Anderson Cleiton José

Physical dormancy in Senna multijuga (Fabaceae: Caesalpinioideae) seeds: the role of seed structures in water uptake

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.

Physiological behavior of Genipa americana L. seeds regarding the capacity for desiccation and storage tolerance

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.

CLASSIFICAÇÃO FISIOLÓGICA DE SEMENTES DE CINCO ESPÉCIES ARBÓREAS DE MATA CILIAR QUANTO A TOLERÂNCIA À DESSECAÇÃO E AO ARMAZENAMENTO 1

Seeds of five riparian forest tree species from the Rio Grande River basin in the State of Minas Gerais - Brazil were classified according to the physiological storage behavior as a way to provide information for future programs on propagation and ex situ conservation. Seeds of Miconia argyrophylla DC. (Melastomastaceae), Allophylus edulis (A St.-Hil., Cambess. & A. Juss.) Radlk. (Sapindaceae), Ixora warmingii Mull. Arg. (Rubiaceae), Aulomyrcia venulosa DC. (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.

Germinação e tolerância à dessecação de sementes de bacaba (Oenocarpus bacaba Mart.)

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.

Changes in gene expression during drying and imbibition of desiccation sensitive Magnolia ovata (A. St.-Hil.) spreng. seeds

Seeds of Magnolia ovata were dried to different water contents to assess the viability and transcript abundance of genes related to seed development, cell cycle, cytoskeleton and desiccation tolerance.The expression of development, cell cycle and cytoskeleton relative genes (ABI3, CDC2-like and ACT2) alone could not explain the germination behaviour of M. ovata seeds in relation to drying damage. Irrespective of their initial water content, the seeds performed in the same way during the initial period of germination and the deleterious effects of desiccation only occurred in later stages. Expression of PKABA1, sHSP17.5 and 2-Cys-PRX did not show a relationship with desiccation. However, the expression patterns of PKABA1 and sHSP17.5 suggested the participation of these genes in protective mechanisms during the imbibition of M. ovata seeds..

Loss of desiccation tolerance and storage behavior in germinating seeds of Senna multijuga: implications for seed germination and conservation

Abstract Orthodox seeds lose desiccation tolerance (DT) and change their storage behavior with advancing germination and with different hydration conditions affect the extent of DT. The objectives of this study were to describe (1) the loss of DT in Senna multijuga seeds during hydration under different conditions and (2) the storage behavior of dry seeds and germinating seeds after desiccation. Seeds lose DT progressively as germination advances, and DT is totally lost before the radicle protrudes. Soaked seeds maintained DT for a longer period of time in comparison to imbibed seeds. Dry seeds tolerated storage even at sub-zero temperatures; however, when germinating seeds were dehydrated, the storability at sub-zero temperatures was reduced. Storage of dried germinating seeds at sub-zero temperature reduced germination and increased the proportion of abnormal seedlings. The hydration conditions changed seed response to desiccation, and this result may be related to differences in metabolism. Thus, the conditions in which seeds remain during hydration can affect the physiological response of seeds, and when studies are conducted to assess the DT, this fact should be taken into consideration. According to the results of this study, S. multijuga seeds can be classified as orthodox; however, storage at sub-zero temperatures is harmful to germinating seeds after drying. Thus, for successful long-term storage, although the current water content of the seeds is important, if the seeds are previously hydrated (and then dried), this will affect seed storability, with consequent implications for ex situ conservation.

Protein expression upon desiccation and imbibition of Magnolia ovata A. St.-Hil seeds

ABSTRACT 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 H 2 O · g -1 dw. The critical water content below which the desiccation sensitivity became apparent was around 0.18 g H 2 O · g -1 dw (-26.5 MPa). Total protein was extracted and separated by 2D electrophoresis from fresh seeds (0.28 g H 2 O · g -1 dw), mild dried seeds (0.25 g H 2 O · g -1 dw) and seeds at low water content (0.10 g H 2 O · 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. Key words: desiccation tolerance, forest seed, legumin, proteomics

Maturation and Desiccation Tolerance in Seeds of Sesbania virgata (Cav.) Pers.

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.

In situ germination of two tropical recalcitrant seeds and changes in activity of ROS-scavenging enzymes

Key messageTropical recalcitrant-seeded species, which disperse seeds at different seasons, provide evidence of the role of oxidative metabolism in seed bank dynamics. Our results indicate that CAT may regulate field germination.AbstractOxidative metabolism during viability loss in recalcitrant seeds has been previously documented, but little is known about the role of ROS-scavenging enzymes in soil seed bank dynamics, especially in recalcitrant seeds. To address this, recalcitrant-seeded species were studied, Swartzia langsdorffii and Persea wildenovii. Diaspores were kept on the soil after natural dispersion, to simulate the seed bank, and were assessed for seed water content, viability, germination and changes in catalase (CAT), superoxide dismutase (SOD) and peroxidase (PRX) activity throughout the field experiment. These parameters were tested for correlations with climatic data. S. langsdorffii start to germinate after one month in soil, with an increase after two months, when CAT activity decreased and SOD activity increased. SOD was negatively correlated with CAT, and CAT was negatively correlated with germination. However, SOD and CAT were positively correlated for P. wildenovii, whose seeds did not germinate even after four months in the soil and with high activity of ROS-scavenging enzymes throughout the period in the soil. Seeds of these species remained viable during the period in the soil with no or little changes in seed water content. ROS-scavenging enzymes respond to environmental factors, adjusting their activity to maintain seed viability. P. wildenovii seeds did not germinate in the soil due to the timing of dispersal being at the end of rainy season, when additional water supply is limited; ROS-scavenging enzymes probably play a role in seed protection during this dry period. Relationship between CAT regulation and soil seed bank dynamics is discussed.

Aspects of Peltophorum dubium Sprengel (Taubert) seeds in an aerial seed bank

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.