ABSTRACT Background: The aim of this research was to investigate the efficiency of methods to overcome primary dormancy and biochemical processes associated with germination of Erythrina falcata Benth seeds. Seeds were submitted to dormancy overcoming treatments and the water uptake pattern was analysed. We then evaluated the activity of the antioxidant enzymes SOD, CAT, and APX, and quantified lipid peroxidation levels, hydrogen peroxide content and total protein content. The experiments were performed in a completely randomized design and the statistical analysis used was Scott-Knott test at 5% probability. Results: Mechanical scarification with sandpaper leads to approximately 94% of germination in E. falcata, while control non-scarified seeds show only approximately 37% of germination. Treatments with hot water led to high mortality in E. falcata seeds. Rapid water absorption was observed in the first 18 hours of imbition when the seeds were scarified with sandpaper, and radicle emergence was observed after 36 hours. During imbibition there was an increase of antioxidant enzyme activity and a decrease in lipid peroxidation and H2O2 production, suggesting an efficient mechanism for regulating imbibition damage. A decrease in the total protein content was observed during germination of E. falcata seeds. Conclusions: Mechanical scarification is an efficient method for breaking dormancy of E. falcata seeds. During germination of E. falcata seeds there is a reduction in the production of H2O2 and lipid peroxidation, and an increase in the activity of antioxidant enzymes. The total protein content decreased along the germination time.

Resumo: Vários estudos têm utilizado com sucesso o polietilenoglicol (PEG) e/ou ácido abscísico (ABA) para induzir a tolerância à dessecação em sementes germinadas de espécies ortodoxas, melhorando nosso entendimento dos mecanismos que fundamentam essa característica. Nesse contexto, tratamentos com PEG e ABA foram testados para avaliar sua eficiência em reduzir a sensibilidade à dessecação e aumentar o período de armazenamento das sementes de Magnolia ovata. A secagem das sementes a 10% de teor de água não afetou significativamente a germinação, independentemente de terem sido previamente tratadas ou não com ABA. No entanto, sementes tratadas com PEG apresentaram menor viabilidade. Após o armazenamento, as sementes tratadas com ABA e dessecadas a 5% de teor de água, apresentaram maiores taxas de germinação, sendo que o tratamento com ABA 100 µM proporcionou a maior capacidade de armazenamento. Não foram observadas alterações na atividade da catalase, peroxidase ou superóxido dismutase ou na abundância de proteínas totais ou resistentes ao calor.

Abstract: Several studies have successfully used polyethylene glycol (PEG) and/or abscisic acid (ABA) to reinduce desiccation tolerance in germinated seeds of orthodox species, improving our understanding of the mechanisms that underlie this trait. In this context, treatments with PEG and ABA were tested to assess their efficiency in reducing the sensitivity to desiccation and increasing the storage period of Magnolia ovata seeds. The drying of seeds to 10% water did not significantly affect germination, nor was germination impaired in seeds that were dried and treated with ABA. However, seeds treated with PEG had lower viability. After storage, ABA-treated seeds with as low as 5% water content (WC) had higher germination rates, the treatment with 100 µM ABA providing the greatest storage capacity. No changes were observed in the activity of catalase, peroxidase, or superoxide dismutase or in the abundance of total or heat-resistance proteins.

ABSTRACT Background: The germination ecology of P. guajava seeds collected in two regions of Brazil was investigated aiming to (1) characterize the seed batches; (2) determine the best temperature for germination; and (3) assess variations in seed desiccation tolerance (DT). For each batch, we determined seed water content and initial germination. To evaluate temperature effects, we tested seed germination. After, we generated the imbibition curves for the two provenance. To evaluate the loss of DT, the seeds were left to germinate along different time intervals. We monitored water loss by regularly weighing the seeds until achieving stabilization, keeping them under these conditions for 72 hours. After drying, the seeds were pre-hydrated and submitted to the germination test. Results:We identified variations in physiological characteristics between the seeds from north and southeast batches. At the temperature extremes, the seeds from both provenance failed to germinate. The highest germination percentages were observed at 20 and 25 °C (constant) and between 20-30 °C (alternating) for the two batches and, for the southeast batch specifically, at 30 °C. The imbibition curve displayed a triphasic pattern with a rapid increase in seed fresh weight in the first 48 hours. Conclusion: The southeast provenance seeds lost DT abruptly, until its complete loss after radicle protrusion, which occurred in both batches. The highest values of germination speed index (GSI) of both provenance were observed after a 9-day imbibition period, suggesting seed hydration memory. Drying resulted in necrosis of the root tissue and death of the seeds with visible roots.

Abstract Some species of the Lauraceae family produce seeds that are generally sensitive to desiccation, which makes them difficult to store. The objective of this study was to characterize changes in seed quality of C. aschersoniana from two lots, as well in the physiological and cellular aspects during 12 months of storage. Seeds were stored with their original moisture content (MC) or after pre-drying to 35% MC in a cold chamber (5 °C) at a relative humidity of 40%. Seeds were sampled and tested at time 0, 3, 6 and 12 months of storage regarding to moisture content, germination and ultrastructural features. The seeds were dispersed with dormancy that was overcame by the cold storage condition and the reserves in undried seeds were partly consumed during storage. Both undried and pre-dried seeds remained viable for at least 12 months.

ABSTRACT Pteridium aquilinum is an invasive species that stands out for its aggressiveness, invading pastures, agricultural areas and forests. In order to improve this situation, several techniques have been tested, although not common to tropical climate areas. Thus, the objective of this study was to evaluate the survival of eleven tree species according to their density, planting model, and way of bracken removal, in the restoration of an Atlantic Forest area invaded by the species after a fire. The experiment was installed in a randomized block design, in a 2 × 3 × 2 factorial arrangement (planting × density × bracken removal methods). Bracken cover and survival were evaluated nine months after planting. In conclusion, more densified plantations with fast-growing species, together with bracken removal by harrowing, were more effective in establishing the species in bracken-dominated areas.

RESUMO A capacidade que determinadas espécies têm de manter as sementes viáveis por longos períodos no banco de sementes é essencial para a resiliência ambiental, o que é utilizado na restauração florestal. Este trabalho teve como objetivo estudar o comportamento de banco de sementes induzido de P. dubium. A indução do banco de sementes foi feita em fragmento de Floresta Estacional Semidecídual. Foram utilizadas 100 amostras de copos de polietileno, compostas por 25 sementes cada. A cada dois meses, 5 amostras foram retiradas para determinação de: conteúdo de água, viabilidade, porcentagem de emergência de plântulas e porcentagem de predação. As sementes da espécie P. dubium podem permanecer por até 16 meses viáveis enterradas no solo. Esse resultado permite a classificação da espécie como formadora de banco de sementes persistente. A predação de sementes foi o principal fator para que ocorresse a redução do banco de sementes do solo.

ABSTRACT The ability of certain species in keeping the seeds viable for long periods in the soil seed bank is essential for environmental resilience, which is used in forest restoration. This work aimed to study the behavior of a buried seed bank of P. dubium. Burial seed bank was performed in a fragment of Seasonal Semideciduous Forest. One hundred samples consisting of 25 seeds in polyethylene cups were placed under the canopy. Every two months, five samples were taken for determination of water content, viability, emergency (root protrusion and seedling formation) and predation. Seeds of P. dubium may remain buried in the ground for up to 16 months keeping their viability. This result indicates that P. dubium is able to form persistent soil seed bank. The predation was the main factor contributing to the seed bank reduction.

ABSTRACT The maturation process of Sesbania virgata seeds was investigated through fruits and seeds at different maturation stages, where they were described morphologically. For the seeds, fresh and dry mass and moisture were determined and structural analysis of the tegument under a light microscope was performed. Germination tests in the presence and absence of drying and the electrophoretic profile of heat resistant proteins were also performed. The results showed that the seeds reached physiological maturity at 44 days after anthesis (DAA), evidencing a secondary cell wall. The acquisition of desiccation tolerance was observed at 44 DAA, with the seeds responding to the drying treatment. Protein bands were observed from 32 DAA, which remained constant until the end of maturation. These results allowed the characterization of the development and acquisition of desiccation tolerance in S. virgata seeds.

RESUMO A compreensão da tolerância à dessecação é de grande interesse para a tecnologia de sementes, visto que tem aplicação prática no estabelecimento de estratégias para a conservação de sementes e produção de mudas. O presente trabalho objetivou estudar a perda da tolerância à dessecação durante a germinação de sementes das espécies arbóreas sucupira (Bowdichia virgilioides), pau-ferro (Libidibia ferrea), cedro (Cedrela fissilis), tamboril (Enterolobium contortisiliquun), ipê-roxo (Handroanthus impetiginosus) e pau-jacaré (Piptadenia gonoacantha). Sementes coletadas na região de Lavras - MG foram usadas para os experimentos, sendo estes realizados isoladamente para cada espécie. Primeiramente foi estabelecida a curva de embebição por meio da pesagem das sementes nas condições de germinação a intervalos regulares. Baseado nessa informação, as sementes foram postas para embeber por tempos determinados pela curva de embebição e submetidas à secagem até atingir o mesmo percentual de umidade encontrado antes da semeadura. Em seguida as sementes foram reidratadas e aquelas que continuaram a germinação e originaram plântulas normais foram consideradas tolerantes à dessecação. Cada espécie apresentou um padrão próprio quanto à perda da tolerância à dessecação, sendo que em todos os casos, não houve tolerância à dessecação após a protrusão da raiz primária. Contudo, foi observada em sementes de pau-jacaré uma redução mais drástica logo no início do processo germinativo. Nas condições do presente trabalho, observou-se perda da tolerância à dessecação nas primeiras etapas do processo germinativo em todas as espécies, o que pode ter implicações em trabalhos que envolvam o condicionamento fisiológico das sementes.

ABSTRACT Understanding the loss of desiccation tolerance is of great importance in seed technology for its implications in the development of strategies for seed conservation and seedling production. In the present work, the loss of desiccation tolerance was studied in seeds of tree species Bowdichia virgilioides, Libidibia ferrea, Cedrela fissilis, Enterolobium contortisiliquum, Handroanthus impetiginosus, and Piptadenia gonoacantha. The seeds were collected in the region of Lavras, MG, and subjected to desiccation experiments individually for each species. Imbibition curve was created for each species by measuring seed weight at regular intervals under germination conditions. Based on this information, the seeds were allowed to imbibe for a time inferred from the imbibition curve, and then allowed to dry until reaching the initial water content measured before the imbibition begun. Then, the seeds were rehydrated, and those that developed into normal seedlings were considered desiccation-tolerant. The loss of seed desiccation tolerance followed a specific pattern in each studied species, but none of the species was tolerant to desiccation after radicle protrusion. A drastic decrease in desiccation tolerance was observed in P. gonoacantha seeds at the beginning of the germination process. Under the conditions implemented in this study, the loss of desiccation tolerance in all species started at the beginning of the germination process. These results have implications in both theoretical studies (seed priming) and the practice (in seedling production).

Resumo: O conhecimento sobre estratégias de regeneração natural é importante devido a sua influência no ecossistema local. Objetivou-se estudar o comportamento do banco de sementes aéreo de P. dubium. Os frutos foram colhidos mensalmente antes e após a maturação das sementes em matrizes localizadas no município de Lavras - MG. Mensalmente, foram determinados o conteúdo de água, aquisição da tolerância a dessecação, viabilidade das sementes, manutenção da dormência e tempo médio de germinação. Verificou-se que a maturidade fisiológica da espécie ocorreu no mês de junho, quando foi observado baixo conteúdo de água, máxima matéria seca, e alta porcentagem de germinação. Verificou-se que não houve alteração na dormência, porcentagem de germinação e no perfil proteico de sementes durante o período em que permanecem no banco de sementes aéreo. A espécie P. dubium forma banco de sementes aéreo de curta serotinosidade, com frutos permanecendo presos à planta por 9 meses.

Abstract: Knowledge concerning natural regeneration strategies is important due to the effect of natural regeneration on the local ecosystem. The aim of this study was to examine the ecophysiological aspects of the Peltophorum dubium aerial seed bank. Fruits were harvested monthly, before and after seed maturation, from selected trees in the municipality of Lavras, MG, Brazil, for determination of moisture content, acquisition of tolerance to desiccation, seed viability, maintenance of dormancy, and mean germination time. Physiological maturity of the species was attained in June, when low moisture content, maximum dry matter, and high germination percentage were observed. We found that there was no change in dormancy, in germination percentage, or in the protein profile of seeds during the period they remained in the aerial seed bank. The P. dubium species creates an aerial seed bank of short serotiny, with fruits remaining attached to the tree for 9 months.

Resumo: Este trabalho teve-se como objetivo avaliar o efeito do condicionamento osmótico na germinação de sementes de Eucalyptus urophylla e do híbrido de E. grandis x E. urophylla em condições de estresse salino. Foram testados dois potenciais de condicionamento induzidos por PEG 6000 (-1,0 e -1,5 MPa) em dois períodos (1 e 3 dias). Após o condicionamento osmótico, as sementes foram colocadas para germinar sob estresse salino em solução de NaCl nos potenciais 0,0 (controle) -0,5, -0,75 e -1,0 MPa a 25 °C. Os parâmetros avaliados foram a germinação e o índice de velocidade de germinação (IVG). Houve diminuição da germinação e do IVG à medida que o potencial hídrico do meio germinativo tornou-se mais negativo, tanto para E. urophylla quanto para o híbrido, entretanto, o E. urophylla foi mais tolerante ao estresse salino, em comparação ao híbrido, apresentando maior germinação em todos os potenciais hídricos testados. O osmocondicionamento no potencial de -1,0 MPa por três dias foi o mais indicado tanto para E. urophylla quanto para E. urophylla x E. grandis, quando submetidos à germinação em solução salina a -1,0 MPa, demonstrando que esse tratamento foi eficiente em favorecer a tolerância ao estresse salino.

Abstract: 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: Em sementes, tolerância à dessecação (TD) e longevidade são necessárias para a melhor dispersão da espécie e para o estabelecimento de um banco de sementes no solo. Ambas são adquiridas durante fase de maturação do desenvolvimento das sementes e perdidas durante a germinação. A TD pode ser re-induzida em sementes germinadas por um tratamento osmótico e/ou com ácido abscísico. Entretanto, não há informações sobre como esses tratamentos afetam a longevidade das sementes. No presente estudo, utilizou-se sementes germinadas de Sesbania virgata como modelo experimental para investigar os efeitos na longevidade de um tratamento osmótico para re-induzir TD. A longevidade de sementes germinadas de S. virgata submetidas ou não a um tratamento osmótico foi analisada após armazenamento ou envelhecimento acelerado. A radícula é o órgão mais sensível e os cotilédones são o órgão mais resistente. A habilidade de produzir raízes laterais é imprescindível para a sobrevivência das sementes. Sementes germinadas de S. virgata com radícula de 1mm de comprimento toleram dessecação e armazenamento por até três meses sem redução significativa na longevidade. O tratamento osmótico melhora a TD nessas sementes, mas não a longevidade. Sementes germinadas de S. virgata são um bom modelo para estudar a TD desacoplada da longevidade.

Abstract: Seed desiccation tolerance (DT) and longevity are necessary for better dissemination of plant species and establishment of soil seed bank. They are acquired by orthodox seeds during the maturation phase of development and lost upon germination. DT can be re-induced in germinated seeds by an osmotic and/or abscisic acid treatment. However, there is no information on how these treatments affect seed longevity. Germinated Sesbania virgata seeds were used as a model system to investigate the effects of an osmotic treatment to re-establish DT on seed longevity. Longevity of germinated S. virgata seeds treated and non-treated by an osmoticum was analysed after storage or artificial ageing. The radicle is the most sensitive organ, the cotyledons are the most resistant, and the ability to produce lateral roots is the key for whole seed survival. Germinated S. virgata seeds with 1mm protruded radicle tolerate desiccation and storage for up to three months without significant losses in viability. An osmotic treatment can improve DT in these seeds, but not longevity. Germinated S. virgata seeds are a good model to study DT uncoupled from longevity. Further studies are necessary to unveil the molecular mechanisms involved in both DT and longevity.

RESUMO Este trabalho foi realizado com o objetivo de estudar o comportamento de sementes de G. americana L. (Rubiaceae) em bancos de sementes induzidos. A pesquisa foi realizada no município de Lavras - MG em uma floresta estacional semidecídua da Universidade Federal de Lavras. As sementes coletadas foram beneficiadas e caracterizadas quanto ao conteúdo de água, viabilidade e tolerância à dessecação. Foram instalados bancos de sementes induzidos em duas áreas distintas (topo de morro e mata ciliar) localizados no sub-bosque da floresta. As sementes foram acondicionadas em redes de náilon e cobertas com camada de serapilheira previamente removida para instalação das redes. Foi realizada avaliação mensal da germinação, emergência das plântulas, conteúdo de água das sementes e do solo e a caracterização do crescimento inicial das plântulas. Foi observado que sementes de G. americana formam banco de sementes transitório, com manutenção de sua viabilidade somente até o quarto mês após dispostas em ambiente natural. De modo geral, o banco de sementes na área de mata ciliar foi o que apresentou o maior potencial para o estabelecimento de plântulas em ambiente natural o que está de acordo com as características ecológicas dessa espécie.

ABSTRACT This work studied the behavior of G. americana L. (Rubiaceae) seeds in an induced soil seed bank. This study was conducted in Lavras-MG in a seasonal semideciduous forest of the Federal University of Lavras. Seeds collected in the area were cleaned and analyzed (water content, viability and desiccation tolerance). Soil banks were installed in two distinct areas (top of hill and riparian forest) located in the understory of the forest. Seeds were placed in nylon nets and covered with a thin litter layer that was previously removed for this purpose. Monthly assessment of germination, seedling emergence, seed and soil water content, and the characterization of the initial seedling growth was performed. It was observed that G. americana seeds forms a transitory seed bank, with maintenance of its viability until the fourth month after disposal in natural environment. In general, the seed bank located in the riparian forest area showed the best potential for seedling establishment in a natural environment, which supports the ecological behavior of this species.

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.

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.

A Bacaba (Oenocarpus bacaba) é uma palmeira típica da região amazônica, muito utilizada para alimentação pela população local, na região norte do Brasil. Objetivou-se com esta pesquisa avaliar o efeito de diferentes temperaturas e substratos na germinação das sementes de bacaba e fazer a classificação fisiológica das sementes quanto à secagem e ao armazenamento. Os frutos foram coletados em Caseara, Tocantins, Brasil. A germinação foi realizada em diferentes temperaturas e substratos após o beneficiamento. A viabilidade também foi avaliada após a secagem a diferentes conteúdos de água para classificação fisiológica quanto à secagem e ao armazenamento. O melhor substrato para a germinação de sementes de bacaba foi sobre areia. Não foi verificado efeito da temperatura na germinação das sementes, exceto quando as sementes foram incubadas a 35 °C, temperatura que não foi observada germinação. Apesar de não haver efeito da maioria das temperaturas testadas sobre a porcentagem final de germinação, quando as sementes foram incubadas nas temperaturas de 30 °C e 25 - 35 °C observou-se maior velocidade de germinação. As sementes de bacaba não toleram a secagem abaixo de 0,36 g H2O g-1 peso seco, sendo portanto classificadas como recalcitrantes.

Bacaba (Oenocarpus bacaba) is a palm species typical from Amazon region, widely used by local people for feeding. This work aimed to evaluate the effect of different conditions of temperature and substrate in the germination of seeds and to determine the seed storage behaviour of bacaba (Oenocarpus bacaba) seeds. Fruits were collected at Caseara, Tocantins, Brazil. The germination was carried out at different temperatures and substrates after cleaning. Seed viability was also determined after drying at different water content in order to determine the seed storage behavior. The best substrate for germination of bacaba seeds was in sand. It was not verified effect of temperature on the germination of the seeds, except when seeds were incubated at 35 °C, which germination was not observed. Although there is no effect on the most of the temperature tested on the final percentage of germination, seeds incubated at 30 °C and 25-35 °C showed higher speed of germination. Seeds of bacaba cannot be dried below 0,36 g H2O g-1 dry weight, and so they are classified as recalcitrant.

The effect of seed drying and imbibition was studied by differential protein expression using two dimensional gel electrophoresis. After drying to a range of water contents, seeds were germinated to assess the viability. Seeds of Magnolia ovata did not withstand the desiccation down to 0.10 g H2O · g-1 dw. The critical water content below which the desiccation sensitivity became apparent was around 0.18 g H2O · g-1 dw (-26.5 MPa). Total protein was extracted and separated by 2D electrophoresis from fresh seeds (0.28 g H2O · g-1 dw), mild dried seeds (0.25 g H2O · g-1 dw) and seeds at low water content (0.10 g H2O · g-1 dw) before and after imbibition for 10 days. The proteome profile revealed the presence of 588 spots on each silver stained gel, from which 21 showed differential expression, correlated with desiccation and germination, by increased or decreased expression. After MS/MS sequencing, three protein spots produced spectra that matched to a Magnolia salicifolia legumin precursor. Results suggested an involvement of this protein in the events taking place during the drying and subsequent imbibitions of the dried seeds.