The 54-1 and 56-1 mutants have been isolated in our lab following EMS pollen mutagenesis (56-1) and as a spontaneous event (54-1). They are recessive embryo-lethals with a small endosperm devoid of carotenoids and anthocyanins. Crosses with the TB-A set of translocations indicate that both mutants are uncovered by Tb-ISb. An allelism test with dek1, uncovered by the same TB, revealed the allelic relationship between the two mutants and dek1.

Tests were then planned to find out whether the pigmenting capacity of the mutant could be recovered by feeding the mutant with pigment precursor. Accordingly immature mutant seeds, obtained on a segregating selfed ear, were cultured as soon as phenotypically recognizable, i.e., 10 days after pollination, on modified LS medium (Gengenbach and Green, Crop Sci. 15, 1975) supplemented with different precursors of flavonoid biosynthesis: phenylalanine, cinnamic acid, dihydroquercetin and malonyl-CoA (5 x 10^-3M for the former, 5 x 10^-4M for the latter) as well as on an unsupplemented medium.

None of the supplements led to positive response as far as pigment production is concerned.

Since the mutants are developmentally blocked at the proembryo stage we wanted to see if they maintain the capacity to grow as undifferentiated callus. Cultures were thus initiated from immature mutant and normal embryos obtained from the same selfed ear.

After two months of culture callus derived from normal seeds looks friable and embryogenic, mutant embryos on the other hand are generally arrested and appear necrotic. In a few cases small callus

masses were observed. They were transferred to an enriched medium where they will be watched for growth and differentiation into somatic embryos.

Milvia Luisa Racchi, Francesca Sparvoli and Giuseppe Gavazzi
 
 

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