Evaluation of essential amino acid overproducers

--Liliana H. Perini, Eduardo A. Bernatené and Carlos A. Naranjo

Different races of maize--native from Argentina--were tested as possible donors of high quality protein, with the purpose of modifying the levels of lysine and tryptophan of the endosperm in the commonmost cultivated maizes.

The evaluations were conducted in a double way. On the one hand, biochemical determinations using traditional methods to quantify the level of lysine (Beckwith et al., J. Agric. Food Chem. 23:194-198, 1975) and tryptophan (Hernández and Bates, CIMMYT, Res. Bull. Num. 13, 1969) were used. On the other hand, based on previous reports (Green and Phillips, 1974; and Rapela, 1980), the retroregulation technique was used to select overproducers of essential amino acids through the culture of mature embryos in media containing lysine plus threonine (L + T). This double method ensures a more efficient evaluation of the endosperm and the preservation of the overproducer embryos.

The native races tested were Pisingallo (originally from Catamarca) and three races from Neuquén. The primary criterion of selection of these races was the degree of endosperm hardness, using only those denoting a high percentage of flint endosperm.

The cultures were carried out according to the methods described by Rapela (1980). They showed a high number of Pisingallo individuals resistant to L + T inhibition. This resistance was shown by the normal development of the radicular zone, considering that this zone is the most affected by the L + T inhibition.

The races from Neuquén studied up to date have been demonstrated to be very sensitive to L + T inhibition. The scarce or null radicular development was reverted by the addition of methionine in the media.

The overproducer individuals were transplanted to the greenhouse 30 days after the seeding in the culture media, demonstrating good adaptation to the environmental conditions.

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