The In Vitro Culture of Immature Barley Embryos on Different Culture Media

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Abstract
Immature barley embryos (Hordeum distichum var. Julia) of between 0⋅20 and 0⋅80 mm in length, were isolated from the developing grain and cultured in vitro on various culture media. The subsequent development of the embryos was followed over a period of weeks, and where germination ensued the growth rate of shoot and root meristems was compared with in vivo germination rates. Various growth media were assessed for their ability to support normal development of immature embryos. A number of published media failed to support satisfactory development of young embryos. The addition of 1–15 per cent coconut milk to Norstog's Medium I (mineral + vitamin solns) enhanced embryo development and lowered the threshold of viability from embryos of 0⋅50 mm in length to 0⋅35 mm. Although in many cases germination ensued, embryo development was largely abnormal. A slightly greater enhancement of growth was achieved with 0⋅05–0⋅30 per cent casein hydrolysate as the growth medium supplement, although abnormal development was not eliminated. A further lowering of the viability threshold to include embryos of 0⋅25 mm in length was obtained by combining 2⋅7 mM glutamine with the casein hydrolysate supplement. Normal development and germination of embryos as small as O25 mm was however obtained on Norstog's Medium JJ and the results were reproduced in four additional if . distichum varieties. In each case the critical threshold of viability was found to lie in embryos of 0⋅20–0⋅30 mm in length.