Deep complex morphophysiological dormancy in seeds of Clematis hexapetala Pall. (Ranunculaceae)

Abstract

Seed germination and dormancy are crucial to the regeneration strategy of plants. Clematis hexapetala Pall. is a perennial herb growing in temperate deciduous forest and grass areas in northeast China, it has great potential as a garden and landscape plant. However, the dormancy characteristics of the seeds and the regeneration strategies of this species that help it adapt to its natural habitat heretofore have not been investigated. The primary aim of this study was to determine the requirements for breaking seed dormancy in Clematis hexapetala and characterize the type of seed dormancy in this species. The phenology of seed germination and growth of the embryo of this species was determined by periodically retrieving seeds sown in the field. The effects of light, temperature, warm/cold stratification, and dry storage on breaking dormancy and germination were analyzed by incubating seeds in the laboratory. In addition, the effects of GA3 on germination were used to determine the specific type of seed dormancy present. The results showed that seeds of C. hexapetala had underdeveloped (small) embryos with physiological dormancy in autumn at maturity. Embryo growth begins in early winter under natural conditions. Before the radical emerges, the ratio of embryo/seed length increased from 0.127 to 0.839. In laboratory experiments, embryo growth occurred in a long incubation period at 4°C. After cold stratification at 4°C, seeds were able germinate over a wide range of temperatures. However, GA3 was not a substitute for cold stratification. We conclude that freshly matured seeds of C. hexapetala have deep complex morphophysiological dormancy. In winter, dormancy was broken by natural cold stratification which allowed the seeds to germinate and produce seedlings at the start of the next growing season.