sodininkystė ir daržininkystė 25(4)

Phenylpropanoids including flavones, flavonols, cinnamoyl esters and anthocyanins
provide a UV-A and UV-B screen. The flavonoids are today the most widely
occurred phenolic derivatives in the biosphere (Harborne, 1964). Flavonoids provide
an effective UV screen that reduces UV radiation transmittance through epidermis,
but allow through visible radiation for photosynthesis (Tevini et al., 1991), prevents
DNA damage and UV-B-induced damage of the photosynthetic apparatus (Regner et
al., 1989). A number of authors proposed, that flavonoids are UV-B-inducible (Mohle
and Wellman, 1982; Barnes et al., 1988; Tevini et al., 1991) and in some cases a
linear relationship between flavonoid concentration and UV-B flux has been observed
(Wellman, 1975). The flavonoids response for UV screening may vary from
species to species and could be developmental stage and tissue-dependent (Cockell
and Knowland, 1999).
As well as flavonoids, other aromatic-containing pigments in higher plants such
as alkaloids absorb in the UV range and may provide additional UV protection in
some species (Cockell and Knowland, 1999).
However, the UV-B-dependent variability of total amount of UV-screening compounds
in higher plants is not yet established. Therefore, this study aims to survey a
relationship between UV-B radiation and total amount of UV absorbing compounds
in few plant species including Raphanus sativus L., Malus domestica, Daucus sativus
Röhl., Fragaria ananassa Duch.
Materials and methods. Research was carried out in the phytotron complex
at the Lithuanian Institute of Horticulture in 2006. Raphanus sativus L., Malus domestica,
Daucus sativus Röhl. and Fragaria ananassa Duch. were grown in 5 L
pots of peat substrate (pH 5.85–6) during the experiment. A photoperiod of 16 h
was maintained. All plants were exposed to 0 (reference), 2 and 4 kJ daily UV-B
doses for 5 days under two climatic modes:
(a) non-stressful conditions, where temperature of 21/14°C (day/night) and
ambient CO 2
level was maintained throughout the experiment (all plant species were
examined);
(b) stressful conditions, where temperature of 25/16°C (day/night) and CO 2
level at 700 ppm was maintained throughout the experiment (only Raphanus sativus
L. and Malus domestica were examined).
Samples from fully developed plant leaves were at random taken immediately
after the end of UV-B exposure.
UV-absorbing compounds were analyzed in acidified methanol extracts according
modified method of Mirecki and Teramura (1984), recording and integrating
absorption spectra in the range of 280–400 nm. Relative amount of UV-absorbing
pigments was calculated according the formula as follows:
RA UVpigm
=
∫
Abs
m
where ∫ A – area of absorption spectra, defined as an integral of the absorption
spectra in the range of 280–400 nm i = 1 → 121 ;m – weight of the sample
(g).
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