Tryptophan Enhancement of Somatic Embryogenesis in Rice

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Abstract
Cereal embryos can produce 2 types of callus. One type, termed embryogenic, consists of small meristematic-like cells and gives rise to many plants by somatic embryogenesis if placed on a suitable regeneration medium. The other is termed nonembryogenic and consists of long tubular cells which gives rise to few or no plants. High concentrations of tryptophan increased the formation of embryogenic callus in 3 rice cultivars (Oryza sativa L. Calrose 76, Pokkali and IR 36) but not in 4 others (Mahsuri, Bg 400-1, H4 and Giza 159). The best concentration of tryptophan for Pokkali and Calrose 76 was 100 .mu.g/ml and for IR 36, 50 .mu.g/ml. IAA at 100 .mu.g/ml promoted an effect similar to that of tryptophan on Calrose 76. The difference between japonica (Calrose 76, Giza 159) and indica (Pokkali, IR 36) varieties is not the causal factor for the difference in response to tryptophan. Kinetin does not appear to be a requirement for embryogenic callus formation in Calrose 76. Plant regeneration from Calrose 76 embryogenic callus occurred at low levels in media containing no hormones. 6-Benzyladenine or 2,3,5-triiodobenzoic acid but not IAA at 0.1-0.5 .mu.g/ml significantly increased regeneration.