Molecular and Biochemical Analyses of Germination of Cowpea (Vigna unguiculata L.) Seeds Inhibited by n-Propyl Gallate Reveal a Key Role of Alternative Oxidase in Germination Re-establishment

n-Propyl gallate (PG) is a phenolic compound that influences enzymatic processes, mostly involving AOX, PTOX, LOX, POD, and PPO. Here, analyses of different PG concentrations (1, 2.5, and 5 mM) during cowpea seed germination at 16, 32, and 48h showed that 2.5 mM PG partially inhibited seed germination at 16 and/or 32h, but by 48h the germination re-established. Thus, this PG concentration was chosen to study the molecular and biochemical mechanisms linked to the PG inhibitory effects and germination recovery. PG inhibition was related to lower H2O2, higher antioxidant activity, and downregulation of genes linked to cell cycle progression, energy status, and the Krebs cycle at 16 and/or 32h, but these changes were reversed at 48h. In general, genes associated with detoxification, germination-related phytohormones, and NAD(P)H metabolism were highly up-regulated across the time points. AOX1 and Pgb1 were continuously up-regulated along the time points, and linked to NR transcript level increase only at 48h. These findings indicated that AOX and the phytoglobin cycle, both systems involved in NO levels regulation, worked efficiently in germination re-establishment. However, genes other than AOX associated with potential target enzymes of PG, such as LOX, POD, PTOX and PPO (except at 48h), were mostly unchanged or down-regulated. Genes linked to glycolysis (PFK and PK) and acetate synthesis (PDC and ALDH) connected with AOX via NAD(P)+ were up-regulated under PG mainly at 48h. The data are discussed in light of AOX's role in cell reprogramming to reverse PG-induced inhibition of germination in cowpea seeds.