Catalase Inhibition Affects Glyoxylate Cycle Enzyme Expression and Cellular Redox Control during the Functional Transition of Sunflower and Safflower Seedlings

Oilseed crops are an important natural resource because they can be used for food and renewable energy production. However, oilseed seedling establishment and vigor depend upon the capacity to overcome functional transition, a developmental stage characterized by the consumption of the remaining oil reserves, through beta-oxidation and glyoxylate cycle, and the onset of autotrophic metabolism. The increased growth and the acclimation to full photosynthetic activity lead to production of reactive oxygen species and a reorganization of the cell antioxidant systems to achieve a new redox homeostasis. In the present study, catalase (CAT) was inhibited by 3-amino- 1,2,4-triazole application during functional transition in sunflower and safflower seedlings to understand the effect of this antioxidant enzyme impairment on the mRNA expression of the glyoxylate cycle enzymes isocitrate lyase (ICL) and malate synthase (MLS), as well as the superoxide dismutase (SOD) activity and ascorbate peroxidase (APX) activity and expression. CAT inhibition led to significant seedling growth reduction and increases in H2O2 content, SOD activity, and mRNA expression of CAT and APX in both species. However, APX activity was induced only in safflower plants. Additionally, ICL and MLS mRNA expressions were upregulated after 6 h of treatment when compared to the control values. These results indicate that under CAT impairment conditions, redox homeostasis at the functional transition phase was partially supported by the SOD and APX antioxidant systems to maintain the seedling photosynthetic establishment.