Metabolic Changes on the Acquisition of Desiccation Tolerance in Seeds of the Brazilian Native Tree Erythrina speciosa

Abstract

Erythrina speciosa Andrews (Fabaceae) is a native tree of Atlantic forest from Southern and Southeastern Brazil. Although this species is found in flooded areas, it produces highly desiccation tolerant seeds. Here, we investigated the physiological and metabolic events occurring during seed maturation of E. speciosa aiming to better understand of its desiccation tolerance acquisition. Seeds were separated into six stages of maturation by the pigmentation of the seed coat. Water potential (WP) and water content (WC) decreased gradually from the first stage to the last stage of maturation (VI), in which seeds reached the highest accumulation of dry mass and seed coat acquired water impermeability. At stage III (71% WC), although seeds were intolerant to desiccation, they were able to germinate (about 15%). Desiccation tolerance was first observed at stage IV (67% WC), in which 40% of seeds were tolerant. At stage V (24% WC), all seeds were tolerant to desiccation and at stage VI all seeds germinated. Increased deposition of the arabinose-containing polysaccharides, which are known as cell wall plasticizers polymers, was observed up to stage IV of seed maturation. Raffinose and stachyose gradually increased in axes and cotyledons with greater increment in the fourth stage. Metabolic profile analysis showed that levels of sugars, organic, and amino acids decrease drastically in embryonic axes, in agreement with lower respiratory rates during maturation. Moreover, a non-aqueous fractionation revealed a change on the proportions of sugar accumulation among cytosol, plastid, and vacuoles between the active metabolism (stage I) and the dormant seeds (stage VI). The results indicate that the physiological maturity of the seeds of E. speciosa is reached at stage V and that the accumulation of raffinose can be a result of the change in the use of carbon, reducing metabolic activity during maturation. This work confirms that raffinose is involved in desiccation tolerance in seeds of E. speciosa, especially considering the different subcellular compartments and suggests even that the acquisition of desiccation tolerance in this species occurs in stages prior to the major changes in WC.

What Do We Know About the Genetic Basis of Seed Desiccation Tolerance and Longevity?

“…Similar results were obtained by Jing et al [39], who found that overexpression of galactinol and raffinose synthases was associated with higher concentrations of galactinol, raffinose and stachyose in Arabidopsis mutants than in WT along with enhanced DT in developing mutant seeds. An increase in RFOs accumulation has been recently observed in the orthodox seeds of the Brazilian native tree Erythrina speciosa as well [40]. These results suggest that the increased expression of genes related to the raffinose pathway and accumulation of soluble nonreducing sugars in the cytoplasm during late seed maturation, among other things, might be one of the keys to obtaining DT in seeds.…”

Respiratory rates and freezing tolerance of embryos of Inga vera Willd. subsp. affinis (DC.) T.D. Penn. from different regions

“…The results of the initial characterization showed that, although all the fruits had been collected when they were ripe, their embryos showed maturation differences: those of RIB, for example, were closer to physiological maturity than the others, because: a) although the embryos from all regions had very high water content, above 50%, typical for species of the genus Inga (Mata et al, 2013;Schulz et al, 2014), those from RIB had the lowest water potential. This result indicates more binding sites, therefore a better structured matrix (Vertucci and Farrant, 1995); b) the embryos accumulated more dry weight (Marcos-Filho, 2015); c) they had a lower respiration rate, indicating that they were among more mature embryos (the more mature, the lower the respiratory rate, Araujo and Barbedo, 2017) and embryos that had already started germination (the more advanced in germination, the higher the respiratory rates, Hell et al, 2019); d) they had the longest mean germination time, indicating that they had not started germination before harvest, which is relatively common for embryos of this species (Andreo et al, 2006;Bonjovani and Barbedo, 2020).…”

Taxas respiratórias de sementes de Eugenia pyriformis Cambess. dispersas em diferentes estádios de maturação

“…E, finalmente, as sementes das demais regiões, em posições intermediárias para todas as características, mas com uma curiosa comparação entre JUM e SBC, em que a primeira teve germinação bem mais elevada e, a 35 °C, respiração bem abaixo de SBC. Considerando-se que quanto mais avançado no processo de maturação está a semente, maior o índice de desligamento do metabolismo (Hell et al 2019), há evidente variação no grau de maturação em que as sementes de uma mesma espécie, Eugenia pyrifomris, são dispersas, conforme as condições ambientais.…”

“…Outras sementes recalcitrantes podem, inclusive, iniciar a germinação antes mesmo de sua dispersão, como ocorre em Inga vera, aumentando sua sensibilidade à dessecação e acelerando ainda mais o metabolismo (Caccere et al 2013, Bonjovani & Barbedo 2019, comportamentos que dificultam o armazenamento. Nas sementes tolerantes à dessecação, por sua vez, é evidente a mudança no perfil metabólico na fase que antecede a secagem da maturação, quando há um desligamento das atividades, especialmente as taxas respiratórias (Hell et al 2019).…”