Polyphenolic antioxidant compounds were studied in three onion varieties (red -cv. Karmen, yellow -cv. Všetana and white -cv. Ala) regarding their total content and qualitative composition of flavonoid complex. The effects of temperature and storage period during onion storage were also studied. The total content of polyphenols was estimated spectrophotometrically with Folin-Ciocalteau's phenolic reagent and individual flavonoid components by HPLC method using Waters TM chromatograph on Watrex 250 × 4 mm Sepharon SGX C18 7μm column with gradient elution. The highest amount of polyphenolic compounds was found in red variety Karmen (108,300 mg/kg DM), the lowest amount in white variety Ala (26,445 mg/kg DM) while the yellow variety Všetana had average content of total polyphenolic compounds 65,210 mg/kg DM. An increase in total polyphenols during storage was found in red and yellow varieties, esp. during storage at a laboratory temperature (22°C). Among the flavonoid and polyphenolic compounds as major constituents spiraeoside (quercetin-4´-O-β-D-glucoside), rutin and quercetin and three other not identified compounds were found. Significant varietal differences were found. The compound with the highest content was spiraeoside (32,234 mg/kg DM in red cv. Karmen, 23,283 mg/kg DM in yellow cv. Všetana and 265 mg/kg DM in white cv. Ala). Rutin ranged from 15 mg/kg DM in cv. Ala to 157 mg/kg DM in cv. Karmen and similarly quercetin from 1 mg/kg DM in cv. Ala to 163 mg/kg DM in cv. Karmen. During storage an increase in flavonoids could be observed, esp. at a laboratory temperature compared to storage at a lower temperature.

Yacon [Smallanthus sonchifolius (Poepp. et Endl.) H. Robinson], a native plant of the Andes, belongs to the family Compositae (Asteraceae). It represents a traditional crop from the original population of Peru. Most of the tuberous root biomass is constituted by water (> 70% of the fresh weight). Saccharides, especially oligofructans, form 70–80% of their dry weight. Four yacon ecotypes originating from Bolivia, Ecuador, Germany and New Zealand were cultivated on the trial fields of the Czech University of Agriculture in Prague in 1995, 1996, 2000 and 2001. Considerable differences among the ecotypes were observed in their content of inulin (141–289 mg/kg d.m.) and lesser for fructose levels (195–217 mg/kg d.m.). No differences were found in glucose and saccharose contents. The highest inulin and fructose contents were found in the harvests from 2001 and 2000, similar trends were found for glucose. Statistically significant effect on the content of all saccharides has the year of cultivation. Tubers contained much higher levels of inulin (179 g/kg d.m.) and fructose (193 g/kg d.m.) in comparison with rhizomes. No significant differences were found for saccharose (higher in rhizomes) and glucose (lower in rhizomes). The contents of inulin and fructose in the upper and lower parts of tubers were reciprocal. During the storage period of 140 days at10°C and 75% a relative humidity inulin content decreased by 48.7% and monosaccharides content increased (fructose by 9.97%, glucose by 31.4%) due to hydrolysis. Likewise saccharose content increased by 12.9%.

The effects were tested of white fleece on the contents of ascorbic acid, nitrates, and polyphenols in 1999 and 2000, and on the carotenoids content in 2000 and 2001 in tubers of two early potato varieties (Adora and Impala) in field trials on two cultivation sites (Pøerov n/Labem and Prague-Troja). Early irrigated potatoes were cultivated according to the uniform methodology for field trials. Two variants were compared -cultivated plants covered with white fleece (Pegas-Agro UV 17) and the controls without any covering. The tubers were harvested three times in intervals of 7-16 days. The results were statistically tested by ANOVA and Tukey's methods. Ascorbic acid content showed a tendency to higher values in the potatoes covered with white fleece as compared with the control samples (average increase by 12.3%). The effect of the fleece was significantly affected by the potato genotype and the year of cultivation (cv. Adora showed a content higher by 12.54% in comparison with the control). The tendency to reduce nitrate levels was observed in potato tubers cultivated under the fleece, especially in the second term of harvest (on average by 14.34%). The decrease between the first and the third term of harvest was apparent. The higher was the maturity of potato tubers, the lower nitrate content was found. Significant differences were found between the varieties (P = 0.0058) and the cultivation sites (P = 0.0399). The effect of white fleece on polyphenol content was not statistically significant. However, the effect of the year of cultivation on the polyphenols content was significant (P = 0.0094). The effect of white fleece on the carotenoids content was not statistically significant but a tendency to lower contents in the variant with white fleece was found (by 7.2%). The sites and the varieties affected the carotenoids contents significantly (P = 0.0028 and P = 0.0417, respectively).

The effect of an abiotic stress caused by cadmium on the total flavonoid content in roots, shoots and leaf blades of spring barley variety Kompakt grown in a climate-control room for 28 days was investigated. Total flavonoid content (F) was determined spectrophotometrically with sodium nitrite, Cd content by atomic absorption spectrometry. Treatment of barley plants with Cd (1.10 -6 mol/l) in nutrition solution caused the decrease of F in the all parts of the plant. The relatively highest decrease was found in the roots (from 20.0 to 3.05 g/kg dry ma�er), lesser decrease in the shoots (from 24.2 to 9.33 g/kg dry ma�er) and the leaf blades (from 58.3 to 27.3 g/kg dry ma�er). Statistically significant decrease (at least P < 0.05) of F and increase of Cd contents in all the investigated parts of the plant was found. Statistically significant differences of F and Cd contents among barley roots, shoots, and leaf blades were found.

The effect of abiotic stress caused by cadmium on the total polyphenols content in root, shoots and leaf blades of barley was investigated in model experiments. Total polyphenols content was determined spectrophotometrically with Folin Ciocalteau&rsquo;s reagent, Cd content by atomic absorption spectrometry (AAS) in 28-day-old plants. Treatment of the barley plants with Cd (1.10^&ndash;6 mol/l) in a nutrition solution caused the increase in the total polyphenols in all parts of the plant. The highest increase was found in the leaf blades (35.2%, 8340 mg/kg d.m.), a lesser increase found in the shoots (16.7%, 3590 mg/kg d.m.), and the lowest increase found in the roots (10.3%, 3650 mg/kg d.m.). The highest Cd increase in the treated plants was found in the roots (10 400%, 240 mg/kg d.m.), the lesser in their shoots (4990%, 16.3&nbsp;mg/kg d.m.), and the lowest in the leaf blades (2580%, 5.78 mg/kg d.m.). There was found a statistically significant increase (at least P &lt; 0.05) in the total polyphenols and Cd contents in all investigated parts of the plant. Statistically significant differences (at least P &lt; 0.05) of the total polyphenols and Cd contents among barley roots, shoots, and leaf blades were found.