Nutrition of winter wheat during the life cycle. II. Influx and translocation of potassium and phosphorus

Abstract

Changes in the K, Na and P content of solution‐grown and soil‐grown winter wheat (Triticum aestivum L. cv. Martonvásári 8) were followed during the life cycle. In parallel experiments the influx of K+(86Rb) and H232PO‐4 and the translocation of these ions to the shoot were also measured. The K content increased during the seedling and tillering stages (autumn and winter period), but then decreased rapidly as the temperature rose. The influx and translocation of K+ increased during vegetative growth and declined in the generative phase. Na+ replaced K+ when K+ uptake was limited. The P content changed less than the K content, but influx was maximal during elongation. Both influx and translocation slowed greatly in the grain‐filling period. For both minerals the ratio of influx to net uptake was estimated for the life cycle. This ratio was high for the soil‐grown plants but low for the solution‐grown plants, suggesting that the supply of K and P was limiting the growth of the former but not of the latter plants. It is suggested that the transport of K and P during the life cycle is regulated by metabolism‐dependent direct routes (i.e. negative feedback mechanisms) during vegetative growth and by passive, indirect routes in the generative stage. The possibility of hormone‐directed transport processes is also discussed.