Differential Effects of Sodium Chloride on Germination and Post-Germination Stages of Two Tomato Genotypes

Salinity induces inhibition and/or delay of seed germination. The imbibition phase re-actives enzymes involved in seed reserve mobilization in order to sustain embryo growth, but also implies reactive oxygen species (ROS) production. A balance between ROS content and antioxidant scavenging activity is necessary to maintain cellular redox state and signalling. Tomato seed endosperm contains large amounts of galacto(gluco)mannans, which are hydrolysed by the synergic action of cell wall enzymes, including endo-beta-mannanase, beta-mannosidase and alpha-galactosidase, leading to the completion of germination. The effect of different sodium chloride (NaCl) concentrations-containing medium (0, 25, 50 and 100 mM NaCl) on germination rate of two Italian tomato genotypes (Ciettaicale and San Marzano) was evaluated. Further biochemical analyses were performed during seed germination under 25 mM NaCl for 5 days. Salt induced the promotion of endo-beta-mannanase and beta-mannosidase in Ciettaicale, as well as starch mobilization contributing the increment of total soluble sugars and providing more energy to maintain organogenesis and scavenge oxidative stress. In fact, a boosted total antioxidant activity and catalase activity coped with high hydrogen peroxide content in Ciettaicale under stress. Conversely, in San Marzano, we found some salinity-induced physiological changes only at the end of our observation, suggesting that seeds were not dormant, but impaired by the stress to conclude properly the germination process.