Anthocyanin instability in basil (Ocimum basilicum L.)
The natural red and purple anthocyanin pigments of fruits and vegetables play an essential role for both fresh market consumers and in the food processing industry. Anthocyanins not only enhance the appearance of many foods and beverages, but also have therapeutic properties. Understanding the regulation of these pigments becomes paramount when developing new sources for the isolation of anthocyanins. The biosynthesis of anthocyanin pigments in plants requires a complex interaction between both structural and regulatory genes. Mutations in both types of genes are not deleterious, yet importantly, they result in easily recognizable phenotypes. One such mutation is prevalent in purple basil varieties (Ocimum basilicum L.) and offers an excellent opportunity to study the regulation of anthocyanin pigments. Purple basil varieties have a tendency to partially revert to a green phenotype by randomly accumulating green leaf sectors throughout a single growing season. In this study, fourteen different anthocyanin pigments were identified in basil, four of which are reported for the first time. Purple basil appears to be an excellent source for unique and stable anthocyanins. Using controlled crosses, the inheritance of anthocyanin expression was found to be a dominant two gene trait, with the inheritance of ruffled leaf texture being controlled by a single recessive gene. Experiments with high light conditions, HPLC analysis, and feeding experiments, determined that the mutation was occurring in a regulatory gene of the anthocyanin pathway. We hypothesized that the introduction of the Lc gene from maize could stabilize anthocyanin pigments in basil leaves and help overcome the instability mutation in basil. A reliable protocol for the regeneration and transformation of basil was first established and confirmed utilizing the gusA gene. This is the first report of genetic engineering in basil. Anthocyanin expression was noted in both transformed tissue and control regenerated green basil tissue, suggesting that stable Lc expression could not be confirmed. Results from these studies will enable future researchers to introduce novel genes into basil for improved production, resistance to pest and pathogens, and for modifying essential oil quality and yield.
Simon, Purdue University.
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