Low temperature acclimation and de-acclimation of the subtropical bromeliad Nidularium minutum: Implications of changes in the NO, sugar content and NR activity

In tropical biomes, abrupt cold events frequently occur in subtropical regions and can be associated with large daily thermal fluctuations. The bromeliad Nidularium minutum Mez is a cold tolerant species from the Atlantic Rainforest, which grows in the subtropical latitude, where temperatures range from 2 to 30 degrees C. We hypothesized that N. minutum plants would implement rapid metabolic adjustments to ensure survival during sudden cold events that occur in seasons other than winter. N. minutum plants were cultivated at 10 degrees C. Under this condition, there was an observed increase in soluble sugar content and nitric oxide (NO) emission, as well as a high nitrate reductase (NR) activity observed within the 72 h of cold exposure, when compared with plants maintained at 25 degrees C. These responses coincided with a decrease in antioxidant activity and an increase in lipid peroxidation (LPO). After 72 h of cold exposure, a subset of plants were de-acclimated at 25 degrees C. These plants displayed reduced soluble sugar concentrations, NO emissions, NR activity and LPO. Additionally, there was an increase in anti-oxidant activity, which indicated that the plants were recovering from cold stress. Furthermore, it was found that plants maintained at 10 degrees C for 168 h acclimated to the cold by reducing the NO content and maintaining the increased sugar concentrations, thus resulting in a less intense stress response. We conclude that rapid changes in NO content, sugar concentrations and antioxidant activity are metabolic adjustments that occur during the acclimation and de-acclimation processes of this bromeliad to low temperatures. During abrupt thermal changes in subtropical regions, such adjustments could enhance cold tolerance and increase the chances of survival for this plant.