Suppressed phenylalanine ammonia-lyase activity after heat shock in transgenic Nicotiana plumbaginifolia containing an Arabidopsis HSP18.2-parsley PAL2 chimera gene

The activity of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) after heat sh ock (HS) in leaves and buds of transgenic Nicotiana plumbaginifolia contain ing an Arabidopsis HSP18.2 promoter-parsley phenylalanine ammonia-lyase 2 ( HSP18.2-PAL2) chimera gene was examined. Immediately after HS treatment at 44 degrees C for 5 h, the PAL activity in both transgenic and normal (untra nsformed) plants was 35-38% lower than that before HS. At normal temperatur e (25-26 degrees C), the PAL activity recovered within 5 h of ending the HS treatment in normal plants, but not until 12-24 h in transgenic plants con taining the HSP18.2-PAL2 gene. Reverse transcription-polymerase chain react ion (RT-PCR) analysis revealed the presence of parsley PAL2 mRNA in transge nic plants, which remained for 8-12 h following 5-h HS at 44 degrees C; the mRNA was not observed before HS. The content of chlorogenic acid (CGA; 3-c affeoylquinic acid) decreased drastically 8-12 h after HS in transgenic pla nts, but only slightly in normal plants. Thus, the decrease in PAL activity accompanied by expression of the parsley PAL2 gene after HS treatment corr esponded to the decrease in CGA synthesis. These results might be attribute d to post-transcriptional degradation of endogenous PAL mRNA triggered by t ranscription of the transgene.