FLUORIDE-INDUCED INHIBITION OF STARCH BIOSYNTHESIS IN DEVELOPING POTATO, SOLANUM-TUBEROSUM L, TUBERS IS ASSOCIATED WITH PYROPHOSPHATE ACCUMULATION

Pretreatment of discs excised from developing tubers of potato (Solanum tuberosum L.) with 10 millimolar sodium fluoride induced a transient increase in 3-phosphoglycerate content. This was followed by increases in triose-phosphate, fructose 1,6-bisphosphate and hexose-phosphate (glucose 6-phosphate + fructose 6-phosphate + glucose 1-phosphate). The effect of fluoride is attributed to an inhibition of glycolysis and a stimulation of triose-phosphate recycling (the latter confirmed by the pattern of C-13-labeling [NMR] in sucrose when tissue was supplied with [2-C-13]glucose). Fluoride inhibited the incorporation of [U-C-14] glucose, [U-C-14]sucrose, [U-C-14]glucose 1-phosphate, and [U-C-14] glycerol into starch. The incorporation of [U-C-14]ADPglucose was unaffected. Inhibition of starch biosynthesis was accompanied by an almost proportional increase in the incorporation of C-14 into sucrose. The inhibition of starch synthesis was accompanied by a 10-fold increase in tissue pyrophosphate (PPi) content. Although the subcellular localization of PPi was not determined, a hypothesis is presented that argues that the PPi accumulates in the amyloplast due to inhibition of alkaline inorganic pyrophosphatase by fluoride ions.