EFFECTS OF TETCYCLACIS ON GROWTH AND ON STEROL AND SAPOGENIN CONTENT IN FENUGREEK

Tetcyclacis, a norbornanodiazetine plant growth retardant, used at 10 mg.L(-1) (36 mu M), caused greater growth inhibition in the shoots of fenugreek (Trigonella foenum-graecum L.) seedlings (60%) than in the r oots (30%), compared with control. This greater retardation was revers ed by a supplement of gibberellin (200 mg.L(-1)). The total sterol com position of control and treated seedlings was analyzed and quantified. In the roots especially, treatment of seedlings with tetcyclacis resu lted in a modification of the sterol profile, leading to an accumulati on of 14 alpha-methyl sterols, presumably as a consequence of the inhi bition of cytochrome P-450-dependent obtusifoliol 14 alpha-demethylase . In addition, tetcyclacis caused a significant increase in the choles terol content of the roots: 38.1% of total sterols against 3.7% in the control roots. However, tetcyclacis was shown to be an ineffective in hibitor of the S-adenosyl-L-methionine (Adomet): cycloartenol-C24-meth yltransferase (EC 2.1.1.41) in fenugreek microsomes indicating that ch olesterol accumulation does not result from the inhibition of the ster ol side chain-alkylating enzyme. Moreover, this accumulation was shown to be concomitant with a significant decrease of the sapogenin conten t in the treated roots. This last result is discussed with respect to the current proposed pathway by which cholesterol is metabolized to sa ponins.