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Ewa Dubas, Maria Wędzony, Beata Petrovska, Jan Salaj and Iwona Żur

Cell Structural Reorganization During Induction of Androgenesis in Isolated Microspore Cultures of Triticale (xTriticosecale Wittm.)

Upon stress treatment, isolated microspores of triticale (xTriticosecale Wittm.) were directed towards sporophytic development (androgenesis). We used fluorescence microscopy to study the cell structural reorganization associated with the process. Changes in the developmental pathway coincided with the character of the microtubular cytoskeleton configuration, the number and direction of nuclear divisions, changes in vacuolization, the distribution of mitochondria, ER and starch grains, and the architecture of new cell wall formation. A band of diffused fluorescence surrounding the nucleus was observed before the first symmetric division of microspores. This structure most likely represents a preprophase band (PPB). Successive mitotic divisions within the microspore wall led to the formation of multinucleate or multicellular structures consisting of one or two domains of cells differing in size. They were later released from the sporoderm and continued further development with features typical for a monocotyledonous embryo. The pattern of internal architecture of androgenic structures depended on their developmental phase. Before and after release from the microspore wall, cortical microtubules (MTs) exhibited various configurations without preferential orientation. They formed a denser network in the region opposite to the sporoderm rupture site. Released multicellular structures showed both intensely fluorescing cortical MTs and more dispersed endoplasmic MTs radiating along the cytoplasmic strands from the nuclear region to the cell cortex. Up to globular stage, isotropically expanding cells of androgenic embryos showed a random pattern of MTs. This is the first report that successive events of androgenic development of triticale microspores are associated with MT reorganization. The results support the view that changes in cytoskeleton architecture are critical during induction of androgenesis.

Open access

Aneta Słomka, Elżbieta Kuta, Agnieszka Płażek, Franciszek Dubert, Iwona Żur, Ewa Dubas, Przemysław Kopeć and Grzegorz Żurek

Miscanthus ×giganteus Greef et Deu. (Poaceae), a hybrid of Miscanthus sinensis and M. sacchariflorus native to Japan, is an ornamental and a highly lignocellulosic bioenergy crop, cultivated in the European Union as an alternative source of energy. This grass reproduces exclusively vegetatively, by rhizomes or via expensive in vitro micropropagation. The present study was aimed at finding the barriers that prevent sexual seed production, based on detailed embryological analyses of the whole generative cycle, including microsporogenesis, pollen viability, megasporogenesis, female gametophyte development, and embryo and endosperm formation. Sterility of M. ×giganteus results from abnormal development of both male and female gametophytes. Disturbed microsporogenesis (laggard chromosomes, univalents, micronuclei) was further highlighted by low pollen staining. The frequency of stainable pollen ranged from 13.9% to 55.3% depending on the pollen staining test, and no pollen germination was observed either in vitro or in planta. The wide range of pollen sizes (25.5-47.6 μm) clearly indicated unbalanced pollen grain cytology, which evidently affected pollen germination. Only 9.7% of the ovules developed normally. No zygotes nor embryos were found in any analyzed ovules. Sexual reproduction of M. ×giganteus is severely hampered by its allotriploid (2n=3x=57) nature. Hybrid sterility, a strong postzygotic barrier, prevents sexual reproduction and, therefore, seed formation in this taxon.