EMBRYOGENESIS AND DEVELOPMENT OF ISOLATED BARLEY (HORDEUM-VULGARE L) MICROSPORES ARE INFLUENCED BY THE AMOUNT AND COMPOSITION OF NITROGEN-SOURCES IN CULTURE MEDIA

Growth as well as embryogenesis and plant regeneration of in vitro cultured barley microspores could be manipulated independently through the nitrogen supply. Microspores of the mid-uninucleate to the early-binucleate stage were isolated from the winter type cv. Igri and the spring type cv. Gimpel and cultured in liquid media. Both the frequency of initial divisions and plating efficiency were higher in Gimpel (up to 28 % and 12 % respectively) than in Igri (up to 14 % and 5 % respectively), while more plants could be regenerated from Igri (up to 759 per 1 x 10(5) viable microspores) than Gimpel (up to 232 per 1 x 10(5) viable microspores). The influence of the total nitrogen content, the NO3-:NH4+-ratio and the ratio of inorganic: organic nitrogen was determined. The different components of the media had no effect on the frequency of initial divisions, only moderate effects on plating efficiency, but had dramatic effects on embryogenesis and plant regeneration. Highest plant regeneration was obtained with 20 - 35 mM total nitrogen, a NO3-:NH4+-ratio of 90:10 and a ratio of inorganic:organic nitrogen between 90:10 and 71:29.