Female gametogenesis and early seed development in Amaranthus hypochondriacus L.

Abstract

Background. Attention to amaranth grains has increased in recent years due to the nutritional value of their seed proteins, which have high levels of the amino acid lysine. However, there is no detailed study describing the stages of seed development in Amaranthus hypochondriacus. Question. How are the developmental patterns of the female gametophyte and young seed in Amaranthus hypochondriacus? Species studied. Amaranthus hypochondriacus L 'Revancha' (Amaranthaceae). Study site and years of study. Plants were growth and collected from 2014 to 2016, in a greenhouse at Instituto Tecnológico de Celaya, Guanajuato, Mexico. Methods. Glomerules were collected before pollination and two weeks after anthesis. The ovules at different development stages were fixed and cleared and were analyzed by light microscopy. A clearing protocol was used to observe the developmental stages during female gametogenesis and embryogenesis. Results. We observed that the Amaranthus hypochondriacus ovule has a campylotropous form. The female gametophyte showed a Polygonum-type pattern of development. We were also able to identify all the stages from the megaspore mother cell to the cotyledon embryo stage. After meiosis, the micropylar megaspore differentiates into the functional megaspore. The embryo did not show symmetric divisions, although the final pattern is similar to that of in eudicotyledons. The suspensor showed additional longitudinal divisions, giving rise to a 2-rowed suspensor, while the endosperm showed a helobial development. Conclusions. These results will be used as baseline to identify morphological changes during seed development and to develop new strategies to improve seed quality or increase the yield. ResumenAntecedentes: La atención al grano de amaranto ha aumentado en los últimos años debido al valor nutricional de las proteínas de su semilla con altos niveles de lisina. Sin embargo, no existe un estudio detallado que describa las etapas tempranas del desarrollo de su semilla. Pregunta: ¿Cómo es el patrón de desarrollo del gametófito femenino y la semilla en Amaranthus hypochondriacus? Especie de estudio: Amaranthus hypochondriacus L 'Revancha' (Amaranthaceae). Sitio de estudio y fechas: Las plantas fueron cultivadas y se colectaron entre los años 2014 y 2016, en invernadero, en el Instituto Tecnológico de Celaya. Métodos: Los glomérulos se colectaron antes de fecundación y hasta dos semanas después de la antesis. Los óvulos se fijaron y aclararon en diferentes estados de desarrollo, se analizaron bajo microscopía de luz en campo claro. Mediante un protocolo de clareo se logró observar todas las etapas de desarrollo de la gametogénesis femenina y la embriogénesis. Resultados. Los óvulos de Amaranthus hypochondriacus son del tipo campilótropo. El gametófito femenino muestra un patrón de desarrollo del tipo Polygonum. Se identificaron todas las etapas de desarrollo desde la célula madre de la megáspora al estado embrionario cotiledonar. Después de la meiosis la megáspora micropilar se diferencia en la megáspora funcio...