New Insights into the Role of Alternating Temperatures and Cyanide in the ROS-Mediated Cardoon Seed Dormancy Termination

Physiological dormancy in wild cardoon (Cynara cardunculus var. sylvestris) can be terminated by achenes exposure to alternating temperatures, likely with the participation of reactive oxygen species (ROS). Cyanide is a natural compound that mediates seed dormancy removal in some plant species in association with oxidative signalling exerted by ROS. To date, no study has been conducted on the cyanide effect on ROS homeostasis during the germination of cardoon. Here, we showed that the addition of cyanide at low concentrations in dormant cardoon achenes promotes dormancy breakage at a constant temperature, speeds up germination to alternating temperatures and promotes ROS accumulation in embryonic axes of dormant achenes. The in-silico transcriptome analysis showed that the expression levels of transcripts of genes associated with ROS signalling and production, calcium signalling, gibberellins biosynthesis and cell wall loosening were significantly up-regulated at the alternating temperatures imbibition condition. In contrast, the expression of gene transcripts associated with the inhibition of germination, ABA biosynthesis and signalling were up-regulated at the constant temperature imbibition. However, no significant difference in lipid peroxidation or protein carbonylation levels was observed when achenes were imbibed at constant or alternating temperature conditions. These results suggest that dormancy termination triggered by alternating temperatures or cyanide could be mediated by ROS production and signalling in the cardoon embryonic axis, but this does not determine extensive protein carbonylation.