Ubiquitous presence of beta-glucuronidase (GUS) in plants and its regulation in some model plants.

The enzyme beta-glucuronidase (GUS) is well characterized in animals and microbes. However, this enzyme is not well studied in plants and is widely assumed to be absent in them. In this study we document the ubiquitous presence of GUS in the model plants Arabidopsis thaliana, Oryza sativa, Nicotiana tabacum and Zea mays and record its expression pattern. The pH of the assay buffer was found to be critical with pH 4.0 being optimum for detection in all the species. GUS in plants appears to be associated with growth. In general, younger regions of the organs showed more GUS activity than the older and more mature tissues. In Brassica juncea roots stained for GUS, intense blue color could be seen in the trichoblast cells and the growing root hair cells as compared to the non-root hair forming epidermal cells or the fully elongated root hairs. Cotton fibers showed high GUS activity during the initial phase of elongation while the seed coat, from which the fibers formed, did not stain for GUS activity. The activity in the fibers disappeared after they were fully elongated. The level of GUS activity increased 2.58 folds in leaf tissues of N. tabacum when cultured in MS medium supplemented with 6-benzylaminopurine, while gibberellic acid enhanced GUS activity 2.9 folds in the inter-nodal regions of rice in 12-h treatment. In addition, elongation of stem, root and root hairs in tobacco seedlings was strongly inhibited by the specific inhibitor of GUS, saccharo-1-4-lactone in a reversible manner. Taken together, these evidences suggest a probable association of plant GUS in cell growth.