UV-B Radiation and the Evolution of Polyphenolics | Ecology

After reading this article you will learn about the UV-B radiation and the evolution of Polyphenolics.

Solar UV-B radiation is known to stimulate the en­zymes phenylalanine amonialyase (PAL) and chalcone synthase (CHS) and other branch-point en­zymes of the phenylpropanoid pathway (Fig. 17.3). PAL catalyzes the transformation of phenylalanine into transcinnamic acid, which may eventually lead to the formation of complex phenolic compounds such as flavonoids, tannins and lignin’s.

UV absorption in the UV-B wavelengths by Cinnamic acid (maximum absorption at 308nm) exceeds that of phenylalanine (maximum absorp­tion at 280nm). The chemical evolution of these and other UV-B absorbing compounds has been assumed to be an important part of the evolution from aquatic plants to land plants.

The complex­ity of polyphenolics tends to increase with evolu­tionary advancement from algae, charophycean algae, bryophytes, pteridophytes, gymnosperms to angiosperms (Fig. 17.4). A high degree of polymeri­sation of phenolics is found in land plants, i.e. fla­vonoids, tannins and lignin’s.

In addition to absorp­tion of UV-B radiation, these compounds serve many other functions such as signal transduction, plant hormones, chemical defence against microbes, herbivory and structureal rigidity (Fig. 17.5).

The physical and chemical stability and the re­sistance to microbial breakdown of complex polyphenolics in plant litter contributes consider­ably to the long-term storage of organic carbon in terrestrial ecosystems.

Conclusion:

Until recently, the effects of enhanced solar UV-B radiation on crops and natural terrestrial plant spe­cies were generally considered to be negative. Reduction of biomass, reduced yields of crops, and disturbed photosynthetic processes have been re­ported as a result of indoor UV-B shades.

Solar UV-B effects is known to stimulate the enzyme phenylalanine amonialyase (PAL) and Chalcone synthase (CSH) and other branch point enzymes of the phenyl propanoid pathway. PAL catalyzes the transformation of phenylalanine into transcinnanic acid, which may lead to the forma­tion of complex phenolic compounds such as flavonoids, tannins and lignin’s. Induction of UV- B absorbing flavonoid synthetic is primarily con­sidered to function as a UV-screen. Flavonoids accumulate particularly in vacuoles of epidermal cells, reducing UV-B levels in the chloroplasts of mesophyll cells.

UV-B also affecting the chemical deference of plants in both terrestrial and aquatic ecosys­tems by altering tropic behaviour, decomposi­tion rates and also distribution of phytochemical substances specially the secondary metabo­lites.