PHOTOMORPHOGENIC RESPONSES TO UV RADIATION III: A COMPARATIVE STUDY OF UVB EFFECTS ON ANTHOCYANIN and FLAVONOID ACCUMULATION IN WILD‐TYPE and aurea MUTANT OF TOMATO (Lycopersicon esculentum MILL.)

Abstract

The UV‐mediated induction of anthocyanin and UV‐absorbing compounds was characterized in etiolated hypocotyls of wild‐type and aurea (au) mutant tomato seedlings. Ultraviolet radiation induced significant increases of anthocyanin and UV‐absorbing compounds in hypocotyls of die au mutant and of its isogenic wild‐type, but the differences in the time courses of UV‐induced pigment accumulation indicate mat different photoregulatory mechanisms are involved for each of these two groups of pigments. It appears mat prolonged presence of adequate levels of UVB (290–320nm) energy and consequently the action of a specific UVB photoreceptor are indispensable for the photoinduction of anthocyanin accumulation in UV‐irradiated hypocotyl of the au mutant that is missing the labile phytochrome pool. The large difference found between the wild‐type and the au mutant strongly indicate the involvement of labile phytochrome as the primary functional photoreceptor for the photoinduction of anthocyanin accumulation in wild‐type tomato hypocotyls. The UVB photoreceptor could at least partly replace the action of labile phytochrome (as far as anthocyanin accumulation is concerned) when the functional phytochrome pool is missing as in the au mutant. The general picture of UV‐mediated induction of total UV‐absorbing compounds shows only a macroscopic difference between wild‐type and die au mutant of tomato: the higher initial level (in darkness) of these compounds in die wild‐type in contrast to the au mutant. Although there is UV‐induced accumulation of UV‐absorbing compounds in bom genotypes, the levels in the au mutant never reach mat of the wild‐type under the same UV exposure. A UVB photosensor may play a more important role in the photoinduction of UV‐absorbing compounds. Indeed, in the absence of labile phytochrome, i.e. in the au mutant, a UVB‐absorbing photoreceptor alone is able to establish high responsiveness for the UV‐induced flavonoid accumulation.

Developmental phase-dependent photosynthetic responses to ultraviolet-B radiation: damage, defence, and adaptation of primary leaves of wheat seedlings

“…Therefore, accumulation of anthocyanin and/or flavonoids in response to UV-B radiation is an adaptive defence mechanism, and their accumulation has been used as a marker of adaptation in our work. UV-B induced enhancement in the contents of flavonoids and anthocyanin in primary leaves of wheat seedlings is in conformity with earlier works (Lindoo and Caldwell 1978, Beggs and Wellmann 1994, Brandt et al 1995, Olsson et al 1998, Gao et al 2004). Accumulation of UV-absorbing substance throughout the leaf development of spinach seedlings has been observed by Hada et al (2001).…”

Why some leaves are anthocyanic and why most anthocyanic leaves are red?

“…Leaf anthocyanin levels often increase in response to UV-B radiation in laboratory trials (Alexieva et al, 2001;Brandt et al, 1995;Lindoo and Caldwell, 1978) and their presence can alleviate DNA damage (Kootstra, 1994;Li et al, 1993). Under field conditions, with balanced UV-A/visible radiation, mildly enhanced UV-B radiation may (Mendez et al, 1999) or may not (Dillenburg et al, 1995) result in increased anthocyanin levels.…”

Seasonal variations in antioxidant components of cherry tomatoes (Lycopersicon esculentum cv. Naomi F1)

“…As regards phenolic compounds, although genetic control represents the main factor in determining their accumulation in vegetable foods, external factors may also have a significant effect on this (Macheix et al, 1990). In many plant species the flavonol content may be enhanced in response to elevated light levels, in particular to increased UV-B radiation (Brandt et al, 1995). As a matter of fact, it has been reported that cherry tomato plants grown in greenhouse under high light accumulated an approximately two-fold greater soluble phenols content (rutin and chlorogenic acid) than low-light plants (Wilkens et al, 1996).…”