Causal Analysis of the Difference in Crude Protein Content of Barley Kernels between Two-rowed and Six-rowed Forms

Abstract

TAKAHASHI, HAYASHI and MORIYA (1975) have demonstrated in their studies with a large number of V-v isogenic line pairs that the two-rowed strains were about two percent higher in general in crude protein content of the grain than the corresponding six-rowed strains. This study was planned to approach the underlying cause of the difference in crude protein content (%) between two types of isolines. In the first experiment change of crude protein content with the progress of the kernel growth was investigated using a six-rowed late cultivar (Kikai Hadaka) and a two-rowed early cultivar (Seijo 17). Seed samples were taken from 17 days after anthesis to maturity at 6-day intervals. The result indicated that percentage of crude protein accumulated in the kernels was not so much different between varieties at any stage of kernel growth (Fig. 1). Next, crude protein content of the central and lateral kernels was compared in the second experiment with three six-rowed varieties, which showed no appriciable difference existing between central and lateral kernels (Table 2). Finally, effects of removing lateral kernels of six-rowed strain at different times of kernel growth on final protein content of central kernel was studied in the third experiment. Three pairs of V-v isogenic paired lines (KA-26, KT-16 and GT-17) which had been produced by TAKAHASHI et al. were used. The removal of lateral kernels was made firstly on one or two days before anthesis, and repeated five times at 5-day intervals after anthesis (from 5th to 25th days). In KA-26 and KT-16, one-half of the spikes within plant was used for treatment and remaining half for untreated control. In GT-17, treatment was made within population regardless of the plant. The removal of lateral kernels resulted generally in an increase in crude protein content of remaining central kernels, and the increasing effect of the removal was most evident when the treatment was made before anthesis (Figs. 2 and 3). However, the increase of crude protein content became smaller and smaller with the later date of the treatment, and the treated spikes reached the same crude protein percent as the intact plot on 25th day after anthesis. Removal of laterals affected a little on 1000 kernel weight. From this study, the cause of difference of protein content between two-rowed and six-rowed isolines may be explained as follows : Protein is mainly synthesized in leaves from nitrogen absorbed from the roots, and is distributed almost uniformely to central and lateral kernels in intact six-rowed spike. But when lateral kernels have been removed from the spike, the protein which ought to be allotted to the lateral kernels will be distributed to and accumulated excessively in the central kernels. Consequently, if so-called source size is not different between two-rowed and six-rowed types, crude protein percent of the kernels will be higher in two-rowed type with small size of so-called sink than those of six-rowed ones.