Verhältnis von Sproß und Wurzel bei der Expression von Genen der Sulfatassimilation in Arabidopsis thaliana

Abstract

The relationship of shoots and roots in sulfate assimilation has been investigated both at the biochemical and molecular level. The model plant Arabidopsis thaliana provides for the first time the possibility to analyse the expression patterns of almost all the genes of sulfate assimilation and cysteine biosynthesis in plants. Thus the troublesome assay of the notoriously low activities and labile enzymes of the pathway is avoided. Quantification of steady-state mRNA levels of genes of sulfate transporters, ATP sulfurylase, APS-kinase, APS reductase, sulfite reductase, serine acetyltransferases and O-acetylserine (thiol)layses in rosette leaves and roots from A. thaliana plants was performed using Northern hybridization. Genes for sulfate reduction were predominantely expressed in leaves, however, substantial mRNA levels were also detected in roots for all genes tested. Similarly, genes that encode iso-enzymes of cysteine and methionine biosynthesis exhibited strong expression in roots comparable to the amounts in leaves. In addition, stored sulfate from roots contributed about one third of the sulfur required for metabolic processes during early stages of external sulfate deprivation. It is concluded that the shoot is not entirely responsible for storage of sulfate and provision of reduced sulfur in A. thaliana. Instead, the root system plays a significant role in sulfate storage and reduction and may even be independent from import of reduced sulfur compounds from the shoot.