Phenylpropanoid compounds in primary leaf tissues of rye (Secale cereale). Light response of their metabolism and the possible role in UV-B protection

The present study was undertaken in order to investigate the suitability of certain markers for UV plant response. In addition, we attempted to link the internal tissue distribution of specific UV-absorbing compounds to profiles of radiation gradients within intact primary rye leaves (Secale cereale L. cv. Kustro). Etiolated rye seedlings irradiated with low visible light (LL) and/or UV radiation were used to study enzyme activities of the two key enzymes, phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS), together with the tissue-specific accumulation of soluble phenylpropanoid products. Plants grown under relatively high visible light(HL) with or without supplementary UV-B radiation were used for further characterization Apparent quantum yield and fluorescence quenching parameters were monitored to assess potential physiological changes due to UV-B exposure in HL-grown seedlings. A quartz fibreoptic microprobe was used to characterize the internal UV-B gradient of the leaf. The response of the phenylpropanoid metabolism to UV radiation was similar in primary leaves of both etiolated and HL-treated green plants. The epidermis-specific flavonoids together with CHS activity turned out to be suitable markers for assessing the effect of UV on the phenolic metabolism. Tile functional role of phenylpropanoid compounds was strongly implicated in protecting rye from UV-B radiation.