Wait or escape? Contrasting submergence tolerance strategies of Rorippa amphibia, Rorippa sylvestris and their hybrid

Abstract

Background and aims: Differential responses of closely related species to submergence can provide insight into the evolution and mechanisms of submergence tolerance. Several traits of two wetland species from habitats with contrasting flooding regimes, Rorippa amphibia and Rorippa sylvestris, as well as F(1) hybrid Rorippa × anceps were analysed to unravel mechanisms underlying submergence tolerance.

Methods: In the first submergence experiment (lasting 20 d) we analysed biomass, stem elongation and carbohydrate content. In the second submergence experiment (lasting 3 months) we analysed survival and the effect of re-establishment of air contact on biomass and carbohydrate content. In a separate experiment we analysed expression of two carbohydrate catabolism genes, ADH1 and SUS1, upon re-establishment of air contact following submergence.

Key results: All plants had low mortality even after 3 months of submergence. Rorippa sylvestris was characterized by 100 % survival and higher carbohydrate levels coupled with lower ADH1 gene expression as well as reduced growth compared with R. amphibia. Rorippa amphibia and the hybrid elongated their stems but this did not pay-off in higher survival when plants remained submerged. Only R. amphibia and the hybrid benefited in terms of increased biomass and carbohydrate accumulation upon re-establishing air contact.

Conclusions: Results demonstrate contrasting 'escape' and 'quiescence' strategies between Rorippa species. Being a close relative of arabidopsis, Rorippa is an excellent model for future studies on the molecular mechanism(s) controlling these strategies.

Fig. 1.

Stem elongation of Rorippa amphibia, Rorippa sylvestris and their hybrid (top), and above-ground and below-ground dry weight (bottom) of control and submerged plants after 7, 14 and 20 d of treatment (n = 6; bars indicate s.e.).

Fig. 2.

Aerenchyma in petioles of 30-d-old control non-submerged plants of (A) Rorippa amphibia, (B) Rorippa sylvestris and (C) their hybrid, and (D) porosity content of 21-d-old petioles. All three genotypes differ in their porosity levels significantly (ANOVA, LSD tests; see Supplementary Data Tables S3 and S4) (n = 4 or 5; bars indicate s.e.).

Fig. 3.

Soluble carbohydrates and starch content of (top) above-ground and (bottom) below-ground tissues of Rorippa amphibia, Rorippa sylvestris and their hybrid in air controls and submerged plants after 7, 14, 20 d of treatment (n = 6; bars indicate s.e.).

Fig. 4.

(Top) ADH1 and (bottom) SUS1 expression in Rorippa amphibia, Rorippa sylvestris and the hybrid roots following 2, 26, 74 h of complete and semi-submergence after 3 d of complete submergence (n = 4; bars indicate s.e.). Rorippa amphibia air control at 2 h was selected as the reference (log₂ = 0) for both genes.

Fig. 5.

Schematic view of experimental timeline (left) . (Top) Survival and (bottom) above-ground and below-ground dry weight of plants at start and after 37 d of complete submergence followed by controlled air contact for 21 and 42 d for Rorippa amphibia, Rorippa sylvestris and their hybrid (n = 12 for survival, n = 9 for dry weight; bars indicate s.e.).

Fig. 6.

Soluble carbohydrate and starch content of (top) above-ground and (bottom) below-ground tissues at start and after 37 d of complete submergence followed by controlled air contact for 21 and 42 d for Rorippa amphibia, Rorippa sylvestris and their hybrid (n = 9; bars indicate s.e.).