RESUMEN
The newly established GUS expression bioassay on the callus extracts of 22 species of plants revealed that the methanol extract of Phytolacca americana callus had the most potent inhibitory activity against agrobacterial plant transformation. A triterpene glycoside phytolaccoside B was isolated from the extract as a genuine plant transformation inhibitor having neither antiagrobacterial nor phytotoxic activity. This compound is promising for use as a biochemical probe for studies on the plant transformation mechanism.
RESUMEN
A convenient and quantitative bioassay method for evaluating the efficiency of plant transformation by Agrobacterium tumefaciens is important to search plant transformation inhibitors, possible biochemical probes for study on its mechanism. Our previously reported method, in which the plant transformation had been detected by the expression of ß-glucuronidase in transformed plants, was improved. The difference between the previous and the improved methods is the use of suspension-cultured cells of Ageratum conyzoides as the host plant instead of Nicotiana tabacum BY-2; this alteration of the host enabled us to measure the ß-glucuronidase activity in plant cells not only fluorometrically but also colorimetrically. The enzyme activity expressed in the cells of A. conyzoides was nearly 100 times higher than that of N. tabacum BY-2, and was enough for detection by colorimetric measurement. The method, therefore, is useful for a convenient determination of inhibitory activity against plant transformation.