The role of calcium in regulating alginate-derived oligosaccharides in nitrogen metabolism of Brassica campestris L. var. utilis Tsen et Lee

Under normal (full-strength) levels of calcium in hydroponics culture, alginate-derived oligosaccharides (ADOs) increased the activity of nitrate reductase (NR), glutamine synthetase (GS), glutamate dehydrogenase (GDH), and endpeptidase (EP) in leaves by 4.04–14.41%, 23.57–190.12%, 103.44–265.21%, and 7.22–157.41% respectively compared to that in leaves of the control plants; increased the concentration of NH4 +-N, total nitrogen, and protein nitrogen in leaves; and decreased the concentration of nitrate in shoots. Under low (5% of the full strength) levels of calcium, ADOs had no effect on the activity of NR and GS. These results serve to confirm the role of ADOs in regulating nitrogen metabolism, which is related to the supply of calcium. ADOs induce the release of calcium from cell organelles and the cell wall into the cytoplasm to activate the enzymes involved in nitrogen metabolism. Thus Ca regulates nitrogen metabolism in Chinese cabbage through ADOs.