Variation in the phenotypic features and transcripts of thermo-sensitive leaf-color mutant induced by carbon ion beam in Green wandering jew (Tradescantia fluminensis)

Leaf color mutants are ideal materials for studying physiological processes in plants. Here, a thermos-sensitive leaf-color mutant of Green wandering jew was isolated after carbon ions irradiation, which was designated as mt. The color of young mutant leaves was more sensitive to variations of temperature, however, the young leaves of wild type remained green under low - temperature conditions (6 °C-20 °C). To elucidate the characteristics of pigmentation in mutant leaves under room temperature conditions (25 °C) and low - temperature conditions (7 °C), the ultra-structural, pigment composition, molecular mechanisms and anthocyanin accumulation involved in this phenomenon have been investigated in four independent experiments. The results showed that chloroplasts of mutants exhibited abnormal morphology and distribution at 25 °C, and under low - temperature conditions(7 °C), the chloroplasts converted into leucoplast in leaves on mutants. Temperature change affected the rate of color transition, chlorophyll and anthocyanin concentrations in leaves on mutants. Molecular analysis indicated that all the anthocyanin biosynthetic genes and regulatory genes were constitutively up-regulated in mutant leaves at 7 °C. The other anthocyanin biosynthesis and regulatory genes showed similar expression levels between mutant and wild type except PAL, CHS, ANS were up-regulated at 25 °C. HPLC analysis of anthocyanins in mutant and wild type leaves revealed that the contents of cyanidin, petunidin and delphinidin were significantly lower than those of under low-temperature conditions (7 °C) except pelargonidin was not detected in mutant leaves under room - temperature conditions(25 °C). The HPLC profile also indicated the highest levels of flavonols in mutant leaves at 7 °C significantly. Overall, above results indicated a close similarity among ultra-structures, pigment compositions, transcript amount and anthocyanin accumulation were tightly associated with temperature variation in leaves of leaf color mutant. These findings would provide better understanding of the mechanism of pigmentation changes in mutant leaves under different temperature conditions in Wandering jew.