DEVELOPMENT OF NUTRIENT MEDIA

Initial progress in the culture of plant tissues came from the work of Molliard (1921) in France, Kotte (1922) in Germany, and Robbins (1922) in the United States, who successfully cultured fragments of embryos and excised roots for brief periods of time. The development of improved nutrient solutions, informed choice of plant material, and appreciation of the importance of aseptic cultures, led to long-term or indefinite cultures of excised tomato roots, and cambial tissues of tobacco and carrot, by White (1934, 1939) in the United States, and Gautheret (1934, 1939) and Nobécourt (1939) in France. The discovery of the naturally occurring auxin indole-3-aetic acid (IAA) and its beneficial effects on plant growth (Went 1928; Kögl et al. 1934; Thimann 1935), soon led to its incorporation in plant nutrient media (see White 1943; Gautheret 1985).
White (1943) and others believed that the nutrient solutions based on Knop’s (1865) and other formulations neither provided optimal growth nor were stable or satisfactory over a wide range of pH values. These concerns led to the development of White’s (1943) medium, which was widely used until the mid-1960s. During this period a systematic study of mineral and other requirements of plant tissues grown in culture was carried out (Hildebrandt et al. 1946; Heller 1953), demonstrating the need for a greatly increased level of mineral salts in the medium (see Ozias-Akins and Vasil 1985). In a similar study, designed to optimize the growth of cultured tobacco pith tissue, a marked increase in growth obtained by the addition of aqueous extracts or ash of tobacco leaves to White’s medium was found to be caused largely by the inorganic constituents of the extracts, leading to the development of the first chemically defined and most widely used nutrient solution for plant tissue cultures (Murashige and Skoog 1962). The principal novel features of the new medium were the very high levels of inorganic constituents, chelated iron in order to make it more stable and available during the life of cultures, and a mixture of four vitamins and myo-inositol.