Antioxidant enzyme activity and dynamics of reserve mobilization during germination and early seedling establishment of royal poinciana [Delonix regia (Bojer ex Hook.) Raf.]

Key message The germination of Delonix regia seeds is mediated by oxidative stress signaling and the activation of antioxidant enzymes. The reserve mobilization is correlated with the morpho-anatomical changes observed during seedling development. A comprehensive picture of structural and physiological changes throughout the germination and post-germination of D. regia (Bojer ex Hook) Raf (Fabaceae) would lead to good knowledge of the germination biology of this woody species. In the present study, we characterized the spatial and temporal variation of the structure, reserve compounds, and the dynamics of antioxidant enzymes during the germination and early seedling establishment of D. regia. Morpho-anatomical and histochemical assessments were performed during germination and throughout seedling development. The total chlorophyll, carbohydrate, lipid and soluble protein contents, and the activity of antioxidant enzymes were also determined. Germination was observed only in mechanically scarified seeds and was a fast process, with 76% of the seeds showing radicle protrusion 5 days after sowing (DAS). Few changes were observed in the content of reactive oxygen species during the transition of D. regia seeds from the dry to the germinative state. However, the dynamics of antioxidant enzyme activities varied during this process. While SOD and CAT were active in both dry and germinating seed states, APX and POX activities were barely detected in the dry stage and during the early stages of seed germination. D. regia seedlings exposed their eophylls on the 11th DAS and were classified as being of the phanerocotylar-epigeal-foliaceous type. A temporal difference was observed in the histological differentiation of the organs that make up the apical-basal axis of D. regia seedlings. Proteins and lipids were quickly mobilized in the early germination phases, whereas carbohydrates were synthesized throughout the seedling development. However, starch reserves were completely depleted by the 30th DAS in a gradual and centripetal mobilization pattern in the cotyledonary tissues.