Vascular Control of Photosynthate Transfer From the Flag Leaf to the Ear of Wheat

Abstract

The movement of 14C-labelled photosynthate from the flag leaf to the ear in wheat was followed when the path of transport was restricted by heat ringing the stem at selected positions and when the demand for photosynthate by the ear was reduced by grain removal. The effect of reducing the temperature of the nodal transfer zone from 21°C to 1.5°C was also examined as a guide to the operation of metabolic controls over movement of 14C-labelled photosynthate. The data provide evidence that the transfer of photosynthate from the flag leaf to the stem traces linked to the ear occurs at the flag node. Furthermore, this transfer does not involve metabolically controlled cell-to-cell movement and probably occurs via open phloem connections. However, there is greater resistance to this lateral transfer between vascular traces at the flag node than at the node below, and reducing the demand by the ear for photosynthate results in movement to the penultimate node before lateral transfer and upward movement to the ear. This pattern of movement is consistent with the vascular anatomy of the wheat culm.