COMPARATIVE ACTIVITIES OF PHENYLALANINE AMMONIA-LYASE AND TYROSINE AMMONIA-LYASE AND PHENOLIC COMPOUNDS ACCUMULATED IN CASSAVA ELICITED CELL

Plants respond to attack by pathogens by initiating a change in cellular metabolism, leading to synthesis of antifungal proteins, production of phytoalexins and/or accumulation of phenolic compounds, namely lignins and salicylic. Lignins reinforce pectocellulosic cell walls and limit the invasion of plant tissues by pathogens; while salicylic acid plays a role in signals plant defense against pathogens. The objective of this study was to evaluate the activities of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and tyrosine ammonia-lyase (TAL, EC 4.3.1.5); and to determine the level of their involvement in the biosynthetic pathway of these phenylpropanoids in cells of cassava (Manihot esculenta Crantz, cv Yacé) elicited with salicylic acid (SA). PAL and TAL activities were demonstrated in crude extract enzyme. PAL activity was 9.8 times greater than that of TAL in the pellet obtained with 20% (w/v) ammonium sulphate. In the extract treated with Dowex 2 (cationic), TAL activity was 36.7 times greater than that of PAL. pH and temperature optima of PAL (8; 40 °C) differed from those of TAL (8.5; 30 °C). In the presence of SA, PAL and TAL activities were respectively maximum 24 and 72 hr after inoculation. TAL activity and induced phenols were much higher than PAL. PAL and TAL activities were optimised respectively, by 75 and 100 μM of SA. The synthesis of phenolic compounds was concomitant with enzymes stimulation. These results show that PAL is different from TAL and the two enzymes are involved in the biosynthetic pathway of phenylpropanoids in cassava.