Voluntary intake and digestibility of teff hay fed to horses.

The objective of this study was to evaluate nutrient composition, voluntary DMI, and apparent DM digestibility of teff hay cut at 3 different stages of maturity to evaluate its potential as a preserved forage for horses. Six mature Quarter Horse mares (12 +/- 3 yr; 553 +/- 39 kg of BW) were used in a replicated balanced Latin square design with 3 periods and 3 maturities of teff hay. Eragrostis tef ('Tiffany' teff) was planted in May and harvested at the boot, early-heading, or late-heading stage of maturity through the summer. Horses were acclimated to a mixture of maturities of teff hay for 8 d before the beginning of the study. After this acclimation period, each period consisted of a 9-d voluntary DMI phase, followed by a 3-d DM digestibility phase. The percentages of nonstructural carbohydrates (NSC) increased from 5.4% in the boot stage to 8.4% in the late-heading stage, whereas concentrations of CP, K, Fe, and Mn decreased. The Ca:P ratio was 2.0 ± 0.3 for all maturities. Horses had less DMI of late-heading teff hay (1.5% BW) than teff hay of other maturities (1.8% BW; P < 0.05), indicating a preference for the earlier maturities. The intake and nutrient composition of the boot and early-heading maturities was sufficient to meet 90 to 97% of the average DE of the horses and most other nutrient requirements. Digestibility decreased from boot to late-heading teff hay for DM, CP, ADF, and NDF (P < 0.05). Digestibility increased from boot to early-heading to late-heading hay for nonfiber carbohydrates and water-soluble carbohydrates (P < 0.05). For all maturities of teff hay, the NSC intake was below 10% of the total intake. In conclusion, the low NSC and DE of teff hay grown in central Pennsylvania under the conditions in this study make it an appropriate forage source for obese horses and those at risk for laminitis or other metabolic disorders.

Gene-dependent flavonoid 3'-hydroxylation in maize.

The influence of the gene Pr on flavonoid 3'-hydroxylase activity in maize is described. Specific activities are presented for the hydroxylase in seedlings and aleurone tissue homozygous dominant and recessive and heterozygous for Pr. Specific activity levels in both tissues increased in a nearly direct proportion with the increase in Pr dosage, which is consistent with Pr being the structural gene for the hydroxylase. Regression analysis of the gene dosage:enzyme activity comparison yielded correlation coefficients of 0.979 and 0.959 for the seedlings and aleurone, respectively. Quantitative identification of the cyanidin and pelargonidin in the aleurone indicated that cyanidin increased with an increase in dominant Pr, while pelargonidin decreased, although the increases and decreases observed were not directly proportional to the gene dosage. Comparison of the cyanidin/pelargonidin ratio to the gene dosage ratio in the different tissues showed a strong correlation (0.998), which demonstrates that the dosage of Pr controls the ratio of cyanidin to pelargonidin. Cyanidin was found at a low concentration in aleurone homozygous for pr. Hydroxylase activity in maturing field plants reaches its peak concentration near anthesis and is present at an appreciable concentration in mature plant tissue homozygous for pr, as well as in seedlings homozygous for pr. Suggestion is made that pr could be a hypomorphic allele or that a duplicate gene for Pr could exist to account for the hydroxylase activity in homozygous pr tissue. Evidence for the hydroxylase in the aleurone and the seedlings and the pigment ratio data from the aleurone suggest that Pr is indeed a structural gene for NADPH:flavonoid 3'-hydroxylase.

Microsomal flavonoid 3'-monooxygenase from maize seedlings.

Identification of flavonoid 3'-monooxygenase establishes another reaction in the biosynthesis of flavonoid compounds in maize (Zea mays L.). The flavonoid 3'-hydroxylase was obtained as a microsomal enzyme preparation by buffer extraction of 5 day old maize seedlings and ultracentrifugation. Seedlings were exposed to light 24 hours prior to enzyme extraction. The extraction buffer required the addition of sucrose or glycerin and dithiothreitol to obtain an active hydroxylase that retained its activity on storage at -70 degrees C. Enzymic activity required O(2) and NADPH, was optimum at pH 8.5 and 30 degrees C, and could be inhibited 79% by carbon monoxide. Carbon monoxide inhibition could be reduced to 21% by irradiation of the samples with 450 nanometer light during incubation. Kaempferol, a flavonol; naringenin, a flavanone; and apigenin, a flavone, all served as substrates for the hydroxylase. Treatment of the microsomal enzyme preparation, previously reduced with sodium dithionite, with carbon monoxide gave a 455 nanometer absorption peak which disappeared on oxidation of the preparation with the formation of a 420 nanometer peak. These results suggest a cytochrome P-450 type monooxygenase enzyme. The concentration of cytochrome P-450 was 0.21 nanomoles per milligram protein. Identification of the monooxygenase provides further biochemical information about a biosynthetic sequence for which the genetics have been studied intensely.

Influence of B and Pl on UDPG:Flavonoid-3-O-glucosyltransferase in Zea mays L.

The influence of the genetic constitution at the B and Pl loci on UDPG:flavonoid-3-O-glucosyltransferase activity is described. More than a 90% reduction in activity is found when either B or Pl was present in the homozygous recessive condition. A positive correlation between quercetin-3-O-glucoside and pelargonidin-3-O-glucoside production is observed for all genotypes tested. Changes in UFGT activity during plant development are described for R-r B Pl plants.

Nitrogen-metabolizing enzymes of Diplodia maydis, a Zea mays L. stalk rot causing fungus.

The nitrogen source available to Diplodia maydis in vivo is reported to affect the severity of stalk rot in maize. Nitrate and (or) ammonium salts were tested for their effect on the type of nitrogen metabolism found in Diplodia maydis in vitro. The level of glutamate dehydrogenase remained essentially constant on either nitrogen salt but nitrate reductase was induced by growth on nitrate salts and was not extractable on ammonium salts. Properties of nitrate reductase reported here are similar to those reported for the higher plant and Neurospora crassa enzymes. Thr relationship of nitrogen metabolism in Diplodia maydis to Zea mays L. stalk rot is discussed.

Liquid culture of Diplodia maydis.

Diplodia maydis, a Zea mays L. stalk rot causing fungus, was grown in Czapek-Dox broth and modifications of Fries liquid media using combinations of 1% cellulose, 1% sucrose and ammonium or nitrate-nitrogen. Conditions are defined to yield consistently maximum mycelial dry weight in two days in contrast to the usually reported five-day incubation period.