Development of the Rice Panicle : III. Timecourse studies of translocation and distribution of ammonium nitrogen top-dressed at early ripening stage

[摘要] Translocation and distribution of nitrogen top-dressed at early ripening stage in rice plant (Oryza sativa L. cv Chyukyoasahi) were studied by using 15N as a tracer. The plants cultured in Kasugai nutrient solution were top-dressed with 15N-labelled ammonium sulfate at 7 days after heading. Heading was designated as the flower-opening day of the uppermost spikelet on the panicle. Incorporations of 15N were detected in culms, leaf sheathes and panicle at 3 hr after top-dressing, whereas in leaf blades it was detected 3 hr later. The amount of 15N in these organs increased markedly up to 48 hr after top-dressing, then began to decrease after 48 hr in culms, after 72 hr in leaf shcathes and after 96 hr in leaf blades. The amount of 15N in panicle continued to increase during experimental periods. These results imply that rctranslocation of incorporatcd 15N into leaf blades began to take place from 96 hr to 120 hr after top-dressing. Therefore, it is likely that the amount of 15N in panicle at 72 hr after top-dressing, accounting for about 25% of total nitrogen, was not transported from leaf bladcs but directly transported from roots. Much of 15N was distributed to early developing grains on each primary branch. This distribution patten was coincident with the differentiation order of spikelet on the inflorescence. In the grains on top and middle primary branches, incorporations of 15N were detectcd at 3 hr after top-dressing, while the grains on the bottom primay branch incorporated 15N at 6 hr after top-dressing. There were little differences in 15N percentages of total nitrogen translocated to the grains on all primary branches till 120 hr after top-dressing, but after that time 15N percentage of newly incorporated nitrogen was decreased in the grains on bottom primary branch. These results seem to be difficult to explain by the vascular bundle connection of each primary branches at the node of the flag leaf and penultimate leaf. The concentrations of 15N in the grains were lower than that of the whole panicle about 10 to 15% during a period when active absorption and translocation of top-dressed nitrogen was occurring. Moreover, increasing rate of 15N in whole panicle exceeded that in the grains during early stage. These results suggest that some of the nitrogen directly transported to panicle from roots is once incorporated into rachis, rachis-branches and husks and then retranslocated to growing grains.

[学科分类] 农业科学（综合）