Annals of Botany 39: 337-346, 1975
© 1975 Annals of Botany Company
RESEARCH-ARTICLE |
The Utilization of P—N Compounds by Plants
I. Root-mediated Hydrolysis of Phosphodiamidate
Department of Plant Sciences, University of Leeds Leeds
1 Present address: Department of Biological Sciences, University of Natal, Durban, 4001, South Africa.
Received: 20 May 1974
The uptake and utilization of sodium phosphodiamidate, a compound containing covalent P—N bonds, was investigated. Growth analysis showed that this compound could serve as the sole source of phosphorus for tomato plants grown in culture solutions, although the growth rate of plants supplied with phosphodiamidate was slightly less than that of plants utilizing diammonium phosphate. Chromatographic analysis of xylem sap showed that phosphodiamidate was not transported in the unhydrolysed form in the sap of tomato plants supplied with this compound. Tomato plants supplied with phosphodiamidate as the sole source of both phosphorus and nitrogen assimilated some nitrogen in a form other than unhydrolysed phosphodiamidate. Comparison with plants supplied with diammonium phosphate showed that the plants receiving phosphodiamidate had lower nitrogen contents, suggesting that the rate of hydrolysis of the compound may have been limiting nitrogen assimilation by the plants. Measurements of the hydrolysis of phosphodiamidate in culture solutions in the absence of plants showed that the plants assimilated more nitrogen than that released by normal chemical hydrolysis of the compound occurring in the absence of plants. The excess nitrogen assimilated, over and above that produced by normal chemical hydrolysis, could not be accounted for solely by the uptake of unhydrolysed phosphodiamidate as this would require the concomitant uptake of more phosphorus than was actually present in the plant. Thus it was inferred that the presence of the plant roots in the culture solution somehow caused extra hydrolysis of the phosphodiamidate.