Expression and enzymatic activity of phenylalanine ammonia-lyase and p-coumarate 3-hydroxylase in mango (Mangifera indica 'Ataulfo') during ripening.

Phenylalanine ammonia lyase (PAL) and p-coumarate 3-hydroxylase (C3H) are key enzymes in the phenylpropanoid pathway. The relative expression of PAL and C3H was evaluated in mango fruit cultivar 'Ataulfo' in four ripening stages (RS1, RS2, RS3, and RS4) by quantitative polymerase chain reaction. In addition, enzyme activity of PAL and C3H was determined in mango fruits during ripening. The PAL levels were downregulated at the RS2 and RS3 stages, while C3H levels were upregulated in fruits only at RS3. The enzyme activity of PAL followed a pattern that was different from that of the PAL expression, thus suggesting regulation at several levels. For C3H, a regulation at the transcriptional level is suggested because a similar pattern was revealed by its activity and transcript level. In this study, the complexity of secondary metabolite biosynthesis regulation is emphasized because PAL and C3H enzymes are involved in the biosynthesis of several secondary metabolites that are active during all mango ripening stages.

Studies on the response of carrot cells to a Sclerotinia sclerotiorum elicitor: induction of the expression of an extracellular glycoprotein mRNA.

A heat-released elicitor (HRE) obtained from Sclerotinia sclerotiorum mycelium induced a transient increase in the activity of phenylalanine-ammonia lyase (PAL) in a carrot cell culture. Differential display reactions carried out on total RNA extracted from cells exposed for 7 h to the HRE revealed a complex cell response involving the induction and repression of several mRNAs. One of these elicitor-induced mRNAs encodes a 42.6-kDa protein. Northern (RNA) blot analysis and reverse-transcription polymerase chain reaction studies showed that noninduced cells have a basal expression of the 42.6-kDa protein mRNA that was stimulated five- to 10-fold by treatment with the elicitor.