Does discontinuous hydration of Senna spectabilis (DC.) H.S. Irwin & Barneby var. excelsa (Schrad.) H.S. Irwin & Barneby (Fabaceae) seeds confer tolerance to water stress during seed germination?

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Abstract

Abstract: Seed hydration memory is the ability of seeds to retain biochemical and physiological changes caused by discontinuous hydration. This study aimed to determine if Senna spectabilis (DC.) H.S. Irwin & Barneby var. excelsa (Schrad.) H.S.Irwin & Barneby (Fabaceae) present seed memory and evaluate the effects of hydration and dehydration cycles (HD) on the seed germination of this species when submitted to conditions of water stress. 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.

Translated abstract

Resumo: Memória de hidratação de sementes é a habilidade que as sementes apresentam em reter alterações bioquímicas e fisiológicas ocasionadas pela hidratação descontinua. Este estudo objetivou determinar se sementes de Senna spectabilis (DC.) H.S. Irwin & Barneby var. excelsa (Schrad.) H.S.Irwin & Barneby (Fabaceae) apresentam memória de hidratação e avaliar os efeitos dos ciclos de hidratação e desidratação (HD) na germinação das sementes dessa espécie quando submetidas a estresse hídrico. As sementes passaram por ciclos de HD (0, 1, 2 e 3 ciclos) correspondentes aos tempos X (6 horas), Y (16 horas) e Z (24 horas) de hidratação, determinados a partir da curva de embebição, com 5 horas de desidratação e postas para germinar em condições de estresse hídrico. A germinação foi avaliada nos potenciais 0,0; -0,1; -0,3; -0,6 e -0,9 MPa, obtidos com a utilização da solução de polietileno glicol 6000. Foram calculados a germinabilidade (%), tempo médio de germinação (dias) e tempo hídrico (MPa.d-1). Sementes de S. spectabilis var. excelsa são sensíveis aos baixos potenciais hídricos, porém, quando submetidas aos ciclos de HD no tempo Y (16 horas), há um aumento na tolerância às condições de estresse hídrico. Além disso, os benefícios observados nos parâmetros germinativos mostraram que S. spectabilis var. excelsa apresenta memória de hidratação da semente.

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How and why to measure the germination process?

Marli A. Ranal, Denise Garcia de Santana (2006)

In the last two centuries, papers have been published including measurements of the germination process. High diversity of mathematical expressions has made comparisons between papers and some times the interpretation of results difficult. Thus, in this paper is included a review about measurements of the germination process, with an analysis of the several mathematical expressions included in the specific literature, recovering the history, sense, and limitations of some germination measurements. Among the measurements included in this paper are the germinability, germination time, coefficient of uniformity of germination (CUG), coefficient of variation of the germination time (CVt), germination rate (mean rate, weighted mean rate, coefficient of velocity, germination rate of George, Timson’s index, GV or Czabator’s index; Throneberry and Smith’s method and its adaptations, including Maguire’s rate; ERI or emergence rate index, germination index, and its modifications), uncertainty associated to the distribution of the relative frequency of germination (U), and synchronization index (Z). The limits of the germination measurements were included to make the interpretation and decisions during comparisons easier. Time, rate, homogeneity, and synchrony are aspects that can be measured, informing the dynamics of the germination process. These characteristics are important not only for physiologists and seed technologists, but also for ecologists because it is possible to predict the degree of successful of a species based on the capacity of their harvest seed to spread the germination through time, permitting the recruitment in the environment of some part of the seedlings formed.