NON-DAMAGING AND POSITIVE EFFECTS OF UV RADIATION ON HIGHER PLANTS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 156

Figure 1. UV action and response spectra for flavonoid synthesis. Solid circles = in parsley
( Petroselinum hortense D.) cell cultures 36,37 ; open circles = same as previous one (Wellmann cited in
ref. 27); triangles = action spectrum for isoflavonoid (coumestrol) synthesis in bean ( Phaseolus
vulgaris L.) primary leaves 35 . To facilitate comparison, the data are normalised to 100.
In tomato ( Lycopersicon esculentum L.), anthocyanin synthesis is also controlled
by phytochrome, but the response (as with mustard hypocotyls) is amplified by UV-B
radiation. Interestingly, a tomato mutant deficient in phytochrome was induced to form
anthocyanins by UV-B radiation 40 .
A specific UV-B photoreceptor is involved in the induction of anthocyanin
synthesis in the mesocotyls of milo ( Sorghum vulgare Pers.) seedlings. However,
synthesis is modulated by phytochrome and Pfr (the active form) must be present. R or
FR radiation alone do not result in pigmentation because there is an absolute
requirement for B or UV light 44 . It was later shown that not only the B/UV-A
photoreceptor and phytochrome controlled this response, but also that a specific UV-B
photoreceptor was involved 45,46 . Further details are given by Mohr 39 .
Action spectra for the regulation of anthocyanin synthesis in maize ( Zea mays L.)
are shown in Fig. 2 35,37 . As far as the authors could ascertain, these were
photomorphogenic rather than damage responses and therefore represent excitation of
the UV-B photoreceptor.