DETECTION, EXPRESSION AND SPECIFIC ELIMINATION OF ENDOGENOUS BETA-GLUCURONIDASE ACTIVITY IN TRANSGENIC AND NONTRANSGENIC PLANTS

With the aim of making a system using the GUS gene as a selection gene, the effects of two toxin glucuronides were tested on transgenic tobacco cells (Nicotiana tabacum L.) containing a beta-glucuronidase (GUS) gene from Escherichia coli and on non-transgenic cells. No significant difference in toxicity was observed between transgenic and non-transgenic cells. We found that this most probably was due to the activity of an endogenous GUS enzyme, which could be detected in all plant species tested, e.g. tobacco, sugar beet (Beta vulgaris L.), oilseed rape (Brassica napus L.), pea (Pisum sativum L.), wheat (Triticum sativum L.) and rhubarb (Rheum rhaponticum L.). This indicates that GUS may be ubiquitous to plants contrary to earlier assumptions. The endogenous enzyme is active at pH 4-5 and the activity is eliminated without reducing the introduced GUS activity when pH is elevated. In addition the endogenous GUS can be selectively inhibited at high temperatures. Modifications according to these Findings can be employed in standard GUS assays to avoid misinterpretations when the expression of tissue specific promoters is tested.