Expression profile of phenylalanine ammonia-lyase (PAL) and phenolic content during early stages of graft development in bud grafted Hevea brasiliensis

Phenylalanine ammonia lyase (PAL) is a key enzyme in the phenylpropanoid pathway responsible for the biosynthesis of many secondary metabolites, such as anthocyanins, flavanols, and lignins. This study investigated the effect of grafting on vegetative growth, PAL expression and phenolic content of RRIM 600 and RRIT 251 bud grafted on different rubber rootstocks: for homografts (RRIM 600/RRIM 600 and RRIT 251/RRIT 251) and heterografts (RRIM 600/RRIM 623, RRIM 600/Clone#1, RRIM 600/Clone#2) (RRIT 251/RRIM 623, RRIT 251/Clone#1, RRIT 251/Clone#2) at 0, 7, 14, 21 and 28 days after bud grafting. For the RRIM 600 scion, the rootstock that provided the highest growth rate was Clone#1 while RRIT 251 showed uniform growth on different graft combinations. The results indicate that grafting alters PAL gene expression. PAL transcripts at higher levels during the early stages of grafting development especially 7 days after grafting. However, no significant differences were detected in the phenolic content at different post-grafting times. These findings suggest that the expression of the PAL gene is related to grafting compatibility in grafted H. brasiliensis.