Sonia Delhaye

Genetic control of lysine metabolism in maize endosperm mutants

The capacity of three maize endosperm opaque mutants (o10, o11 and o13) to accumulate soluble lysine in the seed in relation to their wildtype counterpart, W22+, was investigated. The W22o13 and W22o11 mutants exhibited 278% and 186% increases in soluble lysine, respectively, while for W22o10, a 36% decrease was observed, compared with the wildtype. A quantitative and qualitative study of the N constituents of the endosperm has been conducted and data obtained for the total protein, non-protein N, soluble amino acids, albumins / globulins, zeins and glutelins present in the seed of the mutants. Following 2D-PAGE, a total of 38 different forms of zein polypeptides were detected and considerable differences were noted between the three mutant lines. The metabolism of lysine was also studied by analysis of the enzymes aspartate kinase, homoserine dehydrogenase, lysine 2-oxoglutarate reductase and saccharopine dehydrogenase, which exhibited major changes in activity, depending on the genotype, suggesting that the mutant genes may have distinct regulatory activities.

Improved Method for Isolating and Quantitating α-Amino Nitrogen as Nonprotein, True Protein, Salt-Soluble Proteins, Zeins, and True Glutelins in Maize Endosperm

ABSTRACT The conventional Landry-Moureaux method for selective extraction of maize proteins was modified by reducing the contact time of meal with extractants and by removing 55% 2-propanol as extractant. The new procedure, coupled with a method for quantitating protein at microgram level, was used for assessing the nitrogen distribution of four soluble protein fractions present in 100-mg samples of endosperm originating from six maize inbreds and opaque-2 versions. Proteins extracted with 55% 2-propanol plus reductant were made up of α-, β-, γ-, and δ-zeins. Proteins extracted subsequently with salt plus reductant were minor and poor in lysine (1 mol%).They were associated with zeins. Comparison of present data with those available in the literature showed a close similarity for a given genotype between the percentage of total α-amino nitrogen extracted by 2-propanol plus reductant than by salt plus reductant under conditions of the modified procedure and that of total Kjeldhal nitrogen extracted by 2-pr...

Protein distribution pattern in floury and vitreous endosperm of maize grain

ABSTRACT Alpha-amino nitrogen compounds of floury and vitreous parts of hand-dissected endosperm from eight maize (Zea mays L.) inbred lines, representing a broad range of vitreousness (42–95%), were isolated as nonprotein nitrogen, albumin-globulins, zeins, and true glutelins. The three protein classes averaged, respectively, 13, 48, and 35% of total nitrogen in floury endosperm, and 4, 79, and 15% of that in vitreous endosperm. For six inbreds, floury endosperm was richer in 27 kDa γ-zein than vitreous endosperm; the reverse was found for an Argentine flint inbred (ARGL 256), and only traces of 27 kDa γ-zein occurred in both floury and vitreous endosperm of inbred F113. Results were compared with protein distribution patterns reported in the literature of whole endosperm of wild-type and mutant genotypes of maize, and with wild relatives of maize, Tripsacum, and teosintes. When percentage of salt-soluble nitrogen increased from 2% (Tripsacum) to 22% (in double mutant Oh43o2;bt2), zeins decreased from 87...

The tryptophan content of pearl millet grains as a function of nitrogen content

Abstract The tryptophan content of pearl millet (Pennisetum thyphoides or P. americanum was determined for 17 samples, using a procedure that allowed the true quantity of this amino acid to be evaluated. The linear relationship found between the level of tryptophan in the dry matter and the nitrogen content of the grain was compared with the homologous ones published for foxtail millet and maize. The relationships for pearl and foxtail millets were characterized by close, if not identical, parameters and by positive y-intercepts, indicative of higher tryptophan content in prolamins (2.4%) than in non-prolamin (1.2–1.4%) proteins. Comparatively, the slope of the relationship determined for maize was one-fifth of that for millets and the y-intercept was negative. A variability in the level of tryptophan in grain proteins was evidenced when this parameter was regressed against the reciprocal of nitrogen content.