Germinability and antioxidant metabolism in Passiflora caerulea L. seeds exposed to salt stress

Resumen

P. caerulea is the Passiflora species with the widest distribution in Argentina. Despite the need to cultivate it to decrease the extraction impact on its natural populations, the information on how environmental factors affect seed germinability is scarce. In order to evaluate the greminative response and the role of the antioxidant metabolism against saline stress, freshly collected seeds were germinated in the presence of 0 (control), 30, 60 or 90 mM NaCl. The percentage of germination, the content of soluble and carbonylated proteins, the activity of antioxidant enzymes and the generation of reactive oxygen species both in the pre-germination phase and during germination were evaluated. The removal of the aryl and the micropillar integument after 3 h imbibition proved to induce a rapid germination and activation of the enzymes catalase, glutathione S-transferase and peroxidases, together with an increase and a decrease in the generation of O₂^.- and H₂O₂, respectively, at the root apex. Even though the germination and activity of some of the studied enzymes decreased with the increase in external NaCl levels, when comparing populations of the control and 90 mM NaCl treatments having similar germination percentages, a marked induction of peroxidase activity was observed in the latter group. The proportion of carbonylated proteins did not differ among treatments, which suggests that, despite this species cannot be considered as halo-tolerant, the fact that the antioxidant metabolism efficiently contributed to prevent oxidative damage to the proteome may constitute an important mechanism to facilitate its establishment in environments with moderate salinity.