Development of the Rice Panicle : II. Influences of nitrogen supply at heading on the pattern of accumulating of dry matter and nitrogen in the caryopses at different positions on panicle.

The effects of nitrogen supply (1N, 2N) at heading on the pattern of accumulation of dry matter and nitrogen in the caryopses at different positions on panicle were investigated to clarify the positional differences of caryopsis growth. The photosynthetic activities and the nitrogen contents of leaf blades were also taken into account. Caryopsis position on panicle was selected as shown in Fig. 1. Results are summarized as follows; 1. The superior caryopsis (I) at the upper position on panicle, in the control, accumulated the dry matter and nitrogen rapidly and in a short duration at the first half of ripening period. On the other hand, the inferior caryopsis (VI) at lower position on panicle accumulated these materials slowly and over a long duration at the second half of ripening period. 2. Nitrogen supply at heading increased markedly the rate of accumulation of dry matter and nitrogen in all caryopses, but had little influences on the duration of the accumulation and on the time of the rapid accumulation in ripening period, as compared with the control. 3. Nitrogen content of all caryopses at maturity was clearly increased as the quantlty of nitrogcn supplied increased. Grain weight also increased but not so much as the nitrogen content. The ratios of increase of both grain weight and nitrogen content by the nitrogen supply were very remarkable in the inferior caryopsis (VI) which was ill-ripened ln the control. 4. The increase of grain weight and grain nitrogen content by the nitrogen supply at heading was caused by the rise of accumulating rate of these materials in caryopsis throughout the ripening period. 5. Nitrogen supply at heading maintained the photosynthetic activities and the nitrogen contents of leaf blades at relatively high level during ripening period. Nitrogen contents of leaf blades in each plot began to decrease abruptly at 10 days after heading and reached the lowest level at 25 days after heading relatively. 6. It was suggested that the occurrence of the early increased rate of accumulation of translocated substantes might be need for the improvement of ripening of inferior caryopsis and the factors controlling the accumulation rate of inferior caryopsis might involve not only the supplylng ability of source organs but also the function of inferior caryopsis for sink organ.