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Abstract

The development of megasporocytes and the functional megaspore formation in Deschampsia antarctica were analyzed with the use of microscopic methods. A single archesporial cell was formed directly under the epidermis in the micropylar region of the ovule without producing a parietal cell. In successive stages of development, the meiocyte was transformed into a megaspore tetrad after meiosis. Most megaspores were arranged in a linear fashion, but some tetrads were T-shaped. Only one of the 60 analyzed ovules contained a cell in the direct proximity of the megasporocyte, which could be an aposporous initial. Most of the evaluated D. antarctica ovules featured monosporic embryo sacs of the Polygonum type. Approximately 30% of ovules contained numerous megaspores that were enlarged. The megaspores were located at chalazal and micropylar poles, and some ovules featured two megaspores - terminal and medial - in the chalazal region, or even three megaspores at the chalazal pole. In those cases, the micropylar megaspore was significantly smaller than the remaining megaspores, and it did not have the characteristic features of functional megaspores. Meiocytes and megaspores of D. antarctica contained polysaccharides that were detectable by PAS-reaction and aniline blue staining. Starch granules and cell walls of megasporocytes, megaspores and nucellar cells were PAS-positive. Fluorescent callose deposits were identified in the micropylar end of the megasporocytes. During meiosis and after its completion, thick callose deposits were also visible in the periclinal walls and in a small amount in the anticlinal walls of megaspores forming linear and T-shaped tetrads. Callose deposits fluorescence was not observed in the walls of the nucellar cells.
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Authors and Affiliations

Marcin Domaciuk
Irena Giełwanowska
Agata Leszczuk
Ewa Szczuka
Wioleta Kellmann-Sopyła
Justyna Koc
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Abstract

In this study defense responses in three potato varieties with different levels of reaction to the late blight disease caused by Phytophthora infestans were analyzed after inoculation with the pathogen. In the resistant cv. Pastusa Suprema, increased intensity of H2O2 and callose deposit accumulation was observed beginning at 24 hours after inoculation, followed by a hypersensitive response at the inoculation points. In the moderately resistant cv. Diacol-Monserrate, the same responses were observed as in the resistant variety, but with less intensity over time. For the susceptible cv. Diacol-Capiro, the responses observed occurred later than in the other two varieties, subsequent to the advance of the pathogen over extensive necrotic areas. These results suggest that early, intense peroxide and callose accumulation and a hypersensitive response are associated with the observed resistance of the cv. Pastusa Suprema and cv. Diacol-Monserrate to P. infestans.

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Authors and Affiliations

Astrid Elena Gaviria
Luis Fernando Patiño
Juan Gonzalo Morales

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