The genetic control of seed proteins produced by a spontaneous defective kernel mutant was previously reported (MNL 56:108, 1982). The variation during grain development of the patterns of soluble proteins and lipoproteins was studied in the red flint corn line WK-01 and its isogenic version of defective kernel, de*-7601. By electrophoresis in polyacrylamide gel, the soluble proteins of immature whole kernels were separated at 18, 23 and 28 days after pollination. The defective phenotype is perfectly distinguishable from normal after 14-16 days. As with the mature kernel (MNL 56), de*-7601 conditioned a blockage of certain soluble protein components, and for lipoproteins, new components (Figs. 1 and 2).
From the results obtained it can be deduced that:
1. There are some polypeptides that, no matter the development stage, never appear in the soluble proteins of de*-7601 grains. This can be interpreted as a blockage of the structural genes which codify those components by one or more regulatory genes, or the expression of null alleles of the corresponding structural gene affected by mutation.
2. Some molecular components of soluble proteins have their expression blocked during the first developmental stages in defective kernels, but they appear in more advanced development stages. In this case, it is obvious that the structural gene/genes responsible for the codification of those components have an active allele, but one or more regulatory genes represses the expression with different intensity according to the developmental stage. The regulatory gene conditions a delay in the expression of certain polypeptides in defective grains.
3. The polypeptide patterns vary in normal kernels, as in defective ones, as time goes by during the development of the kernel. Generally, the pattern becomes more complex.
4. For soluble proteins the differences between normal patterns and defective ones decrease as maturity is reached, while for lipoproteins there is a greater pattern difference in the most advanced stages of the kernel development.
It can be said that in general the early blockage in the expression of certain genes which codify some components of the defective kernel proteins and retard expression of others, must possibly be the cause of tardiness in the development of the defective kernel, which brings about a lethal character. This may be interpreted as a phenomenon conditioned by a regulatory gene. Nevertheless, a particular anomaly occurs with lipoproteins of developing kernels similar to that previously reported (MNL 56:108, 1982). In fact, the lipoprotein patterns of defective kernels do not show fewer bands than normal, but have new fast bands. So as to interpret this phenomenon, electrophoretic runs for lipoproteins of normal kernels at a high sample concentration were carried out.
These experiments demonstrated that fast bands are also present in normal kernels, but in a low proportion, and therefore are not distinguishable in an electrophoresis run with normal protein concentration. These results suggest that the excess of those lipoprotein components in the defectives might also be the cause of the defective condition. This phenomenon might be interpreted as the uncontrolled synthesis of those components as a consequence of the mutation of the regulatory locus, which in normal kernels regulated the synthesized quantity. In the defectives, where such regulation is not exercised over the structural loci which codifies those lipoproteins, they are transcribed uncontrollably. All these results tend to strengthen the tests obtained to support the hypothesis that the locus de*-7601 is a regulatory gene that provokes dramatic alterations in the maize seed, becoming a lethal character.
Figure 1. Polyacrylamide gel electrophoretic patterns of soluble whole kernel proteins during grain development. 28 d, 23 d, 18 d-- days after pollination: +-- normal, de-- defective.
Figure 2: Polyacrylamide gel electrophoretic patterns of whole kernel lipoproteins during grain development. 28 d, 23 d, 18 d-- days after pollination; +--normal; de-- defective.
Jorge Luis Magoja and Angel Alberto Nivio
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