Developmental studies on seed germination and seedling formation

--G. Gavazzi and G. Todesco

We have isolated several mutants impairing germination or early seedling development with the aim of using them as a tool to elucidate the genetic program accounting for seedling development. Some of these mutants were obtained following chemical mutagenesis, while the majority were isolated in the selfed progeny of stocks carrying Ac or Mu outcrossed to different lines. Those showing up in a sandbench test as segregating variants were retested by a second selfing cycle and, if showing up again with the same phenotype, were given a tentative symbol (des: defective seedling) followed by a number. This way many bona fide mutants exhibiting slow growth and not confirmed in the progeny of the second selfing were discarded. The mutants so far identified are all recessive single gene mutants exhibiting a broad spectrum of phenotypes. Some impair germination; the most dramatic ones in their effect lead to complete suppression of germination. Others suppress dormancy and, at least in one case, show clear symptoms of water stress in the seedling, while others are recognizable two days after germination or later because of the enlarged coleoptile and primary root, an abnormal (open) coleoptile or leaf morphology, or clear symptoms of dwarfism. The last have been tested for their response to exogenous gibberellins (GA4 +GA7 10-5M) and crossed inter se or with known d mutants (d1, d2, d3 and d5). The allelism test has almost been completed (see MNL 64:86-87 for preliminary results) and has led to the identification of five GA responding mutants not attributable to any of the d genes described in the literature. One of the mutants exhibiting an abnormal seedling development (des17) has been characterized, and the results are presented in the next note, while the others are presently under investigation with the aim of linking the disruption in their developmental program to metabolic or hormonal unbalance.

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