Mercier et al. 2015 (Conference Paper) Bromeliaceae

Flexibility in use of inorganic and organic nitrogen sources by bromeliads: a key adaptative response

Author(s):—H. Mercier, C. Takahashi & A. Matiz in Benko-Iseppon, A.M.; Alves, M. & Louzada, R. (2015) An overview and abstracts of the First World Congress on Bromeliaceae Evolution. Rodriguésia 66(2): A1-A66.

Publication:— (2015).

Abstract:—The leaves of bromeliads have specialized trichomes that can absorb distinct nutrients, including nitrogen (N). Nitrate (NO3-), ammonium (NH4+) and organic N (amino acids, peptides, urea, etc.) may be provided to the epiphytic environments through atmospheric N deposition. Besides that, organic N may be provided by animal excretions (e.g., frogs), and some tank bromeliads are known to grow better when urea is available in the tank. Urea utilization may be an important feature for some bromeliads to colonize and survive in oligotrophic environments. We have shown that leaves of the tank bromeliad Vriesea gigantea can absorb different N forms present in the tank (NO3-, NH4+, amino acids, urea). However, urea uptake is more efficient than inorganic N sources and apparently aquaporins may be involved in its transport across cellular plasma membranes. This organic N source can be hydrolyzed to NH4+ and CO2 by urease. It was very interesting to observe that urease in leaves of V. gigantea showed its greatest activity in the basal portion, which is in close contact with the tank solution. We have obtained evidence that urease may also be secreted in the tank. This fact might give some advantages to the bromeliads for N acquisition during competition with microorganisms inhabiting the tank solution. We have also found that V. gigantea can use CO2 generated by thehydrolysis of urea. Cytochemical CO2 detection has allowed us to observe the presence of CO2 in the cell wall, intercellular spaces and around the chloroplasts, suggesting that urea may be both N and carbon sources for these plants. To confirm this hypothesis, we provided 13C-urea to detached leaves of V. gigantea, and welooked for 13C-labeled malate. Interestingly, we have found a great incorporation of 13C in that organic acid, indicating that CO2 was assimilated when urea was available to this bromeliad. Similar results were observed for Guzmania monostachia, another tank epiphyte bromeliad. Thereby, these results suggest that the use of CO2 from urea is not exclusive to V. gigantea. The use of a N source like urea to obtain carbon seems to be a relevant strategy to cope with N-deficient environments and it might be significant for managing some specific situations, such as drought, when stomata closure impairs atmospheric CO uptake. Therefore, duringwater shortage we might expect assimilation of CO2 from urea. 2

Keywords:—Nitrogen Sources; Urea; Nitrogen Nutrition.