RESUMO
Under natural conditions plants are generally subjected to complex scenarios of combined or sequential environmental stresses. Among the various components of plant biochemistry modulated by abiotic variables, a pivotal role is played by antioxidant systems, including specialized metabolites and their interaction with central pathways. To help address this knowledge gap, a comparative analysis of metabolic changes in leaf tissues of the alkaloid accumulating plant Psychotria brachyceras Müll Arg. under individual, sequential, and combined stress conditions was carried out. Osmotic and heat stresses were evaluated. Protective systems (accumulation of the major antioxidant alkaloid brachycerine, proline, carotenoids, total soluble protein, and activity of the enzymes ascorbate peroxidase and superoxide dismutase) were measured in conjunction with stress indicators (total chlorophyll, ChA/ChB ratio, lipid peroxidation, H2O2 content and electrolyte leakage). Metabolic responses had a complex profile in sequential and combined stresses compared to single ones, being also modified over time. Different stress application schemes affected alkaloid accumulation in distinct ways, exhibiting similar profile to proline and carotenoids, constituting a complementary triad of antioxidants. These complementary non-enzymatic antioxidant systems appeared to be essential for mitigating stress damage and re-establishing cellular homeostasis. The data herein provides clues that may aid the development of a key component framework of stress responses and their appropriate balance to modulate tolerance and yield of target specialized metabolites.
Assuntos
Alcaloides , Psychotria , Antioxidantes/metabolismo , Psychotria/química , Psychotria/metabolismo , Peróxido de Hidrogênio/metabolismo , Alcaloides/metabolismo , Carotenoides/análise , Carotenoides/metabolismo , Folhas de Planta/metabolismo , Prolina/análise , Prolina/metabolismoRESUMO
Climate models predict that plants will face extreme fluctuations in water availability in future global change scenarios. Then, forage production will be more frequently subjected to the destabilizing pressure of sequentially occurring waterlogging and drought events. While the isolated effects of drought (D) and waterlogging (WL) are well characterized, little is known about the consequences when both stresses occur sequentially. We hypothesized that plants sequentially subjected to opposite water scenarios (D followed by WL or vice versa) are less stress tolerant than plants experiencing repetitions of the same type of water stress (i.e., D + D or WL + WL) due to contrasting acclimation and allocation to either shoots (WL) or roots (D). Chloris gayana (a tropical forage grass capable of tolerating either D and WL) plants were randomly assigned to nine treatments (a sequence of two stress rounds-WL or D-each followed by a recovery phase at field capacity). Relative growth rates and allometric responses were measured after each stress round and recovery period. In the first round of stress, both WL and D reduced plant RGR similarly, despite their allocation being opposite-prioritizing shoots or roots under WL and D, respectively. The high recovery displayed after either WL or D overrode any possible acclimation of the plants facing a second round of water stress. We conclude that the tolerance of C. gayana to sequential water stress (either for WL or D) is likely to depend more heavily on its recovery ability than on its previous adjustment to any stress scenario that may evoke memory responses. Knowledge like this could help improve forage grass breeding and the selection of cultivars for poorly drained soils subject to sequential stress events.