Abstract Current biotechnology research is focused on tissue-specific expression of genes of interest in plants. Promoters with specific spatial and temporal expression profiles in targeted organisms are in wide use for this. This study investigated whether the Arabidopsis thaliana seed- and pollen-specific promoter MXL maintains its specificity in transgenic tobacco plants. Histochemical analysis revealed that the MXL fusion promoter drives slightly different GUS expression in that heterologous organism. GUS staining was clearly detected in the bicellular stage of pollen development and later in germinating tobacco pollen grains. Unlike in A. thaliana, where the MXL promoter is active during the whole period of embryo development, in tobacco its activity was restricted to a short temporal and spatial window from late-heart to mid-torpedo stages, mainly in the apical part of the developing embryo. These results point to the need to test the expression profiles of heterologous promoters in targeted species before they are used in particular biotechnological programs.

Abstract Gene flow among individual trees of Pinus sylvestris and P. mugo putative hybrid swarms in Slovakia was fol-lowed at four localities using the species-diagnostic cpDNA trnV-trnH/Hinf I restriction profile. Variable proportions of P. sylvestris and P. mugo haplotypes were revealed among the sampled localities. Low between-habitus consistency of the trees and their cpDNA haplotypes indicates the hybrid nature of the swarms. Molecular analy-sis based on mutual comparison of the haplotypes of a given tree and its embryos suggests direct and recipro-cal hybridization between trees of the P. sylvestris and P. mugo haplotypes. Besides conspecific embryos resulting from hybridization of trees with the same haplotype (P. sylvestris × P. sylvestris and P. mugo × P. mugo), hybrid embryos of P. sylvestris × P. mugo (8.03%) and P. mugo × P. sylvestris (11.50%) were also detected in open-pollinated offspring. The results are discussed from the standpoint of primary and introgressive hybridization between the parental species.