Phosphor belongs to the most important macro nutrients for growth and development of plants. Phosphate is one of a high number of metabolites involved into primary and secondary metabolism. It works as a metabolic energy transmitter via the formation of energy rich esters and represents a regulator of the activity of key enzymes of the primary- and secondary metabolism. In contrast to the extensive physiological examinations about effects of phosphate starvation there is only little knowledge about the role of phosphate for differential gene expression as well as for signal transduction processes in plants. Ribonucleases (RNases) are ubiquitous components of living cells. Dependent on their localisation and specificity RNases are involved in the general breakdown of RNA to recycle carbon, phosphor and nitrogen or could be responsible for a highly selective and differential turnover of individual RNA species, respectively. In the present study, the isolation and characterisation of genomic sequences of phosphate starvation inducible proteins were described. Beside the gene for the RNase LE the gene for a unknown protein (clone PSI14), which is highly inducible by phosphate starvation, was analysed. The gene of the RNase LE contains two introns. The position of one of those introns is similar to that of other S-RNases and S-like RNases described so far. The clone PSI14 is a member of a small gene family containing three members. The coding sequence of all three genes are interrupted by three introns at identical positions. To study the inducibility of the RNase LE promoter upon phosphate starvation, several promoter-GUS-fusion’s were constructed. They were tested in a transient assay system (transformation of a tomato cell culture with particle gun) and in studies using stable tomato transformants. The investigations have shown that a promoter fragment of 316 pb upstream of the translation initiation site is sufficient for the induction upon phosphate starvation. In tomato plants transformed with the promoter-GUS construct there is only a little reporter gene activity under optimal phosphate supply. Moreover, there were no differences in reporter gene activity between roots and leaves. However, upon phosphate starvation a six fold higher induction of the RNase LE promoter could be observed in the roots than in the leaves of tomato plants.