SEX DETERMINATION AND REPRODUCTIVE ORGAN DIFFERENTIATION IN MERCURIALIS

The origin, the morphology and ontogeny of monoecious and dioecious annual mercuries are described. Flowers are strictly unisex. Dioeciousness in Mercurialis annua is controlled by 3 genes. Maleness depends on 2 complementary genes, A and one of the B genes. Male strength (sensitivity to feminizing hormones) depends on the number of dominant B genes. Dominant A, or dominant B alone induces femaleness. Exogenous auxins induce staminate flowers on female nodes; cytokinins induce pistillate flowers on male plants. Endogenous auxin and cytokinins were measured (HPLC/GC/MS) in isogenic lines constructed for the allelic combinations of sex genes. Auxin levels were correlated with each combination (A + B1 + B2 > A + B1 > A + B2 > A). Male and female cytokinins were characterized by a prominent trans-oxidized pathway due to the gene A. For stamens, the path stopped at t-io6Ado. Pistillate flowers develop when the conversion of t-io6Ado to t-io6Ade due to the products of recessive b genes occurred. Sex genes control the phytohormonal balances because t-io6Ade induces IAA-oxidases, then IAA decreases. Sexual differentiation was studied. Tight coordinated peroxidases were demonstrated to be specific for the cell lineages of stamens. They were modulated by hormones. Differences in poly(A)+ populations of each sex were demonstrated. Staminate flowers presented 6.5% specificity. Female flowers contained 97.8% of amplified male transcripts. Feminizing hormones induced the amplification of male transcripts for phenotypic pistillate flower formation. cDNA probes specific for stamens showed the hormonal dependence of the corresponding male RNAs. Sex genes appear to be major regulators acting on specific 'sexual metabolites' that control the poly(A)+ populations specific for each sexual type. Sex determination and differentiation in 'true' unisexual flowers (in contrast with unisexuality by abortion) also furnish data on the establishment of organ pattern in hermaphroditic flowers.