Shikimate Dehydrogenase‐12 Allozyme as a Marker for High Seed Protein Content in Rice

Abstract

Recent studies at the International Rice Research Institute (IRRI) on the N‐assimilating isozymes in rice (Oryza sativa L.) showed that shikimate dehydrogenase high mobility allozyme (specified by the Sdh‐12 allele) was associated with higher protein accumulation. This study was conducted to verify such association in FI and F2 progenies derived from a cross involving parents differing in Sdh‐1 alleles and seed protein content, and to examine the influence of the Sdh‐12 allele on the Osborne's solubility fractions of total seed proteins. The female parent IR36 was characterized by the Sdh‐11 allele and low seed protein content, and the male parent IR480‐5‐9‐3‐3, by the Sdh‐12 allele and high seed protein content. The results indicated that the Sdli‐1 locus assorted in a monogenic mendelian fashion expressing codominance, while the seed protein content segregated in a polygenic manner. When F2 individuals were divided into three groups based on their Sdh‐1 allozyme pattern as determined by starch gel electrophoresis of seeds and tillers, the mean protein content per seed was highest (120.3 g kg−1 brown rice, BR) for Sdh‐12 homozygotes, intermediate (106.0 g kg− BR) for Sdh‐ll/Sdh‐12 heterozygotes, and lowest (91.9 g kg‐a BR) for Sdh‐11 homozygotes. Accumulation of the oryzenin fraction in the heterozygotes and Sdh‐12 homozygotes was significantly higher than in Sdh‐P homozygotes. Since oryzenin is the major component of seed storage proteins in rice, the Sdh‐12 allozyme can be an effective marker in screening for higher seed protein content among different cultivars or segregants from hybrid progenies.