Underdeveloped embryos and germination in Aristolochia galeata seeds

Aristolochiaceae have been described as having seeds with underdeveloped embryos and morphological or morphophysiological dormancy. Aristolochia galeata is a native climber found in the Cerrado biome, associated with road and gallery forest edges. The aims of this study were to investigate: embryo growth rate, morphology and seed germination parameters under different treatments. Embryos were excised to obtain embryo length at four stages: initial, seeds after coat rupture, radicle tip protrusion and cotyledon emergence from the seed coat. Germination tests were conducted at 30 degrees C under three nitrate concentrations (1, 10 and 20 mM), fluctuating temperature (27/20 degrees C) and light and dark conditions. We found that seeds have underdeveloped embryos, which take about 301 +/- 178 h (+/- SD) to achieve seed coat rupture, another 205 +/- 126 h to reach radicle protrusion and 176 +/- 76 h more to the final stage of cotyledon emergence. Germinability was above 52% in all treatments, except in the dark (15%). For all treatments, average germination time was above 290 +/- 123 h. Potassium nitrate increased germinability to > 87%. No particular treatment was required for embryo development, but seeds in the population that continued to germinate after 1 month were probably in various states of non-deep, simple morphophysiological dormancy. Increased germinability in nitrate treatments and light requirement for germination could prevent germination under unsuitable environmental conditions and be a strategy to increase seedling establishment in the cerrado.