Light as environmental regulator for germination and macrocotyledon development in Streptocarpus rexii (Gesneriaceae)

The light requirements for seed germination and seedling development have not been studied widely in Gesneriaceae. Here we report on the effects of light on these aspects in Streptocarpus rexii (Gesneriaceae). Seeds did not germinate in the dark but required light, indicating photoblastic seed germination. Light exposure was also required for the establishment of post-germination anisocotylous development, with the seedlings showing the typical basal meristem in the proximal region of the macrocotyledon. In the dark, however, the basal meristem was not established and the seedlings showed two equally sized microcotyledons. Hypocotyl elongation, a typical skotomorphogenesis, was also observed in the dark. Different wavelengths of light, in the red and blue spectrum, differentially affected seedling development. While seedlings exposed to blue light showed typical anisocotyly, seedlings under red light did not and basal meristem activity was not observed. These results suggest that light quality is an important factor for the establishment of anisocotyly in S. rexii seedlings. Thus, light plays important roles at different developmental stages of S. rexii, which is perhaps linked to adaptation to dense forest habitats where light is marginal. Environmental signals might coordinate endogenous physiological pathways for the extraordinary seedling development in S. rexii. Unraveling these interactions requires further studies.