The Redistribution of Assimilate in Field-grown Winter Wheat

The long- and short-term movement of carbon in a field cropof winter wheat was investigated with the radioactive tracercarbon-14. The flag leaves of individual plants assimilateda pulse of ¹⁴CO₂ and the plant parts were assayed subsequently.Groups of plants were pulse-labelled four times during the mainperiod of growth—twice before and twice after anthesis.Plants were harvested and assayed twice weekly after labellingand the time-course of the changes in the amount of ¹⁴C recoveredfrom the leaves, stems and ears was observed for each groupof plants. Concurrently with these long-term studies, otherwheat plants were pulse-labelled, then harvested and assayed24 h later. The partitioning of ¹⁴C between leaves, stem, earand in some cases roots, was measured over the period from thestart of stem elongation to the end of grain filling. Two distinct types of relocation of carbon were observed. Carbonassimilated early in the growth of the plant and used in thegrowth of new leaves was seen to be partly relocated to theear. Carbon assimilated 8 d after anthesis was partly storedin the stem, and 15 d later relocated to the ear. This relocationcorresponded to a decrease in stem dry mass seen in growth analysis.Little other change in the ¹⁴C content of the plants occurred,suggesting that most respiration used current rather than storedassimilate. Key words: Carbon assimilate, redistribution, wheat