S. Reuber et al., A FLAVONOID MUTANT OF BARLEY (HORDEUM-VULGARE L.) EXHIBITS INCREASED SENSITIVITY TO UV-B RADIATION IN THE PRIMARY LEAF, Plant, cell and environment, 19(5), 1996, pp. 593-601
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.