Enzyme Activities and Leaf Constituents in Barley Seedlings at Different Nutrient Levels

The effect of additional fertilization (NPK) on metabolism was studied in the first three leaves of barley. Activities of ribulose-1,5-bisphosphate carboxylase, alkaline fructose-1,6-bisphosphatase, nitrate reductase and protein content were markedly higher at elevated nutrient levels, but content of main non-structural carbohydrates were lower under these conditions. Nutrient limited plants accumulated large amounts of carbohydrates, but their dry weight was reduced, indicating a limited capacity for photosynthesis and utilization of assimilates. The specific activity of RuBPCase increased at low nutrient levels during development of the second leaf, but not at elevated nutrient levels. Therefore, it is likely that RuBPCase protein is degraded less efficiently than other protein. Alternatively, these findings could be interpreted as an altered response to activation of RuBPCase by bicarbonate.