Structural studies in seeds with physical dormancy (PY) are important to better understand its causes and release when subjected to treatments for dormancy breaking. The aims of this study were to (1) characterize the PY break; (2) examine the role of different seed structures in water uptake; and (3) identify the water gap in Senna multijuga seeds. Imbibition patterns of dormant and non-dormant (subjected to dormancy breaking treatments) seeds and the morphological changes during dormancy breaking and germination were evaluated. To identify the water gap, the micropyle and lens were blocked separately, and the water absorption by seed parts was determined. Structural characteristics of the seed coat were also examined. Immersion in water at 80°C was efficient in breaking seed dormancy and imbibition occurred first at the hilar region, through the lens. Water was not absorbed through the micropyle or the extra-hilar region. S. multijuga seeds have a testa with a linearly aligned micropyle, hilum and lens. The seed coat consisted of a cuticle, macrosclereids, one (hilar region) or two (extra-hilar region) layer(s) of osteosclereids and parenchyma cell layers. The lens has typical parenchyma cells underneath it and two fragile regions comprised of shorter macrosclereids. Heat treatment stimulated the lens region, resulting in the opening of fragile regions at the lens, allowing water to enter the seeds. It is concluded that short-term exposure to a hot water treatment is sufficient for the formation of a water gap in S. multijuga seeds, and only the lens acts in the imbibition process.
-Knowledge of the capacity of desiccation and storage tolerance of seeds is essential to provide adequate conditions necessary to maintain viability after seed collection. Drying rate is one of the factors which have been described as affecting the physiological response of seeds of various species. Literature reports that Genipa americana seeds exhibit an intermediate behavior, quickly losing viability if stored at negative temperatures. Thus, this work aimed to verify the effect of slow drying over the capacity of desiccation and storage tolerance of Genipa americana seeds. Seeds with 47% of water content (recently harvested) were dried over salt solutions until reaching 30%, 20%, 15%, 10% and 5% of water content. After drying to 10% and 5% of water content a reduction in seed viability was observed after 30 days of storage without the total loss of germination after three months in these conditions. The slow drying increased the capacity for desiccation and storage tolerance of the Genipa americana seeds if compared to the information described in literature.Index terms: physiological classification, brazilian forest species, genipapo plants.Comportamento fisiológico de sementes de Genipa americana L.quanto à tolerância à dessecação e ao armazenamento RESUMO -Conhecer a capacidade de tolerância à dessecação e ao armazenamento das sementes tem sido imprescindível para disponibilizar condições adequadas para a manutenção da viabilidade após a coleta. A velocidade de secagem é um dos fatores que tem influenciado na resposta fisiológica das sementes de diversas espécies. Deste modo, buscou-se verificar o efeito da secagem lenta na capacidade de tolerância à dessecação e ao armazenamento das sementes de Genipa americana L. Sementes com 47% de umidade (recém-colhidas) foram secas em soluções salinas até 30, 20, 15, 10 e 5% de umidade, testando-se a viabilidade. Ao atingir 10 e 5% de umidade as sementes foram armazenadas a -20 ºC, avaliando-se a viabilidade a cada 30 dias durante três meses. Sementes recém-colhidas apresentaram 98% de germinação sem perda de viabilidade até 10% de umidade. Sementes secas a 10 e 5% de umidade apresentaram redução na viabilidade após 30 dias de armazenamento, porém não houve a perda total de germinação após este período. A secagem lenta aumentou a capacidade de tolerância à dessecação e ao armazenamento das sementes de Genipa americana se comparada às informações descritas na literatura.Termos para indexação: classificação fisiológica, espécie florestal brasileira, jenipapeiro.
Genipa americana (Rubiaceae) is important for restoration of riparian forest in the Brazilian Cerrado. The objective was to characterize the mechanism and control of germination of G. americana to support uniform seedling production. Morphology and morphometrics of seeds, embryo and endosperm were assessed by light and scanning electron microscopy during germination. Imbibition and germination curves were generated and over the same time interval endosperm digestion and resistance were measured by puncture force analysis and activity assay of endo-β-mannanase (EBM) in water and in abscisic acid (ABA). The gene encoding for EBM was partially cloned and its expression monitored by quantitative real-time-polymerase chain reaction. Embryos displayed growth prior to radicle protrusion. A two-phase increase in EBM activity coincided with the two stages of weakening of the micropylar endosperm. The second stage also coincided with growth of the embryo prior to radicle protrusion. Enzyme activity was initiated in the micropylar endosperm but spread to the lateral endosperm. ABA completely inhibited germination by inhibiting embryo growth, the second stage of weakening and expression of the EBM gene, but EBM activity was not significantly inhibited. This suggests that a specific isoform of the enzyme is involved in endosperm weakening. EBM may cause a general 'softening' of micropylar endosperm cell walls, allowing the embryo to puncture the endosperm as the driving force of the decrease in puncture force.
-The objective of this experiment was to evaluate the effect of priming on the germination of Eucalyptus urophylla and of hybrid E. urophylla × E. grandis seeds under salt stress. Two osmotic potentials (-1.0 and -1.5 MPa) were tested, using PEG 6000 for 1 and 3 days. After priming, seeds were germinated under salt stress in a NaCl solution at 0.0 (control), -0.5, -0.75 and -1.0 MPa potentials, at 25 °C. Seed germination and germination speed index decreased as the water potential of the germination medium decreased. However, E. urophylla was more tolerant to salt stress; it showed a higher germination percentage under all tested potentials, when compared to the hybrid. The osmotic conditioning at -1.0 MPa for three days was more effective when E. urophylla x E. grandis was germinated in a salt solution at -1.0 MPa, indicating that this treatment was more effective in inducing tolerance to salt stress.
RESUMO -Sementes de cinco espécies florestais ocorrentes em matas ciliares da bacia do Rio Grande, no Estado de Minas Gerais, foram classificadas de acordo com a tolerância à dessecação e ao armazenamento, como forma de subsidiar futuros programas de propagação e conservação ex situ. (Myrtaceae), and Metrodorea stipularis Mart. (Rutaceae) were collected and taken to the seed laboratory where they were processed and submitted to drying, storage and evaluation of viability by the germination test. After physiological classification regarding storage behaviour it was observed that seeds of M. argyrophylla and M. stipularis presented orthodox behaviour. Such kind of seeds allow storage at low temperature (-20ºC) and moisture content (£5%), without harming viability. On the other hand, seeds of A. edulis, I. warmingii and M. venulosa were classified as recalcitrant, which did not tolerate moisture contents below 12%, indicating that in situ conservation should be used for preservation of the genetic resources of these species.
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