REGULATION OF PHOSPHATE INFLUX IN WINTER-WHEAT - ROOT-SHOOT PHOSPHORUS INTERACTIONS

Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown at various external phosphate (P-i) levels for 10 days in order to in vestigate the effects of P nutritional status of roots and shoots on P -i influx and efflux measured at intervals the following 7 days. When external A was supplied to plants previously deprived of phosphate, P accumulated in the shoots to levels around four times that of controls due to high influx rates and proportionally large P-transport to the shoot. Efflux was, however, comparatively low. Split-root experiments with plants where one or two of the three seminal roots were pretreate d with P-i for a period of up to 5 h showed increased phosphate influx in the non-treated root(s) when transferred to P-32-labelled P-i solu tion. Pretreatment with elevated light intensity for 5 h prior to spli t-root uptake experiments resulted in higher P-i influx in the part of the root system formerly exposed to P-i. The findings indicate that t he shoot P concentration exerted a great effect in regulating the phos phate influx. The mechanisms involved are discussed.