EFFECTS OF AMMONIUM AND NITRATE ASSIMILATION ON THE GROWTH AND TUBER SWELLING OF POTATO PLANTS

Effect of NH4-N and NO3-N on plant growth and tuber smelling of potato plant (Solanum tuberosum L.) was examined, and the results obtained w ere as follows. 1) NH4-N stimulated tuber swelling, while NO3-N stimul ated the branching of stolons and stems, and shoot growth. 2) In plant s grown with NH4-N, a large amount of (NH4)-N-15-N was mainly partitio ned into tubers and stems, whereas in plants grown with NO3-N, (NO3)-N -15-N was mainly partitioned into leaves, especially into the insolubl e fraction. 3) Aspartic acid plus asparagine (Asx) in tubers predomina ted among amino acids and amides when the plants were grown with NH4-N . Also (NH4)-N-15-N was incorporated into Asx in tubers, while, (NO3)- N-15-N was presumably transported to tubers in the form of Asx, which subsequently was actively metabolized into other amino acids in tubers . Thus, as the nitrogen form of NH4+ appeared to stimulate the Asx met abolism, Asx was transported to tubers, and mainly stored in tubers. O n the other hand, the nitrogen form of NO3- was mainly transported int o leaves, and NO3-N promoted vegetative growth.