3 than 1 2 kb rpl25 2 the difference did not reach a significant level these results suggest that the dna fragment in the region of u2212 1075 to u2212 942 probably plays no role in promoter function the 0 9 kb rpl25 3 promoter fragment was studied further due to its higher activity in transient assays to investigate spatial regulation of the rpl25 promoter the transcriptional fusion construct rpl25 2bgus was prepared by inserting the rpl25 3 promoter gus reporter gene fragment as a cassette into a plant expression binary vector the chimeric promoter gus construct was transferred into tobacco via agrobacterium at least 15 independent transformants were regenerated and allowed to self pollination no gus staining was detected in primary transformants with a low level of gus activity detected in very young leaves our research emphasis was activities seen during seed germination and in younger seedlings t 1 seeds were germinated and the seedlings at different growth stages were harvested for both gus activity measurement and histochemical analysis the results of histochemical analysis are shown in fig5 in comparison with transgenic plants containing rpl34 promoter in which gus staining was observed in the root meristemic region panels f j fig5 gus activity in roots regulated by the rpl25 promoter was undetectable using both gus staining and histochemical analysis panels a e fig5 as for tissues with detectable gus staining high variation in gus activity across different transformants was found data not shown which is a common phenomenon and is probably due to the transcriptional activity of the region in which the construct was inserted gus staining was detectable in seeds after 1d germination and detected strongly in cotyledons 3 d post germination as the seedlings grew gus staining in cotyledons peaked in days 6 8 post.