Translocation and Distribution of 14C-Assimilates Related to Stem Termination Habits in Soybeans

摘要

The primary objective of this research was to elucidate the differences in movement of assimilates between types of stem termination in soybean varieties. Tokachinagaha, Koganejiro and Harosoy were examined as an example of determinate, intermediate and indeterminate types, respectively. These varieties have approximately the same maturity and similar yield potential in Hokkaido(N 42-45°). Koganejiro has been bred from cross between Tokachinagaha and Shika No. 4(indeterminate, originated in north-eastern China), having a intermediate trait on the time of stem termination after flowering. Feeding was done at three growing stages, intial flowering, young pod development and pod filling. Either the 4th (L-4), the 8th (L-8) or 12th (L-12) trifoliated leaf from the bottom of the main stem was fed. The leaves were allowed to photosynthesize 14CO2 (50μCi in each plant) for 15 min. under midday solar radiation. After remaining for 24 hours in the natural conditions, the plants were divided into various parts at each node on the main stem and each branch, and their radioactivities were determined. 1. Efficiency of 14C assimilation (defined as ratio, total 14C divided by fed leaf area) became higher with smaller leaf area and lower with larger one among varieties, among leaf positions and irrespective of leaf age (Fig. 1). 2. Translocation rate 14C-assimilates was ranged from 20% to 50% at the initial stage of flowering. Tokachinagaha showed the highest rate, followed by Koganejiro and Harosoy, and rate of L-4 was higher than that of L-8. At the stage of young pod development, differences between varieties in the rate became smaller, ranged 50% to 60%. Further, at the stage of pod filling the translocation rate from L-12 showed about 80% in each variety, and Harosoy showed higher value than those of other varieties (Tab. 1). 3. Specific activities of 14C in various parts of plant at the initial stage of lowering are shown in Fig. 2. The pattern of activity was simillar between varieties, and the strongest sink was the metabolically active organs, closely located fed leaf. 4. Distribution patterns of 14C-assimilates in each stage of growth were as follows. At the initial stage of flowering, Harosoy showed lower percent distribution from L-4 to branch or from L-8 to underground part, and higher from L-8 to forthcoming parts, comparing with other two varieties (Tab. 2). At the stage of young pod development, 30% to 40% of 14C-assimilates which were seemed to be tentative storage were found in the main stem in each variety, when 14C was fed from leaves of main stem (Tab. 3). On the other hand, when 14C was fed from leaf of branch, about 70% of 14C were distributed to pods of respective branch, and only 9% remained in the stem of branch (Tab. 4). At the stage of pod filling, 80% to 90% of 14C-assimilates were distributed to pods and seeds. While in Tokochinagaha they were translocated manly in the pods and seeds of the node where fed leaf attached, in Harosoy 14C was fed at L-12 they were translocated mainly to the pods and seeds located under, and when it was fed at L-8 they were moved preferably to those of branches (Tab. 5). 5. It was of interest that the distribution of 14C-assimilates into pods and seeds in each node on the main stem was intensively controlled by phyllotaxis in determinate type of variety, Tokachinagaha, comparing with other varieties, as shown in Fig. 3. 6. Based on these observations, it was surmised that mobility of 14C-assimilates of determinate type is higher than those of the indeterminate type at the vegetative stage, but at the reproductive stage especially at the pod filling stage it is reversed among growth types.