Physiological Investigations on Restrictions to Transport of Sucrose in Ears of Wheat

Abstract

Accumulation of sucrose in glumes and pales of detached ears of wheat cultured on solutions of sucrose is directly dependent on external concentration; compared with the external level, sugar builds up to higher levels inside these organs, and the uptake of sugar is not reduced much by metabolic inhibitors. In contrast, influx of sucrose into the grains is saturated at relatively low (external) levels of sucrose; the concentration within the grains is lower than in the supplying solution, and movement into the grains is very sensitive to the action of metabolic inhibitors.

Sucrose enters the cultured ear in the transpiration stream and its build-up in the structures enclosing the grain is due to the evaporation of water. Transport to the grain, on the other hand, is dependent upon translocation in the phloem. It is suggested that the passage of sucrose to the grain is restricted by processes involved in transfer from xylem to phloem, or by translocation within the sieve tubes, or both. It is postulated that similar limitations operate on the transport of sucrose derived from normal assimilation.

The detached-ear technique may be of value as a method of estimating the scale of limitations to grain growth conferred by the supply of assimilates to the grain.