Abiotic stress factors are the main limitation to plant growth and yield in agriculture. Orange sweet potatoes may become major sources of carotenoids in the diet, but the extent of environmental and genetic influences on plant carotenoid biosynthesis are poorly understood. Carotenoid biosynthesis is regulated by several factors such as water, light, pathogen, salinity, nutrients and is susceptible to geometric isomerisation in the presence of oxygen, light and heat which causes colour loss and oxidation. The main problems associated with carotenoid accumulation arise from the inherent instability of pigments. In this study carotenoid biogenesis is investigated in sweet potato callus culture as a potential model system for carotenogenesis by analysing the effects of environmental stress agents such as NaCl (for salt tolerance), PEG (for drought tolerance), salicylic acid (for pathogen stress or disease resistance) and nutrient strength towards carotenoid content and composition. Results of this study revealed that the bioactive compounds detected in orange sweet potato callus were α-carotene, β-carotene, lutein and zeaxanthin. Not surprisingly, the response of sweet potato callus culture to such environments appeared to be highly light dependent. Another factor is the activity of functional enzymes and candidate enzymes that regulate carotenoid biosynthesis, which will determine type and quantity of individual carotenoids. By understanding the environmental factors that affected carotenoid biosynthesis, it should be possible to enhance the amount and type of carotenoid that accumulates in sweet potato tubers. In conclusion, in vitro callus culture is suggested as a successful new alternative approaches to enhance or enrich certain carotenoids through controlled environment.
Carotenoid content in plants differs due to several factors such as cultivar, maturity, climate, locality and storage. Improving the nutritional values of sweet potato is an important breeding goal and understanding the regulation, genetics and inheritance of carotenoid biosynthesis are vital to achieve this. Environmental conditions can have a marked influence on the accumulation of carotenoids in sweet potato tubers. Little is known about the effects of location, post-harvest storage time and harvesting season particularly on carotenoid biosynthesis. Therefore, this study aimed to investigate the effects of growing location, harvesting season and storage time on carotenoid biosynthesis in orange sweet potato tuber flesh. The results showed that orange sweet potato tubers contained α-carotene and β-carotene in the first and second harvesting season (year 2011 and 2012), whereas lutein and zeaxanthin were detected only in the third harvesting season (year 2013). Analysis of carotenoid profiles of the orange sweet potato tubers grown in three different locations confirmed that the harvesting season had a major effect on the total carotenoid content and the individual carotenoid compounds. The post-harvest storage time of sweet potato tubers also appears to have distinct effects on carotenoid biosynthesis, the magnitude of the effects being dependent on the storage time, harvesting season and location. The results of this study will help to understand the effects of location, year of harvesting season and storage time on carotenoid accumulation in orange sweet potato tubers.