MUTANTS OF ARABIDOPSIS AS TOOLS TO UNDERSTAND THE REGULATION OF PHENYLPROPANOID PATHWAY AND UVB PROTECTION MECHANISMS

Plants accumulate certain phenylpropanoid compounds in the vacuoles of their epidermal and subepidermal cell layers thereby protecting the u nderlying tissue against UVB-induced damage. However, a number of muta nts of Arabidopsis thaliana are known that fail to synthesize these pr otective pigments, thereby allowing harmful UVB radiation to penetrate into their dermal layers, Study of several of these nonlethal mutants , defective in various aspects of flavonoid and lignin biosynthesis, h as led to a better understanding of the coordinate regulation and expr ession of important genes as well as of mechanisms involved in plant d efense against UVB radiation. The characteristics of the various pheny lpropanoid mutants of Arabidopsis, viz. flavonoid mutants (banyuls [ba n]; increased chalcone synthase expression 1 [icx1]; transparent testa [tt] and ultraviolet sensitive [uvs]) and hydroxycinnamic acid ester mutants (ferulic acid hydroxylase 1 [fah1] and sinapoylglucose accumul ator 1 [sng1]) are discussed in detail, We have briefly touched upon, wherever relevant, the unique aspects in other plant species too.