Pereira 2015 (Conference Paper) Guzmania

The effects of nutritional and water deficiencies on CAM induction in the leaves of the bromeliad Guzmania monostachia

Author(s):—P.N. Pereira & H. Mercier 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:—Leaves of Guzmania monostachia, an facultative C3?CAM, epiphytic bromeliad, when subjected to a water deficit, have been shown to perform stronger CAM photosynthesis in the apical compared with the basal portion of the leaf blade. To investigate the possible interaction of nutrient deficiencies and water deficits in CAM induction, detached leaves of G. monostachia plants (2 years old) were subjected to treatment for seven days using 30% PEG 6000 plus modified Knudson solution deficient in N, P, K, or Ca. After determining that nitrogen had the greatest influence on the CAM pathway, a further experiment was conducted to test the influence of alternative nitrogen sources on this metabolism. This experiment consisted of supplying the detached leaves with either 5 mM NO3 ? or NH4+ in modified Knudson solution, in the presence of 30% PEG 6000. To assay CAM activity, nocturnal malate and citrate contents were measured together with extractable PEPC and PEPCK activities in the apical, middle, and basal portions of the leaves, in combination with determinations of relative water content. We observed that nitrate deficiencies, plus the presence of ammonium, combined with a water deficit, were the most important factors affecting CAM induction in the apical portion of the leaves of the G. monostachia. Furthermore, the activity of antioxidant enzymes (glutathione reductase, GR; superoxide dismutase, SOD; catalase, CAT and ascorbate peroxidase, APX) were verified in order to test whether or not NH4+ nutrition improves the capacity of G. monostachia leaves to limit oxidative damage by stimulating the activities of the antioxidant enzymes. These results would suggest that the CAM photosynthesis was maintained due to an increased PEPC activity provided by the presence of ammonium.

Keywords:—Bromeliad; Cam; Nutrients.