Effect of reactive oxygen species on germination of Cynara cardunculus (L.) cultivars

Reactive oxygen species (ROS) are chemical compounds containing oxygen. They interact with a wide range of macromolecules propagating the oxidative signal with major effects on the cellular redox status. Their role in seed physiology cell signalling has been demonstrated in model plant species, while it remains mainly unexplored in non-model organisms as Cynara cardunculus. Within this species, the germination of the wild cardoon variety is affected by physiological seed dormancy which recently was shown to be broken by exposure to oxygen donors. Here we evaluated the effect of the presence of ROS compounds on seed germination of C. cardunculus var. sylvestris, altilis and scolymus. Seeds were imbibed at constant (15°C) or alternating (20/10°C) temperatures combined with a gradient of a ROS compound (hydrogen peroxide) and compared with germination in presence of antioxidants (glutathione or guaiacol) for the sylvestris variety. Cultivated cardoon and artichoke germination was not sensitive to constant or alternating regimes while var. sylvestris germinated promptly only at 20/10°C. However, the presence of ROS compounds at constant temperatures released dormancy of sylvestris seeds, while, the addition of antioxidant compounds considerably decreased it. Although further observations are needed, it appears that the presence of oxidative compounds in achenes exposed to constant temperatures replaced the requirement of alternating temperature to terminate dormancy while the presence of antioxidants inhibits germination at this thermal regime. Further investigations will be necessary to understand the molecular and physiological basis of this mechanism including possible interactions between hormones, ROS and alternating temperatures, that regulate seed dormancy termination.