Gravitational stress on germinating Pinus pinea seeds.

In the germination of lipid-rich seeds, the glyoxylate cycle plays a control role in that, bypassing the two decarboxylative steps of the Krebs cycle; it allows the net synthesis of carbohydrates from lipids. The activity of isocitrate lyase, the key enzyme of the glyoxylate cycle, is an indicator of the state of seed germination: stage of germination, growth of embryo, activation and progress of protein synthesis, depletion of lipidic supplies. In order to investigate the effects of gravity on seed germination, we carried out a study on the time pattern of germination of Pinus pinea seeds that were subjected to a hypergravitational stress (1000 g for 64 h at 4 degrees C), either in a dry or in a wet environment, before to be placed in germination plates. During the whole time of germination, we monitored the state of embryo growth and the most representative enzymes of the main metabolic pathways. In treated wet seeds, we observed an average germination of only 20% with a slowdown of the enzyme activities assayed and a noticeable degradation of lipidic reserves with respect to the controls. These differences in germination are not found for dry seeds.