Nutrient imbalances in tomato plants and acid phosphatase activity in the leaves

Tomato plants were grown in sand for 5 weeks and received one of fifteen different nutrient solutions in which the concentrations of various elements were either reduced or increased individually, relative to their concentration in a complete nutrient solution, and the acid phosphatase activity in extracts from the young, fully‐expanded leaves was determined. When expressed on a fresh weight basis, only in the P‐deficient plants was the activity significantly increased with a degree of confidence better than P =0.05; a slight increase occurred in extracts from the plants suffering from B toxicity, but this was only significant at P =0.1. There were no increases in acid phosphatase activity with deficiencies of N, K, Ca, Mg, B, Cu, Fe, Mn, Mo or Zn; or with toxicities of Cu, Mn or Zn. When expressed on a protein N basis, only N and P deficiencies increased the acid phosphatase activity. It is proposed that the acid phosphatase activity of the leaves could be used as an indicator of P deficiency in the tomato.