Some properties of starches of opaque-2, sugary-2 opaque-2, and waxy opaque-2 mutants of two broad-based synthetic cultivars of maize.

Starches of the opaque-2, sugary-2, opaque-2, and waxy opaque-2 endosperm mutants of two broad-based synthetic cultivars (Temp HA and Temp HB) of maize adapted to the more temperate areas of the world are, in general, similar to the respective starches of inbred maize background with regard to amylose percentage and the distribution of linear alpha-D-(1 leads to 4) linked unit-chains of amylopectin, starch-granule susceptibility to amylases, and properties examined by X-ray diffractometry and photopastegraphy. Changes in starch content and morphology of starch granules by scanning electron microscopy in dissected endosperms of the two broad-based synthetic maize cultivars following germination 0, 2, 4 and 6 days after planting were also investigated.

Nutritional value of normal, opaque-2 and sugary-2 opaque-2 maize hybrids for infants and children. 1. Digestibility and utilization.

The opaque-2 (o2) gene increases the lysine and tryptophan contents of maize and its protein quality; the sugary-2 (su2) gene improves vitreousness and density but decreases lysine; the double-mutant surgery-2 opaque-2 (su2o2) has the improved kernel characteristics and an even higher protein quality than opaque-2. Digestibility of energy and protein, and protein quality of normal, o2 and su2o2, both as endosperm (E) and whole kernel (WK) meals, were studied in eight convalescent malnourished children, 10--25 months of age. Diets provided 100--125 kcal/kg/day, 10% fat, with all of 6.4% protein calories from one of six maize meals or casein. Endosperm meals provided 83.2, 91.2 and 82.1% of energy, WK meals 73.2, 68.6 and 67.2% of energy in respective diets. Apparent N retention from E meals was lower than from WK meals, both lower than from casein. For each type of meal (E and WK) there was strong correlation between lysine "absorbed" and N retention, but this was higher from WK at equal lysine intakes. For 50% of children to match N retention from casein, presumably equal to requirement, they would have to consume 203.9, 148 or 122.5% of energy requirement as normal, o2 or su2o2 E meals, obviously impossible. For WK meals, they would have to consume 108.2, 90.3 or 84.2% of energy as normal, o2 or su2o2.

Comparative susceptibility of starch granules of double- and triple-mutants containing amylose-extender, waxy, sugary-1, sugary-2 and dull genes of maize inbred OH43 (Zea mays L.) to amylase.

Starch granules were prepared from 14 double- and 26 triple-mutants containing amylose-extender (ae), 14 double- and 18 triple-mutants containing waxy (wx), 15 double- and 20 triple-mutants containing sugary-1 (su1), 13 double- and 23 triple-mutants containing sugary-2 (su2), and 14 double- and 19 triple-mutants containing dull (du) of maize inbred Oh43 (Zea mays L.). The relative susceptibilities of these starch granules to fungal glucoamylase were determined and the starch granules were examined by scanning electron microscopy. A commercial normal maize starch was used as a control. Starch granules of the double- and triple-mutants containing su1 and su2 were digested two to eight times faster than normal. The ae gene reduced susceptibility and seems to be epistatic to su1 and su2. Starch granules of the double- and triple-mutants containing wx were digested about two times faster than normal and those containing shrunken-2 (sh2) were digested 1.2 to eight times faster than normal. Starch granules of triple-mutant combinations with opaque-2 (o2) showed digestion properties which were comparable to those of their respective monopaque double-mutant counterpart.

Interaction of the opaque-2 gene with starch-forming mutant genes on the synthesis of zein in maize endosperm.

The combination of opaque-2 with starch-modified or starch-deficient mutants produced a cumulative and synergistic effect, respectively in regulating zein synthesis. The double mutant, brittle-2 opaque-2, which almost completely prevented the synthesis of Z1 and Z2, had high RNase activity. The possible involvement of RNase in effecting zein synthesis is discussed.

Comparative susceptibility to amylases of starch granules of several single endosperm mutants representative of floury-opaque, starch-deficient, and modified starch types and their double-mutant combinations with opaque-2 in four inbred lines of maize.

Starch granules were prepared from kernels of eight single endosperm mutants, brittle-1, (bt1), brittle-2 (bt2), floury-1, floury-2, soft starch, opaque-1 (o1), shrunken-2 (sh2), and sugary-2 (su2), and their double-mutant combinations with opaque-2 (o2) of four inbred lines of maize (Zea mays L.), B37, C103, Oh43 and W64A. We compared the susceptibility of various starch granules to Rhizopus glucoamylase and pancreatin. Starch granules of the su2 and su2o2 mutants were digested by amylases much faster than those of the normal counterparts. Starch granules of the bt1, bt2, o1 and sh2 mutants tended to be digested by amylases faster than those of normal maize. Starch granules of double-mutant combinations with the o2 gene were, in general, digested to an extent very comparable to their respective non-opaque single mutant counterparts in each of their four inbred backgrounds. We followed the relative digestion of starch granules by using scanning electron microscopy. Starch granules of endosperm mutants susceptible to amylases showed numerous pin holes on the surface layer and the pores penetrated into the inner layers of the granules during the attack by amylases. In some of the granules the inner portion, which appeared terraced or step-shaped, could be seen. This may be indicative of layered internal structures of the granules.

Nitrogen retention of young men who consumed isonitrogenous diets containing normal, opaque-2 or sugary-2 opaque-2 corn.

Three isogenic lines of corn provided two levels of nitrogen for young men, but the diets were isonitrogenous at 5.5 g. Mean daily nitrogen balances were -0.28 +/- 0.34, +0.31 +/- 0.23 and 0.40 +/- 0.08 g, respectively, when normal, opaque-2 and sugary-2 opaque-2 corn furnished 5.5 g of nitrogen; and -0.07 +/- 0.17, +0.38 +/- 0.21 and -0.04 +/- 0.25 g when corn supplied only 4.4 g of nitrogen. Although these values were not significantly different, both high-lysine varieties tended to be superior to normal corn at 5.5 g of nitrogen and opaque-2 corn caused improvement even at 4.4 g of nitrogen. Lysine and tryptophan were higher and leucine lower in both opaque-2 and sugary-2 opaque-2 than in normal corn. Coefficients of apparent digestibility were between 65.5% and 68.8%.

Endosperm protein synthesis in maize mutants with increased lysine content.

The endosperm proteins of the maize mutants, opaque-2, opaque-7, floury-2, brittle-2, and the double mutant of opaque-2 and brittle-2, were separated into five soluble fractions by the Landry-Moureaux method. As compared to their isogenic normal counterparts, the mutant endosperms had higher concentrations of albumins, globulins, and glutelin-3, and lower concentrations of prolamines. The combination of the opaque-2 and brittle-2 genes enhanced this difference. Although the four mutant genes are located on three different chromosomes, they exert a similar effect on endosperm protein composition. Five other starchmodifying mutants with high lysine content resemble the brittle-2 mutant in endosperm protein composition, when the gene is present either singly or combined with opaque-2. Therefore, the pattern of protein synthesis in all maize mutants with high lysine concentrations may be either identical or very similar. Because no synergistic effect on lysine concentration is obtained when floury-2 is combined with opaque-2, different pathways leading to reduced zein synthesis may exist in the floury and starch-modifying mutants with high lysine concentrations.

Enhanced deoxyribonucleic Acid polymerase activity of chromatin from soybean hypocotyls treated with 2,4-dichlorophenoxyacetic Acid.

Chromatin isolated from soybean (Glycine max L., var. Wayne) hypocotyls was capable of catalyzing the polymerization of labeled deoxyribonucleoside triphosphate in the presence of the three other deoxyribonucleoside triphosphates into a trichloroacetic acid-insoluble product. This product was insensitive to base hydrolysis and ribonuclease, but was sensitive to acid hydrolysis and deoxyribonuclease. Chromatin-DNA polymerase required Mg(2+) and all four deoxyribonucleoside triphosphates for maximal activity. Inorganic pyrophosphate and actinomycin D inhibited the polymerase activity, but 2, 4-dichlorophenoxyacetic acid had no effect in vitro. Chromatin from plants previously treated with 2, 4-dichlorophenoxyacetic acid supported a greater level of DNA synthesis than did chromatin from untreated plants.