The metabolism of the plant growth regulator maleic hydrazide (MH) has been studied in sterile cell suspension cultures of tobacco, soybean, maize and wheat under standardized conditions. Maleic hydrazide was converted to its O-b -D-glucoside in yields between 9.0 % (tobacco) 15.0 % (soybean), 5.1 % (maize) and 2.2 % (wheat) respectively. This glucoside was completely cleaved under simulated conditions (pH 1, 37°C, 24 h) of a ruminant stomach. From these results it is concluded that MH-O-b-D-glucoside (MHG) belongs to a small group of acid-labile pesticide conjugates (11). The participation of a glucosyltransferase (GT) (EC 2.4.1-) in this conjugation reaction of MH was demonstrated in vitro for the first time. In addition, up to 18 % of the applied maleic hydrazide became associated with nonextractable residues (NER) in soybean, whereas in tobacco only 0.2 % could be detected in this fraction. The residue from soybean cells was solubilized only to a low degree (about 3 %) under simulated stomach conditions, but up to 20 % by the white rot fungus Phanerochaetechrysosporium.
