Abstract
Plants mainly absorb nitrogen as nitrate and assimilate nitrate into amino acids. These reactions consume large amounts of energy, and, in illuminated leaves, most of the energy can be efficiently supplied by photosynthesis. However, plants often assimilate nitrate in non-photosynthetic organs and the distribution of nitrate assimilation among the organs differs depending on species, environments and growth stages. The aim of this study is to elucidate ecophysiological meanings of the distribution of nitrate assimilation through estimating the amounts of nitrate assimilation in each organ. Using hydroponically-grown Zinnia elegans, we followed the diurnal changes in the activity of nitrate reductase, the rate-limiting enzyme, and calculated the total amount of nitrate assimilated. Then, from the nitrate assimilated and the changes in nitrogen concentration, we estimated amounts of nitrogen translocated. Based on these data, we discuss the independency of nitrogen acquisition in each organ, and the advantage of nitrogen assimilation in non-photosynthetic organs.
