| In all plants, including tomato (Lycopersicon esculentum), defence and development are critically dependent on products of the phenylpropanoid pathway. Phenylalanine ammonia-lyase (PAL) is the first enzyme of this pathway. In tomato, the PAL gene family comprises at least 5 different classes of PAL genes (PAL1-5) with PAL5 consisting of 5--6 members per haploid genome. Contrary to studies in other plants, analyses in tomato indicate that only one PAL (PAL5) mRNA is expressed in leaf tissue. In the present study, RT-PCR, RFLP, DNA cloning and sequencing were used to further assess PAL gene expression in respect to plant age, tissue type and various stresses. For quantitative RT-PCR assays an internal control also was prepared and incorporated. While PAL expression was elevated significantly in callus and flower as well as wounded, water drenched and young plants, the expression of alternate PAL genes was not observed. The significance of these observations with respect to regulation of tomato PAL genes and their silencing is discussed. |
