USE OF BINDING MEASUREMENTS TO PREDICT ELICITOR DOSAGE REQUIREMENTS FOR SECONDARY METABOLITE PRODUCTION FROM ROOT CULTURES

The strength of binding of a fungal elicitor derived from Rhizoctonia solani to Agrobacterium-transformed root cultures of Hyoscyamus muticu s is assessed. Two techniques are used to estimate the equilibrium bin ding constant: (1) a dose response, which involves the measurement of sesquiterpene formation in the presence of different amounts of elicit or, and (2) elicitor-contacting experiments in which the root tissue i s exposed to the elicitor for a short period of time and then the unbo und elicitor concentration is determined by a bioassay. The equilibriu m binding constants estimated by these two techniques were on the same order of magnitude. The value predicted from the dose response techni que was 6.44 (mmol of glucose equiv/L of medium)(-1), while that obtai ned from elicitor contact was 1.89 (mmol of glucose equiv/L of medium) (-1) The higher binding constant measured by dose response may result from feedback inhibition of secondary metabolite formation at higher e licitor dosages. The magnitude of the binding constant indicates that elicitor dosage is dependent upon both the amount of tissue in the rea ctor and the amount of medium present to dilute the added elicitor. Si nce proposed reactor configurations for plant root culture vary from 2 00 to 2000 g of tissue per liter of medium, elicitor dosage requiremen ts will vary significantly depending upon the reactor operational cond itions. This influence of elicitor binding on reactor design and opera tion is discussed.