media2 - Chapter 4 The Components of Plant Tissue Culture...

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Chapter 4 The Components of Plant Tissue Culture Media ll: Organic Additions, Osmotic and pH Effects, 1. ORGANIC SUPPLEMENTS Growth and morphogenesis of plant tissue cultures can be improved by small amounts of some organic nutrients. These are mainly vitamins (including some substances that are not strictly animal vitamins), amino acids and certain undefined supplements. The amount of these substances required for successful culture varies with the species and genotype, and is probably a reflection of the synthetic capacity of the explant. 1.1. VITAMINS Vitamins are compounds required by animals in very small amounts as necessary ancillary food factors. Absence from the diet leads to abnormal growth and development and an unhealthy condition. Many of the same substances are also needed by plant cells as essential intermediates or metabolic catalysts, but intact plants, unlike animals, are able to produce their own requirements. Cultured plant cells and tissues can however become deficient in some factors; growth and survival is then improved by their addition to the culture medium. In early work, the requirements of tissue cultures for trace amounts of certain organic substances were satisfied by “undefined” supplements such as fruit juices, coconut milk, yeast or malt extracts and hydrolysed casein. These supplements can contribute vitamins, amino acids and growth regulants to a culture medium. The use of undefined supplements has declined as the need for specific organic compounds has been defined, and these have become listed in catalogues as pure chemicals. 1.2. THE DEVELOPMENT OF VITAMIN MIXTURES The vitamins most frequently used in plant tissue culture media are thiamine (Vit. B 1 ), nicotinic acid (niacin) and pyridoxine (Vit. B 6 ) and apart from these three compounds, and myo -inositol, there is little common agreement about which other vitamins are really essential. The advantage of adding thiamine was discovered almost simultaneously by Bonner (1937, 1938), Robbins and Bartley (1937) and White (1937). Nicotinic acid and pyridoxine appear, in addition to thiamine, in media published by Bonner (1940), Gautheret (1942) and White (1943b); this was following the findings of Bonner and Devirian (1939) that nicotinic acid improved the growth of isolated roots of tomato, pea and radish; and the papers of Robbins and Schmidt (1939a,b) which indicated that pyridoxine was also required for tomato root culture. These four vitamins; myo -inositol, thiamine, nicotinic acid, and pyridoxine are ingredients of Murashige and Skoog (1962) medium and have been used in varying proportions for the culture of tissues of many plant species (Chapter 3). However, unless there has been research on the requirements of a particular plant tissue or organ, it is not possible to conclude that all the vitamins which have been used in a particular experiment were essential. The requirements of cells for added vitamins vary
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media2 - Chapter 4 The Components of Plant Tissue Culture...

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