Gene expression during early kernel development in Zea mays

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Abstract
The timing of gene expression in the endosperm of developing F1 maize kernels was investigated. Zymogram analysis revealed the presence of maternally derived allelic gene products on all days investigated, but activity of paternally derived allelic gene products is not detectable until days 6–8 postpollination, depending on the particular cross used and the enzyme investigated. This pattern holds true for eight different isozymes of five different enzyme systems, including catalase, alcohol dehydrogenase, glutamate‐oxaloacetate transaminase, endopeptid́ase, and aminopeptidase. An increase in specific activity for catalase, alcohol dehydrogenase, and endopeptidase correlates precisely with the day of visualization of the paternally derived allelic gene product on the zymograms. Rocket immunoelectrophoresis confirms a dramatic increase in catalase and alcohol dehydrogenase protein levels on the day the paternally derived allelic gene product is first detected on zymograms. Appropriate crosses utilizing three different allelic variants revealed the presence of enzyme of maternal plant origin within the endosperm prior to day 6 postpollination.Maize kernels were cultured in vitro on an agar‐based medium as early as 3 days postpollination. Using medium supplemented with actinomycin D or cycloheximide, it was possible to localize the critical time periods for transcription and translation of the paternally derived allele in the F1 hybrids. For aminopeptidase (AMP‐1, AMP‐3) and endopeptidase (ENP‐1), transcription occurs as early as 3–4 days postpollination, and translation of the transcripts starts at about 4–5 days postpollination. Although the evidence is indirect, it is likely that the maternally derived allele of the F1 kernels is activated (ie, begins transcribing) synchronously with the paternally derived allele during this early developmental time period.