EFFECTS OF PRETREATMENT WITH PHOSPHATE IN NATURAL POPULATIONS OF AGROSTIS CAPILLARIS L.

II. INTERACTIONS WITH ALUMINIUM ON THE ACID PHOSPHATASE ACTIVITY AND POTASSIUM LEAKAGE OF INTACT ROOTS

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Summary

Clones of six populations of Agrostis capillaris L., collected from contrasting soils, were grown in solution culture for a prolonged period at either 1 or 40 mg P dm−3. Large numbers of unrooted tillers were taken from these plants and grown for 8 weeks in similar solutions (low P- and high P-pretreatrnents). Over the subsequent 10-week period, the acid phosphatase (NPPase) activity of intact roots was measured in the presence of various concentrations of cationic Al.

Activity of NPPase was not dependent on membrane permeability, as measured by K+-leakage into the assay medium, suggesting an extracellular enzyme location. The low P-pretreatrnent resulted in, depending upon population, between four and six-fold increases in root-NPPase activity, with the highest activities being found in populations from the most acidic soils. The NPPase activity of the roots was not a linear function of plant P-status and there was evidence that there was a genetic component in the regulation of enzyme activity in low P-pretreated plants.

Increasing Al concentration had little effect on the NPPase activity of high P-pretreated plants, but that of low P-pretreated plants was inhibited to some extent (up to 30%) by the higher concentrations of Al (8 and 16 mg Al dm−3). Populations did not differ in the extent of this inhibition.

The low P-pretreatment resulted in an increase in the K+-leakage from intact roots, and populations differed in the degree of this increase. Populations from colliery spoils had a lower K+-leakage than would be expected on the basis of the low concentrations of P in their shoots. There was some reduction in K+-leakage with increasing concentration of Al in high P-, but not in low P-, pretreated plants.

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