In previous issues we have reported upon some of these mutants. One of them in particular (de*-7601), studied most extensively, conditions modification in the protein pattern of the endosperm, increases the lysine level, causes electrophoretic variants of the soluble proteins of germ and endosperm, and of the lipoproteins (see MNL 56:108). We have also said that the aforementioned mutant and others of defective kernel modify the content of free amino acids of the kernel (see MNL 58:120 and 62:820.
The study of the biochemical modifications conditioned by or related to these mutants offers the opportunity of better understanding the reason why the kernel is defective, and the lethal character, in most cases.
With the purpose of giving more information on these subjects related to the defective kernel mutants, we have begun research work destined to compare the isoenzymatic patterns, with the aim of verifying some kind of association with the defectiveness of the kernels. Defective kernels and their normal equivalents, corresponding to maize inbred lines, carriers of four mutants, were used to analyze the isoenzymatic patterns obtained by electrophoresis. These mutants are recessive genes of simple inheritance, three of which (de*-7601, de*-7670 and de*-7510) condition kernels of very little weight and are lethal. The other (de*-7547) only reduces to half of normal, and the seed is viable. Out of each inbreeding line, 10 normal kernels and 10 defective ones have been taken at random and been individually tested. The seed extracts, obtained after undergoing 24 hour soaking in distilled water, were used in a starch gel. After the electrophoretic separation, the gel was horizontally cut in three layers which were stained for alcohol dehydrogenase (ADH), malic dehydrogenase (MDH) and esterases (EST).
The patterns obtained showed that: 1) with the exception of the de*-7601 and de*-7547 for MDH and de*-7547 for ADH, the isoenzymatic pattern of the defective kernels is different from its normal equivalents; 2) mainly in the kernels carrying the mutants which condition greater defectiveness, the differences are settled by the absence of bands, or less intensity of them, in the defective ones; and 3) in extreme cases, the defective kernels show very altered patterns as a consequence of not resolving in bands, and the activity zones are diffused in the gel.
With the purpose of quantifying these differences in order to verify whether the same are congruent with the greater or lesser defectiveness produced, that is, whether the greater differences correspond to more defective kernels, we have evaluated the similarity between the isoenzymatic patterns corresponding to defective kernels and their normal equivalents, by simple matching coefficients.
The results obtained for each of the systems and in average are shown in Table 1. If the defectiveness degree may be represented by the defective kernels' weight, expressed as a percentage of their normal equivalents (SW%N), it is easy to conclude from the data of Table 1 that the greater the defectiveness, the greater the differences between the isoenzymatic patterns of normal and defective kernels.
Table 1. Seed weight of defectives as percent of normals (SW%N) and simple matching coefficients (SMC).
In the case of the de*-7547 mutant, which slightly reduces weight and keeps the viability of the kernel, the alteration is null for ADH and MDH, and little for EST. On the contrary, the other three mutations, which are lethal, condition greater differences, sometimes to an extreme degree, although without a specific tendency for isoenzymatic system. On average, there is a very good association between isoenzymatic differences and defectiveness.
According to the above mentioned and to what has been previously reported (see MNL 62:82) it can be stated, at least for the few mutants studied, that the degree of kernel defectiveness is significantly associated with the intensity of the biochemical modifications, in this case with greater or lesser alteration of the isoenzymatic patterns.
The analysis of the differences over
a greater number of mutants will result in greater information, which will
surely be used to settle the reason for kernel defectiveness.
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