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

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.