A FLAVONOID MUTANT OF BARLEY (HORDEUM-VULGARE L.) EXHIBITS INCREASED SENSITIVITY TO UV-B RADIATION IN THE PRIMARY LEAF

The aim of the present investigation was to define the role of soluble flavonoids as UV-B protectants in the primary leaf of barley (Hordeum vulgare L.). For this purpose we used a mutant line (Ant 287) from th e Carlsberg collection of proanthocyanidin-free barley containing only 7% of total extractable flavonoids in the primary leaf as compared to the mother variety (Hege 550/75), Seven-day-old leaves from plants gr own under high visible light with or without supplementary UV-B radiat ion were used for the determination of UV-B sensitivity, UV-B-induced changes were assessed from parameters of chlorophyll fluorescence of p hotosystem II, including initial and maximum fluorescence, apparent qu antum yield, and photochemical and non-photochemical quenching, A quar tz fibre-optic microprobe was used to evaluate the amount of potential ly harmful UV-B (310 nm radiation) penetrating into the leaf as a dire ct consequence of flavonoid deficiency, Our data indicate an essential role of flavonoids in UV-B protection of barley primary leaves, In le aves of the mutant line grown under supplementary UV-B, an increase in 310 nm radiation in the mesophyll and a strong decrease in the quantu m yield of photosynthesis were observed as compared to the correspondi ng mother variety, Primary leaves of Hege responded to supplementary U V-B radiation with a 30% increase in the major flavonoid saponarin and a 500% increase in the minor compound lutonarin, This is assumed to b e an efficient protective response since no changes in variable chloro phyll fluorescence were apparent. In addition, a further reduction in UV-B penetration into the mesophyll was recorded in these leaves.