Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/1998
Publication Date: N/A
Technical Abstract: One characteristic of the Zn-hyperaccumulator Thlaspi caerulescens is enhanced zinc influx into the roots and subsequent translocation to the shoots. However, long term Zn uptake resulted in more zinc being accumulated in the root of T. arvense (Zn-nonaccumulator). Efflux (compartmentation) studies indicated that a significant fraction of symplasmic zinc was sequestered in the vacuoles of T. arvense roots and made unavailable for loading into the xylem and subsequent translocation to the shoot. In T. caerulescens, however, only a small Zn fraction was stored in the root vacuole. Moreover, vacuolar Zn could more easily efflux across the tonoplast back into the cytoplasm of T. caerulescens root cell. We conclude that unlike T. arvense in T. caerulescens symplasmic Zn is readily available for loading into xylem an subsequent translocation to the shoot. The xylem sap of T. caerulescens contained approximately 5-fold more Zn than that of T. arvense. However, analysis of the organic compounds indicated similar composition of the sap isolated from the two Thlaspi species. Furthermore, more zinc was accumulated in leaf sections of T. caerulescens indicating that greater storage capacity for Zn in the leaf cell is another feature of this Zn hyperaccumulator species. These results suggest that Zn hyperaccumulation in T. caerulescens involves alteration of Zn transport across tonoplast in both root and shoot of T. caerulescens. Current research in our laboratory focuses on the investigation of Zn transport into the tonoplast vesicles isolated from root and shoot of the two Thlaspi species.