Barley for Food and Health: Science, Technology, and Products

GENETICS AND NUTRIENT COMPOSITION 71
grain protein content was determined prior to the development of quantitative
trait locus (QTL) analysis (Ullrich 2002). Shewry (1993) presented a detailed
summary of the genetic control of hordein synthesis in barley which indicated
that all of the hordein proteins are encoded by structural genes on chromosome
5(1H). Through the use of QTL analysis, it is now recognized that there are
regions on all seven chromosomes associated with the control of barley kernel
protein content (Zale et al. 2000; Ullrich 2002).
Prior to the advent of QTL analysis, the lysine level in cereal grains was
studied intensively in numerous laboratories during the late 1950s and early
1960s. At that time, the research was driven by widespread famine and protein
deficiency in many developing countries. The U.S. Agency for International
Development provided a major part of the funding for this research, which was
conducted at international research centers, including CIMMYT in Mexico and
ICARDA in Syria, and at various state agricultural research stations in the United
States. Research centers in Denmark and Sweden also made major contributions
to the development of high-lysine barley. Since lysine is the most limiting essential
amino acid in barley and other cereal grains, this amino acid received the
greatest amount of research attention. Following the discovery and report of
high-lysine maize by Mertz et al. (1964), high-lysine cultivars were discovered
in grain sorghum (Mohan and Axtell 1975) and barley (Munck et al. 1970). A
high-lysine cereal grain is defined as one having ≥ 4.0% lysine in the protein.
The concentration is often expressed as grams of lysine per 16 g nitrogen. Barley
containing 11 to 13% protein will contain 0.40 to 0.45% lysine (w/w %) and about
3.50% lysine when expressed as grams per 16 g N, whereas a high-lysine barley
having a comparable protein level may contain up to 0.65% lysine (w/w %).
Lysine in barley is a simply inherited characteristic (Ullrich 2002). Following
the discovery of the naturally occurring high-protein, high-lysine cultivar
Hiproly, numerous high-lysine barley mutants were induced by chemical and
radiation treatment, and most have been characterized biochemically and genetically
(Ullrich 2002). Possibly the most studied of the high-lysine types were
Hiproly (about 4.50% lysine grams per 16 g N) (Munck et al. 1970) and a
mutant barley induced by radiation, Bomi Risø 1508 (about 5.50% lysine grams
per 16 g N), produced from the Danish cultivar Bomi (Ingversen et al. 1973) The
1508 barley is considered a hordein mutant, as the change in lysine is due to a
large reduction in hordein (Shewry 1993), whereas the lysine increase in Hiproly
is due to increased amounts of enzymes such as β-amylase that are high in lysine
(Hejgaard and Boisen 1980). Accordingly, the genes producing the high-lysine
effect, lys1 and lys3 , are both located on chromosome 7(5H) (Karlsson 1972;
Jensen 1979). At least 10 high-lysine mutant genes have been reported in barley;
however, the biochemical and morphological alterations on the kernels resulted
in significant reduction in agronomic production (Ullrich 2002). This problem
was 90 to 95% overcome by crossing Bomi Risø 1508 (lys3a) with two Danish
malting varieties, Triumph and Nordal. A selection from this breeding program
produced a cultivar designated CA 700202, which contained about 6.50% lysine
grams per 16 g N. In yield trials CA 700202 equaled the performance of the