Organic selenized yeast enriched with selenoamino acids or inorganic sodium selenate (Na2SeO4) was administered per os three times weekly as a drench for 133 d to previously unsupplemented cows that were grazing low Se pastures. Treatment groups received the equivalent of 2 or 4 mg of Se/d of either supplement form. Control cows did not receive a drench. Samples of blood and milk were collected regularly throughout the trial. Selenium concentrations in blood, milk, casein, and liver and glutathione peroxidase activity in blood and liver are reported as responses per milligram of Se intake. Mean blood Se concentrations in treated cows increased steadily and, by d 133, were 4.7 to 8.8 times that in controls. Selenized yeast was 2 to 3 times more effective than was Na2SeO4, and low Se intakes were 27% more efficient per milligram of Se administered than were high Se intakes at increasing milk Se concentration. Casein Se content mirrored that of milk; among all treated and control cows and throughout the trial, the molar ratio of Se in casein as a percentage of the Se in whole milk was constant at 71 +/- 1.2%. The Se concentration in liver biopsies taken on d 133 was indicative of total Se intake during the trial and ranged from 920 to 3920 nmol of Se/kg of fresh weight. These results demonstrate the differing efficacy of organic and inorganic Se dietary supplements to increase dairy cow Se status and to enhance Se content of milk and casein.

Disease assessments and cytological investigations provided valuable information on the modes of action and efficacies of two prophylactic compounds, Milsana and benzothiadiazole (BTH), against powdery mildew development on long English cucumber. Milsana application significantly reduced disease incidence relative to inoculated controls through induction of localized resistance. Microscopic observations showed most haustoria had collapsed in the localized Milsana treatment and were encapsulated by an amorphous material impregnated by electron-opaque substances. The rapidity of haustorial collapse (within 4 days of treatment application) together with the encasement by electron-dense substances stained blue by toluidine blue O suggest that phenolics are possibly involved in the Milsana defense response. Cytochemical labeling of chitin with a wheat germ agglutinin/ovomucoid-gold complex showed that complete cellular disorganization of the fungus had occurred without disturbance to chitin in the walls of mycelia and haustoria. This may indicate that chitinolytic activity is not important in the Milsana-activated defense response. Application of high doses of BTH induced occasional cell wall thickening and accumulation of a compound that stained purple by toluidine blue O, but the defense response was weak, sporadic, and insufficient to reduce powdery mildew infection on cucumber. Responses to BTH could not be differentiated in terms of timing of the initial application or systemicity.

Extraction of cucumber leaf tissue expressing induced resistance against powdery mildew fungi revealed the presence of two new major C-glycosyl flavonoid products: vitexin-6-(4-hydroxy-1-ethylbenzene) (cucumerin A, 1) and isovitexin-8-(4-hydroxy-1-ethylbenzene) (cucumerin B, 2). In addition, the known C-glycosyl flavonoids apigenin-8-C-beta-D-glucopyranoside (vitexin, 3), apigenin-6-C-beta-D-glucopyranoside (isovitexin, 4), luteolin-8-C-beta-D-glucopyranoside (orientin, 5), and luteolin-6-C-beta-D-glucopyranoside (isoorientin, 6), as well as 4-hydroxycinnamic acid (p-coumaric acid, 7) and its methyl ester (p-came, 8), were found in higher quantities within resistant plants. The structures of 1-8 were elucidated using spectroscopic methods and unambiguously confirmed for 3-8 using co-chromatography experiments with authentic standards. On the basis of the results of this study and the reported biological activities of C-glycosyl flavonoids, these compounds would play a vital role in the defense strategy of this species by acting as phytoalexins.