A spontaneous mutation which produces defective kernels and is a lethal recessive (de*-7601) brings about numerous biochemical alterations, as much in the germ as in the endosperm (MNL 56:108, 1982; MNL 57:71, 1983). We have obtained data on the level of free amino acids in defective and normal kernels. In 21 ears of the red flint line WK-01 segregating defective kernels, and in 10 ears of WK-01 not segregating for this mutation, the protein content and the water soluble free amino acid content (FAA) of the defatted whole kernel was analyzed.

The results obtained are detailed in Table 1. The protein level is not significantly different for the three genotypes studied. In defective kernels, the FAA level is greater than in normal kernels. The defective kernels have an average of three times more FAA than normal ones. The results obtained lead us to deduce that the locus de*-7601 conditions a high FAA level. Nevertheless the high variability for FAA in defective kernels (de/de) and in heterozygous normal ones (+/de) makes us suspect the existence of another variation in the genetic control of FAA content.

Among the ears segregating for the defective character, there are some whose normal kernels have a higher FAA level than normal (intermediate between normal and defective). On the other hand, there are ears (with low frequency) in which the mutants have a FAA level which is not significantly higher than that of the normal phenotype grains.

For a better interpretation of this variation, in ears having normal kernels with a higher FAA level than normal, the kernels were individually analyzed. In one ear where 60 kernels were analyzed, a variation range for FAA content was obtained between 13.1 and 51.8 uM Leu/100 mg prot., with an average 23.0 uM Leu/100 mg prot.

These results lead us to deduce that the content of FAA segregates in those ears. Other ears where a few grains were analyzed also indicated segregation for FAA content. On the other hand, in other ears the character does not segregate. In ears segregating for FAA content among normal kernels, high levels of FAA were found in a proportion of approximately 25% (1/4 of the grains have a low level, 1/2 an average level and 1/4 a high level). These results have induced us to think of the probable presence of a co-dominant gene which controls the FAA content.

From what has been expressed previously the following may be deduced: (1) high FAA levels seem to be associated with the de*-7601 gene with a very high frequency (in most cases); (2) the FAA content in the material studied appeared to be controlled by a co-dominant gene, presumably linked to the de*-7601 locus--with a low frequency cases exist such as the one presented, where high FAA levels do not associate with the defective character (it segregates independently); (3) the de*-7601 gene does not have an effect per se on FAA level.

It is probable that the defective mutation in the WK-01 line has been produced simultaneously with another, which conditions the high FAA content.

Apparently, the gene which conditions the high FAA level is linked to de*-7601 since both characters do not segregate independently in most cases.

The fact that there is a co-dominant gene involved in the control of FAA content, and that it does not produce any modification in the grain's phenotype (the grains being red flint), has a special and practical meaning. In fact, the high FAA levels in normal grains are associated with a much better protein quality (high levels of lysine and tryptophan).

We are actually working to isolate homozygotes for the high FAA content character and high protein quality, and to effect a more critical test to confirm this variant.

The results presented indicate once more that it is possible to develop maize of as high protein quality and "normal genotype" (without floury mutants) as those obtained from other origins (MNL 57:75, 1982).

A co-dominant gene which will condition high protein quality and does not modify the normal genotype of the grain might be of great importance.

Table 1. Protein and free amino acid content (FAA) in normal and defective kernels.

J. L. Magoja, I. G. Palacios and M. E. Streitenberger
 
 

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