Sunlight-induced anthocyanin pigmentation in maize vegetative tissues

cyanin formation have highlighted that multiple photoreceptors, such as phytochrome, blue/UV-A photoreceptor Although, in maize, sunlight-regulated anthocyanin and UV-B photoreceptor mediate the light action (Beggs formation in vegetative tissues is observed only in the and Wellmann, 1985; Beggs et al., 1986). It is assumed cultivars harbouring homozygous recessive pl loci, the that these photoreceptors alter the expression of the identity of the photoreceptor mediating this process is anthocyanin regulatory and structural genes to induce not yet fully established. In this study the nature of the accumulation of anthocyanin. The extensive genetic photoreceptor(s) mediating this response was examined analysis conducted, particularly in maize, have shown using an Indian hybrid maize cultivar (Kanchan-521). The that anthocyanin formation is regulated by the action of etiolated maize seedlings of this cultivar on exposure to more than 20 genes, which govern the temporal and sunlight formed anthocyanin in all vegetative organs. spatial regulation of anthocyanin formation in different Sunlight elicited photoinduction of anthocyanin with a organs (Coe et al., 1988; Dooner et al., 1991). Several slow increase between 4–16 h after the sunlight expogenes encoding either the structural genes or the regusure, followed by a rapid increase between 16–24 h. The latory genes of the anthocyanin pathway have been cloned photoinduction of anthocyanin was primarily mediated (Cone, 1994) and their expression pattern have been by the UV-B component of sunlight and could be elicited determined during development of maize plants (Dooner by exposure to an artificial UV-B light source. The sunet al., 1991; Holton and Cornish, 1995). light-mediated induction of anthocyanin was reduced if In maize, genetic analysis revealed that anthocyanin the sunlight exposure was terminated with a far-red formation is primarily regulated by genes such as the R pulse before transfer to darkness, indicating a coaction gene and its variant and also B, C1 and Pl genes (Coe, of phytochrome in this photoresponse. Exposure to sun1994). These genes code for transcriptional activators light also stimulated phenylalanine ammonia lyase (PAL) which show homology with myb and myc oncogenes activity in all organs with two temporally separated (Consonni et al., 1993; Goff et al., 1992). The transformapeaks. The first peak of PAL between 4–12 h was tion of tobacco and Arabidopsis with the maize R gene induced by phytochrome, and the second peak of PAL increased the pigmentation showing that this gene can between 12–24 h was induced by UV-B light. These also regulate anthocyanin biosynthesis in other species, results indicate that the photoinduction of anthocyanin emphasizing that the above gene may bear homology in maize is mediated by a coaction of UV-B light and with similar genes from dicot species (Lloyd et al., 1992). phytochrome. It has been observed that several maize cultivars show a ‘sun-red’ phenotype, where exposure to sunlight induces