combinations and nutrient media, it is possible to induce plantlets from such callus.  The success of these methods requires a large number of trial and error experimentations, where one has to determine the suitable media for each species and then one has to obtain another proper medium to make the hybrid cells to respond.  The success of these techniques required efforts and imagination and lastly the luck.

 

Introduction of recombinant DNA into protoplasts:

 

Protoplast culturing techniques can be very well exploited in incorporating exogenously supplied DNA into protoplasts.  When protoplasts are incubated in a known medium containing DNA, the cells take up DNA slowly.  The amount of DNA that is incorporated into the cells has to be determined.  More than that, the entry of DNA into the cell is not enough; the DNA has to reach the nucleus and it has to be incorporated into the host chromatin.  The DNA that is supplied may belong to different species or it may be recombinant DNA of a known gene or gene(s).  The DNA can also be injected into the nucleus directly by simple injecting transgenic techniques.  If the protoplasts incorporate such supplied DNA into their nuclei, then the protoplasts can be cultured.  One can develop a new species from the said techniques.  However, one has to find out suitable factors for the expression of incorporated genome.  These methods have been successfully employed in many laboratories.

 

In recent years the technique of cloning of known or desired gene has been perfected.  A cloned gene can be transferred to a bacteria or a phage easily and the same can be made to express.  The same technique can be used to transfer known genes into animal cells by directly injecting the known genetic material into zygotes and by transplant back into uterus it possible obtain the offspring with  the exogenously supplied DNA incorporated into the chromatin material unfortunately plant cells are not amenable for such techniques.  However, the plasmids from Agrobacteriam tumificians (which causes can be like tumors are plants) have been isolated and characterized.  Methods have been developed to inactivate the plasmid into harmless structure, but such plasmids are still active when transferred as exogenously supplied genetic material.  By transferring known genes with using such plasmids it can be used as an effective vector to transfer genes into protoplasts or to the living plant itself either by rubbing the plants into wounds or by using a gene gun.  By this was many desirable games can be introduced into different plants.

 

Application of somatic cell hybridization techniques:

 

Somatic cell hybridization is a reality, but this is a technology of the twenty first century.  The success of this technology has raised new hopes in mankind.  Already plant technologists have succeeded in fusing different species of tobacco protoplasts and also they have obtained a complete plant put of such somatic cell hybrids.  The fusion of potato and tomato protoplasts has produced pomato.  But this hybrid has yielded plantlets which are capable producing a tuber like structures in the terminal region than at the base of the plant.  What one wishes is to obtain hybrids which can yield two crops by a single plant.

 

The most ambitious project that man is thinking of is to develop plant and animal cell hybrid.  In fact, the hybrids between HeLa cell (Human cell line) and an yeast cell has been achieved.  What futurist plant genetic engineers expect is to fuse a plant cell with an animal cell and make the plants to produce animal tissue.  Ex. Plants producing pork or animal cell proteins can be used as vegetables.  Though the wishes are wild the success of such dreams are becoming a reality.

 

Similarly introducing of recombinant DNA into protoplasts has generated

great expectations in the field of agriculture.  For example, if nitrogen fixing genes are introduced into cereal crop plant cells, the plants obtained from such experiments do not need nitrogen fertilizers.  It saves the farmer from providing nitrogen fertilizers and saves him lot of money.  Similarly, introduction of some protein genes, which yield proteins of good nutritional value.  It is of immense help in saving man from malnutrition.  So the application value of this technology has no limit.  Many industries have been established to develop new varieties of plants and plant products which have a greater commercial value.