Expressão de memória de estresse em sementes e mudas de Cenostigma pyramidale (Tul.) E. Gagnon & G.P. Lewis : influência da alta temperatura e da hidratação descontínua

Abstract

In dry ecosystems, seeds may be exposed to pulses of high temperature and discontinuous hydration during germination. Beyond acting as stressors, these events can function as environmental cues that induce persistent adjustments and modulate germination as well as resilience to water deficit. This dissertation aimed to evaluate how exposure of seeds to high- temperature pulses and hydration–dehydration (HD) cycles influences the expression of stress memory in seeds and seedlings of Cenostigma pyramidale, a woody legume widely distributed in the Caatinga. Accordingly, the dissertation was structured into four articles. In Article I, we assessed the effects of HD cycles applied at different imbibition stages on germination and Early growth. HD cycles applied during early hydration increased germination and growth-related parameters, whereas cycles imposed at later stages reduced germination performance and seedling growth. In Article II, seeds were subjected to thermal pulses of 55, 65, and 75 °C for 30, 60, and 90 min. The results indicated high germination resilience, although germination kinetics and synchrony varied with pulse intensity and duration. In Article III, we tested the influence of pre-germinative treatments (high temperature, HD cycles, and their combination) on germination under water deficit induced with PEG 6000. Prior experiences reorganized the temporal dynamics of germination, consistent with stress memory. In Article IV, we examined the persistence of these signals during the seedling stage under intermittent drought, showing that stress memory is also expressed in seedlings, enhancing resilience and recovery after rehydration through physiological adjustments. We conclude that C. pyramidale responds to semiarid conditions not only through resistance, but also through plasticity triggered by heat and discontinuous hydration cues, expressed during the seed phase and early establishment.