Regulation of carotenoid metabolism in response to different temperatures in citrus juice sacs in vitro

The present study investigated the regulation of carotenoid accumulation in response to temperatures (10, 20, and 30 degrees C) in citrus juice sacs in vitro. Carotenoid accumulation was induced at 10 degrees C, but was not affected at 30 degrees C in the Satsuma mandarin, Valencia orange, and Lisbon lemon. In the Satsuma mandarin and Valencia orange, carotenoid accumulation at 10 degrees C was transcriptionally regulated by carotenoid biosynthetic genes. The up -regulated expression of nine carotenoid biosynthetic genes (CitPSY, CitPDS, CitZDS, CitLCYe, CitHYb, CitHYe, CitLCYb2, CitZEP and CitVDE) in the Satsuma mandarin and seven carotenoid biosynthetic genes (CitPSY, CitPDS, CitZDS, CitLCYb 1, CitLCYb2, CitZEP and CitVDE) in the Valencia orange was responsible for enhancing the content of carotenoid at 10 degrees C. In contrast to 10 degrees C, no marked changes were observed in carotenoid metabolic gene expression, and carotenoid accumulation was not significantly affected at 30 degrees C in the Satsuma mandarin and Valencia orange. In the Lisbon lemon, the expression of carotenoid biosynthetic and catabolic genes was involved in the regulation of carotenoid accumulation in response to temperature. The up-regulated expression of biosynthetic genes (CitPSY and CitVDE) and down-regulated expression of catabolic genes (CitNCED2 and CitNCED3) increased the content of carotenoid at 10 degrees C in the Lisbon lemon. In contrast to 10 degrees C, the expression of most carotenoid biosynthetic and catabolic genes was simultaneously up -regulated, whereas carotenoid levels remained unchanged and were constantly low at 30 degrees C in the Lisbon lemon.