Biochemical and physiological studies on dormancy release in buds of field-grown Paeonia lactiflora

Like most plants that are native to temperate and boreal regions, Paeonia lactiflora blooms in late spring; it is a perennial that requires a long period of chilling. In order to study the biochemical and physiological changes of herbaceous peony in response to low temperature, six indices related to cold tolerance were determined over 20 different periods of natural conditions, and morphological and phytophenological observations were made. A larger amount of soluble sugars and reducing sugars and a smaller amount of starch were found during dormancy in comparison with the growing season. The concentration of soluble and reducing sugars increased in buds when P. lactiflora plants were subjected to low temperature from 14 November to 4 January. Starch content decreased significantly over the same period. Maximum soluble sugar content peaked later than reducing sugar, on 14 January and 24 December, respectively. Sugars appeared to play an important role in bud development and dormancy. Soluble protein content decreased from 15 September to 15 October, but increased sharply in response to cold stress, and may play an important role in bud differentiation and cold-stress tolerance. Free proline content in underground buds increased in response to cold stress, while hydrogen peroxide decreased. Proline may positively mediate H₂O₂ degradation and thereby help buds to minimize oxidative damage under low-temperature stress. Our study provides a deeper understanding of these metabolic mechanisms and will play an important role in forcing culture for the study of dormancy release of underground herbaceous peony buds.