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 suitabili ty of certain markers for UV plant response. In addition, we attempted to link the internal tissue distribution of specific UV-absorbing com pounds to profiles of radiation gradients within intact primary rye le aves (Secale cereale L. cv. Kustro). Etiolated rye seedlings irradiate d with low visible light (LL) and/or UV radiation were used to study e nzyme activities of the two key enzymes, phenylalanine ammonia-lyase ( PAL) and chalcone synthase (CHS), together with the tissue-specific ac cumulation of soluble phenylpropanoid products. Plants grown under rel atively high visible light(HL) with or without supplementary UV-B radi ation were used for further characterization Apparent quantum yield an d fluorescence quenching parameters were monitored to assess potential physiological changes due to UV-B exposure in HL-grown seedlings. A q uartz 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 effe ct of UV on the phenolic metabolism. Tile functional role of phenylpro panoid compounds was strongly implicated in protecting rye from UV-B r adiation.