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.
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.