We are studying the expression of the waxy and shrunken genes in developing maize kernels by in situ hybridization, and the expression of both sucrose synthase genes by in situ immunofluorescence. Regarding the expression of the sucrose synthase, we see a tissue-specific expression of the two sucrose synthase molecules. Sucrose synthase 2 appears earlier, and is strongly represented in the aleurone and subaleurone cell layers. This enzyme is seen later and in small amounts in the endosperm (as judged by its appearance in sh bz-m4 mutants). Sucrose synthase 1 is found mainly in the endosperm. More of the enzyme is seen in the apex than in the basal parts, the enzyme thus forms a gradient, which is also seen at the mRNA level by in situ studies.

Both techniques are used to detect sectors of revertant cells after the excision of Ac or Ds elements from mutated genes. The reversion events of sh-m5933 occur only after 30 days and are predominantly single cell sectors in the interior of the endosperm. The reversion of wx-m7 leads to larger sectors that appear earlier and are distributed more evenly over the kernels. The reasons for this seeming discrepancy are being investigated.

Manfred Heinlein, Ralf Link and Peter Starlinger

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