Effects of Shading or Removing Spikelets in Wheat: Testing Assumptions.

Abstract

Shading for 10 days reduces the supply of sucrose available for distribution to the grains, and the amounts of sucrose in the endosperm, but has no effect on the delivery of soluble amino compounds to the grain. Soon after returning shaded plants to full illumination, the supply of sucrose to the ear is restored to unshaded levels. In addition, shading affects the amounts of ethanol-insoluble material in the peduncle and the rachis, and the nitrogen content of this material in the peduncle. Trimming ears to four spikelets (10 days after anthesis) results in an increased supply of sucrose and soluble amino compounds available for distribution to the remaining grains. More nitrogen enters the grains of trimmed ears than intact ones, but inflow of sucrose is not increased by trimming the ear, and no more starch is deposited in grains developing in trimmed ears. While the responses to shading observed in this work indicate that the interpretation of the effects of shading on the growth of cereal grains may not be straightforward, the use of shading as a treatment for investigating physiological processes such as grain growth is not disqualified. However, as removing spikelets results in several unpredicted, and inexplicable, responses in the grain itself, the value of such a treatment as a means of investigating mechanisms regulating the accumulation of dry matter in the cereal grain is questionable.