Bidirectional Zn-fluxes and compartmentation in wheat seedling roots

SANTA MARÍA G; COGLIATTI D

JOURNAL OF PLANT PHYSIOLOGY

ELSEVIER GMBH

Año: 1988 vol. 132 p. 312 - 315

0176-1617

The influx and efflux rates of 65Zn were studied in 20-day-old wheat (Triticum aestivum cv. Klein Atalaya) plants under controlled conditions. The rate of 65Zn uptake changed markedly during the 24 h experimental period. The initial rate was high, then decreased exponentially and finally, after nine hours, it reached a constant value. This changing pattern of tracer uptake suggested the presence of a high Zn-efflux. A direct measurement of Zn-efflux was performed in homogeneously labelled plants. This 65Zn-efflux could be fitted to a triple exponential function during the 24 h period. Zn-efflux was approximately 65 to 85 % of Zn-influx. Zn-compartmentation in the root was estimated from the «wash-out» experiment. A fast exchanging compartment presumably located in the free space accounted for 16 % of total root Zn-content; a slower exchanging compartment, postulated as cytoplasm, accounted for 8 % of total root Zn-content. There was a third apparent compartment that accounted for 76 % of the Zn content of the root, but this fraction could not be shown to constitute a single compartment. The relevance of a high Zn-efflux on Zn-net-uptake and the possibility that the last compartment was the result of a combined exchange from vacuoles and stele apoplast is discussed.