The role and synthesis mechanism of anthocyanins in Sphagneticola trilobata stems under low temperature

Sphagneticola trilobata, originally from the tropical regions of the Americas, has successfully invaded the subtropical regions of southern China and displays a tendency to spread towards colder northern regions. The accumulation of anthocyanins in stems under low temperature conditions exhibits strong cold tolerance, and therefore may be one mechanism supporting the northward spread of the species. However, the role and synthesis mechanism of anthocyanins in the stems of S. trilobata when confronted with low temperature stress are still unclear. Field experiments have shown that compared to in summer, the stems of S. trilobata significantly accumulated anthocyanins to cope with winter. Further short-term low-temperature treatments (0 °C) were conducted on red and green stems of S. trilobata, and the results showed that the red stems exhibited lower levels of reactive oxygen species, membrane damage, and chlorophyll fluorescence changes compared to the green stems. In an indoor low-temperature control experiment, it was observed that S. trilobata exhibited significant accumulation of callus in the periderm of its stems compared to S. calendulacea, which subsequently resulted in increased levels of sucrose, glucose, and fructose contents. Furthermore, there was a significantly induced higher levels of abscisic acid and cytokinin in S. trilobata stems under low temperatures. Under the joint regulation of these carbohydrates and hormones, the key structural genes associated with anthocyanins synthesis pathway in S. trilobata stems were more strongly induced compared to S. calendulacea. The upregulation of CHS, CHI, F3H, and DFR gene expression levels in S. trilobata was higher than that of native species, which directly leads to the accumulation of more anthocyanins in the epidermis of the stem of S. trilobata, thereby reducing the degree of oxidative stress and maintaining normal growth under low temperature. In summary, anthocyanins play an important light filtering role in the response of S. trilobatas stem to low temperature stress, which is one of the important mechanisms for its successful invasion into southern China. In the context of global climate change, we need to increase our vigilance against further invasion of S. trilobata into colder inland regions such as temperate regions. This research holds significant theoretical and practical implications for the prevention and control of S. trilobata invasion.