Karrikins Reduce the Hypocotyl Length of Rapeseed (Brassica napus napus L.) under Continuous Red Light

Karrkins (KARs) are relatively simple molecules originating from the burning of plant material, which have the ability to enhance the germination of many species from the fire-prone environment, but also species, which life cycle is not connected with fire, one example being Arabidopsis (Arabidopsis thaliana L.). KARs do not only improve germination but also alter several physiological processes and morphological features of plants. One of the changes of morphology observed on Arabidopsis seedlings is the shortening of hypocotyl when grown under continuous red light. So far, six biologically active compounds belonging to the KARs group were identified. Most of the plants show the strongest response to the first identified KAR, KAR₁, but Arabidopsis exhibits the strongest reaction to KAR₂. In our experiment, we focused on seedlings’ hypocotyl length of Rapeseed (Brassica napus napus L.), an economically important plant from the same family as Arabidopsis, Brassicaceae. Our results show that the hypocotyl of eight days old seedling of Rapeseed grown under continuous red light was significantly shortened by both KARs examined by us, KAR₁ as well as by KAR₂. When grown in continuous white light, seedlings had generally more than twofold shorter hypocotyls, but KAR₁ could further shorten it. In the darkness, hypocotyl length was altered by neither KAR₁ nor KAR₂. Therefore, we can conclude that similarly to Arabidopsis, Rapeseed’s seedlings possess the light-dependent response of development to KARs, what proves, that these compounds have to date not fully understood roles in the plants’ life moreover to germination induction of fire following species and it is very unlikely that combustion of plant material is the only source of KARs occurring in nature.