Memória hídrica de sementes : implicações ecofisiológicas durante a germinação e o desenvolvimento inicial de espécies da Caatinga

Abstract

Seed hydration memory is the ability of seeds to retain physiological changes caused by discontinuous hydration during seed imbibition process, which may promote benefits in germinative and initial development parameters, such as acquisition of water deficit tolerance and production of more vigorous seedlings. This study aimed to evaluate the effects of hydration and dehydration cycles (HD cycles) during imbibition on seed germination of Senna spectabilis (DC.) H.S. Irwin & Barneby var. excelsa (Schrad.) H.S. Irwin & Barneby (Fabaceae) under conditions of water deficit and on initial development of Mimosa tenuiflora (Willd.) Poir. (Fabaceae). Thus, this dissertation was divided into two chapters in scientific article format, where the first one evaluated the effects of HD cycles on seed germination of S. spectabilis var. excelsa submitted to the conditions of water deficit. In this chapter, seeds underwent HD cycles (0, 1, 2 and 3 cycles) corresponding to the hydration times X (6 hours), Y (16 hours) and Z (24 hours), determined from the imbibition curve, with 5 hours of dehydration and submitted to water stress conditions. Germination was evaluated at 0.0, -0.1, -0.3, -0.6 and -0.9 MPa, obtained with polyethylene glycol 6000 solution. Germinability (%), mean germination time (days) and hydrotime (MPa d-1) were calculated. The seeds of S. spectabilis var. excelsa are sensitive to the low osmotic potentials tested in this study, however, when submitted to the HD cycles of 16 hours hydration (time Y), the tolerance to water stress conditions is increased. In addition, the observed benefits on the evaluated germination parameters show that S. spectabilis var. excelsa present seed hydation memory. The second chapter aimed to evaluate the effect of HD cycles on the germination and initial development of M. tenuiflora seedlings, evaluating the hypothesis that seeds which pass through HD produce larger seedlings with greater accumulation of biomass. Seeds of M. tenuiflora were submitted to 0, 1, 2 and 3 HD cycles. We evaluated parameters of germination and initial seedling growth. Although seed germinability did not change, M. tenuiflora seeds that were submitted to HD cycles germinated in a shorter time than seeds with continuous hydration. In addition, seedlings produced from seeds that were submitted to HD cycles had longer stems, larger stem diameter and higher leaf, stem and root dry mass values. The HD cycles provided the seed hydration memory phenomenon, which may have ecological implications, since seeds that were submitted to discontinuous hydration during the imbibition process produced more vigorous seedlings and seeds more tolerant to the water deficit.