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Organic Supplements - i) Vitamins: Plants synthesize vitamins endogenously and these are used as catalysts in various metabolic processes. When plant cells and tissues are grown in vitro, some essential vitamins are synthesized but only in suboptimal quantities. Hence it is necessary to supplement the medium with required vitamins and amino acids to achieve the best growth of the tissue.
Thiamine (B1), nicotinic acid (B3), pyridoxine (B6), calcium pentothenate (B5), and myoinositol are used more often of these, thiamine is the basic vitamin required by all cells and tissues. Nicotinic acid and pyridoxine are usually added to culture media but may not be essential for cell growth in many species.
Other vitamins such as biotin, folic acid, ascorbic acid, pentothenic acid, vitamin E (tocopherol), riboflavin, and p­aminobenzoic acid are also invariably used, particularly when cells are grown at very low population densities, although their requirement by plant cell or tissue cultures is apparently negligible.

 

Generally, these vitamins are added in the range of 0.1 to 10.0 mg 1-1.
ii) Amino acids: Cultured tissues are normally capable of synthesizing the amino acids necessary for various metabolic processes. In spite of this, the addition of amino acids to media is important for stimulating cell growth in protoplast cultures and for establishing cell lines. Unlike inorganic nitrogen, amino acids are taken up more rapidly by plant cells. Casein hydrolysate (0.05-1>.1%), L-glutamine (8 mmoll-1), L-asparagine (100 mmoll-1), L-gly­cine (2 mmol,-1), 'L-arginine and L-cysteine (10 mmoll-1) are common sources of organic nitrogen used in culture media.
Tyrosine (100 mmoll-1) should be used only when agar is added to the medium. Amino acids added singly prove inhibitory to cell growth while their mixtures are frequently beneficial. Supplementing the medium with adenine sulphate can stimulate cell growth or enhance shoot formation.

iii) Other organic supplements: Culture media are often supplemented with a variety of organic extracts which have constituents of an undefined nature. These include protein (casein) hydrolysates, coconut milk, yeast and malt extracts, ground banana, orange juice, and tomato juice.
In tissue culture the success achieved with the use of coconut milk (5 to 20%) and protein (casein) hydrolysates (0.05 to 1.0%) has been significant. Similarly, potato extract has been found a suitable medium for anther culture. Generally the use of natural extracts is avoided because the quantity of growth promoting constituents vary with age of the tissue from which the extract has been obtained, thereby affecting the reproducibility of results.

iv) Activated charcoal: The addition of activated charcoal (AC) to culture media is reported to stimulate growth and differentiation in orchids, carrot, ivy and tomato. Paradoxically, its effect on tobacco, soybean and Camellia has proved inhibitory. Inhibition of growth is attributed to the adsorption of phytohormones to AC, whereas stimulation could be due to any one of the factors, namely adsorption of inhibitory compounds to AC and darkening of the medium. AC is generally acid washed and neutralized before its addition at concentrations of 0.5-3.0% to the culture medium. It also helps to reduce toxicity by removing toxic compounds (e.g. phenols) produced during the culture and permits unhindered cell growth.

v) Antibiotics: Addition of antibiotics to culture media is generally avoided because their presence in the medium retards the cell or tissue growth. However, some plant cells have a systemic infection of microorganisms. To prevent the growth of these microbes it is essential to enrich the media with antibiotics. Streptomycin or kanamycin at low concentration effectively control systemic infection and media supplemented with these antibiotics do not adversely inhibit the growth of cell cultures.

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