Aclimatação de plantas de milho à salinidade mediada pelo pré-tratamento com nitroprussiato de sódio

Abstract

This study was intended to evaluate the acclimation of maize (Zea mays) plants to salt stress, after pretreatment with sodium nitroprusside (SNP, a NO donor compound). The SNP concentration used was defined in an initial experiment, in which maize plants (variety BR 5011) were cultivated for two days in Hoagland solution plus NPS at 0 (not pretreated plants), 50, 75, 100 or 200 mM and then subjected to salt stress (NaCl at 0 or 80 mM). After seven days, the plants pretreated with NPS at 75 μM showed the best performance in saline conditions, considering that they had a higher growth, a lower lipid peroxidation in leaves, an increased K+ content and a lower Na+ content in shoots compared to other plants in saline conditions. Based on this, it was performed a second experiment, in which the maize acclimation mediated by the pretreatment with 75 μM SNP was evaluated after 7 and 14 days of stress salt (80 mM NaCl). The SNP-pretreatment resulted in an increased leaf area and a fastest growing in saline conditions as compared to non-pretreated plants, but this difference was observed only after 7 days of stress. Although salt stress have reduced stomatal conductance in both time periods, there was an increase in the net photosynthesis and transpiration when plants were pretreated with NPS. In general, the salt stress reduced the macronutrient content in plants, in both times of stress, but this was less evident in those who had been pretreated with NPS, especially after 7 days of stress. Oxidative damages in leaves and roots of maize plants have been partially mitigated by pretreatment with SNP. In saline conditions, the contents of ascorbate and glutathione were generally highest in plants pretreated with NPS than in non-pretreated. In general, the activity of superoxide dismutase, catalase and ascorbate peroxidase in leaves and roots of maize was reduced by pretreatment with SNP, and it also depended on the time of stress to which the plants were subjected. However, there was little correlation between pretreatment with SNP and induction of antioxidant system. The mass spectrometry-coupled liquid chromatography allowed the identification of several proteins in leaf and root tissues, including proteins involved in photosynthesis and oxidative metabolism and, in general, their expression was influenced by the conditions that plants were subjected. The pretreatment with SNP induced important changes in corn plants more closely related to the oxidative homeostasis that protection, which does not persist throughout plant development.