Effect of cycloheximide and renewal of phosphorus supply on surface acid phosphatase activity of phosphorus deficient tomato roots

Changes in surface phosphatase activity of tomato root ( Lycopersicon esculentum L. cv. Marmande) have been studied in relation to its P status. Experiments were performed either with excised roots cultured in vitro or with entire plants (split root method) grown in various conditions (P deficiency, renewal of P supply). In some experiments different parts of the root were separated according to their P status during their primary growth.
The surface phosphatase in different root parts depends first of all on P status during their primary growth. Moreover the cell wall phosphatase of tomato root is stable in vivo . Thus the changes in the surface phosphatase of a root system result mainly from the growth of new roots, which bear an enzyme activity that is either high if they are P deficient or low if they are P provided. The control of the cell wall phosphatase synthesis appears to be a repression-derepression process mediated by the root cell concentration in some P compound, probably orthophosphate. Cycloheximide stops or alters the growth of excised roots, so that this inhibitor was found unsuitable to study the synthesis of cell wall phosphatase under in vivo conditions. Split root experiment shows that the increase in surface phosphatase activity may occur locally, i.e. only in the parts of the root system which are P deficient. Agricultural and ecological aspects of these findings are pointed out.