Physiological seed dormancy increases at high altitude in Pyrenean saxifrage (Saxifraga longifolia Lapeyr.)

Seed dormancy determines population dynamics and it is an essential feature of the ecology of high-mountain plants. Although altitudinal changes in the ecological and physiological performance of Pyrenean saxifrage (Saxifraga longifolia Lapeyr.) has been investigated to some extent, nothing it still know about how seed dormancy is influenced by environmental conditions imposed by altitude in these plants. Here, we evaluated altitudinal changes in seed viability and germination, but also on the endogenous contents of phytohormones and antioxidants in Pyrenean saxifrage. We found that, despite seed germination decreased at the highest population (2100 m a.s.l.) relative to the other two populations (at 570 and 1100 m a.s.l.), the highest population showed the highest seed viability, thus indicating increased seed dormancy. Hormonal profiling of the seeds revealed that this dormancy was modulated physiologically, in particular by increased abscisic acid accumulation, while gibberellin contents kept constant, relative to the seeds of the other two populations. Furthermore, seed xanthophyll contents, in particular those of lutein, neoxanthin, violaxanthin and antheraxanthin increased with altitude, while those of a-tocopherol kept unaltered. We conclude that the lower temperature imposed by altitude strongly influences not only seed viability and germination, but also seed dormancy, and that changes associated to temperature differences among populations are modulated at the physiological level by increasing the accumulation of abscisic acid and xantophylls in mature seeds. Results strongly support the contention that physiological seed dormancy has evolved as a means to increase plant survival under harsh environmental conditions in Pyrenean saxifrage plants growing in their natural habitat.