The researchers studied how different ratios of ammonium and nitrate nitrogen affect the amino acids and enzymes in spinach plants. They found that as the ratio shifted towards more nitrate, the total amino acid content in the plants decreased. Glutamine, arginine, and glutamate were the main amino acids with ammonium, while glutamate, aspartate, and serine were dominant with nitrate. The activity of nitrate reductase increased with more ammonium, while glutamate dehydrogenase activity decreased. The highest activity of glutamine synthetase was at a 50:50 ratio of ammonium to nitrate. Additionally, there was a negative relationship between nitrate reductase activity and glutamine content in the plants.