The effect of nitrogen deficiency on the growth and metabolism of Lemna minor L

When Lemna is deprived of nitrogen, growth and respiration decrease and the pattern of (14)CO2 release from [1-(14)C]glucose and [6-(14)C]glucose is consistent with a relatively strong inhibition of glycolysis. Protein degradation is enhanced but the concentration of free amino acid decreases. It is argued that the biological significance of the increased protein degradation does not lie in its contribution to respiration but as a mechanism to replace one set of enzymes adapted to a particular environmental condition (high nitrogen) with another set of enzymes adapted for low nitrogen in the environment. The change in enzyme pattern associated with the change from high to zero nitrogen in the growth medium has been examined for nine enzymes. The changes in activity observed are consistent with the observed apparent inhibition of glycolysis during nitrogen starvation, but do not explain the inhibition of the pentose phosphate pathway.