AMINO-ACID CONTENT IN GRAIN PROTEIN OF TETRAPLOID OPAQUE-2 MAIZE

Abstract

Amino  acid  composition  in  grain  protein  of  a  diploid (2х=20)  single-cross  maize  hybrid containing  opaque-2  (o2) gene  and  tetraploid  (4х=40)  derivatives  of  this  hybrid  was assayed.  This mutant gene is widely used in maize breeding to improve quality of grain protein. Protein content was determined by  the Kjeldahl  method  and   analysis  of  protein  amino acids  -  by   ion  exchange chromatography.  Tetraploids, depending  on  genotype,  showed  higher  protein  content  in grains  than diploid  forms  and  high  variability  in  amino  acid composition.  Some  derivatives  contained  higher levels of such amino acids like, lysine, arginine, aspartic acid and lower levels of leucine in protein in comparison with the diploid grains indicating possibilities to select valuable tetraploid forms. Grains with  o2  endosperm  from  duplex-heterozygote  self-pollinated ears  showed  higher  content  of  lysine, arginine, valine, aspartic acid and glycine and reduced content of leucine, glutamic acid, proline and tyrosine  than vitreous grains from the same ears, which highlights the specificity of gene effect. The analysis  of  dosage  effect  of  the  o 2   gene  revealed  that lysine  content  increases  proportionally  to  the allele number of o 2  in the endosperm of diploid and, partly, in tetraploid grains. A possible maternal influence is indicated to explain the result.