The evaluation of the extent of gametophytic gene expression and of the type of transcription (haploid or haplo-diploid) of the genes, has been continued. The study was performed using isozymes as genetic markers; the determination of the type of expression of genes coding for multimeric enzymes was based on comparison of electrophoretic pattern of pollen and of sporophytic tissues from plants heterozygous for electrophoretic mobility (M. Sari Gorla et al., MGCNL 58:145-146, 1984).

During 1984, ACP-2, CAT-1, CAT-2, CAT-3, ENP, GOT-2, GOT-3, IDH-1, IDH-2, PGM-1, PGM-2, 6-PGD-1, 6-PGD-2, SOD and INVERTASE were included in the analysis. Some enzymes present in pollen could not be tested for haploid expression because they were monomeric forms (ENP, PGM-1, PGM-2), or proved to be invariant (GOT-3, SOD). The others gave the following results.

For ACP-2, one band was observed in parental sporophytic genotypes and two in the hybrid, thus suggesting a monomeric structure of the enzyme; the pollen produced two and four bands, respectively, which reflected the mobility of the sporophytic bands. This concordance was confirmed in about twenty different genotypes analyzed and indicates that the same gene is active in both phases; the different processing of the enzyme in pollen and sporophyte points to haploid expression.

CAT-1, CAT-2 and CAT-3 are expressed in different tissues and developmental stages. Only one form of catalase is present in pollen, probably CAT-1; in fact, a mobility concordance between pollen and one-day-old scutellum variants was observed; moreover, plants heterozygous for CAT-1 and homozygous for CAT-2 and CAT-3 showed two bands in pollen, while pollen from plants heterozygous for CAT-2 or CAT-3 and homozygous for CAT-1 revealed but one activity band.

GOT-2 formed three bands in the extracts from F/S scutellum and only two in pollen from the same plants: it is a dimer with haplo-diploid genetic control.

IDH-1 and IDH-2 gave the same type of zymogram as GOT-2.

Two enzymatic forms of 6-PGD are present in the sporophyte and only one (6-PGD-2) in the gametophyte; pollen from heterozygous 6-PGD-2 F/S plants produced only two parental bands, thus indicating haploid expression of the gene.

Finally, invertase showed a completely different electrophoretic pattern from gametophytic and sporophytic extracts, suggesting that different genes are active in the two phases.

M. Sari Gorla, C. Frova, G. Binelli and E. Ottaviano
 
 

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