| Identification of chromosomes carrying a locus for
a gene conditioning the production of tyrosinase in wheat grains
A. C. ZEVEN Institute of Plant Breeding (I.v.P.), Agricultural University, Wageningen, The Netherlands Summary Using the substitution lines of Chinese Spring (Hope) and Chinese Spring (Timstein) the presence of loci for genes conditioning tyrosinase production in caryopses was identified on 2A of Hope, and 2A and 2D of Timstein. It is suggested to use Tc as symbol for these genes. Introduction When PIEPER (1922) tried to disinfect wheat seeds that were infected with common bunt, with phenol containing Betanal he observed that after a few hours the seeds turned brown, dark brown or blackish, or remained unchanged. HERMANN (1928) described this phenomenon and heralded its use as a means to identify wheat varieties and to measure varietal purity. An intensive research started in Europe before 1940 (DUTKIEWICZ- MICZYNSKA 1930, FRIEDBERG 1933, LISTOWSKI 1936, MICZYNSKI 1938, PERCIVAL 1934, SNELL and PFUHL 1930, VOSS 1933, 1936, 1938, these publications also refer to literature in Hungarian, Russian, Polish and Ukranian). In Europe the above method is still applied as one of the means to describe varieties (e.g. JONARD 1951, SIMON 1955 and others). This phenomenon was also described for North America (FRASER and GFELLER 1935, 1936). It seems that at present it is not widely known there, because it is not mentioned by PETERSON (1965) and QUISENBERRY and REITZ (1967). The same holds true for other continents. The pigmentation reaction is also identified for other Triticum species (HERMANN l928, FRIEDBERG 1933, BLANCHARD 1953, BHOWAL et al. 1969). BLANCHARD described the pigmented grains of T. durum as having a greyish appearance which is not found in T. aestivum. Barley seeds (FRIEDBERG 1933, LISTOWSKI 1936, SAWICKI 1955, HANSEL 1958) and rye seeds (SCHRODER 1932) also turn brown or blackish in the presence of phenol. The pigmentation is a result of the conversion of phenol (and other phenolic derivatives) into melanin pigments in the presence of tyrosinase (monophenyloxydase) (VOSS 1938). This chemical reaction is widely occurring in nature. For wheat seeds the presence of tyrosinase was established by BERTRAND and MUTTERMILCH (1907). The production of tyrosinase is conditioned in tetraploid wheat by one locus (JOSHI and BANERJEE 1968) and in hexaploid wheat by either one or two loci (FRASER and GFELLER 1936, MICZYNSKI 1938). Tyrosinase production is dominant over no tyrosinase production. JOSHI and BANERJEE (1968) established two dominant alleles. These dominant alleles differ in the speed at which the seeds turn black. This speed might be a result of the production of tyrosinase per unit time, but there may be other causes. It is probably that there are more than two dominant alleles, because different seed samples may show different shades from brown to blackish. The possibility of an additive effect of the two loci should be investigated. FRASER and GFELLER (1936) symbolized the gene with Pk, and Miczynski (1938) with F. JOSHI and BANERJEE (1968) used B. I propose Tc (tyrosinase in caryopsis). Linkage of this locus was shown to exist with the locus for tyrosinase in glumes (proposed symbol Tg) (FRASER and GFELLER 1936, MICZYNSKI 1938). At one time it was believed that there was always repulsion (pigmented grain and white glume, or reversion), but later wheat varieties with genotype Tc/Tg were identified. |
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