Acid phosphatase activity of intact roots and phosphorus nutrition in plants. 1. Assay conditions and phosphatase activity

Abstract

This veries sets out to investigate the possibility of developing root phosphatase activity as an indicator of plant efficiency in obtaining phosphorus from low phosphorus situations. This paper examines the effect of substrate pH, temperature, reaction time, microbial contamination and phosphorus nutrition on the expression of phosphatase activity of plant roots. Rye, wheat, buckwheat and subterranean clover plants have been used. Phosphatase (E.C. 3.1.3.4.1) activity measured by p-nitrophenyl phosphate (PNPP) assay was essentially the activity of the plant root. Increased acidity in the substrate, on its own, did not hydrolyse PNPP nor did microbial contamination significantly affect the plant value. Temperature and reaction time were positively related to the assay value, least variation in assay values occurring with substrate temperatures of 20¦C and reaction times of 60-120 min. Optimum pH for phosphatase activity lay in the range pH 5-6. Deficient plants had greater activities than sufficient ones. There was no evidence of alkaline phosphatase activity with phosphorus deficiency. In wheat, the phosphatase activity increased within the first 4 days of plants being deprived of phosphorus and reached its peak in 8 days. Some of the phosphatase was soluble, but most was associated with the root itself. There was evidence that it could be strongly adsorbed on cellulose nitrate filters.