The imbibition process, which is essential for seed germination, can be interrupted due to lack of water in the environment. Once this occurs, seeds have its germination process interrupted and loses the water absorbed to the environment. The objective of this study was to evaluate the effects of hydration and dehydration cycles (HD cycles) on seed germination of Macroptilium atropurpureum under water deficit conditions. Seeds of M. atropurpureum were submitted to 0 (control), 1, 2 and 3 HD cycles at different hydration times. In addition, the seeds were also submitted to osmotic potentials of 0.0, -0.1, -0.3, -0.6 and -0.9 MPa for water deficit simulation. Although the seeds germinated in all of the osmotic potentials used, the seeds presented a reduction in the percentage of germination, independently of the number of HD cycles and the hydration time between each cycle. In addition, HD cycles also negatively affected the mean germination rate, promoting a reduction of this parameter as seeds were submitted to HD cycles and osmotic potentials. Thus, the results demonstrated that HD cycles did not provide an increase in water stress tolerance in M. atropurpureum seeds during germination. Highlighted Conclusions 1)Macroptilium atropurpureum seeds can germinate even in low osmotic potentials conditions. 2) Discontinuous hydration confers a negative effect on M. atropurpureum germination and does not provide a greater tolerance to water deficit.Seed imbibition is a key process in the plant life cycle determining whether seed germination and individual growth will be successful or not (Ribeiro et al. 2015). The imbibition process, which is essential for seed germination, can be interrupted due to lack of water in the environment. Once this occurs, the seed has its germination process interrupted and loses the water absorbed to the environment (Fenner and Thompson 2005). These interruptions during germination process occur in arid and semi-arid environments, where water presents a limit of space and time in its availability, subjecting seeds to hydration and dehydration cycles (HD cycles) (Lima and Meiado 2017). Dubrovsky (1998) pointed that discontinuous hydration ensures a high survival rate during desiccation, demonstrating that seeds may present seed hydration memory, caused by the discontinuous imbibition process.In addition to the high survival rate during desiccation highlighted by Dubrovsky (1998), HD cycles may provide other advantages during the germination process of the seeds of some species. Rito et al. (2009) demonstrated that seeds of Cereus jamacaru DC. subsp. jamacaru (Cactaceae) present seed hydration memory, since, after being submitted to HD cycles, seeds had their percentage of seed germination increased. Pedrero-López et al. (2016), in experiments with seeds of Dodonaea viscosa Jacq. (Sapindaceae) also observed a significant increase of germinability after HD cycles from 22.5% to 63.3%. Discontinuous hydration may also provide greater tolerance to abiotic stress conditions, as observed by Li et ...

O objetivo deste estudo foi avaliar se o aumento da temperatura reduz a tolerância ao estresse hídrico na germinação de sementes de Pereskia grandifolia Haw. subsp. grandifolia (Cactaceae). O déficit hídrico foi simulado com soluções de polietilenoglicol 6000 nos potenciais osmóticos de 0,0; -0,1; -0,3; -0,6 e -0,9 MPa e as temperaturas constantes avaliadas foram as de 25 e 30°C. Os dados de frequência da germinação de sementes indicaram diferenças no comportamento germinativo entre as temperaturas de 25 e 30°C em todos os potenciais avaliados. O potencial osmótico influenciou todos os parâmetros de germinação avaliados no presente estudo, com exceção do índice de sincronização. Com a redução do potencial osmótico foi constatada a redução da germinabilidade das sementes, independentemente da temperatura avaliada. Entretanto, foi observada uma redução mais drástica na germinabilidade quando as sementes foram submetidas ao déficit hídrico na temperatura de 30°C. A temperatura também influenciou significativamente a germinabilidade das sementes, sendo observadas mais sementes germinadas na temperatura de 25°C. O potencial básico foi de -0,9005 MPa na temperatura de 25°C. Porém, quando as sementes foram submetidas à temperatura de 30°C, o potencial básico aumentou para -0,7540 MPa, indicando uma redução da tolerância ao déficit hídrico. Conclui-se que o aumento da temperatura reduz a tolerância ao estresse hídrico na germinação de sementes de P. grandifolia subsp. grandifolia e sugere-se um estudo com sementes de diferentes populações dessa espécie pra se confirmar a influência da origem da semente na sua resposta germinativa quando submetidas a estresses abióticos associados.