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Oxidative stress and antioxidative defense system activity were studied in buckwheat leaves after complete submergence and re-aeration. The levels of H2O2 and lipid peroxidation were found to be significantly higher in stressed than in untreated buckwheat leaves. Enzymes catalyzing the degradation of H2O2 and peroxides were shown to participate actively, whereas superoxide dismutase did not take part in the buckwheat leaf response to flooding stress. The most prominent increase in antioxidative enzyme activities was noticed upon return to air, when the strongest oxidative stress occurred and the need for antioxidative defense was the greatest.

In spite of the great nutritive and pharmacological potentials of buckwheat, data about the abiotic stress tolerance of this plant species are very limited. The aim of this work was to analyze the biochemical and molecular response of buckwheat plants in the middle vegetative phase against short- and long-term salt stress. Changes in relative water content, level of lipid peroxidation, content and localization of H2O2 as well as changes in antioxidative enzyme activity and expression of ubiquitin and dehydrins, were investigated. Reasons for observed buckwheat salt stress sensitivity as well as possibilities for enhancing stress tolerance are discussed.

Aspartic proteinase gene (FeAP12) has been isolated from the cDNA library of developing buckwheat seeds. Analysis of its deduced amino acid sequence showed that it resembled the structure and shared high homology with typical plant aspartic proteinases (AP) characterized by the presence of a plant-specific insert (PSI), unique among APs. It was shown that FeAP12 mRNA was not present in the leaves, roots, steam and flowers, but was seed-specifically expressed. Moreover, the highest levels of FeAP12 expression were observed in the early stages of seed development, therefore suggesting its potential role in nucellar degradation.

Isolated pistils of distylous buckwheat (Fagopyrum esculentum Moench) were treated with protease inhibitors (PMSF, pepstatin A, and antipain). Pistils were cross- or self- pollinated, and growth of pollen tubes was observed under a fluorescence microscope. Treatments with all inhibitors suppressed inhibition of self-pollen tube growth, suggesting that activity of proteases is involved in rejection of self-pollen during the SI response.

A novel type of aspartic proteinase gene was isolated from the cDNA library of developing buckwheat seeds. This cDNA, FeAPL1, encoded an AP-like protein lacking the plant-specific insert (PSI) domain characteristic of typical plant aspartic proteinases. In addition the corresponding genomic fragment was isolated. It is demonstrated that this gene does not contain introns. Since bioinformatics analysis of the Arabidopsis genome showed that most potential AP genes are intronless and PSI-less, it appears that "atypical" is an inappropriate word for that class of AP. Isolation of this specific buckwheat gene among the small group of those isolated from other plant species provides a new perspective on the diversity of AP family members in plants. .

Aspartic proteinases from buckwheat seeds are analyzed. Three forms of 47 kDa, 40 kDa and 28 kDa, were purified from mature buckwheat seeds, while two forms of 47 kDa and 28 kDa were detected in developing buckwheat seeds using pepstatin A affinity chromatography. A form of 47 kDa was selectively precipitated from other forms by ammonium sulfate precipitation. This enzyme resembles the chymosin-like pattern of proteolytic activity, as it was shown using BSA and k-casein as substrates, clarifying its ability for milk-clotting. The 47 kDa aspartic proteinase form is localized in the membrane fraction. .