Fructan accumulation in wheat stems during kernel filling under varying nitrogen fertilization

Abstract

The authors studied the accumulation of saccharides (glucose, fructose and sucrose) and fructans (1-ketsose, 6-kestose, oligofructosaccharides and polyfructosaccharides) in three different internodes of wheat stems receiving varying nitrogen supply at different stages of growth. Four levels of nitrogen supply, N1 (0, 0 and 100 kg ha-1), N2 (40, 0 and 0 kg ha-1), N3 (40, 120 and 0 kg ha-1) and N4 (40, 60 and 0 kg ha-1, standard fertilization in Hokkaido), were applied before sowing, at the six leaf stage and at the flag leaf stage, respectively. Glucose, fructose, sucrose, 1-kestose, 6-kestose, oligofructosaccharides and polyfructosaccharides were assessed in internodes 1 (upper part), internodes 2 (middle part) and internodes 3 (lower part) of the stems during early milky, middle milky and dough ripe stages. During the dough ripe stage, glucose content decreased in N1 and N2 stems, increased in N3 stems, and varied slightly in N4 stems. Fructose content was lower during the early milky stage and increased significantly during the middle milky and dough ripe stages. Sucrose content of N1 and N2 stems increased significantly during dough ripe stage, while these of N3 and N4 stems did not vary significantly. The levels of 1-kestose and 6-kestose in N1 stems were high compared with N2, N3 and N4 stems. However, their contents decreased during the dough ripe stage for 6-kestose. Oligosaccharides have shown similar variation by decreasing during the dough ripe stage, while polysaccharides decreased in N1 and N2 stems, but varied weakly in N3 and N4 stems. Total fructooligosaccharides (FOS) decreased during the dough ripe stage, particularly in internodes 1, while total FOS of internodes 3 remained quite stable. Comparatively, internodes 1 showed the lowest content compared with internodes 2 and 3. The results showed that fructans accumulated early, while a decreasing gradient was often observed from the bottom to the top of the stems. Results also showed that under N1 nitrogen fertilization rate, wheat plants accumulated high contents of fructans, and this fertilization rate could be applied in the Hokkaido region. Key words: Nitrogen, fertilization, stems, fructans, accumulation, Triticum aestivum