Biochemical, histological and structural characterization of Inga vera Wild. Subsp. Affinis (DC.) T.D. Penn. seeds during maturation and after drying

Orientadores: Márcia Regina Braga, Simone de Pádua TeixeiraDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de BiologiaResumo: Inga vera Pennington produz sementes com alta sensibilidade à dessecação, o que dificulta seu armazenamento. Diversos mecanismos estão relacionados tolerância à dessecação, dentre eles o acúmulo de reservas insolúveis e de moléculas protetoras, redução do metabolismo e dobramento da parede celular. Desse modo, o objetivo deste trabalho foi analisar o comportamento de eixos embrionários e cotilédones de I. vera com respeito a seus teores e composição de açúcares solúveis, de reserva e de parede celular e quanto à ultra-estrutura durante a maturação e após a secagem. Eixos embrionários e cotilédones de I. vera durante a maturação, acumulam altos níveis de amido e armazenam também outras substâncias como compostos fenólicos. O acúmulo de massa seca e o processo de vacuolização durante todo o desenvolvimentos dos embriões desta espécie indicam alta atividade metabólica até o momento da dispersão. Além disso, as paredes celulares de eixos embrionários e cotilédones acumulam galactanos que podem lhe conferir maior rigidez. Embriões de I. vera secos até 35% de teor de água apresentaram redução da capacidade germinativa. Esta desidratação parcial provocou um estímulo metabólico, evidenciado pela mobilização de reservas e deposição de material nas paredes celulares, além de intensa atividade do retículo endoplasmático rigoso, observada nos eixos embrionários. A secagem severa (17% de teor de água) provocou rompimento das membranas resultando no aparecimento de células completamente colapsadas. Dessa forma, pode-se concluir que embriões I. vera mantém o metabolismo ativo durante a desidratação até que os processos de injúria comecem a ocorrer.Abstract: Inga vera Pennington produces recalcitrant seeds, characterized by desiccation sensibility and short post-harvest life span, no longer than one mouth. Mechanisms proposed to explain the ability of organisms to survive desiccation include accumulation of insoluble reserves and protective molecules, metabolic "switch off" and cell wall folding, among others. The aim of the present study was to analyze the behavior of I.vera embryos (axes and cotyledons) with respect to sugar content, cell wall composition and ultrastructure during different stages of development and after desiccation. Axes and cotyledons accumulate starch and phenolic compounds and also showed vacuolization all over development, suggesting high metabolic activity up to the end of the maturation period. Moreover, cell walls of axes and cotyledons cantain polysaccharides, like galactans, that can provide more rigidity to the cell wall. Mature I.vera seeds were dried 35% or 17% and seed variability was skilghtly reduced due to drying to 35% of water content, but no seeds survived to severe desiccation (17% water content). Starch mobilization, increase in the cell wall thickness in axes and cotyledons, and high degree of development of the rough endoplasmic reticulum in axes suggest that drying to 35% of water content enhanced metabolic activity. Severe desiccation resulted in membrane breaking leading to collapsed protoplasm. Therefore we can conclude that I.vera embryos keep high metabolic activity during desiccation until damage processes start.MestradoBiologia CelularMestre em Biologia Celular e Estrutura

Metabolic And Structural Changes During Early Maturation Of Inga Vera Seeds Are Consistent With The Lack Of A Desiccation Phase.

Inga vera, native to South America, is an important leguminous species used for ecological restoration of riparian forests and its seeds are among the most recalcitrant ones described up to date. In this work, we analysed the metabolic profile, cell ultrastructure as well as cell wall polysaccharides of I. vera seeds in order to better understand its maturation, which allows embryo germination without a quiescent phase. Increased amounts of citric, glutamic, pyroglutamic, and aspartic acids from stages I to II (120 and 129 days after flowering (DAF)) corroborate the hypothesis of high metabolism, shifting from fermentative to aerobic respiration at seed maturity. This phase was characterized by an extensive vacuolization of embryonic cells, which also indicate high metabolic activity. The proportion of arabinose in the cell walls of embryonic axis (approx. 20%) was lower than those found in some orthodox seeds (nearly 40%), suggesting that arabinose-containing polysaccharides, which are thought to provide more flexibility to the cell wall during natural drying, are less abundant in I. vera seeds. Taken together, our results provide evidence that the major changes occurred during early stages of seed maturation of I. vera, indicating that the rapid temporary metabolic shift observed between stages I and II may be related to the lack of desiccation phase, moving directly to germination.170791-80