Long-distance Transport of Reduced Sulphur in Spruce (Picea abiesL.)

Abstract

Individual needles of 4-year-old spruce trees (Picea abies L.) were exposed to ³⁵S-GSH via the cut surface of the needle tip for 2–3 h at different times during the growing season. From the previous year's source needle, ³⁵S-GSH was exported into the twig and translocated predominantly towards the twig apex. Independent from the growing season, transport towards the stem did not exceed 20% of the radioactivity recovered from the tissue samples. In July, the new needles appeared to be metabolic sinks for reduced sulphur as indicated by the higher percentages of both soluble and insoluble ³⁵S in this twig section, as compared to the previous years' needles. In October, the new needles were no longer found to be a preferential sink for reduced sulphur. Estimates of the rate of GSH export from the source needle in the light (2.5–11.3 nmol GSH g^⊟1 needle FWh⁻¹, equivalent to 1–5% h⁻¹ of its endogenous GSH content) indicate that GSH transport is an important process in sulphur nutrition of spruce needles. The 4- to 5-times higher uptake and export of ³⁵S-GSH in the dark as compared to light conditions might explain the previous finding of a light-dependent, but temperature-independent diurnal rhythm of the GSH concentration in spruce needles (Schupp and Rennenberg, 1988).