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

Immature barley embryos (Hordeum distichum var. Julia) of between0•20 and 0•80 mm in length, were isolated from thedeveloping grain and cultured in vitro on various culture media.The subsequent development of the embryos was followed overa period of weeks, and where germination ensued the growth rateof shoot and root meristems was compared with in vivo germinationrates. Various growth media were assessed for their abilityto support normal development of immature embryos. A numberof published media failed to support satisfactory developmentof young embryos. The addition of 1–15 per cent coconutmilk to Norstog's Medium I (mineral + vitamin solns) enhancedembryo development and lowered the threshold of viability fromembryos of 0•50 mm in length to 0•35 mm. Althoughin many cases germination ensued, embryo development was largelyabnormal. A slightly greater enhancement of growth was achievedwith 0•05–0•30 per cent casein hydrolysate asthe growth medium supplement, although abnormal developmentwas not eliminated. A further lowering of the viability thresholdto include embryos of 0•25 mm in length was obtained bycombining 2•7 mM glutamine with the casein hydrolysatesupplement. Normal development and germination of embryos assmall as O25 mm was however obtained on Norstog's Medium JJand the results were reproduced in four additional if . distichumvarieties. In each case the critical threshold of viabilitywas found to lie in embryos of 0•20–0•30 mmin length.