Functional Significance and Induction by Solar Radiation of Ultraviolet-Absorbing Sunscreens in Field-Grown Soybean Crops

Abstract

Colorless phenylpropanoid derivatives are known to protect plants from ultraviolet (UV) radiation, but their photoregulation and physiological roles under field conditions have not been investigated in detail. Here we describe a fast method to estimate the degree of UV penetration into photosynthetic tissue, which is based on chlorophyll fluorescence imaging. In Arabidopsis this technique clearly separated the UV-hypersensitive transparent testa (tt) tt5 and tt6 mutants from the wild type (WT) and tt3, tt4, and tt7 mutants. In field-grown soybean (Glycine max), we found significant differences in UV penetration among cultivars with different levels of leaf phenolics, and between plants grown under contrasting levels of solar UV-B. The reduction in UV penetration induced by ambient UV-B had direct implications for DNA integrity in the underlying leaf tissue; thus, the number of cyclobutane pyrimidine dimers caused by a short exposure to solar UV-B was much larger in leaves with high UV transmittance than in leaves pretreated with solar UV-B to increase the content phenylpropanoids. Most of the phenylpropanoid response to solar UV in field-grown soybeans was induced by the UV-B component ( < 315 nm). Our results indicate that phenolic sunscreens in soybean are highly responsive to the wavelengths that are most affected by variations in ozone levels, and that they play an important role in UV protection in the field.

Efeitos na taxa de transporte de elétrons de plantas daninhas após aplicação de amicarbazone

“…A folha adulta manteve ainda redução de 23% do ETR em relação ao momento inicial, em que as plantas estavam ainda sem herbicida em solução. Destaca-se também que algumas pequenas oscilações do ETR no período avaliado devem-se às condições do ambiente (Mazza et al, 2000). Para D. horizontalis, com quatro horas após a disponibilidade do herbicida em solução, ocorreu redução de 17% do ETR para a folha adulta, em relação ao valor de ETR inicial da folha sem herbicida.…”

UV-B effects on leaves—Oxidative stress and acclimation in controlled environments

“…The former strategy is facilitated by UV-induced morphology changes including the increase of epidermal UV absorption [4], and moving the site of photosynthesis away from upper regions of adaxial palisade cells towards the inside of the leaf [37]. An application of UVinducible chlorophyll fluorescence demonstrated the penetration of 305 nm UV-B into Arabidopsis and soybean leaves, and that UV-B reached chlorophyll containing tissues even in sunlight acclimated leaves having strong epidermal UV screening [38]. These results show the need for the second, antioxidant line of defense.…”

Growth and physiological responses of sunflower plants exposed to ultraviolet-B radiation

“…The defence mechanism by increased UV-B absorbing compounds partly counteracts the harmful effects of UV-B radiation. Both field and in vitro studies have shown that certain flavonoids and non-specified phenolics can protect DNA from UV-B induced damage (KOOSTRA, 1994;MAZZA et al, 2000).…”