A normal inbred line of maize, BP, partially insensitive to lysine plus threonine (LT) embryo growth inhibition, was found among several inbred lines of the Instituto Fitotécnico de Santa Catalina. The kernel of the BP lines has a higher lysine content than the common normal lines and has a high level of free amino acids (Magoja, personal communication). This high level of free amino acids and also probably high level of methionine could reverse "in vivo" the external LT growth inhibition. Another explanation rests on the fact that the BP embryo could have a particular amino acid uptake; that is to say a slow uptake of LT. But we think that is not the case. Probably the high free amino acid level is correlated with a high free methionine level. This would be possible if the biosynthesis rate of each amino acid is not higher than the biosynthesis rate of the other amino acids, like the case of free lysine in the o2 kernel (Chibber et al., Cereal Chem. 54:558, 1977).

If this is true, the LT selective method would have another use in the isolating and screening of free amino acid overproducer inbred lines and segregants.

Miguel Angel Rapela

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