A comparative study of the distribution and speed of movement of 14C assimilates and foliar-applied 32P-labelled phosphate in wheat

Abstract

Double labelling experiments with 14C and 32P suggest that the movement of phosphate from leaves is largely determined by the movement and demand for carbohydrate within the plant and not by the phosphorus requirement of the sink.The pattern of distribution of 32P-labelled phosphate applied to either the flag leaf blade or penultimate leaf blade of wheat 15-20 days after anthesis, closely followed that of 14C-labelled photosynthate from the same leaf. With one exception, introduction of additional sugar or phosphate into the stem between the flag leaf and the ear resulted in a similar change in the distribution of both 32P and 14C from the flag leaf. Similarly a change in source-sink relationships, induced by shading the culm between the ear and the penultimate leaf, resulted in an increased movement of both 32P and 14C from this leaf to the ear. Concurrent estimates of the speed of movement through the flag leaf sheath and peduncle of both 32P, shown to be moving as inorganic phosphate, and 14C-labelled photosynthate also gave very similar values for both isotopes. © 1973 CSIRO.