Antioxidant Enzyme Activity in Germinating Seeds Under Salinity Stress

Abstract

Seeds that germinate in saline soil or water face a double problem: the medium holds water back osmotically, and the sodium and chloride that do enter the tissues are toxic. Both pressures disturb the balance of reactive oxygen species, which are at once damaging and necessary for germination to proceed. Antioxidant enzymes such as superoxide dismutase, catalase and ascorbate peroxidase are therefore measured in a large share of the salinity literature, and higher activity is often read as a sign of tolerance. This narrative review asks how far that reading holds for germinating seeds specifically. It draws on published work on seed oxidative biology, on the antioxidant enzyme system, and on comparisons of tolerant and sensitive genotypes, and it reports no new data. Most of the genotype comparisons come from seedlings, roots and leaves, not from imbibing seeds, and the direction of enzyme change depends on tissue, timing, the severity of the treatment and the way activity is expressed. We argue that an enzyme activity is interpretable only alongside a marker of damage, an osmotic control and a clear account of the germination stage sampled, and we set out a short appraisal framework and a reading matrix for that purpose.