In the present work the total DNA content
was measured in both lines (E and Z) with Feulgen cytophotometry with the
aim to elucidate whether the increase in the size of knobs was due to differential
packing, or insertion or endoreduplication of DNA. Moreover, the meiotic
behaviour of both lines was studied to determine if the partial male sterility
of the alloplasmic line E could be due to chromosomal irregularities.
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Although Z does not have regular meiosis,
it has a mean of univalents significantly lower than E. Moreover, in the
E line several meiotic irregularities were observed: desynapsis, cytomixis,
nuclear fusion, nucleolar bodies and pseudomultivalents. These abnormalities
were only observed in some of the flowers of the panicle. This fact could
indicate that the nucleus-cytoplasm interaction alters the canalization
of development, although the origin of the disharmony is yet unknown.
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There is a quantitative change in the total DNA content, being significantly high in the E line. Moreover, the E line presents bigger knobs in pachytene, and bigger C+ bands in mitotic and meiotic metaphases when C-banding technique is applied. These results could indicate that the cytoplasm of ssp. mexicana produces nucleotypical changes in the nucleus of maize, increasing the highly repetitive DNA in the zone of the knobs. This could be affecting the regulatory system.
It can be concluded that the interaction
between the nucleus of maize and the cytoplasm of Z. mays ssp. mexicana
may induce a mechanism that generates rapid genome changes which will be
manipulated to our advantage when more information about the nature of
the phenomena described would be obtained.
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