Abstract
The dynamics of nitrogen in hydroponically grown muskmelons was examined in detail from the stage of vegetative growth to harvest. At harvest, 70% of the plant nitrogen was absorbed after pollination and 76% of it was distributed to the fruit. It was suggested that a substantial amount of the nitrogen absorbed via the roots before and just after pollination was directly distributed to the infant fruit and that, after pollination, the fruit development and maturation were caused by the redistribution of the nitrogen from other organs. In order to clarify this point, we examined the nitrogen dynamics in plants from the viewpoint of the source-sink relationship. In summary, fruit always functions as a large 'sink,' and nearly 50% of the fruit nitrogen at harvest is derived from the redistribution of nitrogen from other organs, mainly from the leaves. The leaves were classified into three groups in terms of their function, either as a source organ or a sink organ. It was then found that they function as a large 'source' of nitrogen after pollination.
