The partitioning of soluble carbohydrates and starch between roots and shoots was investigated in wheat genotypes differing in Zn or Mn efficiency. The plants were grown for 11 d in a chelate-buffered nutrient solution with sufficient or deficient Zn and Mn supply. The Zn-efficient cultivar Warigal had a greater shoot fresh weight under sufficient Zn compared with the Zn-inefficient cultivar Durati. When supplied with sufficient Zn, Warigal had a greater concentration and content of soluble carbohydrates in roots and shoots in comparison with Durati. Under deficient Zn supply, Durati had a greater concentration and content of starch in roots and shoots compared with Warigal. In an experiment with varying supply of Mn, the Mn-efficient genotype C8MM had a greater shoot fresh weight than the Mn-inefficient cultivar Bayonet under sufficient or deficient Mn supply. The concentration of soluble carbohydrates in roots and shoots was decreased by deficient Mn supply in C8MM but not in Bayonet. Starch accumulated in the roots of Bayonet under deficient Mn supply. The results suggest that synthesis of carbohydrates is decreased under Zn deficiency, while they are preferentially partitioned to the roots to increase growth and thus the surface area available for Zn uptake. In the case of Mn deficiency, carbohydrate production was limited, but partitioning between roots and shoots was not altered. (C) 1997 Annals of Botany Company.